Daily Driver 434 - Cathedral heads or LS7 heads?
09-27-2020, 08:21 PM
#81
TECH Veteran
Maybe JR@FED can comment. I have no personal experience w/ their 243 program, but their LS3 821 head is a killer. Also, the M311's and F710's are making power, so we'll see what the cathedral's can do. The Brodix are going to be best bang for the buck, just watch. If it's near as good as their BR7 head, it'll be amazing. The best cathedral porter out their is Greg Good. His stuff puts up numbers anyway you slice them.
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DualQuadDave (09-28-2020)
09-27-2020, 08:26 PM
#82
I am honestly rarely impressed with any ported stock casting. The F110,310, etc are their own castings. Completely different animal. Personally once I know the airflow targets I try to find the smallest port to meet the demands. In my experience they are the best all around performers. I could care less if it is shaped like a square, cathedral, or a dodecahedron
09-28-2020, 12:55 AM
#83
I am honestly rarely impressed with any ported stock casting. The F110,310, etc are their own castings. Completely different animal. Personally once I know the airflow targets I try to find the smallest port to meet the demands. In my experience they are the best all around performers. I could care less if it is shaped like a square, cathedral, or a dodecahedron
09-28-2020, 05:53 AM
#85
TECH Veteran
Alot of knowledgeable guys don't post on here no more. Greg is definitely the man in head porting. Anytime you can make a 408ci car run 9s on motor on pump gas using 5.3 heads you are something serious.
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DualQuadDave (09-28-2020)
09-28-2020, 06:24 AM
#86
Too many argumentative people were giving the professionals hell in the earlier days.
09-28-2020, 02:34 PM
#88
The CID LS7 port heads ported by Greg Good have done some pretty incredible things in the NA world. I would think Mast would be turning out some updated profiles with Darin Morgan on board. The 11* FED stuff looks really nice, the F110's have gone 4.30's to the 1/8th at 162mph in a small tire, single turbo Foxbody on a stock 6.0L block on methanol. That is making a lot of steam anyway you look at it. The F710's for an all out drag engine will not disappoint and take stock style LS manifolds just like the F110's. Cool stuff, too new to see alot of numbers in COVID 2020. I am sure 2021 will be a different story.
In adding a relevant point to the OP's post, I have made 700 FWHP with a set of 237cc FED ported TFS castings on a 416" carbureted engine with peak HP at 6800RPM. I would think in a 99% street car application you would be happy with cathedral port heads, and I don't think you would need the latest, greatest from anyone. 10+ yr technology would absolutely do it. Proper port volume, intake, header size, intake and camshaft selection to match the vehicle weight and gearing will go very far in effort to make the car do what you want it to do. For an all out drag application the LS7 port would win in a NA application, all things on the vehicle being tailored properly IMO.
In adding a relevant point to the OP's post, I have made 700 FWHP with a set of 237cc FED ported TFS castings on a 416" carbureted engine with peak HP at 6800RPM. I would think in a 99% street car application you would be happy with cathedral port heads, and I don't think you would need the latest, greatest from anyone. 10+ yr technology would absolutely do it. Proper port volume, intake, header size, intake and camshaft selection to match the vehicle weight and gearing will go very far in effort to make the car do what you want it to do. For an all out drag application the LS7 port would win in a NA application, all things on the vehicle being tailored properly IMO.
Last edited by helicoil; 09-28-2020 at 02:48 PM.
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DualQuadDave (09-28-2020)
09-28-2020, 06:04 PM
#90
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I'll give it my best shot. It's not easy to communicate, but once you see it, it's not hard to understand. SO if you can't follow what I'm about to type, it's likely my inability to articulate this.
In short, yes, I'm talking about the air going into the chamber drawn in by the pistons going down, but The trick is getting the air to go in and then stay in. Otherwise, we wouldn't need heads in the first place. First, go listen to this podcast --
Don't cheat. Listen to it, and take notes, even if it doesn't make sense the first time around. Now, the top three concerns when designing or selecting heads is airspeed, airspeed, and airspeed.
First, there is the airspeed in the port itself. If you think in terms of cfm (cubic feet per minute), if you get 400 cfm through a 4 sq in hole, it moves slower than through a 3 sq in hole. Similarly, a properly shaped 4 sq in hole has the potential to flow a lot more air than a properly shaped 3 in hole. Now, when I say "shape", I don't mean cathedral or square. I mean in terms of three dimensions, the shape of the runner leading up to the choke point and the shape of the runner after the choke point. In this way. since the choke point is right at the valve curtain until it opens enough, the combustion chamber is part of the intake tract, and so the combustion chamber shape even affects flow. And there is also the problem that air does not have constant volume or density, so a CFM is relative, but I digress...
Basic principles -- You don't trap cfm inside the engine. You trap air molecules. The way you calculate the number of air molecules is mass. So the idea is to trap as high an airmass in the cylinder as you can.
The reason all this is so important is that the air has a limited time to fill the chamber. BUT a significant chunk of that time is spent filling the chamber while the piston is on its way back up. This is where momentum comes into play. Momentum is a function of both mass and velocity, as is kinetic energy. In fact, if you want to know, kinetic energy is momentum integrated by velocity. So there are two ways to increase the momentum of air. One is to increase mass flow. This is done by increasing air density, which is done by either hunting around for a track with a great DA or boost. The other option is to increase air velocity in the port. With increase air momentum, as the piston passes BDC and begins to come back up, the air can, briefly, continue to fill the cylinder even against the obvious pressure gradient. The masses will kind of shop around based on flow numbers, and there is truth in the flow numbers as far as they can show the potential the heads have for making power. But many times, designers will sacrifice peak flow to gain velocity, as long as the engine has enough air to make its intended power. The reasoning is that the engine rotates sometimes 70 degrees before that valve closes, and the momentum of the air filling the chamber makes all the difference in how much total air is trapped.
So head 1 might flow 10 cfm better, but with poor velocity, it stops filling the cylinder and may even allow for airflow to change direction before the intake valve shuts. Head 2 might flow 10 cm less, but with very good velocity, so the cylinder continues to fill until the valve shuts, resulting in more total air trapped in the cylinder. This is one side to the whole cathedral vs square argument. Using cc as a gauge, the cathedral ports are smaller. So, given equal bore and stroke, the port velocity at low flow demands is better on a cathedral head. not because it is shaped like a cathedral, but because the port cross section area is smaller, so the air must flow faster to meet the demands of the engine. The other side effect is that the increased port velocity can somewhat mechanically tame a large cam. This has historically been one the issues with the larger OEM (square ports) heads. They routinely get overcammed, because people are used to camming cathedral heads. If you run a larger cross section head, you need less cam at the same RPM to fill the cylinder. Too much cam for the head, or too much head for the cam makes the motor feel lazy. And it all comes back to that initial airspeed through the port.
Now, the other side of that peanut butter and jelly sandwich... total flow. The head that flows more will support more power. I didn't say "make" more power. I said "support". The rest of the combination needs to be right, or it's a waste of cylinder head. Let's take a 700 bhp 427 as an example to hopefully make the math easy. A cylinder head that flows 330 cfm on an honest bench can make that kind of power if everything is perfect. Now, the reality is rarely perfect, so let's aim high and look for a 350 cfm head. OK. Now that that's done, what's the smallest port out there that flows 350 cfm on an honest bench? it's going to be in the 240-245 range. So, enter the TFS 245 and all the great results that head gets on strokers. Yay, team. Still tracking?
Now, on that same engine, lets put a 270 cc head on there that flows 370. This leads to how I like to evaluate heads for selection purposes. Flow / port volume = port efficiency, which is the best overall indicator I know of for determining port velocity as a customer over the internet. 350/245= 1.43. 370/270 = 1.37. So all things being close to equal, I can expect the engine to perform better with the smaller head, as it will be most likely to consistently trap the highest airmass. And that is why you see TFS 245 cathedrals walking ported LS3s on 40x-41x strokers. Although, I'd argue the guy running a well set up 240cc rectangle port head would change a lot of default cathedral thinking. I know of a 388 with those 240cc heads made 6xx to the tires all motor at 8000 rpm. If you really want to talk port efficiency, look at the C5R heads that reached 370 cm on 225cc, and note the C5R is still the most represented head on the all motor fast lists.
Ok, so now, let's look at a motor I'm more directly familiar with. A 440 with a power goal of 820-850 bhp. To support this kind of power, the head must flow 405 by the math, but let's be real, it needs to flow 415 at least, and really 420's would be even better to allow for some room for imperfection. So then, I start shopping for what heads can hit that flow number and list them out, and then I go to the smallest port on the list. And that's how i ended up working with Tony on this LS7 top end. There are plenty of heads out there flowing in the 420's. Only one is under 270cc that I could find. But wait... I can get a 350cc runner that flows 450 and get even more air! True, although when you look at the port efficiency numbers, you see that the velocity is going to be low. If you really want to talk port efficiency, look at the C5R heads that reached 370 cm on 225cc, and note the C5R is still the most represented head on the all motor LS fast lists.
So then, why would anyone ever want a big port set up? RPM. At high RPM, the length of time it takes for the engine to rotate from BDC to IVC is lower when compared to slower RPM. As a result, the airspeed is less critical. Ever hear that the LS3 heads shine with RPM? They do. The reason is the port is coming into it's own up top, where airspeed is les critical, but gross flow is king. But to achieve that kind of RPM in the first place, the cam must have really large durations, so it'll be a turd until it gets into its intended operating range. Let's face it, nobody on this site is going to go beat a NASCAR engine with their cathedral port builds just because they make more torque down low. Also there is Boost. Air density is so much higher that the speed is less critical to continuing cylinder fill past BDC.
And all of the above is not getting into airspeed differentials between the large radius and short radius, the port tuning, the exhaust scavenging, etc. And most of that comes later in the selection process anyway. For most people, it's really not too complex. Take the 54% of the bore, and there is your optimal intake valve size in 99% of the cases. Choose your power goal and divide by 2 to get your rough CFM demands of the port. Find the head that can use the proper sized intake valve with the smallest intake runner that meets your cfm demand. Overwhelming majority of the time, that's your best performing head.
/rant
In short, yes, I'm talking about the air going into the chamber drawn in by the pistons going down, but The trick is getting the air to go in and then stay in. Otherwise, we wouldn't need heads in the first place. First, go listen to this podcast --
Don't cheat. Listen to it, and take notes, even if it doesn't make sense the first time around. Now, the top three concerns when designing or selecting heads is airspeed, airspeed, and airspeed.
First, there is the airspeed in the port itself. If you think in terms of cfm (cubic feet per minute), if you get 400 cfm through a 4 sq in hole, it moves slower than through a 3 sq in hole. Similarly, a properly shaped 4 sq in hole has the potential to flow a lot more air than a properly shaped 3 in hole. Now, when I say "shape", I don't mean cathedral or square. I mean in terms of three dimensions, the shape of the runner leading up to the choke point and the shape of the runner after the choke point. In this way. since the choke point is right at the valve curtain until it opens enough, the combustion chamber is part of the intake tract, and so the combustion chamber shape even affects flow. And there is also the problem that air does not have constant volume or density, so a CFM is relative, but I digress...
Basic principles -- You don't trap cfm inside the engine. You trap air molecules. The way you calculate the number of air molecules is mass. So the idea is to trap as high an airmass in the cylinder as you can.
The reason all this is so important is that the air has a limited time to fill the chamber. BUT a significant chunk of that time is spent filling the chamber while the piston is on its way back up. This is where momentum comes into play. Momentum is a function of both mass and velocity, as is kinetic energy. In fact, if you want to know, kinetic energy is momentum integrated by velocity. So there are two ways to increase the momentum of air. One is to increase mass flow. This is done by increasing air density, which is done by either hunting around for a track with a great DA or boost. The other option is to increase air velocity in the port. With increase air momentum, as the piston passes BDC and begins to come back up, the air can, briefly, continue to fill the cylinder even against the obvious pressure gradient. The masses will kind of shop around based on flow numbers, and there is truth in the flow numbers as far as they can show the potential the heads have for making power. But many times, designers will sacrifice peak flow to gain velocity, as long as the engine has enough air to make its intended power. The reasoning is that the engine rotates sometimes 70 degrees before that valve closes, and the momentum of the air filling the chamber makes all the difference in how much total air is trapped.
So head 1 might flow 10 cfm better, but with poor velocity, it stops filling the cylinder and may even allow for airflow to change direction before the intake valve shuts. Head 2 might flow 10 cm less, but with very good velocity, so the cylinder continues to fill until the valve shuts, resulting in more total air trapped in the cylinder. This is one side to the whole cathedral vs square argument. Using cc as a gauge, the cathedral ports are smaller. So, given equal bore and stroke, the port velocity at low flow demands is better on a cathedral head. not because it is shaped like a cathedral, but because the port cross section area is smaller, so the air must flow faster to meet the demands of the engine. The other side effect is that the increased port velocity can somewhat mechanically tame a large cam. This has historically been one the issues with the larger OEM (square ports) heads. They routinely get overcammed, because people are used to camming cathedral heads. If you run a larger cross section head, you need less cam at the same RPM to fill the cylinder. Too much cam for the head, or too much head for the cam makes the motor feel lazy. And it all comes back to that initial airspeed through the port.
Now, the other side of that peanut butter and jelly sandwich... total flow. The head that flows more will support more power. I didn't say "make" more power. I said "support". The rest of the combination needs to be right, or it's a waste of cylinder head. Let's take a 700 bhp 427 as an example to hopefully make the math easy. A cylinder head that flows 330 cfm on an honest bench can make that kind of power if everything is perfect. Now, the reality is rarely perfect, so let's aim high and look for a 350 cfm head. OK. Now that that's done, what's the smallest port out there that flows 350 cfm on an honest bench? it's going to be in the 240-245 range. So, enter the TFS 245 and all the great results that head gets on strokers. Yay, team. Still tracking?
Now, on that same engine, lets put a 270 cc head on there that flows 370. This leads to how I like to evaluate heads for selection purposes. Flow / port volume = port efficiency, which is the best overall indicator I know of for determining port velocity as a customer over the internet. 350/245= 1.43. 370/270 = 1.37. So all things being close to equal, I can expect the engine to perform better with the smaller head, as it will be most likely to consistently trap the highest airmass. And that is why you see TFS 245 cathedrals walking ported LS3s on 40x-41x strokers. Although, I'd argue the guy running a well set up 240cc rectangle port head would change a lot of default cathedral thinking. I know of a 388 with those 240cc heads made 6xx to the tires all motor at 8000 rpm. If you really want to talk port efficiency, look at the C5R heads that reached 370 cm on 225cc, and note the C5R is still the most represented head on the all motor fast lists.
Ok, so now, let's look at a motor I'm more directly familiar with. A 440 with a power goal of 820-850 bhp. To support this kind of power, the head must flow 405 by the math, but let's be real, it needs to flow 415 at least, and really 420's would be even better to allow for some room for imperfection. So then, I start shopping for what heads can hit that flow number and list them out, and then I go to the smallest port on the list. And that's how i ended up working with Tony on this LS7 top end. There are plenty of heads out there flowing in the 420's. Only one is under 270cc that I could find. But wait... I can get a 350cc runner that flows 450 and get even more air! True, although when you look at the port efficiency numbers, you see that the velocity is going to be low. If you really want to talk port efficiency, look at the C5R heads that reached 370 cm on 225cc, and note the C5R is still the most represented head on the all motor LS fast lists.
So then, why would anyone ever want a big port set up? RPM. At high RPM, the length of time it takes for the engine to rotate from BDC to IVC is lower when compared to slower RPM. As a result, the airspeed is less critical. Ever hear that the LS3 heads shine with RPM? They do. The reason is the port is coming into it's own up top, where airspeed is les critical, but gross flow is king. But to achieve that kind of RPM in the first place, the cam must have really large durations, so it'll be a turd until it gets into its intended operating range. Let's face it, nobody on this site is going to go beat a NASCAR engine with their cathedral port builds just because they make more torque down low. Also there is Boost. Air density is so much higher that the speed is less critical to continuing cylinder fill past BDC.
And all of the above is not getting into airspeed differentials between the large radius and short radius, the port tuning, the exhaust scavenging, etc. And most of that comes later in the selection process anyway. For most people, it's really not too complex. Take the 54% of the bore, and there is your optimal intake valve size in 99% of the cases. Choose your power goal and divide by 2 to get your rough CFM demands of the port. Find the head that can use the proper sized intake valve with the smallest intake runner that meets your cfm demand. Overwhelming majority of the time, that's your best performing head.
/rant
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09-28-2020, 07:52 PM
#93
TECH Enthusiast
Darth well said above. I would also add we all talk about max cfm - where a lot of the work is done down low especially in the scavaging cycle. In David Vizards book he mentions the lift at sub .200-.300 is very important at this part of the cycle as that is when the engine or piston is creating the most vacuum (getting the party started). I think you will find that Tony's heads probably also have pretty good .100-.300 numbers. I think another thing people over look is Mr. Exhaust port on the LS7 its so-so. The cathedral actually has a pretty good exhaust port. With the LS7 they make it up in cam duration by adding another 4-8 degrees resulting in a 12-16 degree delta with the intake. As I said before, I wish back in the mid-1990s the engine guys at GM were at lunch and said "hey since we are changing everything on the small block for this LS program, lets move that bore spacing from 4.40 inches to a nice even 4.5 inches and that deck height of 9.24 is kind of kooky lets just make it 9.5 inches. We would all have 4.25 bores with 2.25 intakes and 1.70 exhaust valves.
09-28-2020, 08:59 PM
#94
I'll give it my best shot. It's not easy to communicate, but once you see it, it's not hard to understand. SO if you can't follow what I'm about to type, it's likely my inability to articulate this.
In short, yes, I'm talking about the air going into the chamber drawn in by the pistons going down, but The trick is getting the air to go in and then stay in. Otherwise, we wouldn't need heads in the first place. First, go listen to this podcast -- 152 - Power and Speed - Darin Morgan Intake System Design Expert - YouTube
Don't cheat. Listen to it, and take notes, even if it doesn't make sense the first time around. Now, the top three concerns when designing or selecting heads is airspeed, airspeed, and airspeed.
First, there is the airspeed in the port itself. If you think in terms of cfm (cubic feet per minute), if you get 400 cfm through a 4 sq in hole, it moves slower than through a 3 sq in hole. Similarly, a properly shaped 4 sq in hole has the potential to flow a lot more air than a properly shaped 3 in hole. Now, when I say "shape", I don't mean cathedral or square. I mean in terms of three dimensions, the shape of the runner leading up to the choke point and the shape of the runner after the choke point. In this way. since the choke point is right at the valve curtain until it opens enough, the combustion chamber is part of the intake tract, and so the combustion chamber shape even affects flow. And there is also the problem that air does not have constant volume or density, so a CFM is relative, but I digress...
Basic principles -- You don't trap cfm inside the engine. You trap air molecules. The way you calculate the number of air molecules is mass. So the idea is to trap as high an airmass in the cylinder as you can.
The reason all this is so important is that the air has a limited time to fill the chamber. BUT a significant chunk of that time is spent filling the chamber while the piston is on its way back up. This is where momentum comes into play. Momentum is a function of both mass and velocity, as is kinetic energy. In fact, if you want to know, kinetic energy is momentum integrated by velocity. So there are two ways to increase the momentum of air. One is to increase mass flow. This is done by increasing air density, which is done by either hunting around for a track with a great DA or boost. The other option is to increase air velocity in the port. With increase air momentum, as the piston passes BDC and begins to come back up, the air can, briefly, continue to fill the cylinder even against the obvious pressure gradient. The masses will kind of shop around based on flow numbers, and there is truth in the flow numbers as far as they can show the potential the heads have for making power. But many times, designers will sacrifice peak flow to gain velocity, as long as the engine has enough air to make its intended power. The reasoning is that the engine rotates sometimes 70 degrees before that valve closes, and the momentum of the air filling the chamber makes all the difference in how much total air is trapped.
So head 1 might flow 10 cfm better, but with poor velocity, it stops filling the cylinder and may even allow for airflow to change direction before the intake valve shuts. Head 2 might flow 10 cm less, but with very good velocity, so the cylinder continues to fill until the valve shuts, resulting in more total air trapped in the cylinder. This is one side to the whole cathedral vs square argument. Using cc as a gauge, the cathedral ports are smaller. So, given equal bore and stroke, the port velocity at low flow demands is better on a cathedral head. not because it is shaped like a cathedral, but because the port cross section area is smaller, so the air must flow faster to meet the demands of the engine. The other side effect is that the increased port velocity can somewhat mechanically tame a large cam. This has historically been one the issues with the larger OEM (square ports) heads. They routinely get overcammed, because people are used to camming cathedral heads. If you run a larger cross section head, you need less cam at the same RPM to fill the cylinder. Too much cam for the head, or too much head for the cam makes the motor feel lazy. And it all comes back to that initial airspeed through the port.
Now, the other side of that peanut butter and jelly sandwich... total flow. The head that flows more will support more power. I didn't say "make" more power. I said "support". The rest of the combination needs to be right, or it's a waste of cylinder head. Let's take a 700 bhp 427 as an example to hopefully make the math easy. A cylinder head that flows 330 cfm on an honest bench can make that kind of power if everything is perfect. Now, the reality is rarely perfect, so let's aim high and look for a 350 cfm head. OK. Now that that's done, what's the smallest port out there that flows 350 cfm on an honest bench? it's going to be in the 240-245 range. So, enter the TFS 245 and all the great results that head gets on strokers. Yay, team. Still tracking?
Now, on that same engine, lets put a 270 cc head on there that flows 370. This leads to how I like to evaluate heads for selection purposes. Flow / port volume = port efficiency, which is the best overall indicator I know of for determining port velocity as a customer over the internet. 350/245= 1.43. 370/270 = 1.37. So all things being close to equal, I can expect the engine to perform better with the smaller head, as it will be most likely to consistently trap the highest airmass. And that is why you see TFS 245 cathedrals walking ported LS3s on 40x-41x strokers. Although, I'd argue the guy running a well set up 240cc rectangle port head would change a lot of default cathedral thinking. I know of a 388 with those 240cc heads made 6xx to the tires all motor at 8000 rpm. If you really want to talk port efficiency, look at the C5R heads that reached 370 cm on 225cc, and note the C5R is still the most represented head on the all motor fast lists.
Ok, so now, let's look at a motor I'm more directly familiar with. A 440 with a power goal of 820-850 bhp. To support this kind of power, the head must flow 405 by the math, but let's be real, it needs to flow 415 at least, and really 420's would be even better to allow for some room for imperfection. So then, I start shopping for what heads can hit that flow number and list them out, and then I go to the smallest port on the list. And that's how i ended up working with Tony on this LS7 top end. There are plenty of heads out there flowing in the 420's. Only one is under 270cc that I could find. But wait... I can get a 350cc runner that flows 450 and get even more air! True, although when you look at the port efficiency numbers, you see that the velocity is going to be low. If you really want to talk port efficiency, look at the C5R heads that reached 370 cm on 225cc, and note the C5R is still the most represented head on the all motor LS fast lists.
So then, why would anyone ever want a big port set up? RPM. At high RPM, the length of time it takes for the engine to rotate from BDC to IVC is lower when compared to slower RPM. As a result, the airspeed is less critical. Ever hear that the LS3 heads shine with RPM? They do. The reason is the port is coming into it's own up top, where airspeed is les critical, but gross flow is king. But to achieve that kind of RPM in the first place, the cam must have really large durations, so it'll be a turd until it gets into its intended operating range. Let's face it, nobody on this site is going to go beat a NASCAR engine with their cathedral port builds just because they make more torque down low. Also there is Boost. Air density is so much higher that the speed is less critical to continuing cylinder fill past BDC.
And all of the above is not getting into airspeed differentials between the large radius and short radius, the port tuning, the exhaust scavenging, etc. And most of that comes later in the selection process anyway. For most people, it's really not too complex. Take the 54% of the bore, and there is your optimal intake valve size in 99% of the cases. Choose your power goal and divide by 2 to get your rough CFM demands of the port. Find the head that can use the proper sized intake valve with the smallest intake runner that meets your cfm demand. Overwhelming majority of the time, that's your best performing head.
/rant
In short, yes, I'm talking about the air going into the chamber drawn in by the pistons going down, but The trick is getting the air to go in and then stay in. Otherwise, we wouldn't need heads in the first place. First, go listen to this podcast -- 152 - Power and Speed - Darin Morgan Intake System Design Expert - YouTube
Don't cheat. Listen to it, and take notes, even if it doesn't make sense the first time around. Now, the top three concerns when designing or selecting heads is airspeed, airspeed, and airspeed.
First, there is the airspeed in the port itself. If you think in terms of cfm (cubic feet per minute), if you get 400 cfm through a 4 sq in hole, it moves slower than through a 3 sq in hole. Similarly, a properly shaped 4 sq in hole has the potential to flow a lot more air than a properly shaped 3 in hole. Now, when I say "shape", I don't mean cathedral or square. I mean in terms of three dimensions, the shape of the runner leading up to the choke point and the shape of the runner after the choke point. In this way. since the choke point is right at the valve curtain until it opens enough, the combustion chamber is part of the intake tract, and so the combustion chamber shape even affects flow. And there is also the problem that air does not have constant volume or density, so a CFM is relative, but I digress...
Basic principles -- You don't trap cfm inside the engine. You trap air molecules. The way you calculate the number of air molecules is mass. So the idea is to trap as high an airmass in the cylinder as you can.
The reason all this is so important is that the air has a limited time to fill the chamber. BUT a significant chunk of that time is spent filling the chamber while the piston is on its way back up. This is where momentum comes into play. Momentum is a function of both mass and velocity, as is kinetic energy. In fact, if you want to know, kinetic energy is momentum integrated by velocity. So there are two ways to increase the momentum of air. One is to increase mass flow. This is done by increasing air density, which is done by either hunting around for a track with a great DA or boost. The other option is to increase air velocity in the port. With increase air momentum, as the piston passes BDC and begins to come back up, the air can, briefly, continue to fill the cylinder even against the obvious pressure gradient. The masses will kind of shop around based on flow numbers, and there is truth in the flow numbers as far as they can show the potential the heads have for making power. But many times, designers will sacrifice peak flow to gain velocity, as long as the engine has enough air to make its intended power. The reasoning is that the engine rotates sometimes 70 degrees before that valve closes, and the momentum of the air filling the chamber makes all the difference in how much total air is trapped.
So head 1 might flow 10 cfm better, but with poor velocity, it stops filling the cylinder and may even allow for airflow to change direction before the intake valve shuts. Head 2 might flow 10 cm less, but with very good velocity, so the cylinder continues to fill until the valve shuts, resulting in more total air trapped in the cylinder. This is one side to the whole cathedral vs square argument. Using cc as a gauge, the cathedral ports are smaller. So, given equal bore and stroke, the port velocity at low flow demands is better on a cathedral head. not because it is shaped like a cathedral, but because the port cross section area is smaller, so the air must flow faster to meet the demands of the engine. The other side effect is that the increased port velocity can somewhat mechanically tame a large cam. This has historically been one the issues with the larger OEM (square ports) heads. They routinely get overcammed, because people are used to camming cathedral heads. If you run a larger cross section head, you need less cam at the same RPM to fill the cylinder. Too much cam for the head, or too much head for the cam makes the motor feel lazy. And it all comes back to that initial airspeed through the port.
Now, the other side of that peanut butter and jelly sandwich... total flow. The head that flows more will support more power. I didn't say "make" more power. I said "support". The rest of the combination needs to be right, or it's a waste of cylinder head. Let's take a 700 bhp 427 as an example to hopefully make the math easy. A cylinder head that flows 330 cfm on an honest bench can make that kind of power if everything is perfect. Now, the reality is rarely perfect, so let's aim high and look for a 350 cfm head. OK. Now that that's done, what's the smallest port out there that flows 350 cfm on an honest bench? it's going to be in the 240-245 range. So, enter the TFS 245 and all the great results that head gets on strokers. Yay, team. Still tracking?
Now, on that same engine, lets put a 270 cc head on there that flows 370. This leads to how I like to evaluate heads for selection purposes. Flow / port volume = port efficiency, which is the best overall indicator I know of for determining port velocity as a customer over the internet. 350/245= 1.43. 370/270 = 1.37. So all things being close to equal, I can expect the engine to perform better with the smaller head, as it will be most likely to consistently trap the highest airmass. And that is why you see TFS 245 cathedrals walking ported LS3s on 40x-41x strokers. Although, I'd argue the guy running a well set up 240cc rectangle port head would change a lot of default cathedral thinking. I know of a 388 with those 240cc heads made 6xx to the tires all motor at 8000 rpm. If you really want to talk port efficiency, look at the C5R heads that reached 370 cm on 225cc, and note the C5R is still the most represented head on the all motor fast lists.
Ok, so now, let's look at a motor I'm more directly familiar with. A 440 with a power goal of 820-850 bhp. To support this kind of power, the head must flow 405 by the math, but let's be real, it needs to flow 415 at least, and really 420's would be even better to allow for some room for imperfection. So then, I start shopping for what heads can hit that flow number and list them out, and then I go to the smallest port on the list. And that's how i ended up working with Tony on this LS7 top end. There are plenty of heads out there flowing in the 420's. Only one is under 270cc that I could find. But wait... I can get a 350cc runner that flows 450 and get even more air! True, although when you look at the port efficiency numbers, you see that the velocity is going to be low. If you really want to talk port efficiency, look at the C5R heads that reached 370 cm on 225cc, and note the C5R is still the most represented head on the all motor LS fast lists.
So then, why would anyone ever want a big port set up? RPM. At high RPM, the length of time it takes for the engine to rotate from BDC to IVC is lower when compared to slower RPM. As a result, the airspeed is less critical. Ever hear that the LS3 heads shine with RPM? They do. The reason is the port is coming into it's own up top, where airspeed is les critical, but gross flow is king. But to achieve that kind of RPM in the first place, the cam must have really large durations, so it'll be a turd until it gets into its intended operating range. Let's face it, nobody on this site is going to go beat a NASCAR engine with their cathedral port builds just because they make more torque down low. Also there is Boost. Air density is so much higher that the speed is less critical to continuing cylinder fill past BDC.
And all of the above is not getting into airspeed differentials between the large radius and short radius, the port tuning, the exhaust scavenging, etc. And most of that comes later in the selection process anyway. For most people, it's really not too complex. Take the 54% of the bore, and there is your optimal intake valve size in 99% of the cases. Choose your power goal and divide by 2 to get your rough CFM demands of the port. Find the head that can use the proper sized intake valve with the smallest intake runner that meets your cfm demand. Overwhelming majority of the time, that's your best performing head.
/rant
09-29-2020, 07:56 AM
#95
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Darth well said above. I would also add we all talk about max cfm - where a lot of the work is done down low especially in the scavaging cycle. In David Vizards book he mentions the lift at sub .200-.300 is very important at this part of the cycle as that is when the engine or piston is creating the most vacuum (getting the party started). I think you will find that Tony's heads probably also have pretty good .100-.300 numbers. I think another thing people over look is Mr. Exhaust port on the LS7 its so-so. The cathedral actually has a pretty good exhaust port. With the LS7 they make it up in cam duration by adding another 4-8 degrees resulting in a 12-16 degree delta with the intake. As I said before, I wish back in the mid-1990s the engine guys at GM were at lunch and said "hey since we are changing everything on the small block for this LS program, lets move that bore spacing from 4.40 inches to a nice even 4.5 inches and that deck height of 9.24 is kind of kooky lets just make it 9.5 inches. We would all have 4.25 bores with 2.25 intakes and 1.70 exhaust valves.
The other really big airspeed contributor is the differential between short side and large side radius. The lower that differential is, the more overall flow you can move and with the port. and build better overall port speed. Enter aftermarket heads with raised runners. Th stock heads have a pretty sharp short side radius, which makes for a higher differential. One thing I like to do is to look down the port to see how much of the intake valve is visible. More is better.
09-29-2020, 01:51 PM
#96
On The Tree
I am a little shy of Frankenstein. One of the smartest LS guys around mentioned to me that none of the Frankenstein 243 heads that he had seen made the kind of power that their specs would corelate to. That gave me a bad taste in my mouth for them. But DAMN, 265cc from cathedrals? For $4k, they better perform better than LS7 castings.
Yes our F110s are very efficient how we engineered them. There will be a few projects coming out early 2021 with them. Mostly turbo guys and 1 N/A 400ci deal.
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DualQuadDave (09-29-2020)
09-29-2020, 05:00 PM
#97
TECH Enthusiast
On a typical say 295 advertised duration cam say 53 degrees in the .090 lift (.050 x 1.8) another 80 or so degrees from .090 lift to 360 lift (.200 x 1.8) and the remaining say 160 another degrees at above .360 lift to say a .660 lift cam (based on say comp cams .200 tappet lift degrees they show in lobe catalog). So about 54% of the time above 360 valve lift.
09-29-2020, 08:50 PM
#98
I'll give it my best shot. It's not easy to communicate, but once you see it, it's not hard to understand. SO if you can't follow what I'm about to type, it's likely my inability to articulate this.
In short, yes, I'm talking about the air going into the chamber drawn in by the pistons going down, but The trick is getting the air to go in and then stay in. Otherwise, we wouldn't need heads in the first place. First, go listen to this podcast -- 152 - Power and Speed - Darin Morgan Intake System Design Expert - YouTube
Don't cheat. Listen to it, and take notes, even if it doesn't make sense the first time around. Now, the top three concerns when designing or selecting heads is airspeed, airspeed, and airspeed.
First, there is the airspeed in the port itself. If you think in terms of cfm (cubic feet per minute), if you get 400 cfm through a 4 sq in hole, it moves slower than through a 3 sq in hole. Similarly, a properly shaped 4 sq in hole has the potential to flow a lot more air than a properly shaped 3 in hole. Now, when I say "shape", I don't mean cathedral or square. I mean in terms of three dimensions, the shape of the runner leading up to the choke point and the shape of the runner after the choke point. In this way. since the choke point is right at the valve curtain until it opens enough, the combustion chamber is part of the intake tract, and so the combustion chamber shape even affects flow. And there is also the problem that air does not have constant volume or density, so a CFM is relative, but I digress...
Basic principles -- You don't trap cfm inside the engine. You trap air molecules. The way you calculate the number of air molecules is mass. So the idea is to trap as high an airmass in the cylinder as you can.
The reason all this is so important is that the air has a limited time to fill the chamber. BUT a significant chunk of that time is spent filling the chamber while the piston is on its way back up. This is where momentum comes into play. Momentum is a function of both mass and velocity, as is kinetic energy. In fact, if you want to know, kinetic energy is momentum integrated by velocity. So there are two ways to increase the momentum of air. One is to increase mass flow. This is done by increasing air density, which is done by either hunting around for a track with a great DA or boost. The other option is to increase air velocity in the port. With increase air momentum, as the piston passes BDC and begins to come back up, the air can, briefly, continue to fill the cylinder even against the obvious pressure gradient. The masses will kind of shop around based on flow numbers, and there is truth in the flow numbers as far as they can show the potential the heads have for making power. But many times, designers will sacrifice peak flow to gain velocity, as long as the engine has enough air to make its intended power. The reasoning is that the engine rotates sometimes 70 degrees before that valve closes, and the momentum of the air filling the chamber makes all the difference in how much total air is trapped.
So head 1 might flow 10 cfm better, but with poor velocity, it stops filling the cylinder and may even allow for airflow to change direction before the intake valve shuts. Head 2 might flow 10 cm less, but with very good velocity, so the cylinder continues to fill until the valve shuts, resulting in more total air trapped in the cylinder. This is one side to the whole cathedral vs square argument. Using cc as a gauge, the cathedral ports are smaller. So, given equal bore and stroke, the port velocity at low flow demands is better on a cathedral head. not because it is shaped like a cathedral, but because the port cross section area is smaller, so the air must flow faster to meet the demands of the engine. The other side effect is that the increased port velocity can somewhat mechanically tame a large cam. This has historically been one the issues with the larger OEM (square ports) heads. They routinely get overcammed, because people are used to camming cathedral heads. If you run a larger cross section head, you need less cam at the same RPM to fill the cylinder. Too much cam for the head, or too much head for the cam makes the motor feel lazy. And it all comes back to that initial airspeed through the port.
Now, the other side of that peanut butter and jelly sandwich... total flow. The head that flows more will support more power. I didn't say "make" more power. I said "support". The rest of the combination needs to be right, or it's a waste of cylinder head. Let's take a 700 bhp 427 as an example to hopefully make the math easy. A cylinder head that flows 330 cfm on an honest bench can make that kind of power if everything is perfect. Now, the reality is rarely perfect, so let's aim high and look for a 350 cfm head. OK. Now that that's done, what's the smallest port out there that flows 350 cfm on an honest bench? it's going to be in the 240-245 range. So, enter the TFS 245 and all the great results that head gets on strokers. Yay, team. Still tracking?
Now, on that same engine, lets put a 270 cc head on there that flows 370. This leads to how I like to evaluate heads for selection purposes. Flow / port volume = port efficiency, which is the best overall indicator I know of for determining port velocity as a customer over the internet. 350/245= 1.43. 370/270 = 1.37. So all things being close to equal, I can expect the engine to perform better with the smaller head, as it will be most likely to consistently trap the highest airmass. And that is why you see TFS 245 cathedrals walking ported LS3s on 40x-41x strokers. Although, I'd argue the guy running a well set up 240cc rectangle port head would change a lot of default cathedral thinking. I know of a 388 with those 240cc heads made 6xx to the tires all motor at 8000 rpm. If you really want to talk port efficiency, look at the C5R heads that reached 370 cm on 225cc, and note the C5R is still the most represented head on the all motor fast lists.
Ok, so now, let's look at a motor I'm more directly familiar with. A 440 with a power goal of 820-850 bhp. To support this kind of power, the head must flow 405 by the math, but let's be real, it needs to flow 415 at least, and really 420's would be even better to allow for some room for imperfection. So then, I start shopping for what heads can hit that flow number and list them out, and then I go to the smallest port on the list. And that's how i ended up working with Tony on this LS7 top end. There are plenty of heads out there flowing in the 420's. Only one is under 270cc that I could find. But wait... I can get a 350cc runner that flows 450 and get even more air! True, although when you look at the port efficiency numbers, you see that the velocity is going to be low. If you really want to talk port efficiency, look at the C5R heads that reached 370 cm on 225cc, and note the C5R is still the most represented head on the all motor LS fast lists.
So then, why would anyone ever want a big port set up? RPM. At high RPM, the length of time it takes for the engine to rotate from BDC to IVC is lower when compared to slower RPM. As a result, the airspeed is less critical. Ever hear that the LS3 heads shine with RPM? They do. The reason is the port is coming into it's own up top, where airspeed is les critical, but gross flow is king. But to achieve that kind of RPM in the first place, the cam must have really large durations, so it'll be a turd until it gets into its intended operating range. Let's face it, nobody on this site is going to go beat a NASCAR engine with their cathedral port builds just because they make more torque down low. Also there is Boost. Air density is so much higher that the speed is less critical to continuing cylinder fill past BDC.
And all of the above is not getting into airspeed differentials between the large radius and short radius, the port tuning, the exhaust scavenging, etc. And most of that comes later in the selection process anyway. For most people, it's really not too complex. Take the 54% of the bore, and there is your optimal intake valve size in 99% of the cases. Choose your power goal and divide by 2 to get your rough CFM demands of the port. Find the head that can use the proper sized intake valve with the smallest intake runner that meets your cfm demand. Overwhelming majority of the time, that's your best performing head.
/rant
In short, yes, I'm talking about the air going into the chamber drawn in by the pistons going down, but The trick is getting the air to go in and then stay in. Otherwise, we wouldn't need heads in the first place. First, go listen to this podcast -- 152 - Power and Speed - Darin Morgan Intake System Design Expert - YouTube
Don't cheat. Listen to it, and take notes, even if it doesn't make sense the first time around. Now, the top three concerns when designing or selecting heads is airspeed, airspeed, and airspeed.
First, there is the airspeed in the port itself. If you think in terms of cfm (cubic feet per minute), if you get 400 cfm through a 4 sq in hole, it moves slower than through a 3 sq in hole. Similarly, a properly shaped 4 sq in hole has the potential to flow a lot more air than a properly shaped 3 in hole. Now, when I say "shape", I don't mean cathedral or square. I mean in terms of three dimensions, the shape of the runner leading up to the choke point and the shape of the runner after the choke point. In this way. since the choke point is right at the valve curtain until it opens enough, the combustion chamber is part of the intake tract, and so the combustion chamber shape even affects flow. And there is also the problem that air does not have constant volume or density, so a CFM is relative, but I digress...
Basic principles -- You don't trap cfm inside the engine. You trap air molecules. The way you calculate the number of air molecules is mass. So the idea is to trap as high an airmass in the cylinder as you can.
The reason all this is so important is that the air has a limited time to fill the chamber. BUT a significant chunk of that time is spent filling the chamber while the piston is on its way back up. This is where momentum comes into play. Momentum is a function of both mass and velocity, as is kinetic energy. In fact, if you want to know, kinetic energy is momentum integrated by velocity. So there are two ways to increase the momentum of air. One is to increase mass flow. This is done by increasing air density, which is done by either hunting around for a track with a great DA or boost. The other option is to increase air velocity in the port. With increase air momentum, as the piston passes BDC and begins to come back up, the air can, briefly, continue to fill the cylinder even against the obvious pressure gradient. The masses will kind of shop around based on flow numbers, and there is truth in the flow numbers as far as they can show the potential the heads have for making power. But many times, designers will sacrifice peak flow to gain velocity, as long as the engine has enough air to make its intended power. The reasoning is that the engine rotates sometimes 70 degrees before that valve closes, and the momentum of the air filling the chamber makes all the difference in how much total air is trapped.
So head 1 might flow 10 cfm better, but with poor velocity, it stops filling the cylinder and may even allow for airflow to change direction before the intake valve shuts. Head 2 might flow 10 cm less, but with very good velocity, so the cylinder continues to fill until the valve shuts, resulting in more total air trapped in the cylinder. This is one side to the whole cathedral vs square argument. Using cc as a gauge, the cathedral ports are smaller. So, given equal bore and stroke, the port velocity at low flow demands is better on a cathedral head. not because it is shaped like a cathedral, but because the port cross section area is smaller, so the air must flow faster to meet the demands of the engine. The other side effect is that the increased port velocity can somewhat mechanically tame a large cam. This has historically been one the issues with the larger OEM (square ports) heads. They routinely get overcammed, because people are used to camming cathedral heads. If you run a larger cross section head, you need less cam at the same RPM to fill the cylinder. Too much cam for the head, or too much head for the cam makes the motor feel lazy. And it all comes back to that initial airspeed through the port.
Now, the other side of that peanut butter and jelly sandwich... total flow. The head that flows more will support more power. I didn't say "make" more power. I said "support". The rest of the combination needs to be right, or it's a waste of cylinder head. Let's take a 700 bhp 427 as an example to hopefully make the math easy. A cylinder head that flows 330 cfm on an honest bench can make that kind of power if everything is perfect. Now, the reality is rarely perfect, so let's aim high and look for a 350 cfm head. OK. Now that that's done, what's the smallest port out there that flows 350 cfm on an honest bench? it's going to be in the 240-245 range. So, enter the TFS 245 and all the great results that head gets on strokers. Yay, team. Still tracking?
Now, on that same engine, lets put a 270 cc head on there that flows 370. This leads to how I like to evaluate heads for selection purposes. Flow / port volume = port efficiency, which is the best overall indicator I know of for determining port velocity as a customer over the internet. 350/245= 1.43. 370/270 = 1.37. So all things being close to equal, I can expect the engine to perform better with the smaller head, as it will be most likely to consistently trap the highest airmass. And that is why you see TFS 245 cathedrals walking ported LS3s on 40x-41x strokers. Although, I'd argue the guy running a well set up 240cc rectangle port head would change a lot of default cathedral thinking. I know of a 388 with those 240cc heads made 6xx to the tires all motor at 8000 rpm. If you really want to talk port efficiency, look at the C5R heads that reached 370 cm on 225cc, and note the C5R is still the most represented head on the all motor fast lists.
Ok, so now, let's look at a motor I'm more directly familiar with. A 440 with a power goal of 820-850 bhp. To support this kind of power, the head must flow 405 by the math, but let's be real, it needs to flow 415 at least, and really 420's would be even better to allow for some room for imperfection. So then, I start shopping for what heads can hit that flow number and list them out, and then I go to the smallest port on the list. And that's how i ended up working with Tony on this LS7 top end. There are plenty of heads out there flowing in the 420's. Only one is under 270cc that I could find. But wait... I can get a 350cc runner that flows 450 and get even more air! True, although when you look at the port efficiency numbers, you see that the velocity is going to be low. If you really want to talk port efficiency, look at the C5R heads that reached 370 cm on 225cc, and note the C5R is still the most represented head on the all motor LS fast lists.
So then, why would anyone ever want a big port set up? RPM. At high RPM, the length of time it takes for the engine to rotate from BDC to IVC is lower when compared to slower RPM. As a result, the airspeed is less critical. Ever hear that the LS3 heads shine with RPM? They do. The reason is the port is coming into it's own up top, where airspeed is les critical, but gross flow is king. But to achieve that kind of RPM in the first place, the cam must have really large durations, so it'll be a turd until it gets into its intended operating range. Let's face it, nobody on this site is going to go beat a NASCAR engine with their cathedral port builds just because they make more torque down low. Also there is Boost. Air density is so much higher that the speed is less critical to continuing cylinder fill past BDC.
And all of the above is not getting into airspeed differentials between the large radius and short radius, the port tuning, the exhaust scavenging, etc. And most of that comes later in the selection process anyway. For most people, it's really not too complex. Take the 54% of the bore, and there is your optimal intake valve size in 99% of the cases. Choose your power goal and divide by 2 to get your rough CFM demands of the port. Find the head that can use the proper sized intake valve with the smallest intake runner that meets your cfm demand. Overwhelming majority of the time, that's your best performing head.
/rant
I really like the comment that someone that doesn't have much experience will estimate their ability at 200% and someone with a lot of experience will estimate their ability at 50%.
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DualQuadDave (09-30-2020)
09-29-2020, 09:16 PM
#99
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Originally Posted by FCar2000TA
That made my brain hurt. That is a **** ton of information! I never considered that airspeed does not change with air density, it makes a lot of sense, but I had never considered that. Kind of makes me feel stupid that I didn't realize that. It is also interesting that there is no way to get rid of turbulence in the combustion chamber. Most of everything else was over my head.
I really like the comment that someone that doesn't have much experience will estimate their ability at 200% and someone with a lot of experience will estimate their ability at 50%.
I really like the comment that someone that doesn't have much experience will estimate their ability at 200% and someone with a lot of experience will estimate their ability at 50%.
Give it a while to sink in and listen again. It starts to click home.
09-29-2020, 09:18 PM
#100
TECH Veteran
Darth... you telling to much info about the 40Xci to 41Xci on the heads. Just be quiet sometimes 