Effects of piston speed.
01-19-2006, 06:35 AM
#21
FormerVendor
Bret you are saying I am right in everything you just wrote. You say that the piston speed is the limit and then you say that at the same piston speed an F1 engine must have half the weight in rotating parts to have the same loads on it? I thought you just said piston speed was the limit but you are clearly agreeing with ME and saying that the doubling of rpm requires the pistons to have HALF the mass to stay together or they won't go the distance even at that same piston speed? Why can't the parts weigh just as much then if the load are proportional to piston speed. They aren't.
I say rpm is the totally dominating factor in rotating and recipricating loads and I am right as you just clearly stated. Also again show with your math why the loads on a 6 inch stroke engine are half that of a 3 inch stroke engine when you set piston speed equal. They have the same piston speed but the engine with double the stroke only has half the load? Why is this?
Also I would hope you know that you want all the mass possible out of any race engine requardless of all else as this allows the engine to accelerate faster and thus the car to accelerate faster. They aren't lightening up PS and Cup and F! parts to make them more reliable but rather to increase the transient engine acceleration. ALL of these parts are lightened as far as they can WITHOUT compromising reliability as they can be lightened too far and are in testing too see how light they can go. Excessively lightening engine parts does NOT increase relibility even most of the time Bret.
You've got too much in one post but restricted engines are much less loaded Bret than open engine and they do NOT turn the same piston speed as they are induction limited. Also the reason you see PS at the rpm they are at now is like we said they are VALVETRAIN LIMITED primarily at this point. You and your dad are comparing VASTLY different engines that have different problems. You are comparing a pushrod engine to a DOHC engine. A 20,000 rpm engine has GIANT G-forcess on it compared to a 10,000 rpm engine PLUS it will accumulate DOUBLE the cycles of wear and tear in the same amount of time. There are no 20,000 rpm pushrod engine with 1 inch of valve lift.
I think you would agree that doubling the G-force and doubling the cycles per unit time does NOT increase reliability. As you said they are REDUCING RPM to make the F1 engines go a little further. In 24 hour racing they will run huge engine where they can also to REDUCE RPM whether they end up at a higher piston speed or not the reduction in RPM with make them last tons longer.
I say rpm is the totally dominating factor in rotating and recipricating loads and I am right as you just clearly stated. Also again show with your math why the loads on a 6 inch stroke engine are half that of a 3 inch stroke engine when you set piston speed equal. They have the same piston speed but the engine with double the stroke only has half the load? Why is this?
Also I would hope you know that you want all the mass possible out of any race engine requardless of all else as this allows the engine to accelerate faster and thus the car to accelerate faster. They aren't lightening up PS and Cup and F! parts to make them more reliable but rather to increase the transient engine acceleration. ALL of these parts are lightened as far as they can WITHOUT compromising reliability as they can be lightened too far and are in testing too see how light they can go. Excessively lightening engine parts does NOT increase relibility even most of the time Bret.
You've got too much in one post but restricted engines are much less loaded Bret than open engine and they do NOT turn the same piston speed as they are induction limited. Also the reason you see PS at the rpm they are at now is like we said they are VALVETRAIN LIMITED primarily at this point. You and your dad are comparing VASTLY different engines that have different problems. You are comparing a pushrod engine to a DOHC engine. A 20,000 rpm engine has GIANT G-forcess on it compared to a 10,000 rpm engine PLUS it will accumulate DOUBLE the cycles of wear and tear in the same amount of time. There are no 20,000 rpm pushrod engine with 1 inch of valve lift.
I think you would agree that doubling the G-force and doubling the cycles per unit time does NOT increase reliability. As you said they are REDUCING RPM to make the F1 engines go a little further. In 24 hour racing they will run huge engine where they can also to REDUCE RPM whether they end up at a higher piston speed or not the reduction in RPM with make them last tons longer.
01-19-2006, 10:26 AM
#22
Eric,
Any of us can pick up a physics text book and understand this stuff.... g's increase at the square of RPM.
I just like to clear up what you write because you really generalize every situation WAY too much. I like how you try and single me out with easy math ****.... I get the physics and math pretty easily, that point is obvious. I don't think anyone of us can try and take credit for that math. The issue here is interconnecting the systems in front of us, what do they all have in common?
PS is not valvetrain limited.... they are bore limited. Until they get a larger bore spacing on their blocks, to increase bore and decrease stroke they are not going to turn the motors faster.
The answer to the endurance motors is simple for two reasons... 1. Amount of cylces on the motors is drastically higher in a 24 hour race than a 2 hour race. 2. Lemans motors (since they are the only non RPM restricted 24 hour motors), are RPM restricted by airflow with a orifice. The DP cars (24 Hours of Daytona) are RPM limited based on engine type. (LS1=7100rpm)
Here is my question other than the F1 V8 RPM limit....(still waiting on that one):
Why does EVERY set of rules for the top NA racing classes in the world limit bore size? F1 with a set number(96mm), Cup with a set number(4.185") and PS with a set bore spacing?(4.900") But don't limit the valvetrain in terms of mass, stiffness or lobe aggressiveness, the only difference is in the type of valve springs and component layout.... so why do they limit the bores? If there is no interconnection in that area with these motors I would love to know why they ALL do this.....
BTW Why is this the only dam topic you ever want to argue with me about if you say we agree so much? Seems like there are more things out there that are more important than piston speed, g's and force in terms of making HP.
Bret
Any of us can pick up a physics text book and understand this stuff.... g's increase at the square of RPM.
I just like to clear up what you write because you really generalize every situation WAY too much. I like how you try and single me out with easy math ****.... I get the physics and math pretty easily, that point is obvious. I don't think anyone of us can try and take credit for that math. The issue here is interconnecting the systems in front of us, what do they all have in common?
PS is not valvetrain limited.... they are bore limited. Until they get a larger bore spacing on their blocks, to increase bore and decrease stroke they are not going to turn the motors faster.
The answer to the endurance motors is simple for two reasons... 1. Amount of cylces on the motors is drastically higher in a 24 hour race than a 2 hour race. 2. Lemans motors (since they are the only non RPM restricted 24 hour motors), are RPM restricted by airflow with a orifice. The DP cars (24 Hours of Daytona) are RPM limited based on engine type. (LS1=7100rpm)
Here is my question other than the F1 V8 RPM limit....(still waiting on that one):
Why does EVERY set of rules for the top NA racing classes in the world limit bore size? F1 with a set number(96mm), Cup with a set number(4.185") and PS with a set bore spacing?(4.900") But don't limit the valvetrain in terms of mass, stiffness or lobe aggressiveness, the only difference is in the type of valve springs and component layout.... so why do they limit the bores? If there is no interconnection in that area with these motors I would love to know why they ALL do this.....
BTW Why is this the only dam topic you ever want to argue with me about if you say we agree so much? Seems like there are more things out there that are more important than piston speed, g's and force in terms of making HP.
Bret
01-19-2006, 10:54 AM
#23
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Originally Posted by Ben R
Superchargers and Turbochargers don't increase airspeed, velocity, or the volume of air entering an engine. Only the density of the air. Which means it has zero affect on where the engine will operate in terms of RPM.
You should think before you post something like that.
Air speed and volume in the intake port doesn't change significantly under boost conditions, but velocity at the intake valve does. When the valve opens there is a higher pressure differential and faster cylinder filling. This quicker filling of the cylinder along with the extra mass the boost delivers absolutely has an effect on the shape of the torque curve.
01-19-2006, 03:21 PM
#24
FormerVendor
Originally Posted by SStrokerAce
Eric,
Any of us can pick up a physics text book and understand this stuff.... g's increase at the square of RPM.
PS is not valvetrain limited.... they are bore limited. Until they get a larger bore spacing on their blocks, to increase bore and decrease stroke they are not going to turn the motors faster.
Why does EVERY set of rules for the top NA racing classes in the world limit bore size? F1 with a set number(96mm), Cup with a set number(4.185") and PS with a set bore spacing?(4.900") But don't limit the valvetrain in terms of mass, stiffness or lobe aggressiveness, the only difference is in the type of valve springs and component layout.... so why do they limit the bores? If there is no interconnection in that area with these motors I would love to know why they ALL do this.....
BTW Why is this the only dam topic you ever want to argue with me about if you say we agree so much? Seems like there are more things out there that are more important than piston speed, g's and force in terms of making HP.
Bret
Any of us can pick up a physics text book and understand this stuff.... g's increase at the square of RPM.
PS is not valvetrain limited.... they are bore limited. Until they get a larger bore spacing on their blocks, to increase bore and decrease stroke they are not going to turn the motors faster.
Why does EVERY set of rules for the top NA racing classes in the world limit bore size? F1 with a set number(96mm), Cup with a set number(4.185") and PS with a set bore spacing?(4.900") But don't limit the valvetrain in terms of mass, stiffness or lobe aggressiveness, the only difference is in the type of valve springs and component layout.... so why do they limit the bores? If there is no interconnection in that area with these motors I would love to know why they ALL do this.....
BTW Why is this the only dam topic you ever want to argue with me about if you say we agree so much? Seems like there are more things out there that are more important than piston speed, g's and force in terms of making HP.
Bret
I'm not arguing anything I am just stating the facts. NHRA Pro Stock is absolutely valvetrain limited but I guess you do not know that they have essentially been running heads almost the same for 4 years now. ALL the effort is on valvetrain and sealing and friction reduction etc. They have heads that can go over 600 cfm on the 4.700 bores some run but they are stuck with pushrods and big valve lift and big valves to get that airflow.
Now IHRA pro stock is airflow limited or bore limited at 815 inches and they run crazy FUBAR valvetrain hemi style heads that flow even more on their bores but at the much lower rpm they turn they can open big valve very far and very quickly so the engine can fully utilize the heads they have even though the valvetrain on them is NO match for NHRA PS. These guys NEED more airflow but NHRA needs more valvetrain since they already have heads to turn 11000 rpm.
We have people working at all these places Bret. That's that way it is. They are all getting their own Spintrons and they spend tons of time on them trying to get these huge intake valves to open over an inch and still stay in control at 10,000 rpm. ANYONE can turn more rpm but making POWER at higher and higher RPM is much harder. NHRA PS turns more rpm to make more power and they do every year. The bore has been the same for a long time now Bret.
What you and your dad were saying about piston speed being a mechanical limit though is simply wrong. It's a breathing limit set by your heads and intake and valvetrain. Some people understand this and some do not. If I destroke a regular small block enough I can turn 10,000 power peaks and lame out the cam but I will have much less total power. If I set about to maximize the amount of fuel and air I can burn through the engine with a given set of heads I will have a much higher lift and faster more aggressive lobe but it will now limit my rpm to a lower ceiling. If I make it too aggressive the cam may now limit rpm more than the heads. This is real racing.
Like I said and you can not say piston speed is hard on the rotating parts or is a limiter unless you know how you got that piston speed. A big stroker can make much more piston speed at a lower rpm so the heads can now breath better and make more power ala IHRA. Those engines make peak power at 6500 FPM piston speed. They go through the lights around 7500 FPM.
01-19-2006, 03:23 PM
#25
FormerVendor
Originally Posted by SStrokerAce
Why does EVERY set of rules for the top NA racing classes in the world limit bore size? F1 with a set number(96mm), Cup with a set number(4.185") and PS with a set bore spacing?(4.900") But don't limit the valvetrain in terms of mass, stiffness or lobe aggressiveness, the only difference is in the type of valve springs and component layout.... so why do they limit the bores? If there is no interconnection in that area with these motors I would love to know why they ALL do this.....
Big bores are good because you can run big intake valves! Who doesn't know this? Show me where I say big bores and heads are bad for making power! In an unlimited engine you will always try to maximize airflow which is cylinder head related and thus bore related. This does not then mean that you would run a 4.500 bore engine with a 1 inch stroke because it will be a total PIG and make no power since you will not be able to use that airflow with a 1 inch stroke. ANY company can make crap like that but they don't! I wonder why?
Also you need to realize who you are talking to until you've done a tenth the stuff we have with the LS1. We lost the front aluminum rod on our 9000 rpm LS1 engine because its turning 9000 rpm and has to run on aerated oil since we were still running a wet sump engine as thats what the magazines wanted us to do. In fact that engine was seeing 9500 rpm on several passes. All of the LS1 oil drainback is right on the spinning crank. We got by with it for a while but at this rpm it was pushing it. The rod that we lost had a block and blue journal and was number one the furthest from the oil. It spun a rod bearing and detroyed the big end.
I don't know if you know the difference between an oiling failure and a mechanical parts failure but we do. The other rods are in as new condition (lightweight GRPs and 450 g JE pistons) and finally the car is now dry sump so no more oiling headaches from 9000 rpm wetsump LS1s anymore! I do however find it incredible after all you and your dad have done with LS1s (little to nothing) that you even have the ***** to talk about what we did or why something failed when you are a million miles away and have never seen one damn part inside that engine?
I'll will tell you what Bret, and I am not mad (really), but as soon as you can build a 9000 rpm 750+ RWHP ls1 wet sump engine with an OEM LS6 head that YOU or your shop ported and YOU can go 155 mph in a nearly 3300 pound car I will listen to more of YOUR knowledge on this stuff but until then leave our school's name out of your misunderstandings of pistons speed or bore vs. stroke discussions. I could certainly ask you about some of the stuff you have attempted that wasn't even 6500 rpm crap that somehow failed and even I don't know the real story on that one.
01-19-2006, 03:28 PM
#26
FormerVendor
Bret, I know the tone sounds very mean but it is NOT meant that way but I can't listen to anyone make even half assed comments about the School or anything we do because we were and are out there really doing it and no one else is. They're all sitting behind keyboards talking about it. We went 10s and 9s way before anyone else and if that last engine had made one more good pass where it hooked we also would have the first 8s with stock ported GM heads as well! We just do what we can get coverage on for the school though. Now we have a 500 inch LS1 going in another car we have and it will be a crazy street engine if there ever was one.
01-19-2006, 06:59 PM
#27
TECH Fanatic
Eric, How about another take on PS?
I'm not sure why F1 with 18000-18500 power peak rpm, as reported by BMW, Honda and Toyota, Cup power peaks 88-9000 or so and ProStock maybe a tad higher are all occurring about 5000 average PS +/- a couple hundred ft/min. I find it difficult to believe that all three have the same airflow limitations. Cup & Pro maybe, but F1?
F1 stuffs two fairly large intake valves in a 3.8 +/- .04 bore and lifts them maybe as much as .62-.65 inches. We think we know Cup valves' size and lift and probably ProStock. Maybe the flow/cubic inch is very similar and Cup/Pro guys just do a magnificent job. The BMEPs @ power peak are close to the same for all 3.
Could it be that as a certain PS is reached, the air just can't respond? PS, even maximum is just a fraction of average intake port velocity. 5000 ft/min is only about 84 ft/sec, about 1/3 of a good intake port average velocity. I am trying to explain why most engines nose over around 5000-5300 PS. What's your take?
An F1 engine turns over about the same number of total revs in a race weekend as a 500 mile unrestricted Cup engine. 1.2 to maybe 1.6 million. Of course F1 engines now go 2 races, and are designed for about a 20% safety factor in distance (or total revs). I've not heard what number of total revs Cup engines are designed for. Even F1 engines reuse most/many of the non-rotating/reciprocating parts. Except for valve springs and a few other bits, Cup engines could probably be made into 2-race engines. Of course going from a fast 1.5 or 2 mile superspeedway to a bull ring requires quite a different torque curve, so that would be a major hassle. Hope NASCAR doesn't go that way!
With the 2-race rule, some F1 engines got slowed down a couple of %, but they got back up to the 19000 in races except in top gear. Not that they always used the full 19K. Some guys were "short shifting" at 18 or so when they could.
Initially a few of the parts got a little heavier, but now are as light or lighter that on 1-race engines. Mostly it was by refining the design; taking material out where it wasn't needed and adding it where it was. The same never-ending saga of development at the limit.
Whadayathink?
I'm not sure why F1 with 18000-18500 power peak rpm, as reported by BMW, Honda and Toyota, Cup power peaks 88-9000 or so and ProStock maybe a tad higher are all occurring about 5000 average PS +/- a couple hundred ft/min. I find it difficult to believe that all three have the same airflow limitations. Cup & Pro maybe, but F1?
F1 stuffs two fairly large intake valves in a 3.8 +/- .04 bore and lifts them maybe as much as .62-.65 inches. We think we know Cup valves' size and lift and probably ProStock. Maybe the flow/cubic inch is very similar and Cup/Pro guys just do a magnificent job. The BMEPs @ power peak are close to the same for all 3.
Could it be that as a certain PS is reached, the air just can't respond? PS, even maximum is just a fraction of average intake port velocity. 5000 ft/min is only about 84 ft/sec, about 1/3 of a good intake port average velocity. I am trying to explain why most engines nose over around 5000-5300 PS. What's your take?
An F1 engine turns over about the same number of total revs in a race weekend as a 500 mile unrestricted Cup engine. 1.2 to maybe 1.6 million. Of course F1 engines now go 2 races, and are designed for about a 20% safety factor in distance (or total revs). I've not heard what number of total revs Cup engines are designed for. Even F1 engines reuse most/many of the non-rotating/reciprocating parts. Except for valve springs and a few other bits, Cup engines could probably be made into 2-race engines. Of course going from a fast 1.5 or 2 mile superspeedway to a bull ring requires quite a different torque curve, so that would be a major hassle. Hope NASCAR doesn't go that way!
With the 2-race rule, some F1 engines got slowed down a couple of %, but they got back up to the 19000 in races except in top gear. Not that they always used the full 19K. Some guys were "short shifting" at 18 or so when they could.
Initially a few of the parts got a little heavier, but now are as light or lighter that on 1-race engines. Mostly it was by refining the design; taking material out where it wasn't needed and adding it where it was. The same never-ending saga of development at the limit.Whadayathink?
01-19-2006, 07:46 PM
#28
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I'd like to subscribe to this conversation. It slightly reminds me of an article
I read from David Reher regarding component mass and RPM.
P.S. Did anyone see the Andretti's on QLN last week? A cool special on tweaking
their race cars.
I read from David Reher regarding component mass and RPM.
P.S. Did anyone see the Andretti's on QLN last week? A cool special on tweaking
their race cars.
01-19-2006, 07:51 PM
#29
Man
You really have a self image problem... I got **** to do I'll get back to this... none of it was a personal attack on your or the school. I was just giving you examples. You always take this and direct it back at me in an attack. I would expect someone with your age to have more emotional maturity than that. Thanks for making this a adult discussion. One of these days I just wish you would stop grouping the school into "us", the school is where your experience comes from but it's not your shop.
When are you going to answer the F1 RPM limit question?
Bret
You really have a self image problem... I got **** to do I'll get back to this... none of it was a personal attack on your or the school. I was just giving you examples. You always take this and direct it back at me in an attack. I would expect someone with your age to have more emotional maturity than that. Thanks for making this a adult discussion. One of these days I just wish you would stop grouping the school into "us", the school is where your experience comes from but it's not your shop.
When are you going to answer the F1 RPM limit question?
Bret
Last edited by SStrokerAce; 01-19-2006 at 07:57 PM.
01-19-2006, 07:53 PM
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Originally Posted by SStrokerAce
Man
You really have a self image problem... I got **** to do I'll get back to this... none of it was a personal attack on your or the school. I was just giving you examples. You always take this and direct it back at me in an attack. I would expect someone with your age to have more emotional maturity than that. Thanks for making this a adult discussion.
When are you going to answer the F1 RPM limit question?
Bret
You really have a self image problem... I got **** to do I'll get back to this... none of it was a personal attack on your or the school. I was just giving you examples. You always take this and direct it back at me in an attack. I would expect someone with your age to have more emotional maturity than that. Thanks for making this a adult discussion.
When are you going to answer the F1 RPM limit question?
Bret
01-19-2006, 07:57 PM
#31
FormerVendor
Old Stroker I know that the total airflow and total power were extremely similar between all the engines before but the extra friction of super high rpm eats into the power the F1 stuff could be making. If you could run 4 valve heads in Cup the engine would make even more tq as well but not a lot more. The friends I have in that arena say they still design heads that go around 100 M/S average air speed at peak power. Of course in F1 they can redesign stuff instead of porting it but all these engines have similar total intake cross sectional area vs bore area and this is what limits all engines in piston speed.
I could support more piston speed if I can put larger intake valves in there anotherwords but at some point you can't go any further and put the rest of the stuff like exhaust valves in too! The heads that make power at high pistons speeds have huge intake valves as compared to the stuff making power at lower piston speed. A 23 degree Chevy will NOT make good power at 5500 FPM while a CAnted Valve WILL. It's not a coincidence that these same canted valves cam flow 450 cfm on that same 4.185 bore. They have a bigger valve and flow more air. They also have a much straighter and better exhaust port that while having a smaller valve actuall also flow quite a bit more and allows the huge intake valve to be run along with a very large LSA and split in the cam. Again it's all to allow that big intake valve.
You can only run so much intake area before you start starving exhaust area or shrouding intake area. There is simply only so much intake venturi you can run on ANY bore as a total percentage before you lose power due to either shrouding or too little exhaust. If I have 100 Ft/S piston speed and my intake port is 1/3 the cross section of my piston top then that port will see 300 Ft/S average air speed. I know the rod ratio has an effect along with everything else too but that is essentially what controls the flow through the intake system and ports. After some port limiting velocity such as that (300-350 FPS your choice) the engine is now on the downside of it's power curve and sometimes even sooner if you have a rising rate friction curve of course. Intake ports simply start going backward in HP after a certain velocity.
I could support more piston speed if I can put larger intake valves in there anotherwords but at some point you can't go any further and put the rest of the stuff like exhaust valves in too! The heads that make power at high pistons speeds have huge intake valves as compared to the stuff making power at lower piston speed. A 23 degree Chevy will NOT make good power at 5500 FPM while a CAnted Valve WILL. It's not a coincidence that these same canted valves cam flow 450 cfm on that same 4.185 bore. They have a bigger valve and flow more air. They also have a much straighter and better exhaust port that while having a smaller valve actuall also flow quite a bit more and allows the huge intake valve to be run along with a very large LSA and split in the cam. Again it's all to allow that big intake valve.
You can only run so much intake area before you start starving exhaust area or shrouding intake area. There is simply only so much intake venturi you can run on ANY bore as a total percentage before you lose power due to either shrouding or too little exhaust. If I have 100 Ft/S piston speed and my intake port is 1/3 the cross section of my piston top then that port will see 300 Ft/S average air speed. I know the rod ratio has an effect along with everything else too but that is essentially what controls the flow through the intake system and ports. After some port limiting velocity such as that (300-350 FPS your choice) the engine is now on the downside of it's power curve and sometimes even sooner if you have a rising rate friction curve of course. Intake ports simply start going backward in HP after a certain velocity.
01-19-2006, 08:07 PM
#33
FormerVendor
Originally Posted by SStrokerAce
Man
You really have a self image problem... I got **** to do I'll get back to this... none of it was a personal attack on your or the school. I was just giving you examples. You always take this and direct it back at me in an attack. I would expect someone with your age to have more emotional maturity than that. Thanks for making this a adult discussion. One of these days I just wish you would stop grouping the school into "us", the school is where your experience comes from but it's not your shop.
When are you going to answer the F1 RPM limit question?
Bret
You really have a self image problem... I got **** to do I'll get back to this... none of it was a personal attack on your or the school. I was just giving you examples. You always take this and direct it back at me in an attack. I would expect someone with your age to have more emotional maturity than that. Thanks for making this a adult discussion. One of these days I just wish you would stop grouping the school into "us", the school is where your experience comes from but it's not your shop.
When are you going to answer the F1 RPM limit question?
Bret
Get a grip man you are taking this stuff too seriously! That is why I added the extra message for you lil buddy!
I can build a long lived 6500 rpm 572 bracket engine that sees big piston speed but low rpm and it will live forever and so will the rotating assembly like WJs 572 inch GM crate engine. If I destroked that 4.500 inch stroke monster to 2.250 stroke it would be a piece of crap and would blow up if it ever got back to that same piston speed it ran all day long at when it was 4.500 stroke as WJ set it up as.
It will also make no where near the power and have extreme wear if it didn't blow sky high at double the rpm but the same piston speed! Somehow though I doubt we'll see any 13,000 rpm 4.500 bore 2.250 stroke wonders in anyone's rides anytime soon even if you do think they have the same loads since they have the same piston speed!
I just don't like people parading around BS as the truth plain and simple. Pistons speed is NOT a good indicator of any mechanical limit or impending disaster. RPM IS though and that's all we're saying and it's true!
01-19-2006, 08:24 PM
#34
FormerVendor
Originally Posted by SStrokerAce
I was thinking the same thing about Eric.
WOW, I mean I guess I am kinda sexy to some of the LS1tech members but I never knew!
Seriously though I have had a lot of calls today so I never noticed this F1 question you asked?
But I would lay off the caffeine as I have no problem with 90 per cent of what you say in general besides this piston speed equaling a mechanical limit of some kind thing because that is just not a reality.
I just don't think you are seeing the internal combustion engine and it's limitations from the same perspective. I DO think piston speed is very very important because it dictates the airflow through the engine and along with the heads intake and cam determines how this engine will behave.
I am not you or your dad's enemy I can tell you that since we are all love talking about this stuff!
01-19-2006, 08:53 PM
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Wouldn't it be great if LS1tech sponsored an LS1 engine "build-off" between
Erik and Bret?! Any takers? I'd pay to see that...literally.
Once you boys post the numbers, I'll down you both with my set up.
If I'm following the piston speed/valvetrain relationship correctly, are
you both talking about sudden pressure drops in the cylinder exceeding
the air flow abilities of the port due to intake valve obstruction?
By increasing piston speed with relatively slow valve ramp speeds, are
problems going to occur? This is all I can come up with when reading your
replies.
Secondly: Are you debating between reciprocating mass being a limitation on
restricted motors? Will increasing piston speed on shorter stroke combinations
restore pressure drops in the cylinder which were easily attained
by use of a longer stroke?
Erik and Bret?! Any takers? I'd pay to see that...literally.
Once you boys post the numbers, I'll down you both with my set up.
If I'm following the piston speed/valvetrain relationship correctly, are
you both talking about sudden pressure drops in the cylinder exceeding
the air flow abilities of the port due to intake valve obstruction?
By increasing piston speed with relatively slow valve ramp speeds, are
problems going to occur? This is all I can come up with when reading your
replies.
Secondly: Are you debating between reciprocating mass being a limitation on
restricted motors? Will increasing piston speed on shorter stroke combinations
restore pressure drops in the cylinder which were easily attained
by use of a longer stroke?
01-19-2006, 11:01 PM
#36
TECH Fanatic
Originally Posted by racer7088
Old Stroker I know that the total airflow and total power were extremely similar between all the engines before but the extra friction of super high rpm eats into the power the F1 stuff could be making. If you could run 4 valve heads in Cup the engine would make even more tq as well but not a lot more. The friends I have in that arena say they still design heads that go around 100 M/S average air speed at peak power. Of course in F1 they can redesign stuff instead of porting it but all these engines have similar total intake cross sectional area vs bore area and this is what limits all engines in piston speed.
I could support more piston speed if I can put larger intake valves in there anotherwords but at some point you can't go any further and put the rest of the stuff like exhaust valves in too! The heads that make power at high pistons speeds have huge intake valves as compared to the stuff making power at lower piston speed. A 23 degree Chevy will NOT make good power at 5500 FPM while a CAnted Valve WILL. It's not a coincidence that these same canted valves cam flow 450 cfm on that same 4.185 bore. They have a bigger valve and flow more air. They also have a much straighter and better exhaust port that while having a smaller valve actuall also flow quite a bit more and allows the huge intake valve to be run along with a very large LSA and split in the cam. Again it's all to allow that big intake valve.
You can only run so much intake area before you start starving exhaust area or shrouding intake area. There is simply only so much intake venturi you can run on ANY bore as a total percentage before you lose power due to either shrouding or too little exhaust. If I have 100 Ft/S piston speed and my intake port is 1/3 the cross section of my piston top then that port will see 300 Ft/S average air speed. I know the rod ratio has an effect along with everything else too but that is essentially what controls the flow through the intake system and ports. After some port limiting velocity such as that (300-350 FPS your choice) the engine is now on the downside of it's power curve and sometimes even sooner if you have a rising rate friction curve of course. Intake ports simply start going backward in HP after a certain velocity.
You can only run so much intake area before you start starving exhaust area or shrouding intake area. There is simply only so much intake venturi you can run on ANY bore as a total percentage before you lose power due to either shrouding or too little exhaust. If I have 100 Ft/S piston speed and my intake port is 1/3 the cross section of my piston top then that port will see 300 Ft/S average air speed. I know the rod ratio has an effect along with everything else too but that is essentially what controls the flow through the intake system and ports. After some port limiting velocity such as that (300-350 FPS your choice) the engine is now on the downside of it's power curve and sometimes even sooner if you have a rising rate friction curve of course. Intake ports simply start going backward in HP after a certain velocity.
We still haven't decided, at least to my satisfaction, why engines with different configurations as well as valve/piston areas of 15-25% difference reach peak power at piston speeds within 5% of each other. Something else is happening here. Let's keep thinking.
01-19-2006, 11:47 PM
#37
FormerVendor
Old SStroker,
I don't need to keep thinking as I already told you what controls it. It is NOT limited to 5000 fpm or even 5500 fpm at all. When you add stroke the piston speed at peak power can be higher and higher. IHRA PS makes peak power at 6500 FPM and has a horrible rod ratio! They also turn very low rpm so the valve train can open and close the valves much easier and lift them further and faster without falling apart. The cams these cars run would destroy an NHRA PS valvetrain system but they allow the engine to breath much better with the same heads.
You keep comparing engines with vastly different operating ranges and breathing. When you turn higher rpm you must lame out the valvetrain as compared to what the lower rpm engine can get away with.You would need to compare a great 4 valve engine that only turns 10,000 rpm with a 3.3 inch stroke 2 valve engine to really see what the differences in peak power rpm would be between the two. The Cup engine sees much less friction with less pistons and parts and 3 less cams and 24 less valves I can tell you that!
Also you are aware that at extremely large bores and extremely short strokes you can almost put the engine into continual quench with no flame travel possibility at all. The surface to volume ratio can get downright impossible. Also getting any compression in an F1 engine is very very hard. They can not use the kind of cam a bigger stroke engine can due to the piston not getting out of the way of the relatively large valves.
F1 engines are not directly comparable at all even in fuel used. They are multi million dollar engines and as you said in BMEP do not seem to outperform the Cup engines. That should surprise you as an engineer. Also the most efficient gas race engines you will see in racing are the 815 inch IHRA Behemoths that print out of this world BSAC and BSFC numbers. Again how do you explain that fact that the large super strokers put up these stupendous BSFC numbers so easily if you think the high rpm small stroker deals have less friction. Why don't these small high rpm engines make as much power out of the same fuel?
A hint is that IMEP and BMEP aren't as close as the rpm goes up and the engine's stroke gets smaller. If you could see the real cylinder pressure and how far it is carried in rpm I think you would be surprised how long an F1 engine can keep itself filled up to in rpm! Unfortunately we only get to use the power that actually gets out the back of the engine MINUS all the frictional and inertial losses.
I don't need to keep thinking as I already told you what controls it. It is NOT limited to 5000 fpm or even 5500 fpm at all. When you add stroke the piston speed at peak power can be higher and higher. IHRA PS makes peak power at 6500 FPM and has a horrible rod ratio! They also turn very low rpm so the valve train can open and close the valves much easier and lift them further and faster without falling apart. The cams these cars run would destroy an NHRA PS valvetrain system but they allow the engine to breath much better with the same heads.
You keep comparing engines with vastly different operating ranges and breathing. When you turn higher rpm you must lame out the valvetrain as compared to what the lower rpm engine can get away with.You would need to compare a great 4 valve engine that only turns 10,000 rpm with a 3.3 inch stroke 2 valve engine to really see what the differences in peak power rpm would be between the two. The Cup engine sees much less friction with less pistons and parts and 3 less cams and 24 less valves I can tell you that!
Also you are aware that at extremely large bores and extremely short strokes you can almost put the engine into continual quench with no flame travel possibility at all. The surface to volume ratio can get downright impossible. Also getting any compression in an F1 engine is very very hard. They can not use the kind of cam a bigger stroke engine can due to the piston not getting out of the way of the relatively large valves.
F1 engines are not directly comparable at all even in fuel used. They are multi million dollar engines and as you said in BMEP do not seem to outperform the Cup engines. That should surprise you as an engineer. Also the most efficient gas race engines you will see in racing are the 815 inch IHRA Behemoths that print out of this world BSAC and BSFC numbers. Again how do you explain that fact that the large super strokers put up these stupendous BSFC numbers so easily if you think the high rpm small stroker deals have less friction. Why don't these small high rpm engines make as much power out of the same fuel?
A hint is that IMEP and BMEP aren't as close as the rpm goes up and the engine's stroke gets smaller. If you could see the real cylinder pressure and how far it is carried in rpm I think you would be surprised how long an F1 engine can keep itself filled up to in rpm! Unfortunately we only get to use the power that actually gets out the back of the engine MINUS all the frictional and inertial losses.
01-20-2006, 08:08 AM
#38
TECH Fanatic
Originally Posted by racer7088
Old SStroker,
I don't need to keep thinking as I already told you what controls it. It is NOT limited to 5000 fpm or even 5500 fpm at all. When you add stroke the piston speed at peak power can be higher and higher. IHRA PS makes peak power at 6500 FPM and has a horrible rod ratio! They also turn very low rpm so the valve train can open and close the valves much easier and lift them further and faster without falling apart. The cams these cars run would destroy an NHRA PS valvetrain system but they allow the engine to breath much better with the same heads.
You keep comparing engines with vastly different operating ranges and breathing. When you turn higher rpm you must lame out the valvetrain as compared to what the lower rpm engine can get away with.You would need to compare a great 4 valve engine that only turns 10,000 rpm with a 3.3 inch stroke 2 valve engine to really see what the differences in peak power rpm would be between the two. The Cup engine sees much less friction with less pistons and parts and 3 less cams and 24 less valves I can tell you that!
Also you are aware that at extremely large bores and extremely short strokes you can almost put the engine into continual quench with no flame travel possibility at all. The surface to volume ratio can get downright impossible. Also getting any compression in an F1 engine is very very hard. They can not use the kind of cam a bigger stroke engine can due to the piston not getting out of the way of the relatively large valves.
F1 engines are not directly comparable at all even in fuel used. They are multi million dollar engines and as you said in BMEP do not seem to outperform the Cup engines. That should surprise you as an engineer. Also the most efficient gas race engines you will see in racing are the 815 inch IHRA Behemoths that print out of this world BSAC and BSFC numbers. Again how do you explain that fact that the large super strokers put up these stupendous BSFC numbers so easily if you think the high rpm small stroker deals have less friction. Why don't these small high rpm engines make as much power out of the same fuel?
I don't need to keep thinking as I already told you what controls it. It is NOT limited to 5000 fpm or even 5500 fpm at all. When you add stroke the piston speed at peak power can be higher and higher. IHRA PS makes peak power at 6500 FPM and has a horrible rod ratio! They also turn very low rpm so the valve train can open and close the valves much easier and lift them further and faster without falling apart. The cams these cars run would destroy an NHRA PS valvetrain system but they allow the engine to breath much better with the same heads.
You keep comparing engines with vastly different operating ranges and breathing. When you turn higher rpm you must lame out the valvetrain as compared to what the lower rpm engine can get away with.You would need to compare a great 4 valve engine that only turns 10,000 rpm with a 3.3 inch stroke 2 valve engine to really see what the differences in peak power rpm would be between the two. The Cup engine sees much less friction with less pistons and parts and 3 less cams and 24 less valves I can tell you that!
Also you are aware that at extremely large bores and extremely short strokes you can almost put the engine into continual quench with no flame travel possibility at all. The surface to volume ratio can get downright impossible. Also getting any compression in an F1 engine is very very hard. They can not use the kind of cam a bigger stroke engine can due to the piston not getting out of the way of the relatively large valves.
F1 engines are not directly comparable at all even in fuel used. They are multi million dollar engines and as you said in BMEP do not seem to outperform the Cup engines. That should surprise you as an engineer. Also the most efficient gas race engines you will see in racing are the 815 inch IHRA Behemoths that print out of this world BSAC and BSFC numbers. Again how do you explain that fact that the large super strokers put up these stupendous BSFC numbers so easily if you think the high rpm small stroker deals have less friction. Why don't these small high rpm engines make as much power out of the same fuel?
A hint is that IMEP and BMEP aren't as close as the rpm goes up and the engine's stroke gets smaller. If you could see the real cylinder pressure and how far it is carried in rpm I think you would be surprised how long an F1 engine can keep itself filled up to in rpm! Unfortunately we only get to use the power that actually gets out the back of the engine MINUS all the frictional and inertial losses.
I've not seen any BSFC numbers for F1. Burn is critcial with the fairly poor surface/volume ratio, and they still use 1 plug of 10m or even 8mm diameter. Ignition lead at 19K is in the range of a Top Fuel engine 50-60 degrees. They don't have much available in the petrol to increase flame front speed, so even with that lead, the peak pressures occur about the same crank angle/piston position as for the 10k Cup engine.
I don't need to keep thinking as I already told you what controls it.
It's been a slice of life, Eric.
Stay cool.
Jon
"We now return you to our regularly scheduled reality programming."
01-20-2006, 09:19 AM
#39
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OK, so with all high end engine internals could you use a stock LS7 bore and stroke to make peak power at 6800 or where ever it makes peak power now, but be able to rev to 8,000 rpm when you want to without blowing up the engine or having it last only a year or two. I know power would be down at 8,000 rpm, but I would not go there too often. Just want to be able to run out gears longer and hear the magic of 8,000 rpm once and a while.
So can you run a 4" or larger stroke at 8,000 rpm?
So can you run a 4" or larger stroke at 8,000 rpm?
01-20-2006, 09:29 AM
#40
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Call these guys up and get their opinions, much much better that way. As stated here the IHRA pro stock have a way way larger stroke and see that rpm but it is a race motor, not necessarily designed to last that long. These are the kind of things these guys can explain and why it works when you talk to them directly. Good luck!