Are good flow numbers & small runners the [only] keys to HOME PORTING success?
09-14-2006, 05:04 PM
#1
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Are good flow numbers & small runners the [only] keys to HOME PORTING success? I've played around with porting heads before, but I've never put a [finished] set on a car. My last set picked up 28.5 CFM at .550". These were 5.3L heads with the factory sized truck valves. I was impressed by the gains for my quite conservative efforts (there was minimal material removed).
I continue to hear how the average home-porter / novice doesn't know what they're doing in terms of how their changes will affect swirl/tumble/turbulence. I've heard that swirl isn' that all important, but tumble is. I didn't touch the short side radii on the last heads I did for that reason, but did spend some time in the bowl area. I just did the basics and cleaned/opened up the bowl area, and they responded well to it.
So the above leads me to thinking that it'll be hit or miss even if I can do another set of heads with good flow numbers. Can anyone shed some light on this? I'm not convinced that I HAVE to run an aftermarket head to make power. If I do that's fine too. I also have a set of Dart 205s, but the porting projects are more fun than just bolting on a set of finished heads.
Any input guys? Please don't suggest to go get some CNC LS6 heads- that's not what I'm looking for here. I guess I'm looking for some reassurance to invest the time on a set of 241s (?), and to discuss the differences in a 280 CFM head at XXXcc's that sucks VS a 280 CFM head at the same runner size but making good power.
Ben T.
I continue to hear how the average home-porter / novice doesn't know what they're doing in terms of how their changes will affect swirl/tumble/turbulence. I've heard that swirl isn' that all important, but tumble is. I didn't touch the short side radii on the last heads I did for that reason, but did spend some time in the bowl area. I just did the basics and cleaned/opened up the bowl area, and they responded well to it.
So the above leads me to thinking that it'll be hit or miss even if I can do another set of heads with good flow numbers. Can anyone shed some light on this? I'm not convinced that I HAVE to run an aftermarket head to make power. If I do that's fine too. I also have a set of Dart 205s, but the porting projects are more fun than just bolting on a set of finished heads.
Any input guys? Please don't suggest to go get some CNC LS6 heads- that's not what I'm looking for here. I guess I'm looking for some reassurance to invest the time on a set of 241s (?), and to discuss the differences in a 280 CFM head at XXXcc's that sucks VS a 280 CFM head at the same runner size but making good power.
Ben T.
09-15-2006, 08:45 AM
#2
Good flow and small port are the most important, but the means to accomplishing that balance is not trivial. I really don't think much tumble can be achieved with a 2 valve cylinder head, the charge motion will have a natural tendency to swirl. Swirl is important, but a lack of it is not the end of the world. You will know if you seriously missed the mark on swirl if your engine requires several more degrees of ignition timing after the head porting.
09-15-2006, 11:37 AM
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Originally Posted by SStrokerAce
No the right port shape is imporant. A port can flow like crap and make more power than a better flowing port.
Bret
Bret
I can read and understand the basics of what a good port is supposed to be shaped like, but at the same time making that mental realization into a physical reality is whole other ball game. In '97 when the LS1 debuted it was praised for its above average intake flow. Latter heads had better valves and manufacturing techniques and the flow increased even more. Point is, the stock LS1 port flows well and judging by the plethora of cam-only cars that run exceptionally well- it also produces good power. With these things being said, I don't think I want to try anything exceedingly creative on these heads, but I think there are gains to be had, and I'm going to go after them.
After doing more research (since the posting of this thread), I believe my "porting" will comprise basic cleanup work and an exceptional valve job.
A local (and highly successfull, the owner's been on SpeedVision
) dirt track shop can deck and cut my valve job. He wants to do a full-radiused valve job, deshroud the chambers for my 2.02 valves, and open the bowl up with a 85 degree cutter (I think this is similar to a "bowl hawg", but haven't seen it yet). I would imagine the short side radii will have to be reshaped depending on how much material is removed from the bowl.Input?
Ben T.
09-15-2006, 12:25 PM
#5
FormerVendor
Head porting is extremely complicated in reality to get the right results but there's a lot you can do at home that will usually help and not hurt you. Unfortunately the people that really know about this are not usually going to help you or anyone for that matter since they are actually busy and aren't usually keen on educating people about this stuff anyway as it's how they make their living.
You also probably won't know anything about airflow numbers anyway without a flow bench but flow is of course very important. Head flow has gone up over the years and so has performance in almost direct proportion but the airflow numbers are not the entire story.
Also keep in mind that putting a head that flows 400 cfm on any given engine also means it's also a really large head and you may not actually ever see that flow since your engine might be too small or might not be turning enough rpm. The overall air velocity will simpy be lower everywhere unless you change the cam too.
The heads cross section needs to be tailored to the engine size and cam being used and the rpm band you expect or want to make power in along with the rest of your engine combo.
You also probably won't know anything about airflow numbers anyway without a flow bench but flow is of course very important. Head flow has gone up over the years and so has performance in almost direct proportion but the airflow numbers are not the entire story.
Also keep in mind that putting a head that flows 400 cfm on any given engine also means it's also a really large head and you may not actually ever see that flow since your engine might be too small or might not be turning enough rpm. The overall air velocity will simpy be lower everywhere unless you change the cam too.
The heads cross section needs to be tailored to the engine size and cam being used and the rpm band you expect or want to make power in along with the rest of your engine combo.
09-15-2006, 02:02 PM
#6
Ben,
Your local shop could be killer, but unless they do a lot of LS1 work they might not do the right thing with the valve job, it will make killer mid lift numbers but the port will stall early. That's pretty much pointless IMHO. FWIW I do know that a good valvejob on a stock LS1 casting will go 250cfm on a 3.900" bore, closer to 280cfm with a LS6 casting.
As for the Darts they are a good example, and little clean up work with them picks up the flow numbers a bunch. I've seen them gain 30-40cfm with guide work and just blending the VJ in the chamber and ports.
Bret
Your local shop could be killer, but unless they do a lot of LS1 work they might not do the right thing with the valve job, it will make killer mid lift numbers but the port will stall early. That's pretty much pointless IMHO. FWIW I do know that a good valvejob on a stock LS1 casting will go 250cfm on a 3.900" bore, closer to 280cfm with a LS6 casting.
As for the Darts they are a good example, and little clean up work with them picks up the flow numbers a bunch. I've seen them gain 30-40cfm with guide work and just blending the VJ in the chamber and ports.
Bret
09-15-2006, 02:39 PM
#7
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This is from a post I made several years ago...
Just like a dyno, even flowbench results can be skewed. I am not going to name the two heads that were tested, as I am not interested in get into a peeing match with shops about their heads or a he said, she said argument. This information is being posted as that, information. Use information like this to educate yourself, and make informed decisions. For the purpose of this test I will refer to the same vendors a Brand X and Brand Y.
In a test of Brand X heads vs Brand Y heads. Brand Y flows as well on the bench (as good as a Brand X), but don't seem to make the same power on the dyno,etc. From discussing it with the head porter, he was mentioning that Brand Y removes material in areas that will show a gain on the flow bench, but will not make anymore power on the dyno. He says they are big in the wrong spots and too small in others.
A set of Brand Y stage 2s 5.3l heads on a car that had all the bolt ons and a TR224 cam. It made 379/370 or so before adding the heads. After the heads, the car did 413/385 after tuning. A week before, Another car had a set of Brand X stage 2 5.3l heads on a car that already had the TR224 cam as well and the IDENTICAL mods as the other Brand Y car (FLPs, LS6 intake, ASP, stock rear/4:10s,etc). Both dynoed the exact same before swapping heads on (the curves practically overlayed one another). This car pulled 443/418 with the Brand Xs!
On the flow bench, the Brand Ys actually flowed better from .100-.550, while Brand X flowed slightly better past this. Same thing on the exhaust side. This just goes to show that a flow bench is an excellent tool, but not something that should be used as the determing factor in how a head will perform when put on a motor. The CC volumes were identical on the two heads, so compression difference wasn't an issue.
In a test of Brand X heads vs Brand Y heads. Brand Y flows as well on the bench (as good as a Brand X), but don't seem to make the same power on the dyno,etc. From discussing it with the head porter, he was mentioning that Brand Y removes material in areas that will show a gain on the flow bench, but will not make anymore power on the dyno. He says they are big in the wrong spots and too small in others.
A set of Brand Y stage 2s 5.3l heads on a car that had all the bolt ons and a TR224 cam. It made 379/370 or so before adding the heads. After the heads, the car did 413/385 after tuning. A week before, Another car had a set of Brand X stage 2 5.3l heads on a car that already had the TR224 cam as well and the IDENTICAL mods as the other Brand Y car (FLPs, LS6 intake, ASP, stock rear/4:10s,etc). Both dynoed the exact same before swapping heads on (the curves practically overlayed one another). This car pulled 443/418 with the Brand Xs!
On the flow bench, the Brand Ys actually flowed better from .100-.550, while Brand X flowed slightly better past this. Same thing on the exhaust side. This just goes to show that a flow bench is an excellent tool, but not something that should be used as the determing factor in how a head will perform when put on a motor. The CC volumes were identical on the two heads, so compression difference wasn't an issue.
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09-16-2006, 01:33 AM
#8
FormerVendor
Yes control of turbulence will usually mean you can carry power further and you will make more total power especially on the larger motors and the short rod motors.
09-16-2006, 09:34 AM
#10
FormerVendor
Ben,
Any turbulence is usually somewhat bad at high lift or higher pressure drops. When you get rid of this turbulence even is peak flow doesn't improve you usually see more power and the power stays a little longer in rpm.
Usually this involves the short turn shape and cross section VS the valve job area. If the airspeed gets too high in certain areas you will usually start losing power earlier. Like Bret and others have said the shape of a port and the manifold attached to it will affect how the air acts as speeds ramp up.
Then there's chamber work and wet flow thats will not directly show up on a flow bench but can also drop your power if they aren't right as well. I am working on a home porting guide myself but it's a ways off. The professionals have already done 100 sets of heads and thats why we pay them to get the last loittle bit out of a head intake combo though.
Any turbulence is usually somewhat bad at high lift or higher pressure drops. When you get rid of this turbulence even is peak flow doesn't improve you usually see more power and the power stays a little longer in rpm.
Usually this involves the short turn shape and cross section VS the valve job area. If the airspeed gets too high in certain areas you will usually start losing power earlier. Like Bret and others have said the shape of a port and the manifold attached to it will affect how the air acts as speeds ramp up.
Then there's chamber work and wet flow thats will not directly show up on a flow bench but can also drop your power if they aren't right as well. I am working on a home porting guide myself but it's a ways off. The professionals have already done 100 sets of heads and thats why we pay them to get the last loittle bit out of a head intake combo though.
09-16-2006, 09:57 AM
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This is making me wonder what happend on my last set of ported heads. I assumed the 1.97" valvejob in the 5.3L heads was the limiting factor. Maybe it was turbulence? Stock numbers are the third verticle column. These were some mildly ported heads by me flowed with a 2.00" valve. I deshrouded the chambers, streamlined the aluminum valve guide support, lightly opened the bowls up, removed the bump, etc. Everything was done in moderation and with patience. Here are the numbers with the last column being my gains/losses. This was done on the same bench with the same operator.
.10 _68.7 63.3 5.4
.15 102.2 94.3 7.9
.20 137.9 127.9 10
.25 167.5 155.9 11.6
.30 182.1 178.7 3.4
.35 195.0 195.6 -0.6
.40 211.4 210.2 1.2
.45 226.7 218.0 3.7
.50 239.7 222.7 21.7
.55 250.0 221.5 28.5
.60 252.2 226.2 26
.65 244.9 228.3 16.6
.70 246.6 230.9 15.7
Perhaps the low-flow increases were the valves, I don't know. I assumed the higher lift numbers were starting to fall off because of the valvejob. Maybe it was turbulence. I don't know, but I do know that I did not change the shape of the port. The walls, roof, floor, and short side radius were largely untouched.
These numbers were on the stock GM valvejob.
Ben T.
.10 _68.7 63.3 5.4
.15 102.2 94.3 7.9
.20 137.9 127.9 10
.25 167.5 155.9 11.6
.30 182.1 178.7 3.4
.35 195.0 195.6 -0.6
.40 211.4 210.2 1.2
.45 226.7 218.0 3.7
.50 239.7 222.7 21.7
.55 250.0 221.5 28.5
.60 252.2 226.2 26
.65 244.9 228.3 16.6
.70 246.6 230.9 15.7
Perhaps the low-flow increases were the valves, I don't know. I assumed the higher lift numbers were starting to fall off because of the valvejob. Maybe it was turbulence. I don't know, but I do know that I did not change the shape of the port. The walls, roof, floor, and short side radius were largely untouched.
These numbers were on the stock GM valvejob.
Ben T.
09-18-2006, 11:25 PM
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Can I get some input on that last post I made? Did the port stall or was the valve job holding the heads back? They only had a minimal amount of material removed with no significant port reshaping done.
Ben T.
Ben T.
09-19-2006, 07:30 AM
#13
The new straiter path L92 heads have a big advantage over the LS1/6 style cathedral port.
Originally Posted by gollum
"In terms of cross-sectional area to flow, an oval port is the most efficient because it has no sharp edges, air travels travels in the path of least resistance, and eleminating sharp edges minimizes resistance. Some rectangle ports can be reshaped into ovals by filling in the corners with epoxy. Extending this concept into intake manifold, makes incoming air less sensitive to changes in the contour of the port. Air likes consistency, not a lot of sharp changes" CHP
09-19-2006, 07:40 AM
#14
In other words the L92/LS7 head has a straiter and more oval air path than cathedral style port.
If you insist on using the LS1/6 head simply add more cubic inches (402-408) to your motor and port match intake to ports for a killer stock head street combo.
If you insist on using the LS1/6 head simply add more cubic inches (402-408) to your motor and port match intake to ports for a killer stock head street combo.
09-20-2006, 11:17 PM
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I don't know if this will help or not...
But my father once said "Trade-offs and engines are like women and tampons, it's hard to have one without the other, but they both make you hard" (or is it, they are both hard to please?)
Port size (air speed), total flow (DC), and equalization (QC) must all be balanced to have a good time. There are no "ONLY" keys to a good cylinder head. It is a balance of the right air-speed, enough charge, and as little turbulence, that result in the expected outcome.
But my father once said "Trade-offs and engines are like women and tampons, it's hard to have one without the other, but they both make you hard" (or is it, they are both hard to please?)
Port size (air speed), total flow (DC), and equalization (QC) must all be balanced to have a good time. There are no "ONLY" keys to a good cylinder head. It is a balance of the right air-speed, enough charge, and as little turbulence, that result in the expected outcome.
09-24-2006, 08:03 PM
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Originally Posted by Studytime
This is making me wonder what happend on my last set of ported heads. I assumed the 1.97" valvejob in the 5.3L heads was the limiting factor. Maybe it was turbulence? Stock numbers are the third verticle column. These were some mildly ported heads by me flowed with a 2.00" valve. I deshrouded the chambers, streamlined the aluminum valve guide support, lightly opened the bowls up, removed the bump, etc. Everything was done in moderation and with patience. Here are the numbers with the last column being my gains/losses. This was done on the same bench with the same operator.
.10 _68.7 63.3 5.4
.15 102.2 94.3 7.9
.20 137.9 127.9 10
.25 167.5 155.9 11.6
.30 182.1 178.7 3.4
.35 195.0 195.6 -0.6
.40 211.4 210.2 1.2
.45 226.7 218.0 3.7
.50 239.7 222.7 21.7
.55 250.0 221.5 28.5
.60 252.2 226.2 26
.65 244.9 228.3 16.6
.70 246.6 230.9 15.7
Perhaps the low-flow increases were the valves, I don't know. I assumed the higher lift numbers were starting to fall off because of the valvejob. Maybe it was turbulence. I don't know, but I do know that I did not change the shape of the port. The walls, roof, floor, and short side radius were largely untouched.
These numbers were on the stock GM valvejob.
Ben T.
.10 _68.7 63.3 5.4
.15 102.2 94.3 7.9
.20 137.9 127.9 10
.25 167.5 155.9 11.6
.30 182.1 178.7 3.4
.35 195.0 195.6 -0.6
.40 211.4 210.2 1.2
.45 226.7 218.0 3.7
.50 239.7 222.7 21.7
.55 250.0 221.5 28.5
.60 252.2 226.2 26
.65 244.9 228.3 16.6
.70 246.6 230.9 15.7
Perhaps the low-flow increases were the valves, I don't know. I assumed the higher lift numbers were starting to fall off because of the valvejob. Maybe it was turbulence. I don't know, but I do know that I did not change the shape of the port. The walls, roof, floor, and short side radius were largely untouched.
These numbers were on the stock GM valvejob.
Ben T.
