Mister Will

I'm posting this here since I focusing primarily on III gen/LS1 engine.

There are many different head options on the market. Each advertises specific head flow figures for intake and exhaust at different valve lift. Of course the simplist conclusion is to pick the head with the highest flow rates (more air more power, right). But we all know there are other factors involved with choosing heads. My question is how much does a small difference in CFM effect perfomance or power output.

For instance, if head X flows at 300 cfm and head Y flows at 310 cfm. What would be the expected power increase of head Y over head X?

FOr arguments sake, lets assume no variance in flow test benches and the heads would all be applied to the same application (same intake manifold, same exhaust system, same cam).

Thanks!

jdiddyws6

iTrader: (5)

Max flow number are good, but not as good as you would think. If brand x flows 310 at .650, and you happen to have a .650 lift cam, think about how long it is actually taking advantage of that flow rate. If brand y is flowing 250+ by 3000 rpms, and flows 290 max, this should net you better performance, even though max power may be down slightly.Best to look at flow rates under the curve, unless you are going for a "max effort" build.

Paint_It_Black

iTrader: (1)

example: a pro stock team found 20 cfm more flow in one of their heads. however after bolting it up they found they lost 50 hp.

so now, flow isn't everything. it's SOMETHING but definately not everything. see my sig

Paint_It_Black

iTrader: (1)

Head X could win by 30 or more hp. So can head Y.

SOMbitch

iTrader: (8)

Plastic IM's also SEVERELY holds these motors back in big hp builds so in some cases headflow can become almost irrelevant.

Top mount FTMFW..........

Mister Will

I understand what you are saying. What happens on a flow bench isn't the same thing as what happens in the engine ports and combustion chamber.

It's true who cares what a head flows at 0.600 lift if your cam never even goes that high? I seem to remember reading that the LS6 intake manifold only flows at 260 cfm. So all of this 300 cfm at 0.600 lift is pointless. What's important is what the average flow is below the highest lift point (and it's duration).

So lets assume engine X and engine Y are identical except for the heads. Engine Y's heads flow 10 cfm average better than engine X. What difference are we looking at in power output.

I know it's a overly generalized question. I am looking at an aftermarket head and a CNC'd OEM casting. The aftermarket head is good. But the CNC'd head flows noticably better at all valve lift points both intake and exhaust ( <10 cfm). I am trying to figure out what the impact would be on the performance?

02*C5

iTrader: (1)

The important numbers are the 200 to 500 numbers. Yet what every one seems to loose sight of is velocity. Velocity of the air flowing in and out is what separates a good head from a great head. The reason why so many after market heads go to a 205 or 215CC runner. These runners gives better low to mid range response and is able to make HP a lot quicker than lets say something with a 260cc runner(241s). The larger runner is going to make great flow numbers yet the low to mid range response and hp is going to hurt. My advice would be get a set of 243s get them done by a good reputable shop and have them cut the 215CC runners into the heads. I have a set and all my buddies who are a lot more serious than I am w/ (600RWHP) cars run these heads with such runners.

SOMbitch

iTrader: (8)

I disagree with some of this. The two best 243's I have ever seen were both over 235cc's

A lot of companies use the cc thing as a bunch of hype and a marketing ploy

02*C5

iTrader: (1)

Well its relative to where you are and who is running what. When you know guys running 500 and 600 rwhp on 243s with 215cc runners its hard to dispute the facts in front of you. With my set up am running 453 rwhp and 422 trq na.

Now I am not discounting the 235CC runners but you also have to see what the set up is, what they are running the heads on and if the application supports the larger runners. When you get into the 260's like I mentioned in the 241 heads you better have a hefty forced induction system for that velocity to work in your favor.

SOMbitch

iTrader: (8)

You better tell CARTEK that^^^^^^^ LOL They are doing it all wrong

http://www.cartek.net/CustomerRides/AlexV.htm He is WS6TransAm01 on here IIRC.

Not tryng to get in an internet p*ssing match but link us to that 600rwhp car running 243's....I am sure many would like to see it....

outkast6991

iTrader: (34)

215cc runners on a 243 aren't missing much material. stock runners come in around 212cc give or take

Paint_It_Black

iTrader: (1)

You kinda sorta have a small glimpse of what's going on, which is more than I can say for 95% of this site.

Let me ask you this. Why then does an L92 head with a 260cc intake runner perform as well on an LS2 (364) as a popular 205? Why are L92's on trucks that need low end TQ?

Why is the best GM production head ever (LS7) also in that runner range?

02*C5

iTrader: (1)

You actually gave yourself the answer. When you have a larger cube engine it is moving a lot more air. In a 347 you are not moving as much air and you need the smaller runners to produce velocity. The ls1 displaces only 5.665 liters, compared to the LS2's 6 liters and the LS7's 7 liters. That should give you an idea of how much air is flowing through those engines and the heads. The bigger the engine the more air it brings in the easier it is to make velocity through a large runner.

With the right application, right size engine and set up you can have big runners and you still make low to mid range power no problem. Remember that most of this cylinder head technology goes towards one goal: increasing volumetric efficiency. If you pack more air into the cylinders, the engine makes more power. In the ls1/ls6 5.7L config the 243s with the much better intake and exhaust port designs allow better volumetric efficiency at all engine speeds with 215 cc runners. The payoff is higher performance.

The other thing you have to take into consideration in trucks is that the gearing in the tranny and rear end help with how well it can use the torque produced by the engine.

Paint_It_Black

iTrader: (1)

So an LS2 is only 18 cubic inches bigger than an LS1, are you saying that 18 cubes is allowing for 45 more CC's to be an acceptable change simply based on runner volume? C'mon man, you can't mean that! I will say this, you do NOT need small runners to produce air velocity. That is a myth. The port is not the same size from entry to exit. Think about it. You'll get there.

outkast6991

iTrader: (34)

csa, throat diameter relative to valve size, and some voodoo make for good heads or so i hear

Old SStroker

A lot depends on whodo the voodoo.

Jon

outkast6991

iTrader: (34)

yup i feel very fortunate to have found the guys whodo the voodoo well. and to think i almost tossed a handfull of cash out the window thanks again

Mister Will

Yep, this was pointed out to me recently, by Jon (thanks again), that the port volume does not determine the cross sectional area which has a profound affect on the velocity.

THAT'S RIGHT!

So guys, if I get 10 more cfm, how much more horsepower will I see?

02*C5

iTrader: (1)

Well bro let me finalize by saying this. If your set up supports what ever runner your using then keep it. I my self along with about 20 guys that I know who themselves use this application running anywhere from mid to low 11's and some in the 10.99's N/A can't all be wrong. If your application helps you and it works for you great and all others out there that use it.

I never said that the smaller runner is the end all to be all. My post was just stating realistically what where I am from most of the guys use and they are happy with it. If your 235CC+ works well for you and your crew of guys who you run with then hey go with it. That's why there are choices out there and you can choose to run what ever configuration you want.

I choose and have seen great results with a 215CC runner set up on my 5.7 LS1 as you have with your 235CC+ set up. Goes to show how 2 individuals can get great results from a correctly set up H/C package configured differently and still have great performance.

KRAZY K 2000 TA

iTrader: (5)

and when your sick of guessing and wondering you will choose AFR 205's for street strip applications and realize you can still ripp your tires loose at 35 miles an hour which is F@@#king fun as ****!! then go to the track switch your tires there and run tens all day long!