PatriYacht

One of the points to measuring the cfm of a cylinder head is to compare to other cylinder heads. There has to be a standard way of measuring. Perhaps we could get more accurate readings if everyone tested with a pipe, but then what size pipe? A tuned header length pipe, a cast aluminum manifold length pipe? What diameter? Everyone has to play by the same rules if we are going to compare.

bobl

Question for Jim V. I've got a customer that I'm going to build a 502 for. The short block will remain stock(blueprinted) using a Crane 731 cam or similar. Going with a Air Gap intake and 9022 Holley. Obviously the HP is in the cylinder heads. I'm thinking of having you do me a set of heads. We can go iron or aluminum. What head would you start with? Those Iron Eagle exhaust numbers sure looked impressive, what about a fully ported set of those? I want the engine to peak at no more than 5500 RPM.

Thanks,
Bob

2112

This begs the question I posted above.

No doubt those are awesome flow numbers but how many Rs to you have to spin to use them? How does compression and displacement affect this?

Starting a new build up myself, need education here.

JimV

Mike, I have found that airflow increases in all ports when a pipe is used. The AFR's respond better than most. Next week I will flow a full header to see what happens.

JimV

Here are some Dyno numbers from a 454 with fully ported Merlin heads with wedges in the intake ports and similar flowing exhaust ports and a mild hydraulic roller cam. The compression ratio was no more than 8.5:1. The short block has stock dome 365 hp pistons. The combustion chambers are 125 cc's. The block was bore notched, lowering volume an additional 3 cc's.

I don't have an A B compairison on exhaust ports but I dont think too much exhaust airflow hurt this one. The boat picked up four mph over the bowl ported heads.


Keep in mind that the venturi area in the exhaust port does not change from the factory specs. I think this is very important for velosity.

2112

I guess my question is this:

Considering most of us are looking for maximum power (on some variation of pump gas) somewhere between 5500 and 6200 rpms, will gaining those last few cfms at .7" lift or greater help us?

No question your flow numbers are great. Just trying to get your opinion on where the benefits are.

Also, Am I understanding you correctly that the extra flow was picked up by opening the exhaust port further out from the venturi and extreme valve size was not beneficial?

JimV

Increasing airflow at .700 lift wont make any difference at cam lift at .600 but to get a good number at .600 the port usually flows to .700 and above. The exhaust port opening in the 454 dyno was kept to a minimum because of the cubic inches and relitively small cam .578 lift. 540's cid and up will have a larger opening. Generally the bigger cubes need more cam and personnaly I believe more volume as well
---- Also, Am I understanding you correctly that the extra flow was picked up by opening the exhaust port further out from the venturi and extreme valve size was not beneficial?

Yes, the diameter below the seat remains pretty much stock depending on the depth of the port. The Darts stay stock, the Merlins need some tweeking. All valves I have used are stock size of 1.880. I havent seen any airflow increases with a larger valve.

cobra marty

JimV, those 454 numbers look great. What would a 540 do? About 675-700HP and TQ at the same rpm and CR?

bobl

Jim V, I posted a question for you earlier in this thread. If you have a minute, please check it out and respond. I think there are several on here intrested in what you would recommend.

Bob

JimV

MJB

Sorry for the delay. Here are some numbers for a bowl ported 308 Iron Eagle with some chamber work. Intake 2.250-Exhaust 1.880


Lift............Intake.CFM................Exhaust. CFM

.2......................154....................... ......130
.3......................226....................... ......184
.4......................295....................... ......219
.5......................324....................... ......241
.6......................349....................... ......257
.65....................353........................ .....260