d1mbu1b

I noticed several threads on cam head combinations and have a general question probably pertinent to all.

Is there an advantage to using a square cam with a head having excellent exhaust characteristics over a cam with longer duration and lift on the exhaust lobe with a "regular" head.
regular meaning the exhaust side does not flow as well as the intake side.

I have purchased a set of AFR heads that have "excellent" exhaust flow and was recommended to buy a square cam.

What is the benefit?

Is there a disadvantage to mating it with a stock cam grind having a larger exhaust lobe?


My current thoughts are purchasing a special grind of the comp XM270HR intake 270/218 exhaust 270/218 @ 114
114 lobe separation to move the power band lower and guard against reversion
and 270 square pattern to take "advantage" of the good exhaust head flow.

Do you think there is a benefit over the stock XM270HR 112 grind?

PatriYacht

The exhaust flow is not as good as AFR claims. AFR uses a pipe on the exhaust port which raises the flow numbers about 13%. Then you have to consider that marine exhaust is not as efficient as a set of dyno headers. I had my AFR 335cnc chamber and exhaust ported by Jim V ( a member here on the board) and he got the numbers up to what AFR claims but without the pipe. With those numbers, the tech at Comp Cams still advised me to use 4 degrees more on the exhaust.

d1mbu1b

PatriYacht.
Thank you, I always want to believe what I'm told. But what you said seems more realistic.

It seems apparent to go with the standard grind and not spend the money on the custom grind.

Unfortunately, I still don't know if there is an advantage to having a smaller exhaust profile. My guess is that it provides more back pressure at lower RPMs for better low end torque. But, who knows?

RichardCranium572

Seems a bit small, is that going in your RV? Doesn't make sense to spend the money on good heads and not spend an extra hundy for a custom cam that will perform better

PatriYacht

Mine is a 236/240 .630 lift. It seems close maybe a little on the large side in a 540.

KAAMA

I agree with PatriYacht---I have AFR cnc ported heads as well.

Ian, what RPM are you turning with your boat/prop set-up at WOT?

PatriYacht

Hey Mark, how are you doing? I'm still over propped. It went about 75 at 5100 this summer with a heavy load of people and fuel. This winter I'd like to get new 1.5 gears and then try to prop it correctly. It's hard to find a set of labbed 22's to use with my 1.35 gears. How's your boat running?

KAAMA

Running very well and I have just over 50 hours on it so far this season. Turnin' 32" labbed 4-bladed props to 5500rpm with 1.50 gears. I am very pleased.