Cylinder Head Porting and Power Production

rmchrgr said
I was coming at my question from a "real world value" angle. I have an iron head 10.3:1 416" motor that made 500.2 hp on a dyno. (sheet below) According to the published head flow numbers (293 CFM), the combo should have easily made more power but hey, it didn't. Cam is a decent solid FT, around 260 @ .050 and almost .600" lift with 1.6 rocker arms, single plane intake, 1 5/8" step headers. BFSC was over 5 almost all the way through so as I learned that number was an indicator of less than optimal efficiency. The intake might be the cork, it's an old Strip Dom. HV oil pump might rob a few ponies too but it does have a crank scraper. Unfortunately I don't have any ETs because the car has been in storage for a while.

Anyway, I started looking at new heads and for what it's worth compared some published flow numbers. The comparison aluminum head flowed almost exactly the same on the intake as the current iron ones but the exhaust flow from .400" - up was significantly better, to the tune of almost 40 cfm at each interval. Have to think that an aluminum head combo would be more efficient but if everything else stayed the same - cam, intake, exhaust etc., how much of a realistic improvement could there be? I know there's no way to answer that question without actual data, just trying to figure if it's worth the money for a "perceived" improvement based on published flow numbers.

The other benefit of aluminum heads is the idea that they tolerate more compression so in theory more C.R. should help efficiency.

View attachment 1715676588

I hate to say it...but I will...this looks like a perfect case for a burr finish. All that fuel going through the engine isn’t being used, it’s just wall flow that blows out the exhaust or ends up in the chamber as stratified layers of fuel that burns so late it does nothing to make power. As much as I don’t care for EGT’s as a tuning tool, you would have probably seen elevated EGT’s because the late burning fuel is getting into the header. Elevated EGT’s can be late timing, too fat, both and what you may be seeing with wall flow issues.

Too bad you can’t test it. If you burr finish and drop 3-4 jet sizes, even if it makes the same power on the dyno it will be quicker in the car and at the track.

There are engine dyno’s out there that measure the rate of acceleration. I’m going on one here in a few months if everything goes well and it is an inertia dyno, not a water brake. It will tell you if the engine accelerates the load quicker, rather than measure torque against the water brake.