Head porting - put your thinking caps on

[lm6y]

I have done a few sets of heads for carbureted american V-8s, and I know the finish on the intake side should be left a little rough to keep the fuel droplets suspended in the air fuel mixture.

Now here is my question. Since these cars are fuel injected, and the injection pressure is fairly high, and the fuel is atomized before it ever hits the air stream, and it has only about two inches to go before it is in the cylinder, do you think I could go for a finer finish on the walls of the intake ports? I am a professional polisher ( yes, there is such a thing), and I can get the intake port, exhaust port, and the plug/valves area up to a #1 finish, which would be a mirror finish. Do you think this would be beneficial? Or would it hurt power? I could also put a "swirl" polish all the way down the intake port. Would this be better?

We have a lot of thinkers on this BBS, so let me know what you think! I've got a spare head, and I'm just dying to try something on it.

[porscheboi928s/c944t/n]

me personally i'd go with the "swirl" polish..

[EGSMachine]

On fuel injected engines, the most important thing is flow and swirl. You want the swirl to keep the fuel atomized, and we all know why we want flow. i think the swirl will have a "rifling" effect, helping to carry more air into the CC. Port the head to promote both and i think you will be very satisfied. I think a mirror finish in the CC is ok, since it will help prevent preignition, just not what you want in the intake port, but certainly as close as possible.
good luck!
e


[This message has been edited by EGSMachine (edited 05-12-2001).]

[Blackfoot]

my inclination would be swirl. you might try this website, either search their forum archives or register and ask the man (Larry, "T.O.O.) himself:

www.theoldone.com

[lm6y]

Thanks for the input! I thought swirl would be the way to go also. I'll post some pics when I get around to doing it.

[Dave951M]

There was an article in Hot Rod magazine about 20? years ago and they tried polishing the intake runners. What they found was that the polished finish allowed the fuel to condense onto the walls of the runners, leading to highly variable mixtures going into the engine. The best results were with a slightly rough (or "swirl") finish. Edlebrock incorporated a similar feature into the "antireversion" intakes. You could contact them and see what they found before bringing out that particular manifold. My vote is for the swirl.

Dave951M

PS. The swirl creates a "boundary layer" effect on the moving mixture and helps to keep fuel from condensing. Old timers strikes again.

[This message has been edited by Dave951M (edited 05-12-2001).]

[wolfrpi]

I don't think that working the head on a turbo would make much difference. I'm not sure about an N/A.

Lindsey Racing just dynoed their turbo with a stock head and DME/KLR and got 370 hp to the wheels on only 18 psi. They claim their "trick" head will improve hp, but they have yet to dyno the car with the "trick" head.

Probably worth a try though as an N/A can use all the help that it can get in the HP department. Let us know how it goes!

Erick

[lm6y]

Dave, That's the way I've done it before with anything carbureted. But I was thinking since it's fuel injected, the injector atomizes it right off the bat, and since it's such a short distance it would stay atomized with a better finish. But I think a GOOD polish, with a swirl pattern is the ticket. I just wish I had a dyno to try it both ways.

Erick, everything that I've read says that on a forced induction engine, you should do most of the polishing on the exhaust side. And you should get it as smooth and polished as you can get it. Just take the roughness off of the intake side since it's going to be force fed anyway.

[951carter]

you want to test on a flow bench. the intake will be swirled. there is nothing you can do to the exhaust due to the liners. if you started with a 944 head you could do the exhaust and then have it coated, but there are no huge gains to be had, but there are gains.

[mike944]

I recently did a P&P on my head. I smoothed it out, but didn't go for a mirror finish, i left it a little rough. I only gained a little bit in the high rpm's, but i think if you have done some exhuast work, and maybe some intake work, you'll notice a bigger gain.

leaving a little bit of roughness can, under certain conditions, reduce air friction down the port by creating a seperation (boundary) layer between the fast moving air, and the non-moving port wall. I took a class about 6 years ago in aerodynamics, but don't remember enough to come up with a positive answer for you.

Although i'm not a professional at it, I had done it on an american V8 as well. Once i looked at the Porsche ports, i didn't see that much room for improvement. They looked pretty good to me.

If you have a spare head, go ahead and try it. I certainly don't think you could hurt anything, unless you really go nuts with the die grinder and cut into a water jacket. (even then, it's only a spare head)

Mike

[This message has been edited by mike944 (edited 05-15-2001).]

[TheStig]

Extrude-Hone does the same swirl polishing on intake manifolds and heads on these cars and there has been an improvement over the factory. I would say go with the swirl like everyone else and have it flow-benched.

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