Bit rougher is advised.

I was always under the assumption that the "rough" texture being better was kind of a myth. Air with less turbulence and the smoothest path, is best, no?

I've heard in a carburated engine, the turbulence helped mix the fuel with the air, since the fuel was mixed with the air so far away from the cylinder. In a fuel injected engine, with the fuel being injected right above the valve, air flow/speed is most important.

EDIT

This is the best I could come up with. An image of an old (No year given, but 3 valves per cylinder haven't been used since the 80's) F1 intake port. Its not "mirror", but I wouldn't call it rough either.

http://image.circletrack.com/f/14889...fold+guide.jpg

Moar edit

NASCAR "upper level" engine. Note the smoothness.

http://image.circletrack.com/f/31128...ad-gaskets.jpg

what I heard is that if you polished to a mirror finish you wont have a good atomization of the air/fuel is it a myth?

That's taken care of by the injector now days. The fuel hits the intake valve (or damn close to it). It doesn't need help of the intake, and intake ports to keep atomized.

I'm not saying that I'm right. I'm posting as an opportunity for someone to change my mind. I think the "rough" texture is a myth carried over from olden carburator days.



Granted, there is the subject of the boundary layer affecting the speed of the intake flow. However, the "fix" for this is having an impedance in the flow path of the air. I'm not sure whether there is a gain, or a drawback to that. "Roughness" isn't enough to fix it though.

Golf balls are dimpled because it disrupts the boundary layer of the air around the ball, making it fly farther. However there is a difference between air flowing AROUND something and THROUGH something.

Maybe someone should dimple their intake port?

under the same context the intake valve chamber could be mirror polished right?

I think mirror polished is extreme, but I wouldn't worry about purposely leaving it rough. Smooth it out

(Though I am anxious to see what others think about it... with some data to back it up :cheers:)

It depends. Smooth ports are great if the air doesn't need to turn. If it has to turn, it can separate very easily, creating a vena contracta (essentially a choke point from stagnant air) A rough port will disrupt the boundary layer, and prevent the air from separating as easily.

So if the port is tight and has a small radius, you don't want it to be very smooth. If it is darn near upright, and the air has to turn very little, smooth is probably better.

While the 951 has some of the best ports ever because of the shape of the head, it is best to err on the side of keeping it a tad rough. The extra flow from a perfect surface is minimal, but the penalty for separation is HUGE.

Interesting, everything I have read states with forced induction the boundary layer does not play the same role as with normally aspirated. I agree that mirror would be overkill. What would be your reasoning for a rougher surface?

Thanks Patrick. Your pic has what I would consider a smooth surface. Your pic is exactly the surface finish I an shooting for. Where did the 4 valve head come from?

nice thread. definitely love the work...

still not sure if you're really tapping into the most direct route for affordable power.

in my mind the best bang for the $$$....


1. displacement; Gen IV standard rebuilt or factory block w/4.06~8" bore w/ LS-3.662" (or larger) stroke.

2. stock LS3 heads (flow huge for low $$$$ from a discount GM parts store).

3. stock LS3 intake manifold (they flow huge for the money and sell for pennies on ebay).


simple enought to just get an LS3 crate engine... then,


4. a hotter cam and better valvesprings/pushrods, ect...


then:

5. head porting or even

6. moving up to an LS7 block w 4.125" bore and 4.0" stroke.

:banghead::banghead::banghead::banghead::banghead:

But to overcome the boundary layer, you need actual disruption of the air. A golf ball isn't just "rough". It has dimples.

The air just simply flows over a rough surface.

really ?

a friend just built a complete 379 c.i. LS engine for a bit over 5 grand by;

1. rebuilt LS2 block.

2. GM parts store.

3. auto salvage yard.

Why did you friend not buy a vette or a truck in stead ? This thread is about the 944 valves not LS engines.

his work is beautiful. and it sounds terrible to say.... but on the matter of an improved head flow via porting; (short of a full racing program) with this particular engine, you're talking about fractions that can easily be handled purely via the turbine/wastegate/tuning. anything you do to the cylinder head would make only the slightest improvement, when all you have to do is increase boost. if he want's to go past what the turbine can theoretically do on it's own, and he isn't limited to 2.5 litres, then going to V8 is the fastest and least-expensive way to more power.