I tried doing a search and some of my questions I couldn't find answers too. My car is an N/A LT4 headed 350cui, so here goes. . .

I know on the exhaust you want to polish like glass to reduce the amount of carbon build to keep volume of gas flowing out as high as possible. What about the intake side? I've heard several different responses from people. Some say leave a textured finish, they're reason being "so the fuel air mixture can atomize." I've seen other people polish the intake side like glass too but I never heard about how they run or anything. Hoping some of the more experienced people here can shed some light on this.

Also, the chambers. Same question there, polish or leave a rough texture? Some say to leave rough like the intake ports so the air can atomize, others say to polish like hell to reduce carbon build up and detonation problems. Call me stupid but I would think carbon build up would increase the compression after a certain amount of build up and be on + side, then again my theory could be wrong and hence why I'm posing this question.

Thanks in advance
-Rob

 

I have some pics of my GTP heads in my sig. They arent the greatest but they show some stuff pretty good for a visual...

 

these are MY opinions and Bret, Chuck or Phil would probably be a better source but since they have not responded yet, I will give you MY opinions.

intake ports- on my personal stuff I leave rough and for customers that request I leave rough. My opinion is that it does mix the fuel better at lower rpm and I think the smooth, slick surface on the intake ports could allow fuel to puddle under certain comditions. I know there is a "VERY SLIGHT" flow advantage for polishing but the 6000-6500 RPM motors (most of my customers) I do not think ploishing is any advantage. On a 8500 RPM SB2 maybe the polishing has more of a positive effect but I have left them rough and then polished and as long as the ports are strait and correctly shaped there seems to be 5-7cfm increase on a 300 cfm port at peak and less through the curve. The only part that I polish on my personal intake ports is the shortside to remove any bumps that are there. I polish most customers ports because that is what they want (and pay) for.

exhaust- I think polishing the exhaust is more important since you are giving the carbon less to stick to. As with the intake ports, I feel shape is more important than the texture but I do polish them.

chambers- In my opinion it is more important to polish the chambers and remove any sharp edges and if you take a small torch and run across a cast aluminum surface like a combustion chamber and keep moving it you will see the little cast bumps and sharp edges are the first things to turn red. After removing these and polishing these it takes more heat or the same heat for a longer period of time for anything to turn red.

This is probably over-simplifying all of this but hopefully you understand my understanding of these areas however right or wrong they may be.

NightTrain66

 

Shortside? Little confused what your talking about here.

I don't have very much in depth knowledge of car as in areas such as this. But I could see polishing being an excessive unnecessary overkill. Geometry is definitely important in getting the air to flow right. Approx. how much of a texture should I leave, I was informed roughly an 80 grit surface, anyone else have any opinions on this?

I could see by removing the casting flash (correct me if I'm wrong if thats not what it is) on the chambers reducing the tendancy to build up hot spots and reduce detonation like the one told me before.

Thanks for the replies so far guys, anyone else go any opinions or some $change$ to drop on this?

Thanks,
-Rob

 

the shortside is the shortside radius. It is the turn that the port makes from the end of the floor to the seat.

As far as how rough is rough???? in my opinion rough is like 50 grit. 80 grit sandpaper rolls will actually leave a smooth finish if you use the right speed and remove all of the cutter marks.

NightTrain66

 

So your talking about the "bowls" from the valve seat to the ceiling of the port above it?

Are you saying you polish this part, but leave the actual straight runners rough?

 

basically I leave the entire intake port rough other than the TURN from the FLOOR to the valve seat. I leave the bowl's rough as well.

NightTrain66