What surface finish should I apply after porting a stock TPI intake base with a carbide cutter? I've got the SA porting kit with 40 and 80 grit sanding rolls and 2 types of cross buffs. I used the cross buffs on the last base I did but now I'm second guessing that decision. Appreciate any input. Thanks.

 

smooth as possible is fine for a dry flow manifold, you aren't looking for good mixing.

cross buffs should be a good finishing point.

 

For air flow only, you want a mirror type finish, as smooth as you can get it, then polish it.

 

on the street, you'll never notice the difference between a 120 grit finish and a mirror finish. Maybe a HP or two, it's up to you if you think it's worth your time.

 

Guys, thanks for the inputs. Based on what you say I'll go ahead and use the cross buffs to get the nice polish.

 

Only time you want a rough finish is when you have fuel particles that you want to keep suspended. If it's dry flow you're lookng for, then polish the hell out of it.

 

even with that I'm not so sure a perfect smooth finish. I've seen dry flow setups that had dimples or a little roughness in them to prevent the air from "sticking" to the surface kinda just like the fuel does

 

Yea, cross buff is a good idea. TPI's arent exactly totally dry flow, there is some reversion and whatnot throwing some fuel mist around, not to mention EGR and PCV gasses. If you've ever taken off a runner and seen all the black stuff inside... well, thats not air!

 

You can use a 40 or 80 grit flapwheel, see my thread.
Crossbuff isnt necessary.

 

You hit on my two concerns; 1) airflow over a sanded versus polished finish and 2) air-fuel mixture standoff and reversion.

Two examples for concern 1 come to mind. The dimples on the golf ball and the skin friction of a single drop of water as it moves over highly polished glass versus a slightly rougher surface.

And there definitely is more than just air going through the base. The good new is all that junk looks like someone used a black magic marker to show "port here". Even though the injector is pointed toward the cylinder head intake port, I believe that some of the air-fuel mixtures flows back into the base due to standoff and reflected pulses from the back of the closed intake valve.

Conversely I keep thinking about the smooth finish that Extrude Hone puts on intakes which supports the "polish it" theory.

It's good to be able to talk yourself in a circle.

 

You could always polish all the right side, cross buff the left, and see if the engine has an imbalance after that.

 

 

I like it.