Intake manifold porting smooth or rough?

[joat09]

I'm porting my 1g intake manifold to match the gasket on the flange. Should I port and polish or will I make more power if I leave it a little rough on a turbo application?

 

[hubz91talontsi]

Polish

 

[HIGHPSI4]

You want to leave it a little rough to help the air and fuel to mix up.

 

[hotrodssnova]

Being a forced induction engine, where the fuel is squirt into the intake port in the head, you can polish it if you want. Main thing is not to have a big mismatch where the intake meets the head. Usean intake gasket that you will be using when you put it together to mark the head and intake. Then you will know what needs matched up.
I used a marker and it works good..

 

[crazytsiawd]

tbh as highpsi said, leave it a little rough.

 

[joat09]

Do you guys by chance know why you're supposed to leave it rough on a forced inducted engine?

 

[007jimmy]

I dont think you would notice the gains if you left it rough or polished it. You are only going to be able to get at a small amount of the intake runners, not the whole intake manifold unless you extrude hone it. Look at all the high power cars that run a SMIM. I am sure they are not sacrificing anything due to the smooth intake runners. I did port match my 2g manifold when it was off, smoothed it out as far as i could go in and didnt notice any power increase.

 

[joat09]

I can understand that. I want to gasket match the manifold because the head is gasket matched on the intake side. Just makes sense to do it.

 

[007jimmy]

Just makes sense to do it.

Exactly why I did it.

 

[joat09]

Another thing is I actually did look at some smim's before asking the question and it looked to me that the runners were actually somewhat rough or at least not completely smooth or polsihed. Although I haven't seen one in person.

 

[viperlp01]

Up for major debate. Smooth surface creates a layer of stagnant air because the surface is so smooth that the air has something to cling to as it passes by. Rough surface tends to make air tumble. Air(and fuel) are less likely to cling to the wall but it is a turbulent ride.

We do not have carb's so you do not need turbulent air to mix with the fuel. So a mirror polish is a less turbulent ride for the air so I choose that one. But define smooth. Is a 80 grit sand paper that much different than using a fine cross buff?? Our head porter says that 100 grit sand paper is polished enough on a flow bench to give the best numbers.

 

[keltalon]

Being a forced induction engine, where the fuel is squirt into the intake port in the head, you can polish it if you want. Main thing is not to have a big mismatch where the intake meets the head. Usean intake gasket that you will be using when you put it together to mark the head and intake. Then you will know what needs matched up.
I used a marker and it works good..

Polish it. I think those who are saying to leave it rough are thiinking of the intake ports on the head where the injector in inserted and where it sprays to mix with the air, in that section of the head it would do you well not to polish it so that fuel can mix with air properly . But as with the intake manifold, before injector spray, before fuel mixture, polish the heck out of it this will indeed help with more smooth cfm which equals =more horsepower

 

[joat09]

Up for major debate. Smooth surface creates a layer of stagnant air because the surface is so smooth that the air has something to cling to as it passes by. Rough surface tends to make air tumble. Air(and fuel) are less likely to cling to the wall but it is a turbulent ride.

We do not have carb's so you do not need turbulent air to mix with the fuel. So a mirror polish is a less turbulent ride for the air so I choose that one. But define smooth. Is a 80 grit sand paper that much different than using a fine cross buff?? Our head porter says that 100 grit sand paper is polished enough on a flow bench to give the best numbers.

Polish it. I think those who are saying to leave it rough are thiinking of the intake ports on the head where the injector in inserted and where it sprays to mix with the air, in that section of the head it would do you well not to polish it so that fuel can mix with air properly . But as with the intake manifold, before injector spray, before fuel mixture, polish the heck out of it this will indeed help with more smooth cfm which equals =more horsepower

You guys are making great points and helping me out a lot.

Although if the runners are too smooth it will result in laminar flow and cause drag. That's how i'm thinking about it.