I have recently purchased a polished intake manifold and was wonder what people thought about these. I always hear people say how good it is and that it adds some decent horse. I had an instructor at a college tell me that polished intakes are bad because then the fuel particles aren't broken down because the flow isn't rough enough. does this guy know what he is talkin about or not? Thanks in advance

 

i'm gonna go with he doesn't. why would the flow need to be "rough" you would want it smoother, not rougher, that's why you use smooth pipe in a CAI if u make ur own not corrogated carboard...(exageration but u get the point). it would be better for smooth air flow. and did u buy a polished base or polished runners and plenum, if u bought the plenum and runners then there wouldn't be fuel touching them anyway, or there shouldn't be so his theory is again and all these people wouldn't do it if it was bad for the car.

 

I think that guy is right concerning WET intakes. TPI is a DRY intake and the fuel and air get mixed right at the port.

Carbs, and Thorttle Body injection are two types of WET intakes - the fuel and air are mixed before travel thru the manifold.

I don't know about significant horsepower gain from polishing alone - perhaps you are thinking about 'port and polish'.

 

yeah, what he said...

 

Well when i bought it the guy told me that it was ported polished and poweder coated. It definatly looks polished and powder coated but it doesn't look like it's ported much (if at all). That instructor also said that because of the "not rough flow" it will probably cause worse gas mileage.

So what your tellin me if that i was right for buyin it and the instructor doesn't know what the sh*t he is talkin about??
thanks

 

the way it has been explained to me, is that at certain high, very high speeds a rougher surface is better. however you will never need this for two reasons, your intake will not touch the fuel, and you will never reach speeds high enough to make it matter. and smoothing out airflow at speeds that you will be using cannot be a bad thing because, well just because. your instructor may be right with carbs or TBI like the above said, because the fuel and the intake come into contact through odvious ways. what is this instructor and instructor of? i have a friend who is a mech. engineer explain this to me, and said in his fluid dynamics is when he learned that the flow is better at very high speeds with ridges, basically a smooth base and ridges in the base. and based on ur instructors theory, it seems that he would say a free flowing exhaust would cause poor gas milage as well, when infact it typically provides better. plain and simple i think he's wrong.

 

oh and if the intake just looks polished on the outside, then it wont matter anyway... for odvious reasons.

 

Your instructor isn't stupid, he is just applying the wrong theory. I am sure he is thinking of WET intakes. Tell your instructor you have a PORT INJECTED setup and see if he changes his opinion.

 

He is the instructor for the auto tech program and my college. But the intake is powder coated on the out side and the inside is all shiny and smooth. thats why i think it was polished but not ported. I guess i'll wait to see and compare it with another one.

 

yeah, my guess is probably like stroy's he just has the type of injection messed up and thinks your talking about a wet injection not a dry. good luck with it

 

Can you post photos? AFAIK it is pretty rare to polish the inside.

On the subject of turbulence, IIRC you want turbulence to keep the fuel particles suspended uniformly. So, the comment about a dry system seems right.