Plastic Intake Manifold ANYONE?

[Matty2Hotty]

They made Plastic High Temp Intake manifolds instead of the metal ones on newer models... This is a direct bolt on Mod buttttt..... Will i see any potential increase in HP due to the colder air and am sure the plastic is smooth on the inside compaired to the alum. unless you had yours honned and polished. Anyone else ever do this?

[ouch1011]

This is kind of the same idea as phenolic spacers. I've used them in the past and noticed absolutely 0 difference. The air doesn't spend that much time in the intake manifold (especially at WOT) to really heat up alot. You would be better off making sure you have a good cold air intake.

As for the smooth inside...well some turbulence in the intake manifold is good, since it helps atomize the fuel mixture. But usually its only really beneficial where the fuel and air are in the manifold. And composite manifolds aren't totally smooth inside, as the seams aren't really smoothed over.

The plastic manifolds are on new Subarus because they are lighter and cheaper to make. Its not for the heat transfer properties and the smooth finish :)

[green97gt]

i had always heard from the old hot rod guys that you didnt want a totally smooth intake manifold runner, the reason was that turbulent air was thicker than non turbulent air...i dunno if thats true, but thats just what ive heard. thoughts?

plastic engine parts just sound like a crappy idea to me. but then again, i wish everything was cast iron.

[Airgne]

also the plastic intakes were made for only fly by wire from what i know.

[ouch1011]

The hot rodders want some turbulence in the intake because, like I said, it helps atomize the fuel and mix it with the air charge. Same reason that many carbed (stock) cars have heat risers, intakes that draw in hot air from around the exhaust manifold, and exhaust passages that run through the intake manifold. The heat atomizes the fuel and helps it burn better.

[lozanoa11]

Also I heard you want a slightly rough surface so the air moves slower around the walls and acts a lubricant for the rest of the air.