Polished FI intake manifold

[280~Master]

I would like to know if any one has polished there intake manifold? Would there be an increase oh power if I had the inside of the manifold polished as well as the out side? Just wanting to get some info about the subject..

[hls30.com]

John,

There is a processes called "Extrude Honing" that is used inside the intake manifold to smooth the air path-as I recal it is a couple-three hundred dollars to have done, and it essentially biols down to forcing a high viscosity liquid loaded with abraisives through the intake at very high pressure.

Will

[TomoHawk]

I was just going to ask how you'd get in there with the abrasives, although you could probably do it the hard way/slowly and save big $ with sandpaper on a very long & flexible stick.

[SteveK]

There is an argument that says inlet runners shouldnt have a high degree of polish as it can lead to the fuel dropping out of suspension, having a slightly rougher finish can help prevent it by creating turbulence. The stock Nissan FI unit is not known to be a performance part (in NA form anyway) so it is questionable as to the payback.

Just my humble 2 pence worth

[TomoHawk]

So then it makessense to only 'polish' the insiode of the Intake and runners with: 600 grit sandpaper?

[hls30.com]

I have seen info on both leaving rough and polishing, but never the difference between only those two options. From a purely aerodynamic standpoint I can see a benefit in non-polished runners in not allowing a laminar flow to form(as well as keeping the fuel suspended), but from another angle, I can see a benefit in smoothing the rough casting/core edges to lower drag.

Any real numbers out there?

One of the things I want to try is smoothing(not polishing) the interior of the intake(and giving all of the runners a uniform cross-sectional size and volume) and installing a variable vane vortex generator just ahead of the mouth of each runner . This would generate a uniform turbulance to break up the laminar flow, and allow(from the "tornado" web page) a greater volume of air to pass through the runner. It sounds good anyway!

Will

[TomoHawk]

The new Mustangs are using the variable vane thing in the intake runners. It's supposed to increase power, fuel efficiency etc.

[280~Master]

Will,

I like your idea of smoothing out the runners. Just making air flow a little bit better and smoother should give a Z a few more ZZZ's under the hood. As far as the variable vane vortex generator. That would be a dream setup. In theory it would force more air into the cylinder for more bang .

John

[TomoHawk]

In model powerboat racing engines, we open up the case and take off all the sharp corners. It does a workd of good in those little mills, that can spin up to 14,000 RPM- stock.

[LanceM]

First off let me say I'm a carb guy and really don't know squat about EFI. But since the fuel is injected at the head it would make sence to me that the intake should be as smooth and shiny as possible to allow the air to go unimpeaded to the intake port of the head, there is where the fuel is mixed during the intake stroke and the really important things happen. Once it gets to the head is when you don't really want a polished port, you need to mix the fuel with the air....