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After taking everything apart to chase a smog failure I am in he process of re-assembling and replacing exhaust and anything rubber. While cleaning intake I noticed how rough the interior is which I don't have an issue with but this happened just after neighbor kid came over to show me his new intake bio-dad just bought him for his honda. The Plenum had been cut open and the in side reshaped and polished. Has anybody done that with a 951's and if so what were the results.
His car is bone stock but dad tells him that it worth 25 hp.
I'd love to see the dyno chart of 25+ hp from a polished factory intake on any vehicle.
Reducing turbulence usually makes for more power and better combustion. The flow properties of the intake port and valve seat will be the most limiting factor overall.
They would be the preferred method for me as it's not destructive to the intake manifold should someone really want to squeeze the last little bit out of a build.
Please don't send your intake manifold to Extrude Hone. There are several pockets inside the intake mani that cannot be cleaned after the extrude hone process, and it will leave abrasive grit trapped inside the intake mani. It cannot be cleaned out and only loosens up after you start the engine. It will feed a steady stream of abrasive particles into the engine until it's ruined.
Please don't send your intake manifold to Extrude Hone. There are several pockets inside the intake mani that cannot be cleaned after the extrude hone process, and it will leave abrasive grit trapped inside the intake mani. It cannot be cleaned out and only loosens up after you start the engine. It will feed a steady stream of abrasive particles into the engine until it's ruined.
It sounds like someone had an abnormal experience if there was honing grit remaining in any part of the manifold. They've been around for a very long time and have a good reputation amongst the sportsman classes in NHRA. I believe they inspect all enclosed components with high definition cameras now and may not have in the past. If they are aerospace certified for parts finishing, you better believe they have the processes to make sure there is nothing remaining. Of course, there is no telling if that level of attention is given to the one off guy with a 30 year old part.
I agree with you Jay, there is very little to gain from polishing or honing, even less if you cut it apart to do the job.
I've yet to see credible evidence that extrude hone improves the performance of these engines.
Ive actually read in various posts that the rough surface creating turbulence is actually good, but this was pertaining to cylinder head design, it was in the DIY cheapo head porting thread, someone here knows what I'm talking about. Plus in a turbo application I would think the gains would be less than on a N/A application, unless off boost.
WAG, but i am pretty confident any gains after EH are from the plenum tank and runners being slightly enlarged vs stock, rather than just being "smooth".
EH can remove 1mm+ from the ID of the tube it's pushed through pretty easily.
I remember reading threads here on Rennlist about little particles of metal being left behind after cleaning up the intake manifold and messing up people’s engines.
Polishing the inside may provide gains but sound too risky in my opinion.
This question wasn't specifically about EH, the Honda intake was smooth like the EH pictures but had velocity stacks shaped or added inside the plenum. This is a feature that the aftermarket manifold producer's seem to add. I guess we won't know unless somebody has done some testing on a flow bench.
Whatever the benefit, I'm guessing it's pretty far down the list of bang-for-the-buck power-adders on these cars. And probably more in the category of a supporting mod to get more out of a big turbo/displacement/valves/cam, etc. I have a SFR intake and 928 throttle body I used for a while, but replaced it with a stock intake and 951 throttle body by maxbore when I went back to the stock cam. A dyno might reveal some power difference, but with a stock cam and under 20psi on my 3 liter, I'm not sure I feel any difference (other than iffy street manners from the big throttle body). If the SFR intake doesn't make much power difference, it's hard to believe smoothing out a stock intake would, at least for a typical modded street car. If you are pushing the development of an engine and want/need a 951 intake, then splitting it open, polishing it, and welding it shut probably has its place in the world....
As for EH, that was a real thing. In fact, at least for a while, I seem to recall they weren't doing 951 intakes because they couldn't figure out how to get the media out. Not sure if that's changed.
Almost all high end engine builders go with textured surface finish for the intake manifold (boundary layer aerodynamics for uncoupling the air flow). Polished insides to intakes are there to sell to ricers.....thats what my dad told me....
Almost all high end engine builders go with textured surface finish for the intake manifold (boundary layer aerodynamics for uncoupling the air flow). Polished insides to intakes are there to sell to ricers.....thats what my dad told me....
My brother builds and dynos some of the highest flowing superchargers and intake manifolds in an internal combustion environment. Everything he has experienced in 25 years of doing it says smooth transitions and channels flow much greater volumes when laminar flow can be maintained right up to the transition point. In well tuned systems, that should be the valve bowl/seat.
That said, perhaps a turbulent flow is better for the engine characteristics needed for street use and not that of just raw power.
The stock intake will kill the top end by design as the runner length is long and designed for a strong mid-range. The stock extrude honed intake makes no sense as it would be at top end when you need the greater flow and the intake is not designed for that.
Last edited by refresh951; 08-27-2020 at 08:30 PM.
About 18 years ago TonyG had his intake cut open to flow match the runners. I don't recall what the results were, or if he even disclosed them. You should be able to dig up the thread.
08-25-2020, 07:50 PM
Inside of Plenum looks like 40 grit sandpaper
