Larry928GTS

It was somewhere over half a dozen years ago, but they quoted me $600 at that time to do an S4 manifold.

I seem to remember a post either on here or the mailing list where an extrude honed intake and bored larger throttle body were tested on a race stroker, and the dyno results indicated a 4hp loss from those modifications.

RyanPerrella

Thanks Larry

ptuomov

Larry --

Very interesting. Thank you for the info.

Why do you think that is, by the way? One would think that wider runners and wider throttle body would at least not hurt the top end. Kill the mid range, yes, but why would the top power be down? Any guesses?

ptuomov

bcdavis

It would seem like you would want to run the extrudehone media through the whole intake and throttle body at the same time. And maybe the heads as well, if you could rig the whole thing up... It just seems like a waste of money. It probably won't hurt, but won't help that much either. If I was going to do some work on the intake, I would probably just match the ports to the heads, smooth out some of the rough casting areas, powdercoat the whole thing, and call it done...

ptuomov

But the evidence above was that boring the throttle body (I don't think the throttle body can be extrude honed) and extrude honing the intake manifold resulted in a 4 horsepower REDUCTION on a stroker race motor.

My only theory is that the factory has coated the manifold internals with some sort of material that makes the manifold very slippery for air. When the manifold is extrude honed, the slippery coating is removed in the process. The loss of coating may have a bigger impact than the increased diameter. But this is just a theory.

One way to test the theory would be to dyno a stock manifold, then extrude hone the absolute minimum amount and dyno again, and finally send the manifold dry film (or some similar) lubricant coated and dyno once more.

slate blue

By IcemanG17 I plan on making my throttle bodies for my 2 valve and at this stage they will have variable length trumpets to take advantage of the natural ram tuning.

Greg

ptuomov

Sterling -- Is your ITB set up ready? It's hard to do better than the factory with a single throttle body intake, but there are a lot of gains to be had with ITBs. Too bad ITBs are out of my budget, so I have to just follow other people over the web. Best, Tuomo

Jim bailey - 928 International

Smooth is NOT a good thing ! much is counter intuative when it comes to fluid dynamics.

Larry928GTS

The 4hp mentioned would have been less than a 1% difference. Even without making any changes, it probably wouldn't be surprising to see that much variation from one run to the next. Making the runners bigger would result in lower velocity. I don't know how much the extrude honing really changes the size, but maybe that could have something to do with it. I really don't know. I do know that bigger isn't always better, otherwise everybody would be using intake runners with a diameter as big as the cylinders.

I figure that experiment would probably cost around $1,200. ($75 for the before dynos, $600 for the extrude honing, maybe $150 for the bigger throttle body, $75 for the after dynos, maybe $200 for the coating, and $75 for the final dynos.) If anybody tries it without making any other changes to the engine besides those, it would be interesting to see the results.

Fontana

Okay.....?

inactiveuser1

Before porting was legal in SS drag racing some would use muriatic acid in heads and intake as it would increase port size.It was good for class racing where porting wasn't allowed and you couldn't tell as the acid would increase size of the ports but you would never know it was ported because of no grinding marks.Ports were sealed to contain the acid in the ports then changed and repeated and after neutralized the acid.It must of been time consuming to do that process.Sure isn't good stuff to work with thou!I watched guys setup up motors with pistons right at the limit above the deck height.Getting torn down right before tech they use rubber mallet to tap the top of the piston just to make sure the oil was out from under the bearing so they weren't to far above the deck ever .0001 counted to make sure you weren't over the legal limits after a win.Seen smaller clutch drums in automatics for less reciprocating weight but used more clutches as machining drums to fit more clutches but the diameters were smaller and lighter in weight.You would see a big stock case but inside everything was different.Was around SS cars back in the 1980's and thats why my street car ran good back then it had alot of the same things that some SS cars had plus it had a Moldex stroker crank from 3.31" to 4" and that was way back in the late 1980's

simos

IIRC, David Wizard has said that shape is 98% and shiny finish rest 2% Perhaps slightly exaggregated, but still...
This applies also to intake pipes as well as intake port. Actually 60 - 80 grit is good for intake port or just use plain quality casting finish.
The exhaust port is different animal, it can have more shiny finish as it's not carrying the wet flow.Also exhaust port shiny finis prevents exhaust somke and particles to stick to port surface.

Air has a mass just like any fluid and therefore it doesn like to turn quickly. This is getting worse when air is moving at higher velocity.

http://www.popularhotrodding.com/eng.../photo_16.html

One of the problem with 32V(S4 up) intake is that there are way too many strict turnings, which will generate turbulence and slows down the air velocity. This will also cause unequal cylinder filling, which will drop the overall volumetric efficiency. Too little gap between some of the intake bell mouths and intake wall is another issue.

At 2000 RPM a camshaft with 200 degrees of intake valve duration, the intake valve is open for 0.0166 seconds/cycle.
At 6500 RPM the valve is only open for .005128 seconds/cycle. You can imagine of how little time there is to fill the cylinder. Air should speed up it's velocity from zero to max. of 0.5 - 0.6 mach (if port has optimal size) in very little time. Less flow restrictions will help there significantly.

If one would like to improve the original intake, he may want to consider doing something similar, what Jim M. did for Dennis Kaos GT intake as a part of tuning process:
https://rennlist.com/forums/928-foru...the-gap-8.html

Livio928

Raising this thread from the dead. The PO had my S4 intake Extrude Honed and I will be installing Victors S/C unit in a couple of weeks. I have a replacement intake. My question is was there any definitive data whether the Extrude honing made a difference? Created a loss of 4 hp? or with a S/C unit help the system. I also have a set of Carl's intake spacers and wondering if they would make any difference if i added them to the intake (Stock or Extrude honed) with an S/C unit.

ptuomov

Run it in a dyno before you make any changes. The dyno will tell you if the motor is running about right. If the dyno run looks good, everything is ok. If it looks way off, you'll probably have a bigger problem somewhere than just an extrude honed intake. You'll definitely want to know the baseline before going into any modifications as large as a supercharger install.

MFranke

Unless we are talking about significant diameter changes, would the laminar flow layer be a factor? Would a less smooth surface affect that?