ptuomov

I have read on this forum and in other places that extrude hoing of the '87- manifold makes things worse, not better. Why? I have some theories but what's the list consensus?

mark kibort

I dont think it would make anything worse, but there hasnt been the gains one would think you would get. I think some hand porting of the intake as well might help . I think there are other limits though. your MAF screens could be a limitation for example. side cover extenstion, hand porting and extrude hone all might give some gains, along with GT cams!

mk

ptuomov

Mark --

Thanks for your response (and your other posts).

...but I have been hearing about the extrude hone actually hurting. I don't understand why. Does anyone have comparable dyno data on extrude honed and stock s4 intake manifolds? I would very much like to see which part of the torque curve gets hurt.

Mark, I think you have been experimenting with the plenum spacers. My intuition is that they would hurt, not help, but then again I am a complete novice. I posted my logic to another thread. If you can educate me on what the actual impact of the spacer is, I would be most grateful.

Jim bailey - 928 International

Porsche is first and foremost a design and engineering firm that just happens to build a few cars The S-4 intake should you wish to BUY a new one lists for $4,623 , a price which reflects the amount of design , engineering , and testing that went into making the part. It works quite well for the purpose it was intended 320-400 HP some stroker engines have been said to make around 500 hp with the stock intake. The carbon fiber 928 developments dual throttle body intake or individual throttle bodies CAN make quite a bit more , but ONLY on an engine where everything else has been done and the intake was the most restrictive part. What has become clear is that the camshafts are probably the biggest limiting factor to normally aspirated maximum horsepower.

ptuomov

Jim --

Thanks for your response.

I am reading between the lines your message: Why should a random modification such as extrude honing help with the manifold designed by Porsche. If it would help, the factory would have done it. They design that kind of stuff for living.

If this is what you are saying, then I would have to agree with you.

My interest is in why and how the extrude hone experiment failed. Was it because the extrude hone process created variable diameter runners in which air has to accelerate and decelerate? Was it because the process made some of the short runners even shorter and/or some of the long runners even longer? Was it just because the current runner diameter is already large enough and something else is already the bottleneck (cams you suggest), thereby the only effect is to unnecessarily slow down air in the runner just to be accelerated again?

I am trying to understand why Porsche engineers designed the manifold the way they designed it. I am a complete novice and not yet even close to the point where I would understand how that manifold really works, let alone could improve it.

Best, Tuomo

BC

The intake is at best an exercise in packaging and looks - only compromising for performance a bit.

ShawnSmith

I would imagine Porsche checked what kinds of gains were to be had by extrude-honing the intake or exhaust manifolds, found that they were very small (although maybe non-zero), looked at the cost and decided that money was better spent elsewhere on the car.

Jim bailey - 928 International

All aspects of engine design are a compromise. Simply stated larger intake runners are not always better. You can get more horsepower or more torque but you are trading one for the other.....camshafts are much the same they only work well over a small RPM range.

ptuomov

Jim -- If I have understood correctly, extrude hone increases the diameter of the intake runners. A rule of thumb (from I think Graham A. Bell's book) is that increasing the runner diameter will increase the torque at high rpm and reduce it at low rpm. In this case, however, I have "heard" that extrude honing S4 manifold reduced the top range torque as well. I am trying to understand why larger intake runners would reduce top end power. Best, ptuomov

mark kibort

Yes, the design is pretty impressive, giving the highest level of HP from beginning to end. without the resonance flap, the mid range (which I NEVER use, nor anyone would use in a pure top performance evaluation) is compromised. any use of the engine above 3700rpm, does not require this function. Dont fall in to the " if it could have been better, porsche would have done it" bucket! That is not a question. SURE porsche could have designed it better. Think about it, lighter car, ( not crash worthy), headers, (bad for smog and noise), cams, (fuel economy, emmissions), Intake mods (noise, bad low end performance, size, manufacturing ease, etc)
Anyway, the reasoning behind larger runners is reducing the pressure drop. Why do you think they put on restrictor plates in racing series? to create pressure drops that limit mass flow of air to the engine. take a look at ANY high performance engine, and the intake runners will be huge. this is in no way in conflict with the head ports, which combine other theories of operation with velocity, mixing, etc. our intakes , if larger, even with cams and restrictive exhaust, will provide more mass flow and produce more HP, and probably mid and low range drivability, if made larger. the side plates allow for more flow efficiency to the horns that feed the intake runners to the heads. Its like covering a drain with your hand. its flow is restricted. the idea of the horn is to reduce air flow turbulence and draw air from the center to its edges efficiently. a bell mouthed 2" straight pipe can flow more than a 3" pipe without a bell mouthed inlet for example.

This is why the CF intake gained over 70-90hp, with no other changes! Look no farther than the BMWs from PTG and their intake. 450rwhp out of a 3.2 liter. most was done in the cams and intake.

mk

Jim bailey - 928 International

I would agree ...."This is why the CF intake gained over 70-90hp, with no other changes! " but only when many of the other changes had ALREADY BEEN DONE ! We have yet to see what a CF INTAKE would do on an otherwise stock S-4 ....... not one punched out to 6.5 liters , with big cams , real equal length headers , high flow exaust , big cams , big valves , larger mass air etc. etc.

mark kibort

I would be willing to bet anyone that the CF intake on a stock S4 would show substantial gains. why wouldnt it? the cams, if you look at their specs are mild, but even if you look at the better GT cams (or 85cams) they are not that different than a BMW M3. WHICH, even when it doesnt have the ind throttle bodies, can come ALIVE with power with their version of the large CF Intake.
take a look at the runners inside the PTG car! remember, this is a 3.2 liter making over 470ish rwhp!
the ports are all pretty large, MAF is large, nothing is really all that different , when you look at desired performance at the high HP rpm ranges.

We will never know , because no one will probably step up and do it. we had a chance to see something related to this kind of mod, but its going on supercharger with Carl. However, that design intake is just what im talking about It just has to be a large intake plennum, large runners and none of the obstructions and pressure drops the stock intake has.

Look at these BMW runners! they are HUGE!!!! this is how you make big power!

mk

ptuomov

I believe those are just the trumpets. I would bet that the diameter shrinks significantly down the flow path.

Still probably pretty big.

RyanPerrella

extrude hone, now this process is basically they shoot a type of media down the runners in an attempt to remove some of the material and in effect enlarge the ID somewhat and probably clean up the interior surface texture to a degree.

Im wondering if there maybe a better way to do this for the home hobby guy.

Now what i picture is something in shape with your standard cylinder hone, that you put on the end of a cordless drill to hone your Cheby's and what not.

What about something like that, but a much smaller diameter to fit the general runner size, and instead of the ***** on the end, some other type of abrasive media at the ends that will clean up the mag intake runners? This should produce more even results then hand porting would, and would take probably 1/10th the time (assuming it works at all)

Does anyone know of such a honing tool that could work on our runners?

I am then thinking that an air drill or a corded drill would be best for this as you would probably go through batteries in minutes but thats a small concern really,

Does any such honing tool exist?

If not, how difficult would it be to create something like this?

OH AND I CALL DIBS ON THE PATENT !




Maybe something like this? I believe this would be to large but maybe its a start? It comes in 120 180 and 320 grit. I imagine to remove more metal though you would need some other type of abrasive though

http://cgi.ebay.com/ebaymotors/2-5-8...#ht_983wt_1444

RicerSchnitzzle

You mean like these..
http://www.enginehones.com/fl2to2.html

Any size you want. They even have them for Nikasil blocks. And they're prettty cheap. Shoot an hours or two just cleaning up the intake couldn't hurt, could it? Not sure how much you'd increase the diameter, but a little polish might help the air flow a little.