IMB951

Yep, I've seen numerous 944 N/A engines with superchargers on them before, I was asking to see a 951 engine supercharged as 944J stated.

I'm pretty sure that would be pointless to perform, having a perfectly good turbocharged engine and taking it all off to slap on a sugercharger...doesn't make much sense to me at all...

BC

I was just gonna post that Z. Thanks for saving me the scan.

Rich Sandor

What kind of power would a 928 twin turbo put out? Now that would be impressive.

BC

...Where exactly? Backpressure I mean - where? In the freeflowing ehaust header with no restriction? In the intake with 6-26psi of boost?

....Thats not really the point. 1000bhp in a street car, unless there is traction control and a very long road, does nothing. My additions to the discussion here center on some statements made about outlet temps and "same boost" power levels. I'm simply asking for proof.
...Well, here we go again.... Efficiency islands are extremely important in choosing a forced induction system. Efficiency is ONE of the parameters to look at. These sections of displaced info you guys are using are not telling the full story as Z tried to point out. Put that turbo where it goes in the way of 1300 degree exhaust air, and well see how much your compressor outlet temps compare to a CENTRIFUGAL SC, as that was my original point. Anyone care to put an air temp gauge at the compressor outlet on thier 951s? I could probably get the info from a fellow sc 928er - well do the measurements at 14 and 26psi, but it will have tobe on separate cars.
I'll not argue about roots. I will stand here and dispute these false statements about "ouotlet temps" and maybe nag you a bit about the usefullness of 1-2 seconds of lag.

BC

That brings up a good point Rich, thanks. I am in no way saying that an SC of any kind would be ALWAYS the better choice. I am *trying* to dispell the tempature myths. A twin turbo 928 *I think* exists - the owner's id here is "john..." or some derivative of that. I would say, however, that you should take any statements he has made about his car with a grain of salt. Enough said on that.
My point in responding to you here this morning is that the PLUMBING on a 928 with one turbo, let alone two is murderous. You guys have room for HUGE turbos - more power to you and good luck with that. We have an engine compartment that (acording to a published book entitled *Projekt 928* and first hand accounts at the most recent Euro 928 meetings with Porche) was supposed to be 3 inches wider. Heh. Well, that only leaves a few inches on the 2V motors for turbos, and EVEN LESS, if NONE on the 32V engines which take up even MORE room.

We would all love to see a turbo 928 (32v), but it just seems like a feat many wish not to pursue, as we can plunk down 7600 bucks and *if we fuel correctly* can have 550 at the wheels.

The_Phantom

Based on the article attached by Z, which states that Porsche concluded that superchargers are better than turbos, it seems strange that Porsche continues to turbocharge and not supercharge their cars. Why do you guys think that is the case?

2BWise

Supercharging technology has become more expensive than turbo technology. Just look at Mecedes, they have all those high powered supercharged cars, but are now switching over to turbos because of the higher cost of development for their supercharger systems.

John..

Z, you need to stop stirring this garbage up. You talk about Vortech, which is CS, then go and compare boost below 3000 RPM, which was for a positive displacement example. Apple to Orange...YET AGIAN Z.....when will you finally get it, or do you own stock in MURF928? It is hogwash and ANY tuner out there knows that serious mid range and top end power is owned by the turbocharger. Lingenfelter, RUF, Banks, Hennesey...all of them know it and it applies to any car made anywhere. Yes, the CS is nearly as efficent as the turbo in terms of compressor efficiency, but the point you CONTINUE to miss is that the CS simply can't deliver the boost response of the turbo...roll on in 4th gear at 3000 RPM and the turbo has full boost in a matter of a second....while the Vortech has to wait until redline. Talk back pressure all you want, at the end of the day the turbo still makes more power and a boatload more torque. The general public is misinformed...the CS combines parasitic draw off the crankshaft with the worst boost curve of any method of forced induction out there. It is clearly the least desirable of the three. Clever marketing of a clearly inferior product is the only advantage it has. Let's not even get into which one wears out faster because you will lose that arguement too.

You spread all this garbage up on the 928 board about how my TT setup for the 928 isn't worth the extra money and Vortech is the only way to go. Again, have you looked at the closest equally boosted intercooled and supercharged 4.5 liter 928...it is a full 50 ft-lbs shy on peak torque against my Callaway and that is a fact Z. A CS on a 951...now THAT is funny.

Anybody who seriously thinks a Vortech or Paxton or Powerdyne can make a better setup than a turbo on any given vehicle needs to have their head examined.

Porsche, VW, Audi and MB use turbos on their high end cars for one reason...it is the most efficient and effictive way to make the car more powerful and has been for 50 years or more.

BC

OKay John... All I want is for you to tell these people here that the outlet temps are higher with a Turbo. Can you please do that? This is a test on your BS meter.

John..

No, I would not say that at all. It depends totally on the compressor efficiency. Everybody assumes all the heat from the hot side somehow magically appears into the compressed charge....not true, at least not to a significant degree. 10 or 15 degrees here or there...well maybe so, but that isn't enough to worry about. That air is moving very rapidly, the mass flowrates are very high and I don't think you can argue the air would be significantly hotter with the turbo. Any additional heat in the charge still would not degrade the turbos performance to that of a CS. Stick that in your BS pipe and smoke it for a while....

BC

Come'on John. I'm surprised. 14psi CS, 14psi Turbo, and you want to tell these naive young 951 owners that the turbo would be COOLER at the compressor output then the CS? Please.

Geo

Are you for real? Backpressure in the exhaust is backpressure in the exhaust. If you pump more air into an engine, it still has to flow out. Both forms of forced induction benefit greatly from increased exhaust size. Since forced induction does not rely on scavanging like an NA, you cannot go too large on a exhaust (per a Garrett engineer who happens to be a friend of mine).

Go read the forced induction portion of Mike Kojima's "Suck, Squish, Bang, Blow" series in Sport Compact Car a few years back (before it became a punk talking ricer mag). I understand it's in book form now as well.

It's been done. A supercharger will have higher discharge temps due to efficiency. That assumes you have properly sized the turbo which a lot of people either don't know how to do or don't have the maps which tend to be closely guarded.

Prove them to be false.

I'll admit I don't have all the data at my finger tips. Neither am I inclined to do hours or research to pull it all out just to win a stupid Internet argument. I'll tell you where the source of my information comes from.

One is the aforementioned Mike Kojima. In addition to being the contributing editor of several magazines, Mike is an engineer for Nissan. He also used to work in TRD's engine program when Toyota was in IMSA GTP. He's a consultant to many aftermarket performance product companies and has written at least two books. I know he has been contemplating writing one on forced induction to "cut through the bull****" (his quote).

The other source is a mutual friend of Mike's and mine who is an engineer for Garrett turbos and has access to pretty much all the data on this subject. He deals not only with turbochargers, but superchargers as well and has dealt with everything from stationary Diesels to the performance aftermarket.

You're disputing things being written here, but I don't see anything backing up your claims either.

Oh, and BTW, from the Garrett engineer, the heat of the exhaust has very little impact on the discharge temps of a turbo.

Geo

You're welcome. It's true if you have the turbo properly sized. I'm not certain that the stock turbo on the 951 is anywhere near the best size. Although turbos are far from new technology, they get better all the time and the 951 turbos are at least 20 year old designs.

BTW, what are your credentials and/or what is the source of your info?

Geo

Actually, superchargers tend to be more desireable to OEMs due to emissions and packaging issues.

tifosiman

Having met John and had many discussions in person with him about this very subject, I would say that he knows his shiite and is right on the money. Why come over here and stir up this crap? Why is this here and not on the 928 forum?