Fastest928

For me the reason for not supercharging is ultimate reliability....

I can run our 450+ rwhp na engine full tilt for 3-10 minutes at a time and then do it again after slowing for a corner (open road racing)and the reliability is unmatched! And this occurs with 89/90 octane sometimes...all that is available at altitude!

Right now, I am more interested in squezzing out perfromance out of stock, modified stock or strokers to increase the efficiency of the engine and extract power.....then boost the engine,,,more power at less boost = increased reliability! I was with a friend who just supercharged a mustang to the tune of 565 rwhp on a tweaked street engine.

If I were to continue with a "charged" effort, it would be the way of John and twin turbo..I had all the components for a 1000 hp turbo engine, but sold almost all the components...turbos are going to Tom C and he is picking up this insane project.

I think this SC work is all great....and I look forward to applying some of our engine technology to the SC process and adding a little "boost"!

Tim and John and Marcus...keep up the development work, keep posting the results over time and lets see what works and what does not

For me for now, 500 rwhp from a na stroker on pump gas and smoggable is the next metric!

Marc
DEVEK

Tim Murphy

[QUOTE

For me for now, 500 rwhp from a na stroker on pump gas and smoggable is the next metric!

Marc
DEVEK[/QB][/QUOTE]

I think that the setup I have might be smoggable with the supercharger. We don't have that in Green Bay Wi but I'm thinking it will pass. What injectors and what fuel pressure do you run with the strokers?

PeteS

Definitely interesting stuff! Good discussion and stuff to think about.

The stroker motors have proven themselves to be reliable when well built, but is there any inherent reason to think that the supercharger engines wouldn't be? The Devek white car can be run at 450 rwhp for the periods of time mentioned. That 450 rwhp is at 6,000 RPM. On the dyno chart posted in the other thread, Tim's car makes that 450 rwhp at only 4,900 RPM. I'd think 4,900 RPM for fair periods of time should be more reliable than 6,000 RPM for that same period of time, wouldn't it? That wouldn't even take into account that longer stroke/higher piston speed stuff for the stroker engine that was mentioned in the other thread either.

There are a lot of Mustangs, Corvettes, and any number of other kinds of supercharged cars out there that are emissions legal. For those of us living in test areas, is there any particular reason that a 928 wouldn't be able to pass an emissions test if all of those other cars can?

Carl Fausett

Always a pleasure to review Tim's car. While I am trying to reach 400 BHP with my CIS car, Tim's out there trying to reach 600 HP with his 32v unit! What you are doing is good for all of us, thanks Tim!

Carl Fausett
78 Supercharged 928 Euro 5 spd
79 Convertable 928 Euro 5 spd

John..

I like the fact that the turbo allows the engine to make more torque with less piston speed, this is an advantage.

If a rod breaks, chances are it will break while the piston is on the up stroke, because of failure of the metal in tension. Tension is where cracks start, not in compression. So, more RPM does mean more inertial loads on the rods and pistons.

With the turbo, you have the constant pounding on the ring lands and it is possible to bend a rod under extremely high boost conditions...I've seen pictures of this on a 5 cylinder Audi with 30+ lbs. of boost.

As for efficiency, it is a well known fact that the turbo wins here hands down, for power draw on the engine as well as the heating effect on the air.

I do like the simplicity of the centrifugal setups, and the fact that they do not make the engine run high exhaust back pressures, that is nice. I would be curious how much power it takes to run one though. They are obviously a lot bigger than a turbo of the same power capacity. I assume it is because of speed of the unit.

That is impressive, 13 psig on stock cast pistons and 10:1 compression. I didn't have the nerve to try that one out.

Paul, I was referring to the forged pistons in the 944 turbo, not the rods. The piston is the weak link on the turbo engine. Some desirable features would be high strength forged alloys with thick and very strong ring lands. All 944 turbos run forged pistons from the factory.

Unfortunately, several of Callaway's early cars suffered this ring land failure. Must have been detonation caused by that ****ty Califoirnia 90 octane fuel Marc was referring to.

Z,

The plugging of the exhaust is not what heats the intake charge, it is the fact that you are compressing the air along with the efficiency of the compressor side of the system. The air never really has enough time to pick up that much heat from the exhaust side. I would imagine the centrifugal blower runs peak efficiencies in the high 60s-low 70% range

This is one of the best posts yet on here!

Z

When I was refering to the plugging of the exhaust I was talking about the horsepower reduction to the engine from the increased exhaust restriction. The heating I was talking about was from the intake air passing through the hot turbo housing. In addition to the heat from being compressed, the intake air is picking up heat from the hot turbo housing itself. I'm sure you've seen pictures of turbos that are literally glowing red hot. If the intake charge has enough time to loose heat in an intercooler, it has enough time to pick up heat in an exhaust heated turbo housing. That's in addition to the higher underhood temperatures turbos often cause, which can also add to increased intake temperatures. Vortech has centrifugal superchargers with efficiencies listed at up to 79%.

Gregg K

Z,
Good points.
If mechanically driven, then the exhuast (and sound, and heat) which exits the engine is still sitting there full of energy, doing nothing. I contend that since that energy is getting thrown out the exhaust, it is free to take. I THINK that's valid logic.
As for the heating. The surface area in the intercooler is much greater than the turbine compressor. Again, without thermodynamic calcs., it's guesswork. But my sense of heat exchange says that heating in the compressor is minimal compared to the amount of heat exchanged in the intercooler. And then there's alchohol/water injection. I'm just an old school purist.

Tony

I cant quite make it out on the picture but is the inlet for the supercharger on Tims car routed over and then in front of the radiator like on the red car?
Pretty cool set up! (no pun)

Was the radiator lowered/modified to do this or is there just enough clearance to get away with it.

<img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />

Z

That exhaust is being pumped out by the engine. The restriction makes it harder for the engine to pump it out, requiring more power from it to do so. Look at the gains in power from adding a more freely flowing exhaust system. The increased restriction from a turbo does the exact opposite. That's not even taking into account the potential benefit from increased cylinder scavenging without the additional turbo exhaust restriction.

Yes, but that turbo can get extremely hot. The surface area may be smaller than the intercooler, but the temperature differential is also a lot greater.

You mean like those carburator guys?

I know that there's almost no chance of actually changing anyones mind, but again, it is food for thought.

The strong turbo advocates out there might want to skip the section in "Forced Induction Performance Tuning" that discusses Porsche's own testing of a turbo vs a blower on a 944.

Z

Tony:
The supercharger air intake on Tim's car is routed behind the radiator to a cold air intake location. The radiator was not modified or moved in any way. The stock radiator, fans, and fan shroud were not modified on the red car, but there were modifications done to reposition them and have it work the way that it does.

Jim Nowak

The red car has a very unique intercooler. Made from a 944 turbo intercooler? It looks like he has just reversed the flow of the Intercooler - where the air from the engine used to circulate now the water from the heat exchanger flows and where the outside air would cool the intake charge he is now running the hot air of the blower. COOL!!!!! What has he done to keep the water flowing through the intercooler from front to back or will the water just naturally flow from front to back to front again? Most air to water intercoolers have the water pick-up point on the exact opposite side of the water discharge. Wouldn't it have been more efficient to have the water exiting on the exact opposite side of the intercooler?

I'm debating on having one of these built like the red car has and modifying his design but my next choice would be to buy a PWR unit. I'm only using methanol/water injection to cool the intake charge but I think the water to air intercooler would be better for my Supercharged 560 SEC Mercedes and the intercooler and the methanol injection would be really effective. I really like the modified 944 turbo design though. If my 928 is ever released from prison, I may run a supercharger on it too.

Chuck Schreiber

Jim,

What's the update on your car BTW?? Haven't seen you post lately and all us 16v drivers want to know. <img border="0" alt="[bigbye]" title="" src="graemlins/xyxwave.gif" />

Gregg K

Z,
Oh no, you've done it again. You made me think. This is an interesting subject, and I find myself lacking the skills to come to any logical conclusions. And I'm supposedly an engineer. Ugh. Actually, some of this is not intuitive. I'm most interested in seeing how the different configurations perform. Sounds like you already have that knowledge. Instead of doing lots of thermo calculations, the seat of the pants results speak clearly for themselves. I'm not really a purist, just someone who likes simplicity. I'm guessing the "Forced Induction..." is a Rennlist forum. I'll look for it. Thanks.

Z

If that's the case, you're way ahead of a lot of the other people running around out there.

It a book. "Forced Induction Performance Tuning", by A. Graham Bell. It's a pretty good book, but maybe not as applicable as the Corky Bell book that's been mentioned to people who just want to install a supercharger without getting too involved in a lot of stuff.

John..

If the centrifugal blower was the ultimate setup, manufacturers like Porsche and Audi would use it on their vehicles.

The fact still remains that the turbo requires less energy to drive the other options.

I still think the centrifugal blower is the most cost effective way to add major HP. It is what I would have done if starting from scratch.

You want that heat behind the turbo...it is the pressure and heat drop across the turbine which determines the energy given up there.

I disagree on the heating of the air from the hot side, true there may be some, but the fact is the air is in there for a very short period of time. On the other hand, in the charge cooler, the turbulators make sure there is plenty of heat exchange area to drop intake charges.

The 79% is a very good number! Looks like those people have done some R&D on this stuff.