Supercharger?

I know this has been discussed before, but with no consensus. Has anyone put on a supercharger? Might this help out in the quest for a 14 second 1/4 mile?

John

Just for my clarification,

Are you asking for a belt driven supercharger in addition to your turbo charger?

or the replacement of the turbo with a belt driven supercharger?

As the car is already turbocharged, I would think the existence of kits to supercharge it would be scarce. (someone correct me if they know of kits to replace turbos)

I think I've read that the limit on power, is fuel, air and cylinder pressure. Surely, adapting the turbo and fuel system to provide closer to the maximum allowable amounts is an easier route to take to achieving better quarter mile speeds.

It has been stated here, that Superchargers provide better response in the lower RPM range, but if you are revving your engine for a start, I don't imagine the turbo pressure will be significantly different than what the supercharger would be providing at that elevated launch RPM.

But I'm sure I'll be educated on the subject.

Regards

Russ

A supercharger could accomplish as much boost as you want. But a bigger turbo will do the same thing.

The trouble with superchargers is that they REDUCE engine efficiency. Turbochargers INCREASE engine efficiency. Turbos scavenge heat that would otherwise be wasted and use it to produce boost. Blowers use engine horsepower to produce boost. You'd be amazed how much of the extra power produced by a blower is used simply to power the blower! They are extremely inefficient.

So the short answer is: Yes, but why would you want to?

-mickey

Adding a supercharger to your turbocharger would only add more air, not power. You would have to add alot of fuel too.

In additon, the maximum compression pressure would be raised accordingly so you would have to lower compression ratio with new pistons. This would make the engine extremely difficult to start.

In short, what is your goal here, $10,000 upgrade?

I think that a Supercharger COULD help a TDI in the 1/4 mile here is why.

(brainstorm mode so disregard grammer )

The turbo on the TDI is made to produce very low end boost and continue to produce that boost throughout most of the TDI's usable rpm band. However as rpm's increase the turbo is not able to continue to produce a high volume of air for a given pressure. Let me explain further. As the engine revs it (the turbo) can produce I high volume of air and maintain a high pressure 17-20 PSI. Because the engine rpm's are low the turbo can fill the low volume required per second i.e fill a given number of cylinders per second and still maintain a given PSI. As the revs increase's the volume of air required per pound of pressure increases proportional to the rpm's of the engine. The turbo becuase it's compressor is optimised and fixed can only produce air pressure and volume in a very limited amount i.e. more cylinders to fill per second so pressure starts to drop off due to the limits of the compressor wheel design.

What I am getting at is that if you could supplement the turbo's volume of air so that as rpm's increase you begin to feed in "volume" at high pressure to continue to feed the cylinders at a linear rate proportional to rpm. Am I clear???

What I envision is a dual stage or an axial flow compressor or a system that utilizes "bleed valves". This is a common problem in turbojet engines. At low speeds the engine can suck in and digest absolutley huge amounts of air. In order to compensate for the very high pressure on the ground relative to the conditions at high altitudes, the engines must "bleed" some of that compressed air overboard. In the caswe of an axial flow compressor utilizing a "VNT" or "VGV variable guide vane arangement to vary the flow of air through the compressor stage you can develope an extremely efficient unit that can produce not only the pressure at any given rpm but also fill the volume of the engine throughout and even at a surplus for any given RPM. The only problem with an axial flow design is that the centrifigul compressor is far more efficient thus the better solution.

What would happen is at low rpms you use a bleed system to vent off unneeded air and still keep the turbine on speed for low end boost, this really lends itself to the VNT design! since the compressor is also controlled by the ECU, as the rpms begin to increase the turbine begins to spool and the bleed valves are still venting air to limit volume. As the turbo begins approaching it's rpm limits, the bleed valves can begin to close to feed in the otherwise surplus volume of air into volume hungry revving motor. What this also does is utilize a bigger compressor wheel. This results in less heat (Mickey are you paying attention?). This set up would prevent possible surging and overrevving by trying to spin the turbo out of it's design range.

The compressor would not require a larger intercooler since it is compressing the air at a slower rate (fill in the formula skypup) it just is not using that volume until it is absolutly required. Since the air in the compressor is being bled off the air is not impeeding the spinning of the compressor since it under a no load type situation. As the rpms increase the bleed valves close and since the turbine is up to optimum speed the compressor can now start loading the turbine and feed all the volume you could ever need. Now the extra fuel and heat are sufficient to feed the turbine and there is enough air to feed the cylinders in my opinion best of both worlds!

Now all you need to do is get the extra fuel to feed the engine through new fuel mapping and youare in the ball game!

You could utilize a belt driven supercharger to supplement volume but this would require diverter valves or a type of clutch similar to what is on the Air conditioning system, but the size and space constraints are prohibitive. But the problem with this is it takes away a lot of HP to produce any amount of boost and volume. This is why I feel a turbo using some of my ideas above would be better since the turbo is recovering and converting the free energy or rather the recovered otherwise wasted engergy of the exhaut gasses.

I am sure this will get all you guys thinking about a possible 2nd generation of VNT turbo!

DB

[This message has been edited by Drivbiwire (edited February 09, 2001).]

Q: Supercharger?
A: No!

-Lawson

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Über-Beetle: UPsoluted 2000 Yellow New Beetle 1.9 TDI 5-speed
1987 Diamond Blue Mercedes-Benz 190D 2.5 Turbo (sold, but considering re-purchase)

DB, you should patent that idea.

Wow, do you have any idea how cool that would sound? SNEEZER VALVES!! woohoo!!

Awesome brainstorming Drivbiwire, very impressive.

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Über-Beetle: UPsoluted 2000 Yellow New Beetle 1.9 TDI 5-speed
1987 Diamond Blue Mercedes-Benz 190D 2.5 Turbo (sold, but considering re-purchase)

The only reason to supercharge as opposed to turbocharge is to avoid the lag which is only really noticeable with lots of boost.

Both charges can be used on an engine but again the supercharger is only used to reduce the lag when the turbo is off boost(this does not happen on a TDI with a variable geometry turbo).

The only car I know off that had both chargers was a Lancia Delta S4 group B rally car which had a 1800cc engine developing almost 600hp. You can imagine the lag on this baby in the late 80's with no anti lag systems around if it had'nt had a supercharger.

Forget it and stick to turbos.

You guys have to think about the drag the supercharger would put on the engine that the turbo would not. With a supercharger you can't run very much boost because the engine itself has to compress that air not the wasted exhaust that is no longer in the engine.

Running to much boost of a supercharger will blow an engine. I have heard of people blowing engines in Camaro SS for running 8-10 psi because the more boost you put in the engine has to compensate for the drag of the BLOWER and the added pressure in the cylinder.

With a turbo you only have the added pressure in the cylinder.

That is what I have heard.



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Ray

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