Catfood

I pulled into a trucker weigh scale station in my 44 I was like 3200 lbs with luggage and two people. Those scales weigh to the nearest 50 lbs though.

944J

here they are:











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# information below #
# is not from porsche #
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"The --brand name- supercharger is the unique twin-screw design that delivers the instant boost at low rpm you expect from a positive displacement supercharger (like the roots type) - but because it's a true compressor it also delivers constant reliable boost throughout the powerband, with none of the fall-off at the higher end, or the fierce heat buildup of the roots, and no waiting for redline to get maximum boost either - it's available on demand, for all situations. Here's how it works.

• Incredibly high adiabatic and volumetric efficiencies
• Positive displacement design
• Very flat efficiency curve combined with positive displacement design gives the most achievable torque of any method
• Instant boost
• A true compressor
• Direct drive from the crankshaft
• Compact and lightweight design
• Virtually silent operation
• Low temperature increases during operation
• Very little power consumption
• Unique combination of low rpm torque and high rpm horsepower due to the screw compressor design
• Have the ability to run from 1 to 60 lbs. of boost

The twin-screw supercharger was originally invented in the 1930's by Mr. Alf Lysholm who was then Chief Engineer of SRM (Svenska Rotor Maskiner AB). The twin-screw design was developed to fill the tremendous voids the centrifugal, turbo and roots superchargers have. This concept was intended to meet the requirements of a high average efficiency under most varied conditions of pressure and speed, a high maximum efficiency - preferable above 85% - with small bulk, low weight and also suitable for direct drive. This concept lead to the development of the twin-screw supercharger which was compact and light, had a very high efficiency over almost all varied conditions of pressure and speed, and an incredibly high maximum efficiency. This concept became a reality in the late 1930's and early 1940's when the Lysholm twin-screw supercharger was produced. Because of high building cost, the screw compressor did not find its way to OEM use on internal combustion engines, but industrial applications for air compressors, refrigeration and air-conditioning.

With technology ever increasing, the screw-type compressors price to manufacture has come down to a competitive level for the internal combustion engines and is distributed throughout North America by --brand name- Industries. Art --brand name- of --brand name- Industries quickly made use of the major benefits of the screw compressor by placing it on the throttle body injected GM 350ci. The results were outstanding, no more turbo lag, no more hot air, just pure power. Since that time, the --brand name- Charger has become a household name throughout the performance community for providing the most technologically advanced supercharger kits on the market.

The --brand name- Charger creates boost instantly, which gives any motor an instant boost of power. It doesn't matter whether your towing, cruising, or racing, the --brand name- Charger gives you the power when it's needed. Because of the --brand name- Chargers instant boost, you'll achieve more power throughout the rpm range than any other supercharging method.

Twin Screw Supercharger - a positive displacement compressor

The twin screw supercharger is a positive displacement air mover, in that it moves fixed amounts of air per revolution, like the roots type blower. Unlike the roots however, which is only an air delivery system, the twin screw supercharger is also a compressor. The counter rotating lobes and chambers of the twin screw are designed for a screw-like tapering effect which runs its intake air into a smaller space for output, thus compressing it. The rotors have very close tolerances yet never touch. Compressed air is delivered into the compression environment of the intake manifold with very little leakage or energy loss.

Because of the increased mechanical efficiencies of the superior design, the output air temperatures of the twin screw positive displacement supercharger are radically improved from the roots type. The --brand name- twin screw quotes adiabatic efficiency of 70%-80% range across the whole powerband.

As with the roots, since the supercharger is under continual drive, and since it delivers boost practically from idle, overboosting is prevented by the use of an intake bypass system, which allows the engine to breathe normally at cruising or idle: the bypass closes on throttle use, delivering full boost.
Full boost by 2000 rpm

The twin screw supercharger creates boost the instant the throttle is touched, and generally reaches full boost by 2000 to 2400 rpm. Full boost is then available all the way to redline. A positive displacement compressor is ideal for street performance cars or trucks and suv's, and automatic transmissions.

Vehicles used for towing remain very responsive with positive control using this type of supercharger. The instant torque for accelerating, passing, and hill-climbing diminishes the strain on the engine and increases the safety factor. The twin screw compressor is especially useful at high altitude, where physics dictates that all engines lose power, and where our American geography dictates we often take the family vehicle on vacation towing a trailer in heavy traffic.

The twin screw supercharger is essentially silent, producing discernible sound no greater than whisper strength. It has a low profile and generally requires no hood modification. Of all the forced induction systems, the twin screw compressor supercharger is the most obvious for the bootlegger's car, the sleeper, and this is timely in an age where supercharging is no longer just for speed enthusiasts, but for all drivers who have needs for extra power and performance during fairly standard driving conditions.

Which has greatest adiabatic efficiency

The Roots blower has the lowest adiabatic efficiency of all the forced induction designs (including the turbocharger, which has to start off with hot exhaust gases to deal with) - generally around 50 percent. The roots type is so inefficient because it doesn't compress the air directly, but delivers uncompressed air which wells into the intake manifold, becoming more compressed, but with additional heat gain from the turbulence and reverse flows of air mixing. Centrifugal superchargers can vary from 60% up to perhaps approaching 80% efficiency, as can turbochargers; both are more efficient at higher rpm, which is another way of calling them more inefficient at lower rpm. The twin screw supercharger normally delivers lower output temperatures, for adiabatic efficiencies of 70-80% across the whole rpm range.

Turbochargers are quite efficient

In general, turbo compressors are considered more efficient than supercharger compressors, and on diesels turbocharging can actually improve fuel economy and emissions. Because of the exhaust modifications required, and various others, turbocharging is a more complicated add-on at the aftermarket level, although this problem is less constraining at the OEM level. As a design issue the turbo is generally more compact than the supercharger, and it can fit wherever in the engine compartment there's room, although it wants to be close to the exhaust manifold (whereas the supercharger needs the space at the front of the block for the belt drive, an already crowded area).

Turbos spin at often more than 100,000 rpm, and yet they are mostly very quiet. They deliver large torque gains. Older model autos with turbos suffered from cold-weather starting and performance problems, in newer vehicles with fuel injection and modern computer engine controls these problems are now minimal. And some OEMs are trying to address the lag using twin-turbos or more (each smaller and thus quicker to spool up) running in combination.

The turbocharger spins much faster than the centrifugal supercharger, to build as much boost as possible at low rpm, with the wastegate to prevent overboost at higher rpm. Turbo fans prefer it over the centrifugal supercharger in this respect, because the centrifugal makes almost nothing at low rpm (the centrifugal is designed for power at the high end, see our Centrifugal Superchargers page).

Centrifugal superchargers aim for max boost at the high end

A centrifugal supercharger is basically the same type of pump as the compressor side of a turbocharger, but is mechanically driven off the crankshaft instead of by exhaust gas. Internal gearing steps up the spin speed, and gives a distinctive whistling sound, that most drivers enjoy hearing, but the centrifugal supercharger must be classified as noisy.

The centrifugal's type of compressor - like the turbo's - is efficient only at high rpm. Because all superchargers by definition are under continual drive from the crank (i.e. with no comparable turbocharger wastegate system to cut the drive), design decisions set the limits to how much internally to gear-up (overdrive) the spooling: the centrifugal aims for high-end boost and in consequence gives almost none at low rpm.

Centrifugal superchargers build boost relative to engine rpm: boost builds exponentially in the upper half of the powerband - generally they start boosting around 2000 to 3000 rpm, and attain full boost at max rpm - i.e. the quoted maximum boost of a centrifugal happens at redline.

Enthusiasts say that in situations where they demand performance from their vehicle, they spend most time in the mid to high rpm ranges.
Best applications of centrifugals

The centrifugal is good for lightweight, manual transmission (downshift for higher rpm) vehicles, and popular with muscle cars that have plenty of low-end torque already, but not so good for heavier vehicles under load or towing, or automatic transmissions - in these cases a positive displacement supercharger is more suitable (see our Roots Superchargers page and our Twin Screw Supercharger page).

Centrifugal superchargers are generally cooler than turbochargers, with adiabatic efficiencies in the 60-80% range (see our Supercharger Heat page for more about heating and cooling of forced induction systems).

All superchargers generally are less complex to mount than turbos. As aftermarket modifications superchargers tend to be cheaper to install and generally cost less to service and maintain.

The twin screw arrives in America

Finally, in 1988, Art --brand name- of --brand name- Industries brought the twin screw compressor to America from Sweden and developed it for supercharging. The astounding results are covered more fully in our --brand name- section.

NOTE: Mr. Norm --brand name-- writes to correct us:
Gentlemen: The year 1988 is correct, but it was I, and not Art --brand name-, who adapted screw compressor technology to the drag racing application. My --brand name- supercharger prototype won the alcohol dragster class at the U.S. Nationals. Gary Southern drove Dale Smart's car to a win that was as decisive as a machine gun would have been at the Battle of Hastings in 1066 A.D. Incidentally, I called Art --brand name- right after we won, as he was interested in applying our drag racing technology to the street application. Please verify this with Art, but a correction would be appreciated.
Norm Drazy, President, --brand name- superchargers
We're glad to have this amplification of the situation, thanks Norm!

--brand name-- as mentioned has continued throughout to hold the patent on the twin screw design, and licenses its use all over the world to many different manufacturers for a variety of purposes, including gas processing and refrigeration.
[A list of licensees globally may be found at the SRM website here]

But since the 1960s the twin screw's primary application has been to compress air, it is recognized as a superior design for this purpose, and founded on the same positive displacement principles that made the Roots blower such a good air mover.

It is not yet clear how much of the market or future supercharging development the twin screw technology will dominate. We can say that here in 2003, supercharging as a whole is a vibrant and growing industry."

special tool

Very interesting...
The addtonal power of the supercharger below 3000 rpm doesn't seem to help AMG E55's or Cobra Mustangs when I leave them about 7 bus lengths behind on the highway. Hmmmmm

944J

the amg 55 has 470hp and around 510tq so of course you would beat it with your setup... you simply have more power (543 HP/571 TQ at the wheels). it's not a matter of turbo or supercharger.

it would be interesting to see a list of the mods you have on your car and I'd like to know if they are ok for smog in california.

however, if the guy in the amg turned up his boost from 14(stock) to something higher I think that he could blow you away since he has much more engine to start with than you do...

what Im trying to say is that its not a matter of turbo vs sc, they both do the same thing, and each particular turbo or sc has different characteristics.

V2Rocket

Which would you guys rather have out of a SC'd motor: lots of torque or lots of power? Which would be better for making the car faster?

944J

you can get both from either a sc or turbo, it just depends on the engine and overall setup, no one says that a 944Turbo doesnt have a lot of torque.

with our engines it seems that a twin screw or roots type supercharger brings faster acceleration from 0-60 when compared to a turbo, but I dont think enough equal tests have been done with modern super chargers and modern turbos with identical engines (even in the porsche research paper the engines werent identical and that paper is years old, now they have all kinds of new turbos and superchargers that they didnt have back then.)

i'd rather have both low end torque and power and supposedly a twin screw supercharger gives you this, see kenne bell and whipple.

J Berk

http://cgi.ebay.com/ebaymotors/Porsc...23936541QQrdZ1

944J

let's talk about this, what's the max boost an efficient twin screw sc can use on a 944na with the stock compression but with the correct engine management and what exactly is the correct engine management?

hacker-pschorr

I have no idea - no different than a turbo unless the pistons become a failing factor. 928's have similar pistons (material wise) as 944's - so far the max I've seen is 13psi in Tim's car. He will be cranking it up to about 17 soon, we'll see what happens. Todd's 24psi engine is a stock S4 with 951 pistons. So a bit of a safety margin with that setup.

This is assuming there is even a twin screw that efficient that will fit on a 944 engine. There might be, not sure.

What is the stock CR on a N/A 944?
3rd party since L-Jet is not that tuneable. Right now I'm simply using a boost controlled FPR for boost. Not ideal but it works.

Ideal I guess would be a 3rd party system or a MAF conversion.

MAF 928's have the Shark Tuner - so they can adjust timing / fuel any way they want, even under boost.

95Juan

is that why you're having trouble dialing it in correctly?

are there other solutions aside from converting to a MAF to tune the a/f ratios in correctly? i mean- how do you even do that with that system?


that is- you know- if i ever go slumming and buy an early 928 and supercharge it.

not that i'm considering that.

no, that's not it at all.

hacker-pschorr

Juan - it's actually running perfect now, you might have missed an update. I had non-boost related issues on this motor.

FMU (the boost control FPR) works fine - just make sure all of your pressure side fuel lines are 100%.

If there is a way to "fine tune" a barn door system to double digit boost numbers, I'm all ears.

Oh yea, you better find a sunroof delete model.

special tool

Visually no - but that is beaurocratic...
I can, however, tune it to zero emissions with my laptop in about 15 minutes.
Cleaner than the newest Honda by 5 times, probably.
No power, but it would be pretty damn clean.

944J

so what do you have on your engine?

KuHL 951

bluecamaro's 944 S2 w/ a Huntley set-up passed both visual and emissions at a "Test Only" shop I go to. I don't think they knew anything about the 944 and thought it came like that. This is the same place I've never had a vehicle flunk either. If you keep the bling factor down it's not that difficult here in Cali. Juan did fail the emissions part there as his cat was dead and and the FPR was defunct.

944J

he should swap in a twin screw...

how did they tell his cat was dead? what is FPR?