What is the stock Compression Ratio on a 99 C2?

Just curious...

11.3:1

What is the turbo, GT2, and GT3? Similar for 997s?

The turbo and GT2 are 9.4:1, GT3 is 11.7:1, CarreraGT and Cayenne is 11.5:1. I don't have the specs for 997.

Sweet deal...Im sure its in-line with the others... Now its time to develop a twin-screw supercharger kit

Regular 997's have the same long blocks as 996's and the same compression: 11.3. S' models are 11.8. The 997 GT3 is 12.0.

There are already 3 supercharger kits available for the 996: TPC (roots), VF Engineering/EVOMS (Centrifugal) and Ruf (centrifugal). TPC and EVOMS are both 6 lbs of boost bolt-on to a stock motor. Ruf is only sold as a compelte installation, but they remove and disassemble the engine. They then put thicker head gaskets to reduce the compression ratio 1.5 points (9.8 Carreras and 10.3 S' models) and apply 8.8 lbs of boost.

Yes i realize that, but none of them are twin screw applications...

So, what's the problem? Certrifugal is far more efficient at compressing air that a twin-scroll. They don't have as much low end, but make far more power on top end.

Incorrect. The centrif might be SLIGHTLY more efficient on the top end, but only slightly. My twin screwed E36 M3 with about 370 hp at the wheels will outaccelerate a 400 whp centrifugal setup on the same engine in just about any situation. 1/4 mile trap speed is 3-4 mph higher as well. The centrif might get the nod on the top end. The twin screw (lysholm) compressor is one of the most efficient compressor designs in the world, and has higher efficiency over a much broader range than a centrifugal compressor. As I said, the centrif might get a few % nod at the very top end. Other than that, its only advantage is that it is much easier to fit to an engine... Steve PS Hi Keith!!!

Steve, I have to question your numbers because is it an E36 not an E46. Sorry, but your numbers don't add up for what you claim for either example. Start checking dynos on Active Autowerke. Dinan SC E36 only puts out around 280 RWHP in stage 1 and 330 in stage 2. The numbers you claim are more realistic for E46 M3's. Here is a link to the Active Autowerke dyno page: http://www.activeautowerke.com/dyno/dyno.php Here is a link to supercharger offerings and associated dynos from Active Autowerks: http://www.activeautowerke.com/supercharger/main.php If you want a real head to head comparion, get a copy of the Sport Z magazine supercharger test. This is probably the best known independant test. They tested Stillen's intercooled twin-scroll Magnuson against ATI's and Vortech's centrifugal offerings for the 350Z. Not only did the twin scroll lose on the dyno, it lost on the drag strip and the road course. http://www.sportzmagazine.com/Z_Downloads.htm You can either purchase the issue or search for the rest of the article on the Z forums. Sorry to disappoint you. There are actually 2 problems with twin-scrolls: they are less efficient and they consume more HP. How much depends on the application. For C5 and C6 Corvettes Magnuson twin-scolls make almost 100 rwhp less than ATI and Vortech centrifuals at the same boost level. Although Kenne Bell's larger twin scoll superchargers make big gains on 03-04 Mustang Cobras, swapping intakes and going with either the Vortech or ATI superchargers leaves them in the dust. At 18 psi, there is again almost a 100 rwhp difference. Twin scrolls do make more low end (make the engine feel like a bigger displacement engine), but it is are under the curve (whichever makes the most average hp across the rev range in each gear). It doesn't matter if it makes 50 ft-lb more torque or 30 more hp at 3000 rpms if you are never under 4500 or 5000 rpms when racing. One last thing, I am curious why you went with the twin scroll on your M3? For the same money you could have a good turbo that would make a lot more power than any of the superchargers (no compressor to drive by belt and lose engine hp and an even more efficient compressor). For a 996-997, a turbo conversion would be quite expensive. Hence why the SC's came out(althought they aren't tha cheap). With an E36 M3 on the otherhand, you have that as a reasonable option.

Talk about opening a can of worms!! Are you comparing PEAK to PEAK numbers?? Because you know that what reallly matters is the are under the dyno curve... And make sure that you are comparing eqaul boost levels. One kit might achieve similar power levels at 6 psi, and the other at 8psi, and BOTH still be considered stage 1's... Remember, a centrifugal supercharger runs directly off of the engine crank, therefore building boost linearly to RPMs(aka full boost at redline), where as a TS supercharger makes its fool boost nearly instant(say 2400 RPMs) and can almost sustain it through out... -Keith

Oh my goodness, where do I start? Let me fill you in on a few things: Go here and read: http://www.activeautowerke.com/super...e36m3/main.php I am Hurtig Motorwerks. I developed the hardware for the Active Autowerke Twin SCREW kit for the E36 BMW. Our production kit on a 1997 BMW E36 M3 makes 330 horsepower at the wheels on the AA test car on their Mustang dyno. That is at ~9 psi max boost. For comparison, our Level I 6.5 psi non-IC kit made 285whp on their dyno, and 306whp on a dynojet in 100 degree weather. My car is currently running almost 12 psi on stock compression (10.5:1, but extremely conservative timing) for testing purposes. I had my car on a dynojet locally several months ago, and made 355 whp, however I was blowing out the spark and having misfiring issues above 5200 rpm due to what I found out later was a set of spark plugs that had a 0.080" gap instead of the 0.028" that I should have had. Guess I should have checked them!!! Look more closely on that AA web page at the bottom and see MY time slip from Cecil County Dragway last April. This run was done with the same spark plugs I mention on the dyno, and was my FIRST run ever with drag tires and the supercharger. I launched easy, and drove like a grandma. The car will be in the 11's this fall or I will die trying. Now, to your other comments. No matter what they tell you, the Stillen kit is NOT a true twin-screw or Lysholm compressor. The Stillen kit is an Eaton Roots supercharger (blower). The Magnuson kits are Eaton blowers. Totally different animals. The Eaton blower makes great low end boost, but suffers on the higher end. When I designed the BMW kit, I did all the calculations and comparisons of efficiency between the Lysholm and Eaton. The Eaton required 60%+ more hp from the crank to drive it. The Eaton efficiency ranged from 33-50%, while the twin screw is a consistent 62-65% across the entire rev band. This is TOTAL ADIABATIC EFFICIENCY, and includes the drive power loss required to MAKE the air move. Centrifugal compressor efficiencies that you see reported of 70-80% are thermal efficiency only, and do not factor in the drive power. The thermal efficiency of the twin screw can reach 80+%. I didn't design the kit to make a race car, I designed it to make a wonderful street car, where TORQUE matters more than peak hp. Yes, the centrif will make more peak at the top end, but what I told you about comparisons on the E36 M3 is real. Are the ATI and Vortech kits compared to the twin screw at the same boost level? If they are, while I would expect some difference, a 100whp difference in my opinion would be attributed as much to the design of the kit hardware (inlet housing and intake) as the efficiency of the compressors. Why didn't I go turbo? Because I had been playing with turbo cars for several years prior to buying my BMW. I did not want lag, I did not want the rubber band connection between the throttle and the engine. I wanted direct, nearly instantaneous response. I wanted my car to retain its character, but feel like someone simply increased the displacement of my engine SIGNIFICANTLY. That is exactly what I got. Also, people were already making turbos and centrifs for the BMWs. Nobody was doing a positive displacement setup. I did not set out to develop a kit, I set out to engineer something cool for MY car. I wanted it to be different. That is what I got!! At Active, we have had several customers come in to get work done on their centrifugally blown BMW's. They took a ride in the twin screw car, and came back and told us to take out what they had, and put the twin screw in their car. No Joke. I am not necessarily about the big numbers, or how fast I can get around a track. I am about the driving experience, and the twin screw is second to none in that regard for CERTAIN PEOPLE. The Turbo will always be king, and centrifugals will always appeal to people that want a certain type of feel and power delivery. That is a good thing, since if there are offerings in all categories, then everyone can get what they want! My brother is a Porsche fan and owner, I am a BMW guy. It is great to have choices, and I like how people are able to choose what works for THEM. That is why I sometimes lurk on various automotive forums. It is fun to see what other people do, and what they like. Feel free to go to bimmerforums.com in the forced induction section, and do some searching there for my screen name, and twin screw. You will see there is a lot of history, and a lot of information there. I apologize if any of this response is coming across as harsh, or consescending. I certainly do not intend it to be such. I just happen to be quite passionate about this, and I am a major stickler for engineering detail. It is hard to convey my passsion in words, while still coming across as a nice guy!!! Whew! Now, can someone please tell me how to edit my sig? I can't find it in my profile, and it still lists my original development car from when I signed on here 3 years ago!!! Steve

Steve, It would appear that you have to be a paying member to change your sig now. . Hi Keith, TS on air cooled would be fun too! TS on 996 sounds like fun too! Ed

I sense a strong presence of the darkside with this one i do...

Darkside........hmmm, would that be the area under the curve?! Seriously though, I think the logistics of hardware placement would be similar. Both Engine bays are rather stuffed.