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M3 princess
12-19-1998, 11:58 PM
Has anyone here tried changing the gear ratio in their M3?<br>The stock ratio is 323. Would changing to something like a 346 make a worthwhile difference? I have a 97 M3 with a mcturbocharger on it.<p>M3 princess

Bruce
12-20-1998, 12:12 AM
suzy...i understand the nick, but most people on here may not :)<p>Bruce<br>98 M roadster<br>01 E46 M3

m3niko
12-20-1998, 08:50 AM
Suzy,<p>Going to a numerically higher gear ratio with a turbocharged engine will not make the car faster. Turbos work when the engine is under load. By letting the engine wind up quicker (with a 3.46 gear ratio), the engine will have less load on it, hence less time under boost. I'm sure you've noticed that you're making a whole lot more power when the engine is under boost. You want a low numberical gear ratio to keep the engine under load, hence the turbo will be boosting and providing more power.<p>N/A and centrifugally supercharged cars are another matter. A N/A car needs the proper gear ratio to get the engine into its powerband quickly. A cent. S/C car needs a higher ratio (numerically) to spin up the S/C quickly, since it makes boost w/rpm, not load.<p>Nick<p><br><i>: Has anyone here tried changing the gear ratio in their M3?<br>: The stock ratio is 323. Would changing to something like a 346 make a worthwhile difference? I have a 97 M3 with a mcturbocharger on it.<p>: M3 princess<p></i>

PM3
12-20-1998, 06:36 PM
With my friends AA stage II/Gen II, first gear was useless, and the car didn't even boost properly until 3rd gear, where it really rocked. Your car (if I recall makes around 330hp) is probably set up nicely with the ratios. With you going to higher ratios and shorter gearing, it seems that you would be getting closer to those ratio problems my friend has..<p>PM3<br>www.geocities.com/motorcity/pit/7144<br>(Pablo Mazlumian)<p><i>: Suzy,<p>: Going to a numerically higher gear ratio with a turbocharged engine will not make the car faster. Turbos work when the engine is under load. By letting the engine wind up quicker (with a 3.46 gear ratio), the engine will have less load on it, hence less time under boost. I'm sure you've noticed that you're making a whole lot more power when the engine is under boost. You want a low numberical gear ratio to keep the engine under load, hence the turbo will be boosting and providing more power.<p>: N/A and centrifugally supercharged cars are another matter. A N/A car needs the proper gear ratio to get the engine into its powerband quickly. A cent. S/C car needs a higher ratio (numerically) to spin up the S/C quickly, since it makes boost w/rpm, not load.<p>: Nick<p>: <br>: : Has anyone here tried changing the gear ratio in their M3?<br>: : The stock ratio is 323. Would changing to something like a 346 make a worthwhile difference? I have a 97 M3 with a mcturbocharger on it.<p>: : M3 princess<p></i>

David
12-21-1998, 12:31 PM
I changed from a 3.15 to a 3.46 on my 95 M3. Changing the gearing is a trade off. You will gain in acceleration but you will loose top speed. In the jump I made it cost me about 500rpm per gear. On the otherhand the car is a jackrabbit that will break traction if you are not carefull. This is about the top ratio you want to go to and still have a street/track car.<p>

john W
12-26-1998, 12:42 PM
Best to leave the 3.23, multiplying 1st gear (4.20)times 3.23 leaves 13.56. Best range is 12-14. Anything higher winds the engine up too quick...you have to shift sooner and often can lose traction if not careful. BMW engineers have set the engine power band and tranny/rear end ratio gears to match nearly max. acceleration in 1st/2nd gears while still retaining fairly good driveability on the highway. Hard to improve on what they've done. Perhaps, when the M3 gets a 6-speed, they may increase the rear end ratio ever so slightly.<br>On my previous vette, I changed the 3.08 ratio to a 3.75 which put the overall multiplier to over 14. The car was like a Mack truck off the line, but you had to shift quick and the backend lost traction nearly every time. Alot of power, but some loss in workable acceleration.


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