M42club.com - Home of the BMW E30/E36 318i/iS
DISCUSSION => Engine + Driveline => Topic started by: e3091318is on April 13, 2013, 03:51:54 AM
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I noticed the previous owner replaced the stock diff with a 3.73 LSD. I am almost finished my engine rebuild and was wondering what differences this 3.73 is going to make. I have did some reading online and got mixed review. Some say its all around better with the 0-60 in 2nd gear, better MPG on the highway and lower RPM on the highway. On the other hand I have some people saying it makes the car a complete slug. Does anyone actually have personal EXPERIENCE with the diffs on the M42? This is my first manual transmission car and I am not the best in the world. So I am hoping the 3.73 will help me a bit considering I won't have to shit to 3rd just to get to 60. Sorry for the ignorance. Appreciate any helpful answers.
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I'm looking for one to install on my car. Most of my driving is rural with a little highway. I took a 400 mile round trip last week and averaged 30MPG @ 74 MPH and was quite happy with that, but I feel first gear is too low and I'd like a lower RPM on the highway.
Desktop Dave is running a 3.73 and has commented quite favorably several times on its performance.
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Yep, that's exactly what I'm running. The car is slightly slower at times, but there is much less shifting. Around town, I can still start in 2nd gear even on slight uphill grades. The 4.10 makes 1st gear useless for my driving style. That makes the car feel a bit handier IMHO. The car is at its bets on the highway though. Given that I prefer to average about 75MPH, the motor is turning about 3K RPM (just under the motor's torque peak). It's a great setup for quick passes.
But I'm no speed freak by any definition. The best part is the excellent fuel mileage with this setup - 31MPG overall average during my ownership. I always figured I'd get a 328i or M3 if I wanted to go fast. I am also running OEM BMW 14" rims with cheap 195/70 tires, ~25" circumference IIRC - don't forget to factor that into your desired final drive ratio.
But if you're an acceleration junkie...you'll be far happier with a 4.10, or even the seek the exotic 4.27 & 4.45 LSDs I've heard are out there. ;D
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Yep, that's exactly what I'm running. The car is slightly slower at times, but there is much less shifting. Around town, I can still start in 2nd gear even on slight uphill grades. The 4.10 makes 1st gear useless for my driving style. That makes the car feel a bit handier IMHO. The car is at its bets on the highway though. Given that I prefer to average about 75MPH, the motor is turning about 3K RPM (just under the motor's torque peak). It's a great setup for quick passes.
But I'm no speed freak by any definition. The best part is the excellent fuel mileage with this setup - 31MPG overall average during my ownership. I always figured I'd get a 328i or M3 if I wanted to go fast. I am also running OEM BMW 14" rims with cheap 195/70 tires, ~25" circumference IIRC - don't forget to factor that into your desired final drive ratio.
But if you're an acceleration junkie...you'll be far happier with a 4.10, or even the seek the exotic 4.27 & 4.45 LSDs I've heard are out there. ;D
I appreciate the good answers! I am not too much of a speed freak either. I would rather have easier shifting by a gear then half a second 0-60. I won't be punching it very often. This may be a dumb question but how fast can you expect to hit in 2nd gear? I too also have 14 inch rims but I think mine are 205/65 if I am not mistaken.
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Funnily, the car is faster to 60mph as I don't lose time with that 3rd gear shift! The car will do almost 70 in 2nd IIRC. First is good up to about 35. If I take the car out I'll post some data. Alternatively, I could do it the easy way with a calculator...
Found this very interesting site (http://www.bokchoys.com/differential/GearRatios.htm) with transmission ratios (unfortunately not the E30 >:( ), and this one with the E30 'box ratios (http://www.e30zone.net/e30zonewiki/index.php/Gearbox#Gearbox). :) Found this online speed calculator (http://www.kabamus.com/garage/gears.html). I used 195/65 R14 OEM sizes with the 3.73.
Given three engine RPM (1000 RPM idle - 3500 RPM torque peak - 6500 RPM red line), a 3.73 results in the following speeds:
1st gear (3.72) 5-23-33mph
2nd gear (2.02) 9-43-62mph
3rd gear (1.61) 12-53-77mph
4th gear (1.00) 19-86-124mph
5th gear (0.80) 24-108-155mph
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Very nice. I will definitely keep my 3.73 if I can hit 60 in 2nd. The 3.73 seems much more practical for all around driving.