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E36/7 Z3 (1996-2002)
E36/7 Z3 Roadster, Z3 coupe, Z3 M Roadster and Z3 M Coupe talk with our gurus here.

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  #1  
Old 05-31-2003, 12:16 PM
Edwin Huang Edwin Huang is offline
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S54 M coupe 3.73 diff impression

I have the 3.73 diff in my 01' S54 M coupe for a little over a week now, and it still amazes me every time I drive it how much the 3.73 diff has transformed the character of S54 M coupe. With 3.15, it used to feel like the power delivery is always lagging a little behind. That always bothers me considering how flat the S54 torque curve is. The 3.73 diff really makes the S54 M coupe come alive, I now feel perfectly in sync with the engine. The engine feels a lot more flexible, it pulls smoothly at low rpm even in high gear and the top end rush is really addicting. It makes you appreciate how good the S54 really is and this is the kind of little monster I imagined the S54 M coupe should be in the first place.
Big thanks to MarkL for the head up on 3.73 diff. He showed up on the day of installation, and was kind enough to let me try out the sweet gound controll setup on his white(same as mine) S52 M coupe. Mark is right about Louis at Rush Motorsport, he has done a great job rebuilding the 3.73 diff. Total cost for the 3.73 diff is $1500.

Ed
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  #2  
Old 06-01-2003, 09:56 AM
EYT EYT is offline
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3.73 vs 3.46

Hi Ed:

It must be a blast shifting to third at 70 mph and flooring it. I switched to a 3.46 about 12k miles ago and loved it. My question is in your research for the 3.73, have you tried out the 3.46 in a friend's S54 Coupe? and therefore could comment on the differences?

I am a little bit intrigued by the performance of the 3.73 diff. teamed with the S54. Would love to hear more about your experiences. Somebody mentioned the 3.73 diff from the 325 3 series would work just fine, any modifications needed in order for it to fit?

Thanks,

Eric
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  #3  
Old 06-01-2003, 03:24 PM
Edwin Huang Edwin Huang is offline
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Mein Auto: 2001 M Coupe
3.73 vs 3.46

Hi Eric,

I haven't tried out a 3.46 S54 coupe, so really can't comment on the differences. 3.73 is about 18% lower-gearing than 3.15 while 3.46 is about 10%, so I assume the difference will be similar to going from 3.15 to 3.46.
As for the 3.73 diff from E36 325, I believe it should be a direct fit. Quite a few people have done this without problem, a lot cheaper too.
And what a blast it is. The harder you drive, the more you can feel the difference. Wish I had switched sooner.

Ed
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  #4  
Old 06-01-2003, 03:48 PM
Shawn Fogg Shawn Fogg is offline
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Ed,

"As for the 3.73 diff from E36 325, I believe it should be a direct fit."

No, it wouldn't be. The direct swap (excepting output flanges) would be E30 differentials excepting the non-M3 4 cylinder diffs.

Shawn
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  #5  
Old 06-01-2003, 04:21 PM
EYT EYT is offline
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E30 3.73 differentials

Ed: Thanks for your inputs. Continue to have loads of fun driving your car.

Shawn: Thanks for clearing up the question in my mind. Do I understand you correctly that a E30 M3's 3.73 diff. would fit perfectly for the S54 M Coupe? Please clarify.

Thanks,

Eric
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  #6  
Old 06-01-2003, 05:40 PM
Shawn Fogg Shawn Fogg is offline
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Eric,

Yes, it should bolt right in. You may need to swap output flanges though so they mate up with your existing half shafts. You can swap your rear diff cover over to the E30 diff too.

The E30 non-M 4 cylinder differentials are the narrow case diffs like used in 318ti and 1.9l Z3s. All the other E30 diffs (the sixes and the E30 M3) used the same diff case as all the six clylinder Z3s.

Shawn
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  #7  
Old 06-01-2003, 06:23 PM
EYT EYT is offline
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Shawn:

Thanks very much for the info. I am going to have a lot of fun searching for a reasonably low mileage one. :>)

Cheers,

Eric
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  #8  
Old 06-02-2003, 03:10 AM
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What kind of revs are you turning at highway speeds?
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  #9  
Old 06-03-2003, 08:46 PM
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QikSilver QikSilver is offline
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Eric,

If you're looking for a 3.73, I am a buyer for your 3.46. I'm getting ready to buy one, but I'll wait if I can make a deal with you. Knowing you have cash coming in might make your hunt for a 3.73 a little easier.

John
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01 M roadster, F: GC/Koni short coilover struts, Eibach, Wilwood front brakes, GC tubular swaybar. R: TC Kline springs, short Bilsteins, IE sub & swingarm bushings & shock mounts, 3.23 gear, Rogue dual-ear cover, Eisenmann 4x83 pipes. MISC: Sport mode, Rogue pulleys, keyless, RG Motorsport intake, OZ Superleggera 18" 3 piece.
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  #10  
Old 06-03-2003, 09:35 PM
EYT EYT is offline
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John:

I actually got my 3.73 diff today, I am very excited about it, will be installing it this Saturday.

I want to keep the 3.46 diff though, thinking I can remain flexible.

Good luck with your purchase.

Cheers,

Eric
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  #11  
Old 06-10-2003, 07:06 AM
DrM DrM is offline
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I'm thinking of swapping in a 3.46 or 3.73 diff. Where did you guys get the new diff? I want to keep the stock one just in case.

Price?

Also, for those of you who have done this - how difficult is it on a scale of 1 to 10? I've done quite a bit of engine work on other cars (inc. two rebuilds) but they were much older cars (1980's Mini's) so that's where I'm at on the competence ladder.

TIA
DrM
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  #12  
Old 06-10-2003, 07:52 AM
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bob lindquist bob lindquist is offline
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Rev's?

Quote:
Originally posted by Pinecone
What kind of revs are you turning at highway speeds?
I'd be curious to know what rev's are being turned at 70 mph.

looks like 3560rpm

3469 if I installed the same in my S52 with 265/35-18's, of course I would have a much lower redline
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Last edited by bob lindquist; 06-10-2003 at 07:59 AM.
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  #13  
Old 06-10-2003, 09:11 AM
EYT EYT is offline
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3.73 vs 3.46

Bob:

In my S54, with my speedo at 70 mph, the 3.73 shows 3300rpm, while the 3.46 shows around 3000 rpm. ( Very un-scientific observations )

Cheers,

Eric
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  #14  
Old 06-10-2003, 09:35 AM
Edwin Huang Edwin Huang is offline
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Shawn:

Thanks for correcting my mistake, hopefully no harm is done.

Pinecone, Bob:

Go to this site http://www.368s.com/tools_rpm.phtml and use the handy rpm tool to figure out rpm changes. 70mph should be at 3,551 rpm with 245/40/17 rear tire.

Eric:

Congratulations on your 3.73, now you know what kind of fun I'm having. Have you done the Sport mode mod? If so, I'm curious to hear your opinion.
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  #15  
Old 06-10-2003, 11:20 AM
EYT EYT is offline
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Sport mode

Ed:

I have not done it, mainly due to feedbacks from a few local e46 M3'ers who autocross their cars; on course throttle modulation is hard as the gas pedal becomes overly sensitive, but they tell me the only time they would have it on would be on the freeways.

I have 275/40/17's rear and 255/40/17's for the front, I wonder would the slightly taller tires lower the engine rpm ever so slightly?

Cheers,

Eric
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  #16  
Old 06-10-2003, 12:44 PM
Edwin Huang Edwin Huang is offline
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Eric,

Thanks for the feedback. Taller tires do indeed lower engine rpm. If my calculation is correct, that means your final drive ratio should be about 3.59 (3.8% taller). Another factor to take into consideration is speedo error. Mine is about 10% higher, so 70mph on speedo means I'm only doing 63mph.

Ed
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  #17  
Old 06-10-2003, 12:48 PM
EYT EYT is offline
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3.73 diff

DrM:

It's a direct bolt-on, relatively simple if you are mechanical.

The switch from 3.15 to 3.73 would be awsome.

In my research, prices varied from $600 from a recycling outfit to $1,800 for rebuilt. Ed got it for $1,500 installed?

Cheers,

Eric
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  #18  
Old 06-10-2003, 12:56 PM
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bob lindquist bob lindquist is offline
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Speedo is accurate!

Quote:
Originally posted by Edwin Huang
Eric,

Thanks for the feedback. Taller tires do indeed lower engine rpm. If my calculation is correct, that means your final drive ratio should be about 3.59 (3.8% taller). Another factor to take into consideration is speedo error. Mine is about 10% higher, so 70mph on speedo means I'm only doing 63mph.

Ed
for what its worth.....

I changed the tire size on my S52. now with 265/35-18's on the rear my speedo is exact, no error. I used the 386s.com calculator and checked with local cops using radar.

The whole inaccurate speedo thing was driving me crazy. The cops around here are on every street using moving instant on and stationary radar. 35 mph then 45mph then 25....I was ready to buy a digital rally speedometer. so I used the calculator and I was pleasantly surprised to find my spedo is correct. It was just a lucky thing I picked that size tires.
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2000 Imola Red M Coupe

Dinan suspension, M rotors /Axxis pads
Eurosport Cam Kit 1, touch lane change
Zaino polish, Beach Sand
Garys mirror adapter, S54 Oil Cooler
seat tilt coupling nuts, spare tire

"life's to short to drink cheap beer"



Last edited by bob lindquist; 06-10-2003 at 01:02 PM.
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  #19  
Old 06-10-2003, 12:59 PM
DrM DrM is offline
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Thanks for the info Eric.

It seems like this mod is the best bang for the buck without messing too much with the S54 engine.

Is metricmechanic the best place to go for this - anyone else who has done it let me know where you got your diff.

Having owned a 2002 M3 I also miss the sport mode - but don't want to do that mod for warranty reasons.

cheers
DrM
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  #20  
Old 06-10-2003, 03:44 PM
Shawn Fogg Shawn Fogg is offline
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Keep an eye on ebay and you can usually pick up a used one cheap.

For example:

http://cgi.ebay.com/ebaymotors/ws/eB...tem=2418661907

Shawn
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  #21  
Old 06-15-2003, 05:04 PM
H&RMcoupe H&RMcoupe is offline
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what would you say the acceleration difference is from say 0 to 60, 30 to 50 etc... with the 3.46 and 3.73 versus 3.15. I would imagine it would be faster?
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