wolverine

I recently installed a Dinan 3.91 differential (stock is 3.62). I figured this would be a great mod because there is no reason for us in the US to have Euro gearing to go 204 mph. The Dinan diff gives 8% more torque to the rear wheels in all gears, at all engine rpm, but doesn't stress the engine or tranny any more than stock. Below are results of my car, basically stock, with charcoal filters and resonator removed (probably 10-15 HP gain), and then with the differential installed. Below are the results.

I calibrated the Gtech at our local dragstrip with the exact setup I used for these runs, so it should be pretty accurate. The conditions were very similar for all the runs, temperature varied from 58 deg to 62 deg. I did 9 runs, 2 aborted with the stock car, and 7 runs, 1 aborted with the 3.91 differential (I used the 60' and 0-60 times on the aborted runs).

There is a substantial difference in the acelleration. Here are the results, using average numbers:

------------------------Stock -----------------------Dinan ----------------------Difference

60 ft. time ---------2.229 sec------------------2.225 sec----------------0.004 sec

0-60 mph ---------4.56 sec---------------------4.40 sec------------------0.16 sec

Quarter Mile -----12.78 @ 115.59 ---------12.54 @ 118.24 -------0.24 sec, 2.65 mph

50 - 110 mph-----7.86 sec---------------------7.31sec-------------------0.55 sec


Interestingly, my 60' times were really not much better with the new diff - the traction was just not great, and with more torque, it's not really any easier to modulate the throttle. Also, with the Dinan I got a fair amount of wheelspin in second gear, and had to modulate the throttle slightly. With the stock car, I could just mash it once I hit second - a good chirp, but it didn't break traction.

These numbers don't really show how much harder the Dinan is pulling in gear. Some of my Dinan 0-60 times included a 2-3 shift at 59 mph if I didn't quite hit redline. All of the quarter mile times included a 4-5 shift at about 117 mph. If the rev limit was raised slightly (listening Dinan?) the car would have easily trapped over 120, and the times would come down .15 sec.

Note - I just edited the table to include the 50-110 mph times. These give a good indication of how hard the car is pulling in third and fourth gears. As a reference, Road and Track has the M5 running 50-110 mph in 8.0 sec, and the M6 at 7.6 sec.

Bubbarossa

It's not gonna be a huge difference in your 0-60, it's not a big jump (3.62-3.91). I changed my r/p's on my jeep from 3.73 to 4.56 and there really wasn't much difference. Yes, you can notice it, but not huge.

I don't know the price you paid, but changing ring-and-pinions are usually the best bang for your buck and you don't have to mess with the engine. You may loose some top-end, but honestly, you're gona do most of your driving below 100mph.

BTW, what was the price and do you know if it's only avaiable for the M5?

vegastrashed

There's a Dinan diff available for 545/550. $2K for the diff.

Wolverine,
I've been reading your threads over on M5board and bimmerforums. You've made good use of the new diff already.

tachyon

Well done, Wolverine. I have also been following the threads on the M5Board and it looks like you guys have found an excellent modification - well worth the money. It also sounds like your seat-of-the-pants experience is even more noticeable than the numbers might otherwise indicate. Thanks for sharing with us. Are you contemplating any other Dinan mods such as the rear shock tower brace or the high flow throttle body?
Go Blue.

wolverine

Yeah - go Blue! That's going to be one heck of a game in Columbus if both teams are undefeated.

I'll definitely go with the Dinan software modification. If they do a slight remap, and raise the rev limit, I think you'll be looking at a low 12 second car with trapspeeds over 120 mph. The diff alone is basically equivalent to a 40 HP increase - a good deal on the M5 for $3,000. With the software, (est. cost about $500), the car will be quicker than anything under $200,000 save the z6 vette.

wolverine

Another good test on the Dinan 3.91 vs stock. This guy tested his M6 before and after the Dinan install - he's been pretty rigorous about posting dyno numbers on all his mods, so these are good numbers:

GREAT news on the Dinan diff. Dyno'd today after diff install and torque went from 304.1 to 328.1. That's right around the 8% they claim. That's all I have for now.

Tulsa545

Thanks for sharing. The rear end ratio (2.93) on my 545 manual is the biggest complaint i have about the car. I have to downshift to 3rd gear to pass efficiently at highway speeds. If I decide to keep the car, I will mod the diff.

AlexFW

Tulsa, have you called Dinan to ask for the 3.45 LSD ?
Can you ask if is it possible to have 3.38, 3.23, 3.15 ... ?
3.45 would give too short gears ...
And the price .
And WHEN it will be released .

Thank you and pls open a new thread on parts&mods

JetBlack

I know for a fact that they will only offer the 3.45's for the 545/550 and 3.91's for the M's. The reason they will stick with this ratio is because it will still allow you to hit 60 mph without a 2-3 gear change.

(my brother works there, in sales)

AlexFW

I know of the 0-60 time .. But here in EU we have 0-100 .

And I'm scared that with 3.45 the car would be abrupt .

The only thing to do is change 275/30 R19 with 285/30 R19, so to extend the final drive ratio of another 1% .

Can tou ask to your brother when it will be released and at what price ?

Really thank you!