Getting 3.45 diff installed NOW! ill let u know... - Page 5

FAST 5 · 7th April 2003, 23:04

What's the bottom line in your opinion? #.45 rear diff. good or worth doing to the M5? Or is it a waist of cash????
Lets forget the fact that is an expensive mod $3800.00 (including labor) Does it make the car better, when driving?
Can you answer my questions in detail. Thank you.
Robert

tonyo · 29th May 2003, 14:26

FAST 5,

Sorry about the long delay...

I really don't know if it's a waste of cash. However, like many of us here, I don't care too much about that part. I just have no reason to know if the car is faster or slower with it.

The important thing to me is that there is no evidence that the car goes faster with it. Theory, so far as I can take it, does not predict it to be faster. Without repeatable scientific comparisons the issue becomes purely psychological.

People tend to be fond of performance enhancements (or investments in general) whether they work or not, so debating the effectiveness of unmeasured enhancements is usually a losing proposition for the one who thinks differently.

Theory does not offer a clean answer to this question because there are too many unknown variables, particularly "traction vs. power (torque)" on the low end and "drag vs. power" on the high end. I would not be shocked if it proves to be faster, but it could just as easily prove to be slower.

Even though I can't be sure whether the 3.45:1 diff is better, I can still take my usual strong stand against the specious logic and feeble physics that have been offered up in support of it. When doing so, I do try to make sure that I don't make the wrong conclusion, after all, the diff might really be faster, even if the reasons claimed are wrong.

Tony

Teutonaddict · 29th May 2003, 14:58

Quote:

Originally posted by tonyo
People tend to be fond of performance enhancements (or investments in general) whether they work or not, so debating the effectiveness of unmeasured enhancements is usually a losing proposition for the one who thinks differently.

Well stated, Tony. Although, we could factor in the increased speed due to lightening......of the wallet! Seriously, this statement explains the rash of "you're with me or you're an idiot" (a.k.a. "if it's not Scottish, it's CRAP!") statements lately about this mod or that mod. As the rocket scientists at NASA say, "In God we trust. All others bring data!"

Quote:

Originally posted by tonyo
Even though I can't be sure whether the 3.45:1 diff is better, I can still take my usual strong stand against the specious logic and feeble physics that have been offered up in support of it. When doing so, I do try to make sure that I don't make the wrong conclusion, after all, the diff might really be faster, even if the reasons claimed are wrong.

Again, well put. Nice to see a return to healthy debate and disagreement.

-Dave

Alaris · 29th May 2003, 15:08

I can't see the appeal of this mod, really... first gear is way too short already IMHO. I hardly ever use it as it is. It would be like making it a 5-speed with 2nd being the new 1st gear if I changed the differential.

XrayMD · 30th May 2003, 00:27

Did you look back up at Kirkland's post about doing this yourself for under $700?

AvusM5 · 1st August 2003, 08:11

I did a diff swap. It was not in a M5 but i had a 1995 auto M3. the gearing on those cars are so long i decided to upgrade. i went from 3.23 to 3.91 (yes a whopping 22% increase in torque).

I must tell you it was the BEST MOD I EVER DID !!!

The torque was absolutely phenominal. My 1/4 dropped by 0.9 seconds !!! ALMOST A FULL SECOND!!

Honestly i've done a shitload of mods on bmws. the only way to get a true substantial (almost forced induction type gains) then differential is the only real way to go. intake exhaust etc is nice for noise and etc but in reality it would do ****. GET THE DIFFERENTIAL.

on a side note. if E46 M3 diff fits that would be a very cheap alternatice.... HOWEVER, you have to realize the M5 is an absolute torque monster, if you multiply teh torque TOO much it will = wheelspin, wheelspin, wheelspin.

Honestly i never bought into the whole "but your 0-60 may increase" bullcrap. in a race you will be faster period, its that simple 3.45 will rape 3.15 M5 hands down by about 0.3 tenths every time. its that simple

Apples · 1st August 2003, 16:54

Question 1...If you raise the RPM limit by 9.8% in a 3:45 diff then the top speed in each gear would be the same...upto the 155mph limit that the M5's stuck in (stock ECU)
It's fair to say the the 3:45 with the extra RPM would be much quicker to 155mph
Question 2....Max speed isn't really an issuse and once you're over 155mph because you're really haulin *** anyhow, but with the 3:45, could it be fair that it may have a higher top speed because it can reach higher into the power band at speeds over 180mph
If a 3:15 M5, unrestricted hit's it's max speed 185mph that many have seen @ 6,250rpm in 6th that shows it's not made it's peak power yet....then wind resistance is the reason. Have the 3:45 car along side the 3:15 at that the same speed the 3:45 is doing 6,860RPM....IF the 3:45 could touch 7,000RPM you've got a higher top speed in the 3:45....Problem is that the engine at 7,000RPM could be making the same power as the 3:15 car at 6,250RPM and they both end up topping at the same speed at 185mph.
Anyone shed some light on what l'm going on with????
I sapoke to Whayne at PC and he said the 3:45 feels awesome and it gives the car a new powerful feel. That could be the next mod on the N500
APPLES

MIB · 1st August 2003, 17:13

Hey Apples,

Which one are you considering, Dinan? I'm watching the Group buy carefully.

FAST 5 · 1st August 2003, 20:28

14 potential/interested paties but I oly have 8 guys who responded. If I don't get at least 12 guys. it won't work out. Its that simple. Its up to you guys to get me the necessary info, sent to my E-mail address.
Robert

AvusM5 · 2nd August 2003, 00:32

Quote:

Originally posted by Apples
Question 1...If you raise the RPM limit by 9.8% in a 3:45 diff then the top speed in each gear would be the same...upto the 155mph limit that the M5's stuck in (stock ECU)
It's fair to say the the 3:45 with the extra RPM would be much quicker to 155mph
Question 2....Max speed isn't really an issuse and once you're over 155mph because you're really haulin *** anyhow, but with the 3:45, could it be fair that it may have a higher top speed because it can reach higher into the power band at speeds over 180mph
If a 3:15 M5, unrestricted hit's it's max speed 185mph that many have seen @ 6,250rpm in 6th that shows it's not made it's peak power yet....then wind resistance is the reason. Have the 3:45 car along side the 3:15 at that the same speed the 3:45 is doing 6,860RPM....IF the 3:45 could touch 7,000RPM you've got a higher top speed in the 3:45....Problem is that the engine at 7,000RPM could be making the same power as the 3:15 car at 6,250RPM and they both end up topping at the same speed at 185mph.
Anyone shed some light on what l'm going on with????
I sapoke to Whayne at PC and he said the 3:45 feels awesome and it gives the car a new powerful feel. That could be the next mod on the N500
APPLES

question one... true.

question two... this is a common misconception and you are pretty much right in this aspect. On my 95 auto M3 my top speed actually INCREASED b/c the gearing was so long and the poewr just wasn't enough to reach the theoretical top speed.

there is a possibility that your top speed will be the same or even HIGHER than before. There is much more torque (9%) and that becomes a big factor when the car is under amazing aerodynamic stress at 155mph. Honestly this whole top speed debate is bullshit in my opinion, who the F*CK goes that fast anyways (maybe only 1% of us).

basically with higher differential you can get closer to the theoritical top speed, where as longer gearing will have higher theoretical top speed but not enough grunt to get there. So again top speed may be the same or higher, theres only 1 way to find out

My only concern.... TRACTION (this is a big concern, especially on M5). on my AUTO 95 M3 i was having traction problems with just 225lb of torque, imagine M5 torque. again my M3 only had 225 kuhmos on it but still i hear M5's have some traction problems as well. whats the widest tires you can run on stock height M5? 285, 295?

I honestly want to do the 3.62 from the E46 M3, its much cheaper and more cost effective (alot more power per $$), however traction will be a VERY BIG issue unless some really wide rubber is possible.