Rear diff question... testing the waters...
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Ok, this is where the crazy number is coming fromfranka said:
Diff ratio changes do not increase horsepower.
Diff ratio changes do however change torque, you get higher torque multiplication BUT (and this is a bit BUT) for _shorter_ amounts of time because the shorter gears.
The result is an increase in the "butt dyno" because of the strong but short torque bursts but you are not getting a big increase in acceleration.
This has been discussed alot on m5board, see this thread for one: http://www.m5board.com/vbulletin/showthread.php?t=67150
The result is an increase in the "butt dyno" because of the strong but short torque bursts but you are not getting a big increase in acceleration.[/url][/QUOTE]
A higher numerical diff ratio is going to improve acceleration.
An extreme example to make the point obvious would be to imagine starting a drag race in 2nd or 3rd gear. Dropping to 1st gear would yield the same type of improvement as going to a numerically higher diff ratio. It would improve acceleration.
Most drag racers run a 4.10 or 4.56 diff because it works.
A higher numerical diff ratio is going to improve acceleration.
An extreme example to make the point obvious would be to imagine starting a drag race in 2nd or 3rd gear. Dropping to 1st gear would yield the same type of improvement as going to a numerically higher diff ratio. It would improve acceleration.
Most drag racers run a 4.10 or 4.56 diff because it works.
I assume you are not talking about BMW 540/M5 and keep in mind that you cannot compare diff ratios between different cars because their gearbox ratios may be way different.franka said:
My point is this. I have not been able to get ANY hard data on performance improvement in 0-60 og 1/4 mile times with the change from the stock 3.15 diff to 3.45 or 3.64 in the M5. I have repeatedly asked people to show me that this mod does result in better times - nobody has been able to. And in the thread I pointed to earlier it is suggested that the cars with stock gearing 3.15 do better 1/4 mile times than the 3.45 ones.
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I never stated that a change in diff ratio increases HP :dunno:s62 said:Ok, this is where the crazy number is coming from
Diff ratio changes do not increase horsepower.
Diff ratio changes do however change torque, you get higher torque multiplication BUT (and this is a bit BUT) for _shorter_ amounts of time because the shorter gears.
The result is an increase in the "butt dyno" because of the strong but short torque bursts but you are not getting a big increase in acceleration.
This has been discussed alot on m5board, see this thread for one: http://www.m5board.com/vbulletin/showthread.php?t=67150
However, and I quote Jim Blanton from Performance Gearing "... and changing your diff from a 3.45 to a LSD 4.10 in a 530 will result in a net gain in accel. of approx. 18.5%."
I have not gone to the track / strip (yet) to test my times - however from a daily driver perspective (yes, I do drive my car hard), I can tell you that the increase in accel. is SIGNIFICANTLY noticeable and an absolute blast to drive (especially when combined w. the s/c) :thumbup:
Final drive changes only affects the torque multipication factor to the rear wheels. The engine still puts out the same amount of torque. So 3rd gear feels like 2nd and 2nd feels like 1st.
It may or may not be faster on the drag strip, but a higher final drive is definitely more fun on the streets.
It may or may not be faster on the drag strip, but a higher final drive is definitely more fun on the streets.
Sorry, I did not mean to imply you said it increased HP - I was just stating that diff ratio changes have no effect on power output, just torque to the wheels.AirFrcd said:
I think it would be very interesting to have Mr. Blanton back up his claims with some hard empirical data. I think this just goes to teach people not to trust salesmen
I think it is just the SC that is giving you the quicker acceleration
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Is he running a 4.5 0-60... that would be cool.franka said:
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I think the main problem with an increase in 0-60 times with a diff change is that the increase in acceleration is offset by the fact you have to shift into third before you hit 60 mph. That's why the butt dyno registers faster. The car runs through the gears faster, but that extra shift ruins the 0-60. However, I'd bet on an improved 1/4 mile. :dunno: Just my $0.02.s62 said:
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Keep in mind that Airfrcd's car is a 530, not a 540......our 540/740's come with either 2.93 or 3.15's.AirFrcd said:Depending on what your final drive is geared at now, let me tell you, upgrading my diff. from a 3.45 to a 4.10 LSD was by FAR the best mod that I ever performed to my 5'er :thumbup:
A net increase in accel of 18.5% is very noticeable, and a match made in heaven w. the forced induction (as the s/c kicks in only past 3K RPM's, and the shorter gears kick in as soon as you touch the skinny right pedal
Cost was approx. $3,600 from Jim Blanton at Performance Gearing - btw, he is an awesome guy to deal with, and the authority in BMW gearing. I highly recommend his work and services
Personally coming from a car that made first gear useless after changing ratios (91 MR2 Turbo) I'd never go anything above 3.64 N/A or 3.46 F/I in the 540/740 if you lookin to still remain streetable without making your car drive rediculously high RPM's on the freeway....just my 02.
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wrong. the auto tranny is longer than the 6 speed tranny in the M5 and you need a custom driveshaft to fit between the auto tranny and the M5 dif. He wouldn't know the length of the driveshaft until after the dif was installed and doing him absolutely no good. Akin to asking what kind of underwear one should buy for a SuperModel.franka said:
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Blanton's been doing Bimmer gears since before I started driving. He and Jim Rowe USED to be biz partners in Metric Mechanic from whom I bought my '02 tranny... well.. lessee.. 18 years ago now? Yipes. It developed a lil catch into 2nd 4 years after purchase and they replaced it with no questions from my mechanic. The man knows his gears.franka said:
Having said THAT, I bought my E39 Quaiffe from Jeff @ Koala. Great guy who also really knows his stuff. Since I wanted a quaiffe and he had 'em, he was my choice.
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You are. Both difs are not the same. The M5 LSD dif is longer.
A longer auto tranny meets up to a longer auto driveshaft to meet up with a shorter auto (or peg leg six speed) dif.
It's been tried and failed by a former moderator here who S/C'ed his auto tranny 540 and wanted an M5 dif. He needed a cutom driveshaft and sold the dif instead.
A longer auto tranny meets up to a longer auto driveshaft to meet up with a shorter auto (or peg leg six speed) dif.
It's been tried and failed by a former moderator here who S/C'ed his auto tranny 540 and wanted an M5 dif. He needed a cutom driveshaft and sold the dif instead.
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