Coupe ratios ?

[rsporsche]

i think it all depends on what transmission you are using. if you are using a close ratio 5 spd box (dogleg box), then you want a higher ratio. with an overdrive 5 spd box, a lower ratio diff will significantly increase acceleration, and lessen the dropoff between gears. e30 M3 uses a 4.11 box w/ 200 hp and a 5spd O/D tranny ... but it doesn't have the torque of the big six. many drivers have increased the diff to an even lower ratio for track driving or autocross. but street driving, i have to agree - you're going to be higher in the revs at lower speeds.

 

[John Buchtenkirch]

Just a guess on my part but maybe BMW installed the lower ratio rear end (numerically higher) because of the smaller 2500 engine that was in the 75 cars. Cool rear if you’re into racing the rice rockets from stoplight to stoplight :shock:, however not the rear you would want with today’s gas prices :cry:. ~ John Buchtenkirch

 

[echappe]

A few years back I put a 3.07 lsd from a euro 635 in mine and found that in 5th gear in long uphill climbs on the interstate I had to go to 4th gear. With the new torquier 3.5L I wish I still had the 3.07.

 

[Gosch]

You are mistaken

E3 and E9 automatics: Final drive stamped with 11:40 ---> ratio 3.64:1, W=0.758 on speedo

E3 and E9 4-speeds: stamped with 11:38 ---> ratio 3.45:1, W=0.718 on speedo

CSL: stamped with 12:39 ---> ratio 3.25:1, coefficient W=0.677 on speedo



Now then, anyone have a W=0.638 speedo for me? (took a 3.07 out of one of my euro 635s and want to get the speedo accurate in 2270011)

Hallo,
I think you are mistaken

the w-coefficient are only for EU-cars with km/h
US and UK- cars have another w-coefficient with m/h

Try this links and read complete http://www.e9coupe.com/forum/showthread.php?t=2464

Gosch

 

[dp]

Hallo,
I think you are mistaken

the w-coefficient are only for EU-cars with km/h
US and UK- cars have another w-coefficient with m/h

Try this links and read complete http://www.e9coupe.com/forum/showthread.php?t=2464

Gosch

Thank-you!

I'd be just as happy with km/h as m/h as long as it is accurate, but is the (ratio) stamping on the back of the mph speedo for a 3.07 different for an kph?

 

[gkb]

Orangener - probably stupid question, but simple

The w that you quote for the various diffs. Is this a correction factor? If so why are none 1.0? I am trying to figure out the correction factor for my e9 with a 3.07 diff (dogleg 5 speed) - I know the speedo reads low, probably 10 mph at 60. I presume this also affects the odometer. Obviously need to also correct for any wheel/tire fitment, but this question is about effects of diff swap.

Many thanks.

 

[Gosch]

Thank-you!

I'd be just as happy with km/h as m/h as long as it is accurate, but is the (ratio) stamping on the back of the mph speedo for a 3.07 different for an kph?

Yes, the w-marc on the speedo are different between m/h and km/h

...........................................m/h....................................km/h
diff = 3.64 / w-marc speedo..= 1,21 Version for 2,5 CS........= 0,758 Version for 2,5 CS
diff = 3,45 / w-mark speedo..= 1,1 Version for 3.0 CS..........= 0,7125 Version for 3.0 CS
diff = 3.25 / w-marc speedo..= 1,08 Version for CSi-CSiL......= 0,69 for CSi-CSiL
diff = 3,07 / w-marc speedo..= 1,02 (never built as I know)..= 0,638 for e24 635CSi

may be their was built an early US/UK e24 635CSI with Miles-speedo and 3,07 diff, you can read the w-marc in blue books