Changing my speedometer from mph to km... what's wrong?

[hdavis]

Ok. Thanks will keep looking.

Yes, vin #2240175. Imported into Mexico when new and transformed to a CSi in the early 90s by a local BMW dealer.

 

[hdavis]

Here's the number on the diff.

So it's a 3.64! The worst possible one IMHO

Thanks for the help. A lot was learned

 

[HB Chris]

But better acceleration and great with the OD 5 speed

 

[WISE9UY]

I soon hope to be taken on a drive in an E9 with the 3.64 and 5 speed OD. My alternative is a 3.07. I have not yet seen a 3.25 offered for sale.

 

[hdavis]

A 5 speed would be a good thing....maybe someday

 

[Honolulu]

That's what I'm running: 3.64 LSD with Getrag 265. A good combo for matching available torque of my stock engine, Zeniths, and the speeds I drive. The headers I put on didn't seem to make any difference at all. The single biggest change was swapping out the auto trans for a 4-speed, then later the 5-speed when it became available. I hadn't realized how sick the auto trans was until...

Henry I realize that giving you the "3.73" number on the back of my speedo means nothing. I'll have another look at the "W" number and edit this post.

 

[hdavis]

Henry I realize that giving you the "3.73" number on the back of my speedo means nothing. I'll have another look at the "W" number and edit this post.

Charlie in the pictures you sent me (one of which I posted above, see post #36), you can clearly see the W number: 0.68, and per Chris' post #33, your speedo is calibrated for a 3.25 differential.

 

[OCCoupe]

3.64 is probably the best differential for a 3 litre m30. You are always in the power band at highway speeds. 3.45 is also a good differential but harder to find. 3.07 is way to tall, you'll never get out of 3rd and 4th gears and will struggle in 5th.

 

[WISE9UY]

3.64 is probably the best differential for a 3 litre m30. You are always in the power band at highway speeds. 3.45 is also a good differential but harder to find. 3.07 is way to tall, you'll never get out of 3rd and 4th gears and will struggle in 5th.

I have some concerns with of the 3.07, but bear in mind it will be behind either an M90 or this type of power band...

 

[OCCoupe]

I have an m90 bored to 94.5 and stroked to 90mm making it a 3.8l motor. With that said I am putting out quite a bit of torque from 2,000 rpm on up. I still wouldn't consider the 3.07 perhaps the 3.25 but not the 3.07 with a 5 speed od. Your turbo isn't going to come to life until you are north of 3,000 rpm making that 3.07 difficult at normal highway speeds.

 

[WISE9UY]

I have an m90 bored to 94.5 and stroked to 90mm making it a 3.8l motor. With that said I am putting out quite a bit of torque from 2,000 rpm on up. I still wouldn't consider the 3.07 perhaps the 3.25 but not the 3.07 with a 5 speed od. Your turbo isn't going to come to life until you are north of 3,000 rpm making that 3.07 difficult at normal highway speeds.

This is great feedback because I am still not sure which way to go I have a 3.64 also but do you think you need the engine revving that much? Are you running the 3.64 with OD with your M90? Actually sorry to hijack the thread... perhaps PM me. I would welcome your feedback as I see you have a few of these so perhaps you could share the pros and cons. There is already so much torque with my twin weber M30 so for that reason think taller gearing could be OK considering the car has a 3.45 now.

 

[OCCoupe]

I'm running a 3.45 and would like to try a 3.25 but am very happy with the 3.45. I was very happy with the 3.64 with a 3.5 and a 5 speed. I just wanted more cruising versus performance. Now I have both with the 3.8 and 3.45 combo. Either is a good choice. The engine spins at around 3,300 at 77 with the 3.64 and at roughly 3,000 with. The 3.45 so it does feel a bit more relaxed with the 3.45.

 

[ES 1800]

I am going to make an educated guess from looking at the parts books:

W=0.679 kmh on CSi and CSL is for the 3.25 differential
W=0.7125 kmh euro CS and CSA is the 3.45
W=1.078 mph euro CS and CSA is the 3.25
W=1.14 mph US/NA CS and CSA is the 3.45
W=1.2164 mph US/NA CS and CSA is the 3.64

The differential ratio is stamped on passenger side of the diff on the large flat spot behind/under the CV joint: 39/12=3.25, 38/11=3.45, 40/11=3.64
A large stamped S above the ratio indicates Limited Slip diff

I just looked on the back of my newly installed mph speedometer. It says W=1.207. I think this is the production date: 11.74. (My car is a '73.) The rear axle is, I believe, a 3.64. The stamp on the housing is 11 40 The metric speedometer I removed is marked W=0.69, Production date (?) 10.70.

I'm going to call a few speedometer places to see what can be done. Just surprising that the change needs to take place in the speedometer and not in the transmission.

 

[HB Chris]

More plastic gears in the speedo, only one drive gear in the tranny and you wouldn't want to mess with that!

 

[Wladek]

I just looked on the back of my newly installed mph speedometer. It says W=1.207. I think this is the production date: 11.74. (My car is a '73.) The rear axle is, I believe, a 3.64. The stamp on the housing is 11 40 The metric speedometer I removed is marked W=0.69, Production date (?) 10.70.

I'm going to call a few speedometer places to see what can be done. Just surprising that the change needs to take place in the speedometer and not in the transmission.

According to Blue Book you have 2800CS speedo