engine and drivetrain Rpms At 5500 At 65Mph?

[McKinney]

Edited April 29, 2014 by McKinney

[ray_]

Hmm. We need a video. With sound.

 

Good luck,

 

Ray

[McKinney]

Hmm. We need a video. With sound.

 

Good luck,

 

Ray

I'll try to safely do that on the way home tonight.

[Conserv]

I went onto the first site Google listed after I typed in "speed vs. rpm calculator."

http://www.powerblocktv.com/resources/

A 195/60/14 is 23.21" in diameter, just slightly smaller than the original 165/80/13.

Assuming that site's calculator is correct, at 60 mph in 4th gear, car should be turning 3,163 RPMs with a 3.64 diff, 3,389 RPMs with a 3.90 diff, and 3,571 RPMs with a 4.11 diff.

Do you have an emissions schematic sticker under your hood, on the driver's side inner fender just forward of the upper strut mount? While it is entirely possible your car's diff has been swapped, the emissions schematic sticker will reveal whether your car is a 49-state or CA-only version and thus provide a glimpse at what diff your car came with from the factory. But NO readily-available diff is going to achieve the RPMs-vs-MPH results you've seen. I believe your speedometer and/ or your tachometer are wacko!

Steve

Edited April 30, 2014 by Conserv

[McKinney]

I'm starting to get the feeling this is a larger problem than I expected. I'll try to get video when I get off in a few hours

EDIT: That's good information Conserv I'll double check my sticker. I know that I have one there. I hope it's only my tach and speedo not reading correctly but the rpms do sound high and out of the power band which makes me think it's accurate

Edited April 29, 2014 by McKinney

[Conserv]

I'm starting to get the feeling this is a larger problem than I expected. I'll try to get video when I get off in a few hours

EDIT: That's good information Conserv I'll double check my sticker. I know that I have one there. I hope it's only my tach and speedo not reading correctly but the rpms do sound high and out of the power band which makes me think it's accurate

I keep coming back to the speedo and/or tach!

Steve

[ray_]

Yeah. 5500rpm is... expressive from an M10.

 

I was too lazy to make a comparative vid today.

 

Cheers,

[McKinney]

http://www.bmw2002faq.com/topic/55176-re-calibrated-my-tach/

I guess I could try this?

Possibly set it to read 4k at 65 mph

I don't know if that's a good idea or not.

Because the car runs through its power band and kind of plateaus when i get above 6K rpm it makes me believe that the reading is correct.

[TobyB]

I think you have a 2 cylinder tach.

 

Or a 5.10 rear end.  They DID make a few for racing...

 

Actually, what seems most likely is that your tach is reading abnormally high, due to an electronic defect.

 

Spring for the inexpensive meter with the tach in it at your el-cheapo-chain- auto- parts store, and

see...

 

If you are really spinning 6k on the freeway, you'll hear it.

 

t

[Conserv]

If you go back to the calculator site I used earlier in this thread:

http://www.powerblocktv.com/resources/

you can calculate that a 5.52:1 diff would yield 4,000 RPMs at 50 MPH, 5,200 RPMs at 65 MPH, and 6,400 RPMs at 80 MPH, precisely as you described in the original post. I will bet a Borrani that your car does not have a 5.52 diff (if one even exists). But this illustrates that the tachometer vs. speed numbers you are seeing are moving in a strictly proportional and consistent manner. Does that get us anywhere? Well, it means that a slipping clutch -- always a long, long, shot -- becomes virtually inconceivable as a culprit! So I'm back to the "wacko tacho" or "wacko speedo" theory.

(Sorry to bring up again this thread's "low point" -- when first preyupy, and then I, accused you of driving in 3rd gear -- if you multiply 3.64 by the 3rd gear ratio of 1.32, you'd get an overall ratio of 4.80:1, multiplying 3.90 by 1.32 yields an overall ratio 5.15, multiplying 4.11 by 1.32 yields an overall ratio of 5.43. I'm not saying anything, but you wouldn't want us to be anything less than thorough in our contemplation of the issue. Right?)

Steve

Edited April 30, 2014 by Conserv

[pkchopp]

I'm in Santa Monica by the airport, Call me and i'll take a look.   Norm      310 9086488

Edited April 30, 2014 by pkchopp

[PaulTWinterton]

Good on ya Pkchopp! Something fishy going on. McKinney's numbers are just TOO extreme to be ratios IMHO.

[McKinney]

Hey Norm,

I get out of work around 430 and I'll give you a call.

I really appreciate that!

Conserv

I appreciate you being thorough. I was just joking that I was insulted. It's a very valid question.

Edited April 30, 2014 by McKinney

[Chamoix]

I have the opposite problem with my car. I have an original 4 speed, 195/80R14's on 14" basket weaves and a 4:11 LSD in the car and it reads 60mph+ when I am only going 40ish. There is a school zone near my house with one of those "Your Speed is ......." radar signs where I check mine. Got stopped for speeding not long ago and when the cop asked if I knew how fast I was going I said "approximately". Led to a long discussion about how the modifications affect the speedo accuracy, to which he finally said " Well, just get it fixed or you can get cited for malfunctioning controls."

[PaulTWinterton]

One malfunction that I've experienced is the speedo hanging-up. Speed indicated was MUCH higher than actual. This happened for a while before the speedo finally packed it in.

I carefully dismantled the speedo and found that the outside ring, which is pressed in, had come loose and was spinning with the central armature (my words, probably not correct terminology).

The way I understand it is, the central armature(?) spins creating an electro-magnetic field which controls the needle. If the outer ring is moving the field is not created properly, thus affecting the needle motion.

I used a bit of crazy glue and refitted outer ring.

Problem solved.

This may or may not be your problem.