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workingonit · #4 08-26-2024, 12:43 PM

Quote:

Originally Posted by andrewwynn

X5 RPM is darn high. The V8 models have a lower ratio rear end to help lower the RPM but with 5 speed it's still pretty high.

I don't think the auto had overdrive just lock so depending the top gear ratio it could be the same as auto.

I seem to recall 2600 RPM at 75 on the speedo 72 actual just as a baseline of m54 e53.

With a final drive ratio of 4.1, my '01 M54 automatic runs about 2525 rpms on the 17 inch tires (29" tall) at 75 mph, in 5th gear. My '04 Chevy 2500HD, also with 4.10 gearing, but with 245/75-16 (30.5" tall) tires, goes 2450 rpms at 75 mph. My wife's '98 GMC, with 28" tall tires and 2.73:1 final drive, is great for cruising on the highway, though, as it lopes along at 1800 rpm. Tire height and gearing makes a lot of difference.

I don't consider those rpm's so high, after years of driving vehicles with 2 or 3 speed transmissions, with no overdrive. But, those vehicles started out with higher final drive gearing (lower numerically), as low as 2.29:1 on one of my cars, so you could achieve very high speeds only if you had the horsepower (my '67 Dodge Monaco 500, with 14" diameter tires, had a modified 383, and the 2.29 gearing, with lotsa horsepower, and I often drove it over 100 mph).

On the other hand, the final drag race configuration, on my '66 Chevelle, had a final drive of 4.88:1, a 2-speed Powerglide race transmission (1:1 ratio at top speeds), and 28" tall MT slicks (which would grow in diameter a bit, at top speed). At 75 mph, the 427/441 c.i. engine would be turning around 4500 rpm, at 80 it would be around 4700 (IIRC), and at 125 mph (at the 1/4-mile finish line), it would be at a screaming 7400 rpms. I doubt that any M54 could survive that.

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