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Discussion Starter #1 (Edited)
Might be a silly question, but, is it any "harder" on the M5 powerplant to be at 3000 rpm for an extended period of time versus being at say 5500 rpm for the same length of time? Also, has anyone done a definitive rpm matrix I could memorize for greater downshift efficiency? i.e. 3200 rpm in 2nd equals what ?? speed. For example: if I am going 45 in 4th and want to drop to 2nd (or 3rd) to horse her around, where should I rev her before letting loose of the clutch?

Just curious.
 

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kcdoyle said:
Might be a silly question, but, is it any "harder" on the M5 powerplant to be at 3000 rpm for an extended period of time versus being at say 5500 rpm for the same length of time? Also, has anyone done a definitive rpm matrix I could memorize for greater downshift efficiency? i.e. 3200 rpm in 2nd equals what ?? speed. For example: if I am going 45 in 4th and want to drop to 2nd (or 3rd) to horse her around, where should I rev her before letting loose of the clutch?

Just curious.
Well, if every engine has a finite number of rpms in a lifetime before rebuild, then tecnically the answer is it is harder at higher rpm. As a practical matter, as long as you are not living at the redline, I don't think you are doing any real harm. The service indictors will go more quickly, so assuming you properly service the car, all other things being equal, there is no practical downside to the car.
To get the different speed in gears, check out www.smokemup.com. Put in the tire diameter in inches (25.7 stock), rear end ratio (3.15 is stock), the gears, (4.23, 2.53, 1.67, 1.23, 1.00 and .83) and set the torque slip to 0. It will show the speed in gears (not corrected for any speedo error). Enjoy.
Regards,
Jerry
 

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I thought Greg posted a nice graph many many moons ago (probably 4-5 years back).. haven't run the search yet, though.
 

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Graphs are great to learn with, but in the end downshifts should be done by feel if that makes sense. I dont usually ever look at my tach, and can downshift many different cars without knowing their numbers. Once you get it down it will be butter, and you'll rarely botch downshifts even if you are in someone elses car.
I just have a hard time doing things by the exact number, rather I do things by what feels right and what doesnt. It keeps your eyes on the road longer and with less distraction.
:cheers:
 

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The idea of a 'finite' number of revolutions before an engine wears out does not seem to pan out in the real world. Common sense dictates however that at some point, excessively high RPM will wear an engine faster - however lower RPMs causes higher cylinder pressures and higher temperatures in the top of your cylinders which can be much harder on your engine than simply cruising at a higher RPM.

For reciprocating aircraft engines for instance, redline is typically 2500 - 2800 RPM. Recommended "cruise" engine speeds are typically 2200 - 2500 RPM. Engine rebuilders seem to agree that operating in the higher "recommended cruise" RPM bands will prolong the life of the engine (albeit higher fuel consumption due to friction losses).

Paul

P.S. - about downshifts - agreed, don't look at the tach while downshifting - I'll look down just to see "where I'm at" - as I decelerate through about 2,000 RPM I give it a blip while shifting - the amount to rev up is approximately the same for each single gear downshift so after a while you'll get used to the sound/feel of "what's right".
 
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