Originally Posted by
altiain
Warning! ::Teacher: moment ahead!!!
An overrev is an overrev, regardless of whether you do it by missing an upshift or downshift. If the rear wheels (and the input shaft of the transmission to which the rear wheels are mechanically connected when the tranny is in gear) are spinning faster than the output shaft of the engine and you disengage the clutch, those two shafts will try to match speeds. They have three ways to do so: overrev the engine, slip the clutch, or break traction on the rear wheels. The energy in the system will follow the path of least resistance, which is usually to overrev the engine. There is a lot less resistance in this path (assuming you’ve got a good clutch in the car).
Don’t believe me? You can test this theory without overrevving the engine. On your way home tonight, run the car up to redline in 1st, engage the clutch, shift to 2nd, and let the revs drop to idle. This will simulate an overrev because we'll have the input shaft of the transmission spinning at a fater rate than the output shaft of the engine. The transmission will backdrive the engine ust as it would in a missed shift. Then, lift your foot off the clutch abruptly. What happened? Did the tires break loose, or did the revs on the tach suddenly jump? I’ll bet you a case of Shiner it’s the latter. :wink:
Not that I need convincing. I’ve overrevved three cars (RX7 2nd to 1st upshift, 6-speed NB 2nd to 1st upshift, 5-speed NB 3rd to 2nd upshift on two occasions), and the rear tires have never lost traction. In all three cases the engine overrevved.
As for synchros, they actually make overrevving easier, since their sole purpose in life is to allow you to shift the transmission without having to match input and output shafts speeds.
On a totally unrelated note, Miata engines are surprisingly resilient to overrevs. :wink: