am i right?? gear change q's. sciency types needed
right, i know some of you like putting science theories into practice on cars, so am i right in saying this on another forum? its in relation to taking cars to the 'pod - the engines in question have peak torque at ~4,500rpm, and peak power at ~5,900 - stock volvo b200e redblocks for those who want to know..
Quote:
5lab wrote:
purely out of interest - where were you boys changing gear? just that the peak power on a b200e is at 6000 rpm so i would have thought you'd be best to change at ~6500 rpm..
SteveP wrote:
Around 5500-5700rpm... theres not alot of point revving to 6500rpm, peak power may be at 6000rpm.. but peak torque isn't!
5lab wrote:
yes but there is a reason why you mesure a cars power in power, and not torque. you see, when you change gear, your torque goes down - so that in 5th gear you can never get as much torque as you do in 4th. however, your power remains the same - because while at 3,000 rpm in 3rd gear you have more torque than at 3,000 rpm in 4th, you're wheels are going the exact amount quicker in 4th to compensate, providing the gearbox does not create more friction (or similar) in 1 gear than another (which it probably does but to negligable effect).
so, you should apparently change gear at the exact point where the engine speed in your old gear (say, 3rd) provides the same amount of power as the engine speed in your next gear.. you can work it out using the little 'mph per 1000 rpm' table in your owners manual and a torque graph. seeing as your car slows down a tiny bit every time you change gear, you should probably compensate by changing a tad later, as your next engine speed will be a tad lower
of course, this can be tricky as the power curve often drops off very quicky, yet rises slowly - so while this can be the most efficient way of changing gear, if you get it late by a small amount it can make a big difference to your accelleration.
i think i'm right, but not 100%. any thoughts?