Best time to change gear (rpm)

[-GT-]

What numbers were you using to calc back? 7200 is too low, should be 7800. Also, i'd expect greater losses than 15%, and yep, that's with a C52 attached to it.

[Roundy]

yeah i know 7200 is too low, but it is what i came up with

anyways
tyre size 205/45/16
3rd Gear 1.310
Final Drive 4.312

also searching for the C52 i found varying final drive ratios, 4.312 was the shortest, so i used that one

but at 140km/h road speed in 3rd it calculates back to ~7200rpm
edit: (hmms just re-did it and got 7050 )

as for the 15%...it is sorta academic really, it probably is closer to 20% looking at the numbers i got, but it shouldn't change the results at all.

Cheers
Nathan

[-GT-]

Varying final drive ratios?? Didn't know that, did you find any mention of what models had what?

You're heading the wrong way, 140km/h in third is a stretch for me, redline, 8k, maybe a touch over, think i just fall short on the limiter. That's on the speedo anyway, i think my actual road speed is more like 150+, think my speedo is out by a good 10%. Not sure why it's that bad, think i remember calculating % difference with tyre size change only being a few %?? 185/60/14 -> 205/45/16

[Roundy]

i know the RPM doesn't sound right, but based on the dyno graph, and the tyres/gearing 7050rpm is what i get, which is miles off 8k unless you have a different 3rd gear or final drive ratio

also your speedo should only be ~2.3% out

[JetspeedCamry]

for a 4A-GE, absolutely.

Every dyno I've seen for one, they make power pretty much to the limitter, peak torque is @ ~6000RPM. So what you want to do is change gears so your rev's aren't far from 6000 at the end each change. That's where the bight of the engine is and the engine will pick up it's speed better from that point.

This is exactly what i've been told. Optimum shift is archieved if the RPM's AFTER the shift is at the peak torque point. This means the engine will pickup after the shift much better. If shifting is done AT the peak torque point, your acceleration after the shift will be slower since your not producting as much torque.

[Hiro]

In my opinion, it's a bit of Column A, Column B, and it all depends on the characteristics of the car you drive. There is no point thrashing the car long past the torque peak when it would be better spent shifting up a gear and getting the engine back into it's mojo zone. On the other hand, if the torque curve is relatively flat after the peak, then keep it revving instead of changing gears.

In short:
If the torque curve drops off rapidly after the peak, then shift
If the torque curve is relatively flat after the peak, keep revving
If it's in the middle, then rev for a bit then shift

If the curve drops off faster after the peak than it climbs before the peak, then obviously shifting early is better. However, if the curve is flatter/fatter after the peak than before, then it is beneficial to wait for the point where the gear change will drop the engine back to near it's peak level

[jonra23]

The optimum point to change gears is at the point that the gear above the gear you are in produces the same or more torque than the gear you are in.

To work this out you have to stagger torque curves for each gear and where they cross over is optimum change point.

This is not affected by final drive ratio as it only the gearbox ratio splits that determine the rev reduction between gears.

http://www.bgsoflex.com/shifter.html for a fairly basic online calulator.

regards
jon