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Old 10-07-2003, 19:42   #1 (permalink)
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Calculating RPM drop from gear change?

Hey guys.

Just wondering if anyone can help me out with calculating how much gap there is between gears in terms of rpm.

Gearbox ratios are
1 3.50, 2 2.14, 3 1.39, 4 1.00 (5 speed manual)

Taking 1st gear to 5500rpm, and the rest to 5000rpm, what, rpm would the next gear be at?

Also, 5500rpm, 1:1 gearbox ratio, 3.9 diff, MPH running stock 15" tyre height?
Any help would be great.

Simon
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Last edited by Bass Crazy; 10-08-2003 at 00:02.
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Old 10-07-2003, 20:13   #2 (permalink)
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Re: Calculationg RPM drop from gear change?

somone sounds like they are getting serious about the 1/4 :)

give me 2min and ill work it out dude
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Old 10-07-2003, 20:32   #3 (permalink)
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Re: Calculationg RPM drop from gear change?

Well if you were using 205/65/15's your speeds would be as such

1st to 2nd 2137rpm drop @ 49km/h (5500 to 3363rpm)
2nd to 3rd 1752rpm drop @ 73km/h (5000 to 3248rpm)
3rd to 4th 1403rpm drop @ 113km/h (5000 to 3597rpm)

top speed
1st 49km/h...30m/h
2nd 73km/h...46m/h
3rd 113km/h...71m/h
4th 156km/h...97.5m/h
5th 224km/h...140m/h (assuming 0.7:1ratio at 5000rpm)

any more help just ask
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Old 10-07-2003, 20:41   #4 (permalink)
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Re: Calculationg RPM drop from gear change?

well. 5500rpm in 4th gear equates to

172kmh or 107.6mph
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Old 10-07-2003, 23:57   #5 (permalink)
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Re: Calculationg RPM drop from gear change?

FANTASTIC!!

Thanks heaps for that. I need this to adjust the switching points on the runners of my manifold for this weekends drags. At the moment, its switching at 3500rpm. This is the best switch point for 1st gear according to the dyno(rate of rpm pickup), however, it is most likely setting the car back down the 1/4.

Might bump it back up to 3800rpm to give me more torque in 3rd and 4th.

You are a champ!

Simon
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Old 10-08-2003, 00:20   #6 (permalink)
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Re: Calculationg RPM drop from gear change?

be nice if mine was adjustable......stupid EL ECU
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Old 10-08-2003, 00:33   #7 (permalink)
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Re: Calculationg RPM drop from gear change?

LOL.. at least you get the ignition alterations!
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Old 10-08-2003, 03:49   #8 (permalink)
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Re: Calculationg RPM drop from gear change?

Someone needs a 2.95 ratio first gear box.
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Old 10-08-2003, 04:49   #9 (permalink)
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Re: Calculationg RPM drop from gear change?

I know! The car would drive so much better with closer gears and a taller 1st, too bad it will cost me some decent $$$$ to do :(
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Old 10-08-2003, 04:53   #10 (permalink)
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Re: Calculationg RPM drop from gear change?

Also, with such a short 1st gear, I'm guessing I'd have to change to 2nd before the 60 ft mark? Provided there is no wheel spin that is.

My previous 60ft times are around the 2.1-2.2 mark with 3.23 diff.

Simon
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