Project : Optimal shift points
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Project : Optimal shift points
Ok, let's find out where our optimal shift points are. In other words let's find out where the best RPM to shift at in any gear.
First we need someone who is good with spreadsheets...anyone?
First we need someone who is good with spreadsheets...anyone?
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I would think this would be pretty easy. Dyno your car. Find the highest point for the HP curve. Shift a few hundred RPM's above this so when you reengage the clutch, the engine is still in its peak powerband. I'm not sure what you can find with an excel spreadsheet. I just realized that whatever you find anyways doesn't matter, because it will change depending on the mods you have done to the car.
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From: Colorado Springs, Colorado, US
Rep Power: 0 Holy sh**t someone from Colorado actually posts in these forums???? I'm a noob, but I think our shift points will be different from other places because of our altitude too. Of course I could be wrong.
6800 it is! 
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From: bay area, california
Rep Power: 337 << Well, we'll find out won't be. The optimal shift point is not always redline... >>
actually, it technically is.
Drive Wheel Torque = (flywheel trq x gear ratio x Final drive x Efficiency)/ tire radius
RPM after shift = (Ratio shifted to/ratio shifted from) x RPM @ shift
this means, that even if you shift at 7200 RPMs (my own redline) you lose a SUBSTANTIAL amount of torque. in fact, the ideal shift point was way above 7000 to stay in a stock civic "powerband" but the fact remains, that the minimum power loss occurs at redline. so acatually, if you do teh math, you will find out that for at least 1, 2, and 3rd gear, optimum shift is redline. and there is good evidence to suggest that redline is best for 4th, too, but thats where my speed govenor hits [IMG]i/expressions/face-icon-small-wink.gif[/IMG]
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From: Ottawa, Ontario, Canada
Rep Power: 0 I once heard somebody say that optimal acceleration would be shifting so that you start the next gear at the point of maximum torque.... so 4500rpm for the LX/DX cars.... and 4800rpm for the Si's (EX in US)..... good idea? yes? no?
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From: bay area, california
Rep Power: 337 << I once heard somebody say that optimal acceleration would be shifting so that you start the next gear at the point of maximum torque.... so 4500rpm for the LX/DX cars.... and 4800rpm for the Si's (EX in US)..... good idea? yes? no? >>
read above, man. you dont want to shift to the point of maximum torque, you want to shift so that you have minimum torque loss. This is why a spreadsheet was reccommended. because you want to know your flywheel torque at every single gear, at every single RPM. that means 11 columns if you have increments of 500 from 2000 to 7000 RPM. If you did 100 RPM increments, you spreadsheet would be HUGE!
then you must take into account what RPM range you will be in after a shift, depending on what you shift from. again, its a huge spreadsheet if you do it with 500 RPM increments, much less 100.
But none of it really matters. noone in a race will shift at 3000 RPM, we can cut down complicity by focusing around our powerband, which, sadly, is half cut-off by our redline govenor. The fact is, that MINIMUM torque loss occurs at redline. every time.
these measurements were taken off an LS: (Honda Builders Handbook, Vol. II)
Shift RPM
torque loss in shift 5500 6000 6500 7000
1 to 2 772 762 669 630
2 to 3 375 375 310 287
3 to 4 193 185 137 105
4 to 5 115 103
you tell me what the units are, i dunno, doesnt matter. the point is, that you can see that you lose the smallest amount of torque at redline. period. So I really dont care what you "say" you can feel (cause I know that is coming) we are now talking about FACTS, and the FACT is, that you will get your fastest time by shifting your stock civic at redline, every gear.
if you REALLY wanted to, you could calculate the real points, but ti would be different for every engine (DX/LX, HX, and EX) and would just confirm what I just have stated here.
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Rep Power: 0 In 1st, 2nd, and 3rd gear i usually redline it myself. The engine feels like its got plenty more to give and I find myself bumping the rev limiter during some hard driving if im not watching the tach. What exactly is holding it back from say a 7500-8000rpm redline? What would need to be upgraded besides the ECU, belts, pistons, valves?
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