Had a interesting thought....
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From: Foster City, CA
Originally Posted by JonBoy,Aug 2 2007, 02:04 PM
Most of you are looking at it the wrong way.
Let's say your 1st gear is a 4:1 and 2nd gear is 3.5:1, the car redlines at 7000 rpm but makes max power and consistent torque at 6000 rpm (and drops off torque thereafter).
If you multiply the 1st gear ratio by 85-90% of the peak torque, it will invariably be more than the 2nd gear ratio multiplied by 100% of the peak torque.
Ergo, you have less "apparent" torque at the wheels, which means the car will accelerate more slowly.
There are some cars where short shifting (which is what this is called) makes sense, but generally most cars benefit from being wrung out all the way to redline.
Of secondary importance, the higher you rev in one gear, the less "fall off" you'll get in the next gear, meaning you'll be at a higher power/torque peak as you shift to a higher gear.
Let's say your 1st gear is a 4:1 and 2nd gear is 3.5:1, the car redlines at 7000 rpm but makes max power and consistent torque at 6000 rpm (and drops off torque thereafter).
If you multiply the 1st gear ratio by 85-90% of the peak torque, it will invariably be more than the 2nd gear ratio multiplied by 100% of the peak torque.
Ergo, you have less "apparent" torque at the wheels, which means the car will accelerate more slowly.
There are some cars where short shifting (which is what this is called) makes sense, but generally most cars benefit from being wrung out all the way to redline.
Of secondary importance, the higher you rev in one gear, the less "fall off" you'll get in the next gear, meaning you'll be at a higher power/torque peak as you shift to a higher gear.
But, sometimes people claim differently for certain cars like the evo. I have seen both schools of thought. I am more of the rev it all the way out crowd, but I think in some cases short shifting might work for the 1/4 depending on gearing, etc.
The evo for example takes a big dip up top as the boost tales off. The HP keeps climbing, but slower. My thought was so what? You should rev it out as the HP at 7200 rpms is still higher then the HP at 5000 rpms in the next gear. Some people agree some don't. I think it depends on what you are trying to accomplish maybe.
Joined: Apr 2006
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you want the most area under your power curve when you're considering your shifts, athat said going up to peak and then shifting and then going back down may have less area than say going to ur peak, going over it a bit, then shifting, and therefore starting higher. So your average power during that gear will be higher if you pass the peak and then shift than shifting at the peak (of course, your results may vary depending on engine nature and such). But in essence, timing your shift points is basically doing this.
Joined: Feb 2007
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From: Pawtucket, RI
It's very simple: for max acceleration you want to shift such that you don't gain or lose power in the next gear. i.e., you're far enough on the downslope PAST power peak in the lower gear that when you upshift you're at exactly the same power level on the power curve upslope (below power peak) in the next higher gear. This results in max area under the power curve TheDonEffect mentions above.
For engines with a lot of rpm "headroom" above peak power rpm, optimum shift rpm is different for each gearchange. Typically higher-rpm shift points in the lower gears, and slightly lower-rpm shift points in the higher gears (which generally have closer ratios)
For vehicles like the S2000, with peak power rpm so close to redline, for max acceleration you will want to shift right at the rev limiter.
It can be that you shift such that you're always above peak engine torque. Doesn't matter, as keeping power to the ground maximized maximizes torque at the drive wheels, which DOES matter.
Another point: At peak power rpm, engine torque will by definition already have been falling off, yet you will still want to rev even higher prior to shifting.
For engines with a lot of rpm "headroom" above peak power rpm, optimum shift rpm is different for each gearchange. Typically higher-rpm shift points in the lower gears, and slightly lower-rpm shift points in the higher gears (which generally have closer ratios)
For vehicles like the S2000, with peak power rpm so close to redline, for max acceleration you will want to shift right at the rev limiter.
It can be that you shift such that you're always above peak engine torque. Doesn't matter, as keeping power to the ground maximized maximizes torque at the drive wheels, which DOES matter.
Another point: At peak power rpm, engine torque will by definition already have been falling off, yet you will still want to rev even higher prior to shifting.
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