when to shift during a race

[low&slo16]

hey i have a 98 civic ex d16y8 i/h/e with stock tranny. and i was wondering when is the best time for me to shift during a race. my friend says around 7100-7200 rpm but that sounds way too high to me.

[clawhammer]

What's the redline? My 91 CRX with a d16a6 i/e has a redline of 6500, and when racing, i shift between 6700-7000.

[curtis73]

The best way to do this is to know where the HP peaks. You should shift just above the HP peak so you're always dancing around the peak power.

[Whisper]

Originally Posted by curtis73

The best way to do this is to know where the HP peaks. You should shift just above the HP peak so you're always dancing around the peak power.

Best advise. Peak power is usually slightly lower then redline. (Check the dyno sheets)

[low&slo16]

Originally Posted by clawhammer

What's the redline? My 91 CRX with a d16a6 i/e has a redline of 6500, and when racing, i shift between 6700-7000.

my redline is at 7000, how much danger is involved when u take it past redline but only about 200-300 rpm past

[curtis73]

It depends on many factors. I have an Olds 307 that redlines at 4500. I could spin it to 6000 or more without damage, but the cam and headflow prevent that. In that case, redline is strictly dictated by where it makes power. High-strung 4-cylinders are typically limited in that realm. Getting 4-cylinders to make adequate power for the world to buy them means they usually spin at or near their limits.

That might be a question for a honda tuner and you might get one here. If you don't, there is a Honda forum here that might.

If you rev past a redline that is dictated by powerband (like my 307 example) you don't really run much risk. If you spin one past redline that is dictated by design parameters you run high risks. Piston inertia at redline can top 3000 Gs. 3000 times the weight of the piston itself is suspended on the pin. At 7000 RPMs, that weight is cycled in opposite directions 233 times per second. Keep in mind, too that inertia is exponential. The amount of Gs you add going from 6000-7000 might be on the order of six times more than going from 5000-6000 RPMs. It depends on rod/stroke ratio and piston acceleration, but that's a different topic. I guess what I'm saying is, going from 7000-7200 rpms might double the Gs on the piston and cause more stress than we imagine since we tend to think of it linearly. If the pins and piston are up to it, it might be fine, unless...

If the pistons are up to it, the oil pressure may not be. The inertia also pulls harder on the oil barrier in the bearings and can shear allowing metal to metal contact. 3000 Gs on a bearing might not be pretty. The other factor (which is probably not a consideration on your OHC engine) is valve float. If the spring pressure on the valves can't close it in time you hit valve float. If the tolerances are close, it could let the valve float long enough that the piston contacts it. On a stock engine, none of this is really applicable. Almost all engines are limited in their ability to breathe, close valves, and most have RPM limiters to keep you really safe. They are designed so that valve float can't contact the pistons. They design them so that the limiting factor is fuel, breathing, or electronic; not self-demolition I only mention it since if you're a racer it means you've already modified it or you will be soon Then you alter the limiting factor to something else. Here's where a Honda tuner needs to take over since there are others who know max RPMs and the shift points for several Honda combos.

[cshky04]

With your engine....You should be shifting at 6700 RPM's ..... so either adjust your light, or watch the tach and shift just before your hit redline. Your peak power is made at 6600 rpm's.... considering the i/h/e and just to be a little above that, shift at 6700... Some people have their engines making peak power 1-2000 rpm below redline. It's very strange to beat another car without winding up the engine to redline, but thats whats best.