Shift Points

I've heard differing theories on how to determine what RPM to shift at for maximum acceleration. They calculate RPM drops from one shift to another, which vary depending on the rear gear ratio, they also factor in the power curve of the engine, some say torque is the most important factor when determining your best shift point and others say horsepower is. I know that the best way to find the best shift point for my car will probably just be the trial and error method, but most of the time, their's very limited time for trial runs at my track so I'm looking for a simpler way ( if their is one ) to get a good ball park shift point to start at. I have a 350SB Chevy in a 3700 lb. car, a 350 turbo auto trans., a 3000 stall converter, and a 3.90 rear, it makes maximum torque at 4000 rpm and maximum HP at 4900 rpm. Any comments or suggestion would be appreciated.

 

the way its always been told to me, is that torque GETS you moving, horsepower KEEPS you moving. shift up right before you run out of the HP curve, and get it into the next hole before it drops below the torque curve. in other words, find the "sweet spot" in the rpm curve where you're making the best of both HP and torque. you have a dyno sheet for this mill?

 

how do you know where the peak hp/torque is comming in?{cam card?}4000rpm peak torque?thats pretty high comsidering that you said peak hp 4900!what kind of cam be you have that peaks out so low{i dont even think a stock cam peaks out so low}3000 rpm converter!!!holly cow batman!!why such a big converter.your slipping your converter the hole time.buy the time it starts to lock up you need to shift!!

 

i think you need to check out why your cam is peaking out so early.what are the #s?{hp/ft lbs}?any ways i have found out that for me the best rpm is about 500 after peak hp,that way when i shift im back in good torque and hp.but it still will take time at the track to dial it in.i have fun playing around with the shift points in my cars.just take your time and dont forget to {write down!!!!!} your times and shift points{dont think,i can remember them}!!!

 

A compelling theory I've encountered is that you want to shift at that point where the power you're making just after the shift is the same as the power you're making just before the shift. That means, shift at a few hundred rpm over the power peak rpm. Just how many hundred will depend on the ratio spread of your transmission: the closer your ratios, the sooner you shift.

Don't worry about the power/torque thing. Power is the rate of torque: they always go together. It's almost two ways of seeing the same thing.

 

Thanks for the reply. Those numbers are from my dyno sheet. The cam is the one that was in the 350/290HP crate motor when I bought it ( Lift: .450" I, .460" E, Duration @ 0.050": 222Deg. I, 222 Deg. E ) . I changed to Vortec heads and an Air Gap intake. I probably should upgrade the cam, but I wanted to see what it would do with the cam that's in it now before I make a change.

 

Correct to a point. The objective is to have the engine in the regime where it makes maximum horsepower.

The problem is that lots of motors are redlined before the power drops off enough for this to happen. In that case, you shift at the redline. Power available after the shift is not as much as before the shift, but increasing RPM past redline is usually not recommended.