In looking at dyno sheets, is it best to shift at the rpm's where it shows you are making the most torque or the most horsepower, or does this even play into the equation? This is with a M6.

 

Shift at a point higher than your peak horsepower, all cars are different depending on tranny and overall car gearing.

 

When your HP starts to drop off, it's time to shift. You'll be accelerating less (feet/second) if you let the rpms go above where HP starts to drop off.

Torque is the amount of work done, HP is how fast the work is done. Your goal is to keep the rpms near the peak HP all the way down the track so the work is being done as quick as possible.

That's why race cars like mine have a converter that stalls very high. It never lets the rpms drop below the stall speed all the way down the track. After I launch, my rpm window is 5700-7400 rpm right where the HP curve flattens out at the top of the curve.

Some people will short shift through the lower gears to get into high gear. Once in high gear, it's a brute strength pull to the finish line. ET will usually be slower but also more consistent.

I normally shift (2 speed) just before half track. If I was throttle stop racing, I'd probably be shifting just after the 60' mark.

Read this
http://www.hardtail.com/techtips/hpandtorque.html

 

With a manual transmission, if you have dyno numbers, you can calculate out the power delievered to the wheels in each gear at a given rpm. Once it is higher in the next gear up, it's time to shift. Or, you can folllow the advice above about shifting a ciouple hundred rpm past peak power, which usually ends up about the same. With an auto, the calculation wouldn't be quite the same, but practically speaking the same rules apply and it is best to shift a couple of hundred rpm past peak hp.

Rich

 

I'd love to dive deeper into that discussion and pick your brain. Specifically the auto part.

Given this dyno graph (real numbers from my 350 LE setup VS computer simulation of the new 355 setup)
It seemed to me that shifting higher (yellow line) yielded a huge advantage
in the 1/4 VS shifting at my current lower shift point (blue line)
Spending more time above 375rwhp and avoiding the dip below 250.

Is there more to it that I am missing?




I'm in the process of finishing up the install, which will be followed by a shift point change
(governor weights and springs in my case)
Those changes are a bit of a pain, so getting my target RPM right the first time sure would save me a lot a trouble.

Someone pointed out to me the other day that I should in fact be looking at peak TQ, not peak HP.
That doesn't seem to make a whole lot of sense to me.

 

Just eyeballing it, you should be shifting at about 6,500rpm with the new combo. Think about that versus shifting at ~5,500 - which is where you would be if you shifted a couple hundred rpm past peak torque. You never want to drop much below peak torque, ever. That why you never see a properly set up race car with an auto tranny that stalls much less than peak torque.

Don't even think about torque for racing - think horsepower. If you want to get a little insight into why, ask yourself which would accelerate faster - a Corvette with the LS7 (505 horsepower @ 6200 rpm 475 lb.-ft. of torque @ 4800 rpm) or the same car if you dropped in the 6.6L Duramax (365 horsepower @ 3200 rpm 660 lb.-ft. of torque @ 1600 rpm). Assume the engines weigh the a same, for the purposes of the experiment.

Rich

 

Rich, I must be missing something really important here. Forgive my ignorance.
I'm not arguing here, I'm simply looking for an explanation.

Why would I want to shift so soon after peak HP?
There's still plenty of meat between 6500 and 7000 that could be used
instead of dropping to 3500 where I don't have nearly as much power.
Is there something about declining HP that makes it bad?

I mean 375hp should be just as effective at accelerating a car on both sides of peak. Right?

 

We are on the same page, I looked quickly at the graph and just eyeballed it. You will need to do a little experiementing, but you should go AT LEAST to 6,500.

Rich

 

Yeah, experimenting is time consuming with this non-e setup.
I'll get a new dyno once the new motor is broken in, set it and see what I can do at the track.

I'm needinto log some data before I decide what I want to do with the rear end anyhow.