Hi all, thought I'd mention this here. FES has made a free shiftpoint calculator... It's a bit of an odd topic, so I originally posted it in the vendor discussions and it's not getting much play there...

thread link here

Download is here

Anyway, I figured the track rats might appreciate it.

Matt

 

Great post, Matt. Sure beats the heck out of plotting thrust curves in Excel!

I also like how the program accepts "total driveline" ratios instead of just taking the transmission ratios and the "final drive" ratio. A lot of cars (like the MINI 'S') have two different "final drive" ratios depending on what gear you're in, so being able to specify the overall ratio for each gear is the only way to get good numbers out of this kind of program.

 

so instead of having the hassle of doing some sort of excel like transmission description, total drive ratio per gear just seemed easier.

BTW, I did a bunch of searching on shift point calculators, and there are tons out there for sure. But none I've found includes effects for rotational mass. Try playing with those numbers, it surprising what happens!

Matt

 

If you have a program wanting final drives, can't you just put in 1 for it and use the total ratio where it wants the transmission ratios?

 

Two things,

1. Cool seeing inertia of the driveline components into account, hard to calculate but very useful if you can figure it out.

2. My beef with shift point calculators is always that keeping in a lower gear is always more beneficial because the transmission is multiplying the engine's torque more, meaning faster acceleration. What is your explanation there. Does it have to due with the equation for rotational kinetic energy, KE=(Iw^2)/2? If the needed change in rotational KE combined with the change in the cars kinetic energy becomes greater than the change that would have to happen in higher gear, with slower driveline components I could see where this makes sense.... maybe I should be thinking of this in terms of work... I'll have to pull out my text books and monkey around with the equations, this is basically what I am doing in my physics for engineering class so I may as well try and apply it to something.

 

You're correct that to maximize acceleration, you want to maximize the torque at the wheels. But that doesn't always mean staying in a particular gear all the way to redline. Depending on how quickly the torque drops off as RPMs increase, and how much the torque multiplication from the transmission/differential changes from one gear to the next, you may run into a situation where the loss in torque multiplication from an upshift is more than made up by the fact that you're lowering the RPMs and moving back down to the fatter part of the torque curve after the upshift.

All of this is in addition to the "effective mass" effects, which Matt explains in the thread he linked to in the first post.

 

True, but cars that behave the way you describe are arguable few in number. Likewise I am nearly certain that is not the case with the r53 (especially pre 05), hence my focus on the rotational aspect. It is not that I really disagree with what is being said, it is more that I am just curious about how the conclusion was reached.

 

1) Torque curve shape.
2) Gear ratios.
3) Inertial effects.

after that, it's just math. As far as our cars, it's the inertial effects that lower the shift points in the R53 (30 lb flywheel and an inertial effect that's based on the square of ratio of the gear ratios, dereviation is left as an excersize for the student! ). In the turbo, take a look at the torque curve. It starts to drop rather significantly over 5k or so. Take a look at the torque curve of pretty much any street driven N/A car, and they all have high RPM fall off. Variable valve lift and timing make the less severe, but it's present none the less.

Really, going to red-line and feeling that slam of power when you shift makes you feel like the best is happening, but it's not. Best shifts the accelerations would be the same both before and after the shift.

Matt

FWIW, the torque curves in the graphic above are from a stock 02-24 MCS....

 

This looks great, I can't wait to play with it.

 

so if you run into issues that aren't covered in the help file, e-mail me at mattr@fes-auto.com

Matt