06 GTP Vehicle Performance Predicter Spreadsheets

[mbiker97]

I updated a spreadsheet that I had from my engine design class. It shows acceleration, traction ability, and gearing speed limits based on some common factors.

I have a couple of them done. 06 GTP with the stock LS2 all seasons, 06 GTP with a 245/40-18 tire (my new size), and the 07 GT with the sport option (3.9L and 6 speed), now a 06 GTP with an auto.

My work computer won't let me access my ftp, and I run open office on this one so unfortunately I can't post any graphs right now.

Long and short of it is that our gearing sucks, and that you should always shift at redline for maximum acceleration.

06 GTP w/ 6 speed

06 GTP - 6 speed - with 245/40-18s

06 GTP - auto trans

07 GT w/ sport package

Here are some of the acceleration ability charts.

06 GTP with a 6 speed.


06 GTP with an auto


Comparison between 06 GTP manual and auto


Shift points are based both on the torque curve, and your gearing. Since the torque curve is so wide on the 3.9L and the gearing is so far apart the lines never cross so shifting at redline will always be the fastest way.

As you can see the gearing with the manual is way better for acceleration than with the auto. This is all theoretical though, and can't account for missed or slow shifts.

[TLS2000]

Sorry, I need an education on the shift point here. I thought that the torque curve determined your shift point and not the gearing?

[mbiker97]

Sorry, I need an education on the shift point here. I thought that the torque curve determined your shift point and not the gearing?

Nope. If acceleration of the higher gear is more than the acceleration of the lower gear than that is a shift point. As you can see with the spacing of our gears the lower gear will always accelerate faster than the higher gear. I have other ones where the accel curves cross (which would be a shift point), but they are on cars with more geometric gearing than we have.

[TLS2000]

Well, I understand that, but what I'm getting at is that if you have a great torque curve, like we do, your car will always be accelerating best at a lower gear. I dunno, I'm still confused.

edit: What I'm trying to say is: Please dumb it down for us common folk.

[mbiker97]

edit: What I'm trying to say is: Please dumb it down for us common folk.

Okay try this......with our gearing (6 speed mind you) you will always accelerate faster using the lowest possible gear.

...and with the provided math data I prove it. Acceleration is just a formula like most other things engine related. The sheets linked above just uncomplicate the complicated if you just look at the charts.

[TLS2000]

Ok, I agree with you that redline is the best shift point, but I still don't see how the gearing influences that more than what the engine puts out.

I'll go over the charts once more to try and figure it out some more. lol

[TLS2000]

Ok ok, I've got it now. Gearing AND the torque curve BOTH determine the shift point.

Damn I feel stupid tonight.

edit: I had to REALLY think about how gearing works to figure that out. I must be too tired or something.

[mbiker97]

Since the output has to go through the gearing, gearing is everything.

Check out this one for the STi:

http://freebmw.net/mbiker97/Smart/Vehperf%20STi.xls

If you notice the acceleration charts cross each other, which would be shift points.

BTW good work on figuring it out yourself. I had to edit the last section of the STi one since I redid the polynomial equation for the torque curve earlier today.

I'll check the STi sheet tomorrow with excel to make sure it is correct.

[blkGTPcoupe]

since it's best to shift at redline and from those charts, the manual can basically max out speed wise in 3rd, which is the same for the 4 speed auto, is the manual actually noticeably faster than the auto since you wouldn't even be using the higher gears?

[bristol16]

3rd gear tops out at 100mph for me. so i would need 4th to hit the top speed limiter.

[mbiker97]

You can only go just over 100 with 3rd from my charts too. You have to go to 4th to hit the speed govenor (if your car has the one at 114).

I'll find some time this weekend to make one up for the 4 speed auto.