915 Custom gearbox questions

[jjwood]

Here's the "projected gears"
1st --- 11-35 3.18
2nd --- 17-34 2.00
3rd ---
4th --- 23-29 1.26
5th --- 26-26 1.00

Here's the questions
a) what would you suggest as a good 3rd gear choice?
b) given 8:31 R&P and 315/35x17's what should I anticipate top speed in 5th at 7300RPM?
c) does anyone have a "used" contact source for the suggested 3rd gear choice?

thanks,

[Peter Zimmermann]

Jeremy; you will have to plot your gear ratios on a chart that shows rpm drop between each pair of gears. Then you have to figure out why you need those ratios (AutoX, slalom, specific course time trial, etc.), and decide if they will work. In other words, you must have a reason to do a gearbox a specific way. After spending time with gear charts, found in factory manuals, you will have to measure the OD of your rear tires, and see if there is a significant difference in size from what was stock on your year car.

[Bill Verburg]

Originally Posted by jjwood

Here's the "projected gears"
1st --- 11-35 3.18
2nd --- 17-34 2.00
3rd ---
4th --- 23-29 1.26
5th --- 26-26 1.00

Here's the questions
a) what would you suggest as a good 3rd gear choice?
b) given 8:31 R&P and 315/35x17's what should I anticipate top speed in 5th at 7300RPM?
c) does anyone have a "used" contact source for the suggested 3rd gear choice?

thanks,

As Pete pointed out it depends on what you want from the trans

the 26/26 5th gives an awfully low top end of ~139 and some really funky drops to boot

I took the liberty of making a few changes




I still thank that its hard to beat the gearing on an SC/RS

[Dan J]

Dang you're quick Bill

[Peter Zimmermann]

Bill, awesome job! After I answered the OP I hoped that you would see this thread!

[Bill Verburg]

Originally Posted by Dan J

Dang you're quick Bill

One of the perks of retirement

[winders]

Bill,

What software are you using to generate those charts? I would like to get that infor for my transmission....

Thanks,

Scott

[kandhmfg]

I have messed around with this site. Fairly close. Plug Tire size or diameter, RPM, R&P Ratio and Gear Ratios. Easy to copy and paste into excel.

http://www.f-body.org/gears/