 Tranny ratios, diff, tire sizes and RPM's, ...is there one like this for Porsche |
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| boxsterfan |
 Sep 16 2003, 10:23 AM
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#1
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914's are kewl  Group: Members Posts: 1,776 Joined: 6-June 03 From: San Ramon, CA Member No.: 791 Region Association: Northern California  |
First of all, I will state that I am not a mathematical wizard. From my previous days restoring Datsun Z's, I would use this calculator to get my engine RPM and MPH on a Z-car.
Z Tranny Calc Is there such an animal for the 914? Should be able to plug in the tranny ratios and diff ratio and tire sizes on this one to get approximate results. |
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| porsche735 |
Sep 16 2003, 10:26 AM
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#2
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Member Group: Members Posts: 189 Joined: 10-January 03 From: Los Altos, CA Member No.: 127 |
I have one. Let me see if I can get it uploaded...
Chris Attached File(s) 
901transmissionratios.xls ( 21.5k )
Number of downloads: 83 |
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| porsche735 |
Sep 16 2003, 10:29 AM
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#3
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Member Group: Members Posts: 189 Joined: 10-January 03 From: Los Altos, CA Member No.: 127 |
Here is another one I used for scratch....
With this one I checked the % difference between the gears to choose the optimal setup. You can see we did the swap between 3 and 5 and then put an S gear in place of the old 4th. You could leave 4th alone, as you can see by the math, but it works out very nice with the S there. Chris Attached File(s)
Gears_on_Porsche.xls ( 19k )
Number of downloads: 121 |
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| john rogers |
Sep 16 2003, 10:31 AM
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#4
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Senior Member Group: Members Posts: 1,525 Joined: 4-March 03 From: Chula Vista CA Member No.: 391 |
You could go over to the Pelican site and download the GEARS.exe program I wrote a few years ago, it is in the 914 tech section. It lets you input gear ratios, tire diameter or turns per mile or circumference (most accurate) and final drive ratio and the slider will show RPM in each gear vs speed. Good luck.
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| porsche735 |
Sep 16 2003, 10:44 AM
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#5
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Member Group: Members Posts: 189 Joined: 10-January 03 From: Los Altos, CA Member No.: 127 |
John,
Looks like the same one I just posted. Mine has the gear ratios we tried highlighted. Boxsterfan, Take a look at the scratch sheet. What you want to do is make your percentage changes very even through the gears. We chose to make our 4th to 5th a lower percentage and chose a lower top end gear. This will give you close to redline (5700rpm) at the end of the longest straights on the West Coast (Thunderhill and Laguna Seca). The ratios are perfect for just about every track out here.... Chris BTW. the 22.8" diameter is a 205/50/15 bothe Hoosier and Kumho |
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| Brad Roberts |
Sep 16 2003, 11:12 AM
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#6
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914 Freak! Group: Members Posts: 19,148 Joined: 23-December 02 Member No.: 8 Region Association: None |
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