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VHR + FD Gear Ratio upgrades - 3.9 and 4.08

Originally Posted by wstar You? I'm starting to really think about just moving mine up to the 6MT's rear end (3.692 instead of 3.357 that came with my 7AT). I

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Old 08-05-2009, 10:46 AM   #1 (permalink)
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Originally Posted by wstar View Post
You? I'm starting to really think about just moving mine up to the 6MT's rear end (3.692 instead of 3.357 that came with my 7AT). I need to go run the numbers again and think about high-speed RPMs more though (that, and wait for a programmer like UpRev that can tell the ECU about it too)....
Why do you have to "wait for a programmer like UpRev that can tell the ECU about it too?"

Maybe i'm wrong but...

I do not see the reason to advise the ECU.

If you call a gear downshifting, ECU-tranny will give you it anyway, just checking the RPM, not speed...

Or I'm wrong?

Anyone has experience with changing ratio in AT (infiniti, 350Z etc)?

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Old 08-05-2009, 11:14 AM   #2 (permalink)
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Quote:
Originally Posted by javol View Post
Why do you have to "wait for a programmer like UpRev that can tell the ECU about it too?"

Maybe i'm wrong but...

I do not see the reason to advise the ECU.

If you call a gear downshifting, ECU-tranny will give you it anyway, just checking the RPM, not speed...

Or I'm wrong?

Anyone has experience with changing ratio in AT (infiniti, 350Z etc)?

Bye!
I meant so the speedo will be correct.
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Old 08-05-2009, 11:22 AM   #3 (permalink)
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Oh and as far as upgrading the rear end ratio in the 7AT, aside from spacing out all the cash I'm throwing down, and having to consider whether I want to get rid of VLSD while I'm at it (perhaps the 1.5-way Carbonetic that Mike@DDM likes so much), the other thing holding me back is I'm not sure if it will make 1st gear too short. The 1st gear ratio on the 7AT is way out there compared to the 6MT. In stock form on the sports model, 1st gear ends at about 36mph @7500rpm.

My tire/wheel upgrades that are coming soon (moving to 295/30R18 in the rear) already drop that number a bit, and when I ran the numbers, the combined effect of the tire/wheel change and moving to 3.692 in the rear would put 1st gear topping out at more like 30mph @7500pm. 1st gear already ends so quickly that it makes timing the 1->2 upshift optimally challenging, so I'm worried this will make it insane. On the other hand a higher redline from the ECU stuff would offset this a little. We'll see what happens when I get to all this I guess.
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