VHR + FD Gear Ratio upgrades - 3.9 and 4.08

ssqpolo

i agree. FD gear mods are pretty cool, but i drive on the highway alot, so i dont wanna be cruising at like 4500-5k rpm. oil temps are all ready high

wstar

Yeah that's a concern for me too. In the 7AT our rear end is even worse ratio than you 6MT guys (7AT is 3.357, 6MT is 3.692). However, at the speeds I like to cruise at on the highway (when possible), I don't want the revs going any higher in 7th than they are now. 7AT really could use an 8th gear (or just taller transmission gearing in 6 and 7 both) for us high-speed cruisers

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kannibul

Did you type that backwards on the ratio = transmissions part?

A 3.357 would give a lower RPM...


That, and I thought the rear on the 7AT's had a higher ratio...

jchammond

i'm a new member & have been looking over a lot of pages,,,,i am wanting to swap the 3.36 diff from my base/auto 370 for a 3.69 manual diff..
top end would still be the same-just closer to the 7500 redline in 5th.
currently limits out at 7k in 5th-showing 158mph on speedo.
dont drive like that a bunch/but it's an adrenaline rush!
has anyone done this and does it affect the traction control or cruise.
thanx for any imfo.

blueranger

I swapped the whole pumpkin from a manual 3.69 VLSD on my 7AT with the Z1 rear diff kit and my car runs much better and torquier! This swap did not affect anything on my car and everything works normal.

This is one of the best Mods you can do

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KLRCADI

It would not be anywher near that high. I used a gear calculator, and with a 4.08 @ 70mph in 6th would = 3000 rpm.

check out the link below for reference
[link]http://www.kabamus.com/garage/gears.html[/link]

I think this would rock, however, the more I think about it this might throw off the SRM more then a flywheel. The SRM system must have a preloaded wheel speed vs gear table. It probably see's wheel speed "x" for gear "y" and revs to rpm "z". The wheel speed will be off by 10%, meaning it would have to rev 10% higher for a given wheel speed and gear. So it might be 10% off on the rev match to engine speed. Then again I might be completely off on my assumptions on how the SRM works. Either way, I can't Imagine 10% off would make a huge difference in smoothness of the system. If you manually heel toe like a pro, I bet most are still off by a few hundred RPM. Anyhow, some needs to break the seal and try this out. It will be killer for NA setups.

wstar

Great, so I'll be at 3K when a cop is following me

With the stock 7AT setup, for example 4K rpm in 7th is only 122 (according to your gear calculator page, but it sounds about right). Moving to a 4.08 puts us at 5K rpm in 7th to reach the same speed. I might consider just swapping into the manual's 3.692 gearing though (once we have a programmer so I can tell the ECU about it).

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ssqpolo

nah man. im above 3k cruising at like 85-90. like 4k actually. i will let u know soon what exactly it is. but either way, its an awesome mod. actually, my friend in a 350 just put 4.08 gears in his. we're running tomorrow so i can tell u all how he feels about the mod.