VHR + FD Gear Ratio upgrades - 3.9 and 4.08

KLRCADI

In the Z33 world, the combo of the HR motors and upgraded Final drive gears in the R200 diff seems to be pretty potent combo, and really transforms the acceleration in the car. Especially in Modded NA cars. The 370 has a 3.69:1 ratio ring set. I am think 4:08's would drop another 3-4 tenths off the 1/4 mile times and really help the VHR get into the power range faster. I would hazard a guess that a fully bolted on 370z, with a 8000 RPM tune making 320-340 whp and a 4:08 gear would be a mid 12's car all day long. I think this would be the first mod I would do. The diff's are exactly the same, so anyone looking to do this can get everything you need to right now. I think the only question is the same we have about flywheels. What will happen to SRM? Thoughts?

Zat_Zuma

I was thinking the 3.9 gear set might be a better choice for all around driving. 4.08 seems a little too much of a high gear for the street and general everday driving

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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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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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RCZ

This sounds great, except I do a lot of highway driving at 85+. If not for that I'd be all over it.

KLRCADI

Man you guys drive fast! I don't see myself doing 122mph on a remotely regular basis. Anyhow, I think for the folks using the car as a part time car, or track toy, this is the ticket. I hope to move from my CTS-V into a 370Z in a few months. I had a 1990 Z32 2+2 With a 400 whp VG30DETT swap done for many years, and to date still one of my favorite cars. Looking to come back to the Z brotherhood and continue my sickness of Mod Hell on the Z. This will definately be something I look into ASAP.

wstar

Meh around here on the TX highways, big fat SUVs cruise the highway at 85. Low-speed driving with lots of corners is more fun anyways, but if the road is clear, the conditions allow, and my V1 isn't bleeping at me, I tend to get where I'm going with uhhh... maximum time efficiency

A lot of good mods are out and tested in the field now, it's a good time to get onboard

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NYBladeZ

I definitely agree that 4.08s are great for those looking to improve at the track. I had 4.10's on a 2004 Mustang GT and I loved them. It's an ongoing debate about how high of a gear can you go and still stay comfortable and I can say I drove around 10k on the Stang with no complaints. Low and power and torque were immediate and in the quarter mile it definitely made a difference. I say go for it, it'll probably need an oil cooler but if you're willing to spend the $ get a cooler also, full bolt ons plus higher gear=awesome. DON'T FEAR THE GEAR

NA&CH

First mod I would do. I alwasy wanted to do that to my 03 track. I barely touch the highway

Chris

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.

shabarivas

Do post his speeds and rpms ... very interested in details

RCZ

Roughly 80mph=3100rpm in 6th.

SOLISIMO

WHat should I get on my 5AT G37?