4.08 or 3.90 gear questions...

6MT

I was wondering when zatzuma would chime in on this thread. He tried the 4.08's. His results were: first gear was useless. Second was better, but pretty hard from a stop to start in 2nd. He changed it back to stock after a short time.

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Andrew

2009 370Z Sport/Touring 6MT sold
2013 Honda Civic Si coupe D/D

m4a1mustang

Most of the people interested in 4.08s are N/A guys worried about 1/4 mile times, though, so you'd imagine they'd be running a tire that could put the power down.

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BrianMSmith

I did a 3.42 to 4.11 on my last car, Camaro SS, and the difference in performance was astounding. You feel it most in the mid range, the engine has a much better mechanical advantage over the wheels. This is a significant loss of fuel economy when driving on highway. If you drive a lot off highway it's not so bad because you can simply shift at lower rpm to compensate, which the higher gear is happy to do.

BrianMSmith

Oh, and in my Camaro (post above), with the 4.11s the gearing was similar to the stock MT6 Z between rpm and speed. So in the Camaro 1st gear was still usable for normal driving, but I would never use more than half throttle, just too violent and too easy to spin. In the Z, I agree that 1st gear will be useless with the 4.08s, you'll never need it.

Zat_Zuma

Not quite. I changed it over to the 3.9 gearset (5% increase)

Like it much better for all around driving. 1'st gear is out of RPM in 2 sec or less at full throttle. The 4.08's ran out of RPM even faster! It's no fun bouncing off the rev limiter that quickly.

Now that I've used the 3.9 gears for awhile, it seems normal for me to shift to second almost immediately after accelerating from a stop.

The rev matching (SRM) is a lot closer with the 3.9's vs the 4.08's.

In retrospect, I would have left the 3.7 gearset in with the supercharger as I'm always loosing traction in the first two gears at full throttle.

But in 3'rd and 4'th gears and the SC the acceleration is fantastic ...... right wheee!?

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Blakestyle521

Trying to decide which final drive would be best. I have a bone stock 09 370 nismo, that i plan on boosting with the gtm TT kit. This kit alone will give me approx 500whp. However, i want to do gears first. Any thoughts on this delema?

Tickwomp

FWIW, I'd have the shim kit on hand before starting the swap. It's faily inexpensive, but absolutely vital if you need it. If you don't need or use it, you take it back. If you need it, you could possible find yourself with downtime tracking the shim kit down.

370ZilverZ

Will a 7AT loose cruise control with a manual differential running 3.9 gears?

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370ZilverZ Journal

BMW Z4

XwChriswX

This is what I was thinking of doing with mine... From the 7AT ratio of 3.3 I believe? To just going for a Manual pumpkin which is still better than ours, instead of a full 4.08 swap... would this be worthwhile? Or a waste of time... and how does it affect drive-ability?

- Cruise Control
- Speedometer accuracy
- Tire Sizing to Compensate??

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370ZilverZ

Will UpRev take care of recalibration of the speedometer? Is there an option to input your final gear ratio in to make that correction? I was planning on scheduling an UpRev tune as soon as I install my exhaust the end of the week, but will change out the rear diff first if the UpRev will make the speedo correction too.

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370ZilverZ Journal

BMW Z4

370ZilverZ

Quote:
Originally Posted by daemon1957
Will a 7AT loose cruise control with a manual differential running 3.9 gears?

This is what I was thinking of doing with mine... From the 7AT ratio of 3.3 I believe? To just going for a Manual pumpkin which is still better than ours, instead of a full 4.08 swap... would this be worthwhile? Or a waste of time... and how does it affect drive-ability?

- Cruise Control
- Speedometer accuracy
- Tire Sizing to Compensate??Any help out there? Please

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370ZilverZ Journal

BMW Z4

cc370z

In another post I asked about CC as I do a lot of freeway driving. The lost in mpg doesn't really matter to me. I've been told that yes for sure you lose CC as the wheel/speed sensors are affected. But then I was told by another member that he's works on and off. Are there no tunes that can fix this? I've talked with a few local shops and no one has an answer.

OKC Z

I wanna do 4.08's on mine but I was told that by changing tires is like changing the gearing ratio? I had never heard anything about that. Can someone confirm how accurate this will be. Im running drag radials 285/40/R18. Wel Im one of those guys that is worried about 1/4 mile times. But I dont have money for FI. I wanna get my Z into the high 12's all day. Thanks

tranceformer

That drag radial is slightly taller than a stock sport package tire.

Specification Sidewall Radius Diameter Circumference Revs/Mile Difference
275/35-19 3.8in 13.3in 26.6in 83.5in 759 0.0%
285/40-18 4.5in 13.5in 27.0in 84.7in 748 1.5%

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Ray
2009 370Z Base Sport 6MT / 12.860 @ 109.09mph / 1.921 60ft / street tires
official 1/4 mile track times

OKC Z

Thank you, I gave u some rep for that tranceformer. So ive increased my gearing by 1.5% or the tire? That is very minimal. To where the driver cant tell the difference. So if I install some 4.08 gears I should still benefit from ~10% acceleration increase correct? I was told it wouldnt make much of a difference once the tires were in place.