Is there any associated noise and or whine after installing the 3.9 FD?

 

Yep, lots of noise....like:

DAMN that F'in AT just took the hole shot away from me in my MT!!!!

OR

How'd you get here so fast? ...and the friend lives a QUARTER MILE AWAY!!!

I love mine - 5AT and 3.92's for about 1.5 years now - they rock. Remember - these gears are REALLY for track needs and 1/4 mile racing needs with a decent build-up NA or FI car. Not the best choice for a regular daily driver, unless your MT - then it's only a 10% change v. 20% for the AT.

You'll only get noise if the gears are not setup properly - hence the right place and the right shims!

I always wondered...5AT with 3.54MT gears...Cruise control? Yes or no?

Rick

 

If you're listening for it, there can be a little bit more gear whine. There's always a little bit more gear whine when you go to a shorter gear ratio on an equivalent diameter ring. The only time mine is even audible is on deceleration from ~40-30 mph if I don't have any other road noise.

I'd disagree. My car is my DD and I have no regrets going from the 3.358 to the 3.917. I'm only around 3500 rpm at 80 mph so its not that big of a deal for highway driving and I can still get 22-23 mpg on longer trips. Top gear on the 5AT is only marginally shorter than top gear on the 6MT. 0.834 vs 0.794.

If somebody was too worried about it, I'd tell them to go with the 3.692. That's what the new G35's are using and the transmission ratios haven't changed.

Yes and no. It doesn't work at all for some people, but for most, it still works at highway speeds in 5th gear.

 

Mine is a daily driver as well. As long you know what your getting into before you get them, then you'll accept some of the small drawbacks, like no cruise control and less mileage at freeway speeds, higher average RPM level/related car noise, etc.

Rick

 

3.9 on an auto is a bit different from a 6MT for the simple reason that the MT driver is shifting completely manually.

As far as the AT, the only real downside to the 3.9's might be the MPG. But in MT, I already feel as if 1st gear is a bit too short. So going to 3.9, it might be more of a hassle for DD on a 6MT.

As of now, I think ill stick to the stock 3.5. I bet 3.9's are great for the track, but I will lose alot by going 3.9's on my daily driver. I do alot of city driving, and like I said, 1st gear already feels short enough on my 6MT.

I think 3.7's or 3.9's are great for a 5AT, even if its a DD. On a 6MT, it might get a bit tiresome [for DD].

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Have most of you gotten your gears installed at a specialty shop, or can dealerships usually install them?

 

I'm thinking about the 3.7 and Quafie setup for my 5AT, can someone explain the loss of cruise controll, what does a gear change have to do with it??

 

The vehicle speed sensors will be out of sync with the gears - and therefore, the cruise control will not work.

 

I thought the speed senors where at the wheels and only changing the diameter of the tires would effect them

 

There are 3 different sensors that the computer takes samples and comparatives from. I don't remember all 3 right now, but the wheel speed, trans speed and another.. When numbers don't match up, within a certain % - the cruise wont work.

I have heard of some 3.3 conversions to 3.5's that still work..and some 3.5's to 3.7's that do as well, but rare and not at all reliable operations.

Rick

 

Thanks, I'm going to have to think about it more now

 

Alot of people are switching to 3.3 gears in 500hp cars. Anyone hear of than on here?

 

There is something to be said for high HP and high gears. Some, at certain HP levels and combinations, will see better times due to better traction and longer gear usage, in comparison to the shorter gears.

There is such a thing as too much gear, or not enough, or the improper amount of gear for the specific application.

I would venture to guess that most who convert, really use their cars everyday, and mileage and effect on the car suffer, when the RPM's are constantly 1000RPM's or higher on average freeway or other trips. I.E. a car with 3.92 gears will average about 3600 RPM at 80, and about 3000 at 60 - not 2000'ish.

The raw power at those levels, outweigh the gearing much of the time, unless the car is purely a track car. Keep in mind - cars like the Z06 have sub 3.* gear FD ratios. They are extremely efficient, pack lots of power, still hit low 12's off the show room floor and have great top end...

Rick

 

The ECU compares the wheel speed sensor to the transmission speed sensor. When there is more than a (IIRC) 7 mph difference, it kicks the cruise control off and will not let you reengage it until the car is shut off for 10 seconds.

Trust me, I know. I swapped from 3.3 to 3.5 gears and can't use my cruise above 75 mph. When I plug in Cipher, the transmission speed will show about 81-82 mph while my wheel speed (the actual speed the car is traveling) will show 75 mph. Speedo maintains the correct speed.

As to another comment earlier about not ever hearing of the speedo being incorrect with a gear change, most older RWD cars have the speed sensor (an electo-mechanical device) mounted on/in the differential. When the gears are changed, the speedo sensor is thrown off. This is an easy fix usually, as all you have to do is install the correct sensor for the gears being used. Corvettes (owned one) and Mustangs (according to another poster here) are well known for this issue. I'm not sure if the C6 or even C5 vettes have the speedo sensor issue. I know my C4 did.

 

Good point.

FYI: C6 Z06's are about mid 11 second cars (potentially). Yet they still average about, if not better gas milage then our G35's

Now that's excellent gearing efficiency!

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