what are you opinions on running a greddy TT at 5.5-7psi with 3.9FD? im looking to runn low boost for reliability till i build my motor. will 3.9 be over kill even with 5.5-7psi??

 

yes, torque numbers will be at 350 lbft or more with that setup. no first or second and most likely top of third for you. there is a reason why no one is running this setup.

 

im currently running 3.9 in the rear. i hav my stock 3.55 so i should put it back in.

 

yea traction becomes a major issue with the 3.9 as its 10% more power in very gear. it works well in conjuction with lower whp superchargers, but the high hp numbers the turbos put out, itll overwhelm it, and you'll have no traction.

 

it would be fun on some slicks though..

 

It has nothing to do with high or low hp, but where high torque leves are developed in the power band because gears are torque multipliers. It doesn't work well with a 300whp Stillen setup because it makes large amounts of torque by 3000 rpm and makes for tricky launches, but it'll work great with a 400whp CSC setup because the torque increases under 4000 rpm are more moderate. On a turbo setup, really depends on how its tuned and what kind of torque curve you get.

 

Is there a step down from the 3.9? What are the options for 2003 Z's?

 

You can get 3.3, 3.5, 3.7, 3.9, and 4.1 ratios to fit. I rounded some of these off.

There is a difference in the differential for the low and high gears. A MT can run 3.5 and lower. An Auto can run the 3.3 and (I think) the 3.5.

 

Alberto is running which gears? Can't remember.

 

6MT's come with the 3.538 stock. It is interchangeable with the 3.692, 3.917 and 4.083 for a rebuild.

5AT's come with the 3.357 stock. The ring gear design is different, so the only diffs available are the Cusco or the stock VLSD. You cannot swap the 3.538 for the 3.357 unless you do a complete rebuild and purchase a compatible differential.

To swap 3.538 to 3.357 its easiest to do a complete pumpkin swap with somebody who has a 5AT. If you want to go to 3.692, 3.917 or 4.083, you have to rebuild the internals.

 

I'm a Newb to the gear changing.

 

I have a 5AT VLSD. Well had. Sharif at ForgedPerformance was able to source me a used 3.538 ring gear and put in a carbonetics LSD at a great price. I guess that means he did a complete rebuild - I was so far into the build I didn't even ask . Thanks for your help helldorado in evaluating all the options.

 

I have a 5AT with a 6MT pumpkin swap.
I am a bit curious as to why this will not be a good gearing setup for a Greddy TT set for around 375whp.

 

I agree with Jeremy.. Would be fun with some slicks

Here you guys go.. I put this together when i changed over to the 4.083 gears.. I dont have FI but this will give you a idea of how the final drive will change each of the 6 gears.

https://my350z.com/forum/engine-and-drivetrain/301451-4-083-gears-final-drive-installed.html

Todd

 

Bert is running a 3.3 fd.

 

How do you like the Carbonetics diff?

Did you follow the extensive break in routine?

 

I also have a 3.5 in my 5at with the greddy twins and i think it a great choice.But i had to put in a vb so i would stop bouncing off the rev limiter everytime it shifted when stomping the go pedal.

 

Same here on the Greddy.
I think its better as get the longer throws with the power to push it.
Alberto will definitely have more info on this for you though.

 

So, did he swap with an 5AT? And from my understanding, wouldn't a 3.3 final drive lengthen the times between shifts than the stock 3.5xx? So in theory, shouldn't/wouldn't it be faster with the stock gears vs a 3.3?

Smaller # = longerbetween shifts/and higher top speed

Larger # = Shorter between shifts/but a decrease in overall top speed

Correct me if I'm wrong.

 

Cool, glad to hear that in works well in real life. BTW, GTM VB is next on my to-do list.