I am thinking about putting these in my car, my dad is a mechanic and should be able to do it. I just need alittle info.


prices and where to buy
any special tools
should I change the lsd
any one have a procedure
any one have pics
list of all parts to do it right



Thanks guys

 

Here is some Starter INfo;

https://my350z.com/forum/showthread....hlight=pumpkin

 

Quick question- what does this mod do?

 

If you have to ask you don't need it.


Search is your friend.

 

it changes the gears in the diff



it makes your gears shorter and you will run through them faster, but loss of top speed...

 

1. Your car will accelerate or pull much faster, but also shift sooner because every gear is shorter. 1st gear will go by really quickly.
2. You will lose cruise control, due to the ECU not being able to adapt to the new gearing. (Doesn't always happen)
3. Your mpg will lower by about 2-3 mpg. This happens because you will be in a higher RPM in every gear, due to the shorter gearing. The higher the RPM, the harder your motor works, the more fuel you burn.
4.Your top speed will lower by about 10-15 mph. This occurs to the shorter gearing. You sacrifice top speed for faster acceleration. This doesn't really bother most people, because no one really tops out their car every single day. Top speed is about 165 for the coupe, your new top speed with the 3.9FD will be about 155.
5. Buck for buck, this mod is the best bang for your buck. You will lose about
.2-.4 seconds off your 1/4 mile time, and also shed about the same off your
0-60.

This 3.9FD isnt good for FI cars. For one reason, 1st gear would basically be useless, as you will not be able to get traction. If you have FI, taller gearing (3.2 out of a 5AT) would be better, as your able to stay in your powerband longer and also gain in top speed.
(Im from G35driver.com - chilibowl )

 

I actually Gained 2.2mp gallon with a move from 3.3 to 3.5 gears for some reason. Best I can figure is my car isnt down shifting as much in the hills. (There are no level stretches of road at all in this state it seems).

 

no with the 3.9 final drive your top speed is 166mph with the 287hp engine and 176mph with the 300hp engine

the ECU limits it to 160mph either way unless you remove the limiter

FYI, the stock 3.5 final drive is geared for 184mph with the 287hp engine and 195mph with the 300hp engine

you'll never reach those speeds and overcome the aerodynamics though without FI



the 3.9 gears work just fine on the street - it's faster accelleration. Driving on the highway will lose 1-2mpg, but you'll also notice that 6th gear actually becomes useful for passing - it's pretty noticable at higher speeds as well as faster low speeds. You get a lot more oomph in each gear.
city mpg is about the same cause you'll just shift into the next higher gear.

to get an idea how much it helps other than accelleration, look at a dynochart. Say you were going to race someone on the highway starting at 60mph
A normal Z would be in 3rd gear at 4350 rpms
Your Z with the 3.9 FD would be at 4800 rpms in 3rd gear
you'd be not only further up the power band with more power (this works especially great with a centrifugal supercharger btw), but the gearing is 10.74% stronger (3.917/3.537)

 

Wow thanks for the responses guys.

So basically is if ...
1. I go NA -Yes to 3.9 FD
2. Turbo -No to 3.9 FD
3. Stillen SC- Yes to 3.9 FD (since its centrifugal)

 

There is also a 3.7 gear too that might be better suited to supercahrger applications.

 

there would hardly be a difference between a 3.7 and 3.9

I lost exactly 0 miles per gallon with my gears....I still get exactly the same per tank as I did when I got the car (325-335 miles every tank)

 

stillen is not centrifugal, and actually I'd stay away from the 3.9 gears with the stillen since the stillen's deal is making power down low, you'll just spin tires - vortech, HKS, and ATI procharger would work well

 

There is a pretty big difference between the 3.3 and 3.5... (Very Noticable when driving).

 

Theroreticaly, turbo kit with a boost controler that is set in a scramble mode will be able to utilize the 3.9. Set the scramble map to stock boost and the main map to the higher boost setting you will be able to hook it.

However this would only be useful for road coarses set to like 3 seconds; because every time you shift the scramble resets. The count starts over at boost. So any time under 0psi its not ticking time.

 

this is something i plan to do too, especially since i can get the Central20 for around AUD $550 through my Jap dealer

but can those with the 3.9 confirm whether they did lose their cruise control?

 

From what I understand, 5ATs loose cruise with the 3.9, 6MTs Dont. Please correct me if I am wrong.

From what Jason at Performance was telling me, the 3.7 Gear is much less expensive than the 3.9 and you won't loose criuse on the 5AT, but I cant seem to find the thread to support that, so I might be wrong there too.

 

thanks mate

 

Is there any way to correct that? Maybe a resistor in line with the Axel Stub sensors on the FD?

 

Yeah if this is true then whats with 4.11's? I know its a diffrent car but many old Muscle cars switch out to 4.11's. I know personaly I wad 4.11's in my 73 camero it out would not hook up for **** on my street tires but as soon as I put the beefy street slick on it, damn it would run. HARD! So how is an SC Chevy 350 MT any diffrent than the Z.... Except for the 800hp not hooking up on street tires.

Id say get a set of 315-325 Exotic/street legal race tire of your choosing and youd be hard pressed to spin em under 500WHP from (unless your trying to burn um), and when heated at a 35 role yeah They should pland well.

just my.02 from chevy v8 experience.