4.08 FD vs Stock FD on tracks : your choice
 

Hello Guys,

I was wondering how many of you guy were on 4.08 FD for your track Z.

I'm asking the question because i have one somewhere in my garage, that i tested 2 years ago. It was badly setup (whine). I decided to rebuilt it (bearings and good pignon adjustement).

With it the car felt faster but was not in terms of straight line acceleration. I liked it on the track but i wasn't faster also... same speed at the end of each straights...

Since i'm gonna buy a Quaife diff, i thought it could be another chance to test the 4.08 FD. (and i know that i could put the quaife on my standard diff if it doesn't suit me in the 4.08)

So, for your track cars, 4.08 or not ? If yes, why, and are you faster on a overall lap ?

I precise i have the HR engine with PPE long tubes headers, Uprev, Stillen intake, so the car is quite happy between 5000 and 7600 rpm, but lacks of torque under 4000-4500. I find that 170 km/h (106mph) in 3 is really too much on twisty roads and mountains, and perhaps small tracks, and not really a problem on fast tracks like Le Mans (France)...

Thank you for your insight !:thumbup:

I ran 4.08 gears on my 2004 Track model when it was still N/A. While the gearing helped to pull the car out of corners, it required so much additional shifting (for me with the DE engine at least) that the overall benefits were just not there.

Matt

I have the 3.9 FD and yes I agree everything that was said. With that said tho, I'm willing to shift more and able to exit the corner with more TQ, especially combined that with my Cusco LSD. I have a Revup with PPE and intake/exhaust mods.

:)

Seem's i'm not the only one to have this impression...

Would be great if Terramask, Dkmura, 03threefiftyz could say what they use since they seem to be hardcore track Z users...

For information this italian guy said that the 4.08 FD fits perfectly his HR Z, and he seems fast...

I noticed that too on my HR when I tested it on a track for the first time a few days ago. In some 3rd gear corners the revs were dropping to 3000-4000 revs and there was just not enough torque to really push the car out of a corner with decent speed. Although I didn't have TC off completely (need to install the ESP killswitch) and that might have affected it too. I tried to shift down to 2nd a few times but that on the other hand was too high revs.
The car is great on a highway with these gear ratios but I think that I won't even get to use sixth gear on the Nordschleife with this set up!

I'm going to caveat this with the fact that my transmission gear ratios are different than a normal Z....

I prefer the 3.5 and have even considered going 3.3. I do have a 3.9 pumpkin that I used for a short while but it put my shift points on most GP style circuits in some cruddy spots. The 3.5 was faster than the 3.9 on the 2 courses (Nurburgring GP and Hockenheim GP short) that I have back to back data on with no other changes to the car. I would swap the 3.9 back in for autocross or rallye though or a particularly tight course.

SCCA rules mandate we use the stock USDM 3.5 final drive for the D2D racing classes I've competed in.

Hi, what gear ratio are you using ? Quaife gear set ?

With your gear ratio, what are the top speed in each gear ?

My Z with stock 3.53 diff and 4.08 diff and stock gearbox: (in kph)

1 : 65 58
2: 118 100
3: 170 140
4 : 220 185
5 : 270 ? 230
6: ? ?

I saw the same thing as you, it seems i was faster on stock ratio, but sometimes the car lacks torque when i go out of corners with the stock FD ...For example at 100kph when i'm on 3rd it's lacking juice, and it's too high for 2...

Some owner of 4.08 say that the car loose some top end, like if the car looses some power... I felt that too...thought my diff wasn't correctly set up (some noises and heat). I'm rebuilding it, and since i just received my Quaife it's worth the question on which one i should install it...:confused:

The guys who says the 4.08 is miles better are the one who don't use their car on the racetrack and only use their buttdyno... I have trouble to find someone who says with facts that the 4.08 is better on the racetrack (roadcourse)... except this Italian guy...

I've got a T-56 Magnum short ratio gears.

Attachment 385092

I've got no shortage of torque... anywhere. But thats because of the motor. Thinking back to before the swap, I think I would still stick with a OEM gear ratio unless you are going for 1/4 mile.

Man, all of you make my choice difficult.:icon38:

armt350z with a LS3 and your gear ratio no wonder the 3.53 is better for you.

Big gap between 3 and 4 gears though...

Yeah 4th kinda feels like it falls flat if I shift too soon. The good thing is that I can carry third through most long sweepers and rocket out to 4th on the straights. The 3.9 was having me either take 4th in those at a bad RPM or bounce the redline.

Also keep in mind as a general driving tip that relates to this choice. It is generally faster to be up a gear and lower rpm with less power, than riding the redline coming out of the corner. Lower rpm will let you carry more momentum and get on the gas much sooner. Less upsetting engine torque and engine braking will allow you to be smoother and carry more speed.

FD gearing has a lot to do with the track you're running... ideally you would tailor your FD to the track you're running on (topping out at the end of the straight). This is done very easily on motorcycles by just carrying a bunch of rear sprockets but obviously not practical for a car. Keeping that in mind, you must know your local tracks or the tracks you will be frequenting at so use those to make your decision. Some of it is personal driving preference... as you can see many members above have stated they dont like to be busy shifting all the time. Im currently running 4.08 with a quaife LSD on my DE and love it. I feel like it offers optimum drive out of corners and have plenty of top speed on the straights (even mid ohio)... that being said, i do end up rowing the shifter back and forth a million times a lap, but to me thats not a bother. Just my 2 cents.

I agree with you...but it's quite a pain in the ass to change the diff, it's so heavy...
I have 2 small tracks and Le Mans near my home...:) For me the 4.08 should be better since at Le Mans i end up being to low on rpm on certain corners...but i also need top end... and the other tracks the short diff is better...
I will give a try to the 4.08 + quaife combo...if it doesn't rock i will put it in the 3.53, it's not so big deal...

Noob question yo, what's actually involved in upgrading the final drive from stock to 4.08? I have OS Giken ready to be installed but I was planning to do it next year. Should I do it together with changing the FD?
I have 08 HR.

I actually prefer to be in a lower gear when entering and exiting the corner. More torque to control the car balance. Driving preference I guess. On a very high powered car it's probably safer and easier to be in a higher gear so you don't lose traction going out of the corner but in this heavy 300hp car? nah.

If you're pulling your diff out its only a little bit more work to change the FD... the extra work comes from pulling the pinion gear out and having to set the preload and depth properly... other than that you're actually saving yourself work with the ring gear because you wont have to pull your old one off of your stock unit...
So in essence...
1) pull the diff off of the car
2) remove cover, drain the fluid
3) remove rear bearing caps which will free the entire diff unit
4) remove pinion nut (can be done on the car with wheels on the floor to prevent the pinion from spinning, making this easier) and pull out the pinion gear, crush washer and any spacers (cant remember if z has a spacer?)
5) *Not necessary step but highly recommended since the whole diff is apart* Press out side and pinion bearings as well as their respective races as well as all 3 seals.
6) Clean everything up
7) Press in new races and bearings
8) Insert spacers, crush washer and pinion gears and tighten to specified torque and check for drag torque (dial in-lb torque wrench required)
9) Bolt new ring gear to your diff and drop diff into case
10) Insert appropriate shims and check to make sure your backlash is set right and you have the proper contact pattern.
11) Tighten caps down
12) Fill that sonnnabiotch with fluid and install the rear cover (fluid can be added when diff is in the car but i prefer doing it when its easily accessible because its a pain to get to the fill bolt if you dont have a hoist).

The wrenching part is super easy but setting the crush washer/sleeve, preload, backlash and gear pattern is tricky and if you dont know what you're doing itd be a VERY good idea to have a buddy thats done it help you out with it. IF dont improperly you can have excess noise or fry your bearings.

BTW where in poland are you from... im from Swientochlowice.. .moved to the states when i was young... you still live there? and own a z?!?!? Its rare to see anything over a 1.0L in Poland :D

Try some lap time comparison. Curious to see your result vs others.

I don't care about it. Not racing, only doing track days for now. So for me it's a matter of driving preference over lap times :) Maybe i'll get into this time attack mode next year, we'll see ;)
I do wish we had more tracks and at least one racing series for amateurs with cars like this (like the ones in the US) but in this s...hole, we have none!

@dblock55. Mate, cars are good but not many places to race them or even do track day! Only 1 proper circuit in the whole country. Luckily there are a few good ones not far away from where I live in Slovakia, Chech Republic, Hungary, Austria and Germany of course. I am actually doinf a track day on Hungaroring next weekend

I live in Cracow by the way.

PS. What exactly do I actually need to buy to go with 4,08 FD? Sorry but I'm a total noob in this area.

My advice is.... if you dont know what is required to change your FD ratio you probably wont do this job right... just drop the pumpkin and hardware off to a shop and have them do it properly... will save you the time and money after you destroy your pinion bearing and potentially ring and pinion gears. If you do go the shop route, just pull the diff itself out of the car yourself... thatll save you an hour in labor cost THis would also be a good time to check your differential bushings (stock rear subframe bushing is impregnated with silicone and tends to pop. All this being said, if you want to continue on your own, keep reading...

This is sold but the first picture (ring and pinion set) is what you need to buy to change the actual gearing of your FD ( https://my350z.com/forum/drivetrain/...iff-cover.html )... along with that you need gasket, bearings with races, seals, diff fluid, crush washer and shims. I think Z1 performance sells a rebuilt kit that includes all that and a few shims...

Do you really live in poland? The fact you spelt krakow with c's is quite ridiculous... especially if you'd pronounce it in polish using c's. Not calling you a liar but definitely questionable :bowrofl: