VHR + FD Gear Ratio upgrades - 3.9 and 4.08
 

In the Z33 world, the combo of the HR motors and upgraded Final drive gears in the R200 diff seems to be pretty potent combo, and really transforms the acceleration in the car. Especially in Modded NA cars. The 370 has a 3.69:1 ratio ring set. I am think 4:08's would drop another 3-4 tenths off the 1/4 mile times and really help the VHR get into the power range faster. I would hazard a guess that a fully bolted on 370z, with a 8000 RPM tune making 320-340 whp and a 4:08 gear would be a mid 12's car all day long. I think this would be the first mod I would do. The diff's are exactly the same, so anyone looking to do this can get everything you need to right now. I think the only question is the same we have about flywheels. What will happen to SRM? Thoughts?

I was thinking the 3.9 gear set might be a better choice for all around driving. 4.08 seems a little too much of a high gear for the street and general everday driving

i agree. FD gear mods are pretty cool, but i drive on the highway alot, so i dont wanna be cruising at like 4500-5k rpm. oil temps are all ready high

Yeah that's a concern for me too. In the 7AT our rear end is even worse ratio than you 6MT guys (7AT is 3.357, 6MT is 3.692). However, at the speeds I like to cruise at on the highway (when possible), I don't want the revs going any higher in 7th than they are now. 7AT really could use an 8th gear (or just taller transmission gearing in 6 and 7 both) for us high-speed cruisers :p

It would not be anywher near that high. I used a gear calculator, and with a 4.08 @ 70mph in 6th would = 3000 rpm.

check out the link below for reference
[link]http://www.kabamus.com/garage/gears.html[/link]

I think this would rock, however, the more I think about it this might throw off the SRM more then a flywheel. The SRM system must have a preloaded wheel speed vs gear table. It probably see's wheel speed "x" for gear "y" and revs to rpm "z". The wheel speed will be off by 10%, meaning it would have to rev 10% higher for a given wheel speed and gear. So it might be 10% off on the rev match to engine speed. Then again I might be completely off on my assumptions on how the SRM works. Either way, I can't Imagine 10% off would make a huge difference in smoothness of the system. If you manually heel toe like a pro, I bet most are still off by a few hundred RPM. Anyhow, some needs to break the seal and try this out. It will be killer for NA setups.

Great, so I'll be at 3K when a cop is following me :rolleyes:

With the stock 7AT setup, for example 4K rpm in 7th is only 122 (according to your gear calculator page, but it sounds about right). Moving to a 4.08 puts us at 5K rpm in 7th to reach the same speed. I might consider just swapping into the manual's 3.692 gearing though (once we have a programmer so I can tell the ECU about it).

This sounds great, except I do a lot of highway driving at 85+. If not for that I'd be all over it.

Man you guys drive fast! I don't see myself doing 122mph on a remotely regular basis. Anyhow, I think for the folks using the car as a part time car, or track toy, this is the ticket. I hope to move from my CTS-V into a 370Z in a few months. I had a 1990 Z32 2+2 With a 400 whp VG30DETT swap done for many years, and to date still one of my favorite cars. Looking to come back to the Z brotherhood and continue my sickness of Mod Hell on the Z. This will definately be something I look into ASAP.

Meh around here on the TX highways, big fat SUVs cruise the highway at 85. Low-speed driving with lots of corners is more fun anyways, but if the road is clear, the conditions allow, and my V1 isn't bleeping at me, I tend to get where I'm going with uhhh... maximum time efficiency :)

A lot of good mods are out and tested in the field now, it's a good time to get onboard :)

I definitely agree that 4.08s are great for those looking to improve at the track. I had 4.10's on a 2004 Mustang GT and I loved them. It's an ongoing debate about how high of a gear can you go and still stay comfortable and I can say I drove around 10k on the Stang with no complaints. Low and power and torque were immediate and in the quarter mile it definitely made a difference. I say go for it, it'll probably need an oil cooler but if you're willing to spend the $ get a cooler also, full bolt ons plus higher gear=awesome. DON'T FEAR THE GEAR

First mod I would do. I alwasy wanted to do that to my 03 track. I barely touch the highway :D

Chris

nah man. im above 3k cruising at like 85-90. like 4k actually. i will let u know soon what exactly it is. but either way, its an awesome mod. actually, my friend in a 350 just put 4.08 gears in his. we're running tomorrow so i can tell u all how he feels about the mod.

Do post his speeds and rpms ... very interested in details :)

Roughly 80mph=3100rpm in 6th.

WHat should I get on my 5AT G37?

Thats w/ 4.08? I dont think so... should be close to 4k no?

I think he meant stock rear end on 6MT (3.692)

correct. i went driving today. i was around 3200 at 85 in my 6MT. so i guess with a 4.08 it would be like 3700-3800?

what's the average price of a rear diff swap out??

I think this would be a great mod, the 370z is a little sluggish exiting a sharp turn in second gear, this would help put it more into the powerband. :tup: My only concern would be drivetrain wine/noise. I've done this swap before on my last few mustangs 4:10's and the drivetrain noise went up considerably. Maybe the gears weren't set right.

Has it been confirmed that the final drive gears for the 350Z will fit the 370Z? If so, how difficult is it to install them?

I can probably answer this question for you. Were they Motive gears (or other), or Ford Racing Performance Parts gears?

Price depends.

4.08's are a nissan part ( ring gear from a nissan frontier ) +/- $400
3.9's are aftermarket ( Central 20 ) +/- $600

Install requires a few OEM parts (Pinion bolt, crush sleeve, some seals,etc)

All in, installed probably about a grand. Considering it's less then some exhausts, it's a no brainer to me.

And yes, this is the same R200 diff in the 350z, G35, G37 ( and about a dozen other Nissan cars/Trucks)

Pete

sweeeeet. this will be an awesome mod for us

I'd definately consider this mod for people who aren't commuting in their Zs to work/school/wherever 5 days a week. Good for the weekend warrior type where gas mileage isn't so important. I'll consider this mod after I find a suitable daily driver!

had a chance to ride in my buddies 350 with the 4.08 swap from Z1. all i can say is wow!! what a diffference. its like u shift down a gear...2nd pulls like first, as does 4th pulls like 3rd. it makes the car soooooo rev happy. it's a lot of fun. the only downside was that it made some noise. this seemed to be a problem with a couple other ppl. maybe becuase it had not been broken in, but i will ask him to update after 1k miles. he bought the stage 2 (or whatever) which came with all new bushings, etc. so it was basically a brandddd new rear end. cool mod. some1 should do it to the 370

You? :) I'm starting to really think about just moving mine up to the 6MT's rear end (3.692 instead of 3.357 that came with my 7AT). I need to go run the numbers again and think about high-speed RPMs more though (that, and wait for a programmer like UpRev that can tell the ECU about it too).

Edit:

7th gear on a stock 7AT setup with stock Sport wheels/tires is approximately 32.78 revs/mph. Swapping in the 6MT's rear end would put it at about 36.04 revs/mph. This is what the revs would look like with the two options, cruising in 7th on a very long track:

mph | rpm | rpm
100 | 3278 | 3604
110 | 3606 | 3964
120 | 3934 | 4325
130 | 4261 | 4685
140 | 4589 | 5046
150 | 4917 | 5406

In the lower 100's it's not too bad a difference. Even at 150mph it's only 500rpm. Hmmmm....

me. nah. i drive wayyyyyyyyyy too much on highways. im not really racing anyway. but u should look into it. that would be a nice swap (the AT to MT).

Pete, I got a 350Z with 4.08s on it... so if I had a 370Z, I could take it to a shop and swap pumpkins?

This sounds like good news to me. My next question like the OP has asked...

How does changing to a lighter flywheel (like JWT) affect Synchro Rev Match shifting? Will it over compensate the rev? Or will it rev match instantly?

Why do you have to "wait for a programmer like UpRev that can tell the ECU about it too?"

Maybe i'm wrong but...

I do not see the reason to advise the ECU.

If you call a gear downshifting, ECU-tranny will give you it anyway, just checking the RPM, not speed...

Or I'm wrong?

Anyone has experience with changing ratio in AT (infiniti, 350Z etc)?

Bye!

I meant so the speedo will be correct.

Oh and as far as upgrading the rear end ratio in the 7AT, aside from spacing out all the cash I'm throwing down, and having to consider whether I want to get rid of VLSD while I'm at it (perhaps the 1.5-way Carbonetic that Mike@DDM likes so much), the other thing holding me back is I'm not sure if it will make 1st gear too short. The 1st gear ratio on the 7AT is way out there compared to the 6MT. In stock form on the sports model, 1st gear ends at about 36mph @7500rpm.

My tire/wheel upgrades that are coming soon (moving to 295/30R18 in the rear) already drop that number a bit, and when I ran the numbers, the combined effect of the tire/wheel change and moving to 3.692 in the rear would put 1st gear topping out at more like 30mph @7500pm. 1st gear already ends so quickly that it makes timing the 1->2 upshift optimally challenging, so I'm worried this will make it insane. On the other hand a higher redline from the ECU stuff would offset this a little. We'll see what happens when I get to all this I guess.

I changed the diif on my 7 AT to a 4.08 gear set up. The rev matching in city driving takes some getting use to. It uses to turn 2100 at 100 km. Now it turns 2750 at 100.
Fuel consumption went from 7.8 up to 8.7 L / 100 km. I took it to the track and it ran a best of 13.201. Average pass was 13.32 to 13.43. The colder the moter the faster it goes.Going down the track i shifted at 7400 and the RPM only drops to 6300. I have to put in 5th. On the 13.201 pass i hit the limiter in 4th as i tried to make the pass in 3th
It ran at 102.8 mph in that pass. Mt best trap was a 107.9.
The only mod is a stillen G3 intake. Base line was 266 and 286 RWHP after the intake.
The next Z drag day is in Septmeber and it will have a stillen CBE. Berk cats, Stillen headers and the underdrive pully. It should run 12.8 on the 19 inch wheels. Its hard to hook the bridgestones. Best 60 ft 2.01 to 2.09.

Z Eliminator: How's the 1-2 shift with the 4.08? Given the slight input lag clicking the button, and how fast the car rips through first gear, I'm worried that a better gear ratio is going to make timing the 1-2 shift nearly impossible.

Which model did you end up putting in, what was part#, cost, etc. Also, how is drivetrain noise now, is it much louder, or pretty much the same?

thanks!

The 1 to 2nd gear change is very quick. 2nd to 3rd is quick. It feels like your changing gears every 1 to 1.5 seconds.
It was built by a nissan mechanic. I bought it with 2000 km on it. I paid 1000.00 cdn for the whole diff. The only thing i did was i put royal purple gear lube in it. Im not sure what vlsd is in it.
There are no issues of hitting the rev limiter in first or second, lots of miliseconds to change gears. It very very fast. My 0 to 60 times based on the 8th mile time and traps is 4.4 seconds with a 2.01 60 ft time. It burns more gas. and it is in 7th gear at 58 to 60 km.

Does anyone know of any 4.08 or maybe higher gear sets or where one could order them? If we have the same diff as the 350's there has to be a few sets out there.

My Z32 comes with the 4.08 stock. people sell them very cheap on 300zxclub.com

I live in Chile, no 370Z here yet, few 350Z, no Z-culture, help me US mates!!! :bowrofl:

1) I'm going to change the final ratio of my imported (from USA) 7AT 370Z to 4.08, wich i read is "stock" on Nissan Frontier.

2) Change the whole diff is the only way to go with?

3) Is it not enough to buy an OEM Frontier pinion-ring couple?

4) If yes, anyone knows how many parts are necessary (any bolts?) and the serial # of each of them?

Thank you in advance!

So, does anyone know where the syncro rev match gets its speed signal to match the engine speed? If it is from the tranny itself then changing the rear end ratio won't affect it right? The reason I ask is, I think changing the ratio on my 6 speed to 4.08 is next on my list since I really only drive my car for fun and the occasional errand. I auto-crossed it last weekend and the car is just a little weak coming out of the slower corners in second and this would be a very stealthy way to fix that. Now I just need to find a shop in the SFV to do the swap and get approval from my "boss".

SRM is based solely on the engine RPMs and the gear ratios in the 6MT. Your rear diff ratio can't affect it. Changing out gears in the 6MT would though.