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Discussion Starter · #1 ·
Hi Guys,

This is for Australian people only.

We are placing an order for Central 20 final drive ring and pinons, they come in 3.9 or 3.7 ratios. They are about AU$580!! shipped to Sydney, if anyone wants one let me know here and we'll order one for you as well.

The price does not include dutys but I will try to get around most of it, but factor in a little more for duties.

This mod is one of if not the most noticable bolt on power mod you can do to your car without going to FI. Do a search on the my350z forum if you want to hear what people think about it.

FYI the 350EVO 3.9 final drive is AU$1100 not shipped with no duties factored in! So this is a VERY GOOD deal! Its about half the price.

Let me know ASAP, i want to order soon as my diff is on it way already. Thanks

Orders

Murray 3.9 x1
Nizmo_Pete 3.9 x2
 

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Murray:

DId you get the contact info. that I gave you? and what will the top speed in each gear for both 3.7 and 3.9 actually?! Thanks!

cheers,

richie
 

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Discussion Starter · #3 ·
I did thanks alot Richie, he is being very helpful!

I believe the 3.9 top speed is around 270km/h as the stock 3.5 is top speed is around 300km/h and the 3.9 is a 10% reduction as far as I can remember.

The 3.7 FD would be between 270km/h and 300km/h.

Here are the 350EVO started threads regarding their final drive. What i said above it correct.

http://www.my350z.com/forum/search.php?searchid=338689
 

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Murray:

how about the top speed in each gear position??? that's actually what I am asking.. sorry mate! :)

cheers,

richie
 

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Discussion Starter · #5 ·
DavidM, Know how to work out the speed in each gear for the 3.7 final drive?

Here is the stock vs 3.9 in MPH, i'll convert it to km/h now. I just grabbed the values from the 350evo one and converted to km/h. Not sure if this is for 4.0 or 3.9? It says [email protected] for some reason?

3.538 OEM 3.917
Gear/ max speed km/h OEM / max speed km/h 4.0 @ 6850 RPMS
1st/ 62 / 56.5
2nd/ 102 / 92
3rd/ 146 / 131
4th/ 186.8 / 168.6
5th/ 236.5 / 213.8
6th/ 297.7 / 269.7
 

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Thanks murray!!! THat's very helpful!!! This final drive sounds like a great mod to everyone who has it though... I cannot wait to see you guys get this fitted!!

So that means with 3.7 ratio, in 2nd gear, it is possible to go up to 100km/hr too... and also I think the stock diff setup will only go up to 97km/hr or so at 6600rpm... am I correct here?

Thanks heaps!

cheers,

richie
 

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Discussion Starter · #8 ·
For your increased rev limit it would be possible to reach 100km/hr with the 3.7FD.

I believe you are correct that the stock 3.5 at 6600rpm does not get you to 100km/h.

It probabally worth mentioning that in the real world getting to 100km/h in two gears means nothing. The car will be alot faster everywhere in the rev range with this mod.
 

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Excellent price, but don't think it would be worthwhile to me as my car is SC at the moment.

Open to opinions though
 

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Here is an interesting read got posted by Sevs2K on the other form about the final drive:

---------------------------------------------------------
Pros:
-Going from 3.54 to 3.9 will increase thrust available at the wheels by 10% throughout the power band. To see a similar gain from an engine mod, you basically need a mod or mods that will give you 10% approximately 20-25 WHP throughout the band which is impossible. With these gears, the car will pull 10% harder everywhere and in every gear. These gears will give you a significant acceleration difference that YOU WILL FEEL.
-3-4-5-6 rd gear on acceleration will be sigficantly improved even with the stock tires since they will be able to put the power to the ground.
-Top speed will not be affected by this mod
-Definately the best NA mod for the buck for road racers

Cons:
-A car like the s2000 stands to benefit a whole lot by a gear set like this one, thats why they are very popular with the s2k crowd, the s2000 can use more thrust, especially down low.
However, as it stands, the 1st two gears in the 350z are already short, almost too short, buying gears like these and putting them on a stock tired car will not net a siginificant improvement in the 1/4 mile. It's simple, the stock tires car only put so much acceleration to the ground. Therefore for there to be a benefit out of the hole (1/4 mile), wider rear tires + grippier tires will be neccessary.
-Although you will be accelerating 10% faster, every gear is also 10% shorter, which means you have to shift 10% sooner. Example: You accelerate with both cars, assuming that the car with the gears is able to put the whole power to the ground, the car with the gears will accelerate 10% stronger but will shift earlier while the car with gears will go to 2nd, the stock car will still benefit from the gear multiplication and thrust of 1st for a little longer pulling back some of that lead, same thing for 2-3, 3-4, 4-5, 5-6...

- Installation is a real ***** as you need someone that has experience doing differentials, if the gears aren't installed properly they will wear out and be caput very soon, you are looking at the very least $300-500 depending on your local prices for install. ***Don't cheap out here, you need an experienced installer***


Whats the net affect of all this:
The net effect however, will still be postive AS LONG AS YOU CAN PUT THAT EXTRA THRUST TO THE GROUND, I can draw a chart showing this but I am too lazy

So in conclusion, this is an excellent mod for road racers, lazy shifters and anyone who wants to get more neck snapping acceleration . For 1/4 milers, to be a significant gain, you will need wider rear tires + stickier tires to be able to deliver this thrust to the ground, otherwise you will just spin your wheels since you will have 10% more wheel torque or thrust even at 1000 RPM

----------------------------------------------------------

cheers,

richie
 

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Originally posted by mchapman@Aug 4 2005, 08:58 PM
It probabally worth mentioning that in the real world getting to 100km/h in two gears means nothing. The car will be alot faster everywhere in the rev range with this mod.
[snapback]141828[/snapback]​


Yeah.... thanks for that... understand this :)

Also do you know how much will the installation cost roughly? I read a few posts back then and it seems to be quite dear to carry out the job though. and also will this diff gives extra noise at all? that's what I would like to find out... :)

cheers,

richie
 

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sounds like it can make some worthwhile power gains for the money

but am i the only one who thinks 1st is already too short, and my rev limit is 7000. I often start in 2nd bcoz 1st gear below 3000rpm doesnt even get u across an intersection

would still like to see what gains at wheels this mod does on a dyno
 

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Discussion Starter · #13 ·
Originally posted by MR RIZK@Aug 4 2005, 09:10 PM
Excellent price, but don't think it would be worthwhile to me as my car is SC at the moment.

Open to opinions though
[snapback]141831[/snapback]​


Mike ive been thinking about a FD on your car and the only benefit I can see with this mod for you is that it will allow a increase in performance without adding any extra strain motor! As you motor is already under more strain than a normal NA motor. But if your planning to increase boost or increase the output of your system, i think the gear would render first completely useless. Your making less than a turbo 350z so it might be something to consider but if you had a TT you wouldnt even consider it.

How is first gear at the moment with your current power output?
 

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DavidM, Know how to work out the speed in each gear for the 3.7 final drive?

Yep, I can work it out for you ... not hard at all. Though, what is the ratio of the OME final drive?

ps. Guys, just make sure you realize that changing the final drive ration (whether going shorter or taller) will meke the car accelerate quicker at some speeds and SLOWER at some other speeds. Changing the rations is always give/take scenerio ... you make the car quicker somehwere, but also slower somehwere else.

As soon as someone posts the OME final drive ratio, I'll tell you exaclty where you'd be quicker and slwoer with the 3.7 final drive.

I believe you are correct that the stock 3.5 at 6600rpm does not get you to 100km/h.

Is the stock one 3.5 ratio? The OME cars with 6,6000rpm limiter can reach 'only' 98kph in 2nd.
 

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David,

I think the stock final drive is 3.538!!! Thanks!

cheers,

richie
 

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How is first gear at the moment with your current power output?


I find first gear too short even without the SC. With the SC for me anyway you need good throttle control to get a good launch otherwise the rears just light up. The reason I was sort of thinking about the the FD is not because I find the car underpowered but since the SC's power is linear I might find that the FD will give me better exit speed out of the corner.
 

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I think the stock final drive is 3.538!!! Thanks!

OK, to start of this is the gearing for the OME (ie. 3.5) final drive (at 6,600rpm):
- 1st gear = 60kph
- 2nd gear = 98kph
- 3rd gear = 142kph
- 4th gear = 181kph
- 5th gear = 232kph
- 6th gear = 292kph

Following is the same car with 3.7 final drive (at 6,600rpm/7,200rpm):
- 1st gear = 57/62kph
- 2nd gear = 94/102kph
- 3rd gear = 135/147kph
- 4th gear = 173/189kph
- 5th gear = 221/241kph
- 6th gear = 279/304kph

And finaly here the same car with 3.9 final drive (at 6,600rpm):
- 1st gear = 54kph
- 2nd gear = 89kph
- 3rd gear = 128kph
- 4th gear = 164kph
- 5th gear = 210kph
- 6th gear = 265kph

So that's what those final drives will do to the speeds-in-gear. Though, the acceleration will not always be quicker for 'shorter geared' cars. It will be quicker when in the same gear as the OME car, but the OME car will be able to stretch each gear further. Also across the gears the OME car may sometimes be quicker. ie. let's take the 3.5 and 3.9 geared cars ... this is what will happen when accelerating from stand-still (rolling start):
- between 0 - 54kph the 3.9geared car will be a quicker as they are both in 1st and the 3.9 gear is a a little bit shorter.
- between 54 - 60kph the OME geared car will be a quicker as it is still in 1st while the 3.9 geared one is in 2nd. This 2nd gear is a lot taller than the OME 1st.
- between 60 - 89kph the 3.9geared car will be a quicker as they are both in 2st and the 3.9 gear is a a little bit shorter.
- between 89 - 98kph the OME geared car will be a quicker as it is still in 2nd while the 3.9 geared one is in 3rdnd. This 3rd gear is a lot taller than the OME 2nd.
- etc ...

It just happens that I had my car entered in the catTest simulator and it pretty much reflects it's perfromance ... I even punched in my own power curve and shift-speed times. I changed the final drive to the 3.7 and 3.9 ones to see what acceelration difference it will make and here are the results:

Acceleration for 3.5, 3.7, 3.9 geared Zed:
- 0-40kph = 2.0, 2.0, 1.9sec
- 0-60kph = 2.8, 3.1, 3.0sec
- 0-80kph = 4.4, 4.3, 4.3sec
- 0-100kph = 6.1, 6.1, 6.1sec
- 0-120kph = 8.0, 7.9, 7.8sec
- 0-140kph = 10.1 10.3, 10.3sec
- 0-160kph = 13.2, 13.1, 13.0sec
- 0-180kph = 16.5, 16.8, 16.8sec
- 400m = 14.1 @ 166.0kph, 14.1 @166.8kph, 14.1 @165.0kph,
- 1000m = 25.4 @ 213.3kph, 25.3 @ 214.2kph, 25.3 @ 212.6kph

As you can see, some increments are covered quickest with the OME, some with 3.7, and some with 3.9 .... there's no such this as gearing for every possible situation. For instance if an OME 350Z lined up a 3.9 geared one at 80kph, and you raced it to 180kph, then the OME car would win. On the other hand if you lined up these two cars from 60 to 160kph then the 3.9 geared car would win.
 

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Discussion Starter · #18 ·
Thanks David.

Did you see the posts from the guy measuring his results with a G-Tech?

Found it. Not sure about the 0-60 times because of the shift involved, but the 0-400 is good.

http://www.my350z.com/forum/showthread.php...ighlight=g-tech

Below:

Hello,

I just got my car back from the shop. (Z Car Garage in San Jose) They installed the 3.9 final drive into my Z. While I haven't had too much driving time, the shop did some tests pre-3.9 and post 3.9. They used a g-tec meter. Main thing was to see any gains. Here is what they got.

Stock..
0-60
5.81
5.84
5.90

1/4 mile
[email protected]
[email protected]

w/3.9 drive installed
0-60
5.70
5.80
5.90

1/4 mile
[email protected]

I really like the 3rd gear pull the car has now! Can't wait to drive it more!
 

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Discussion Starter · #19 ·
Originally posted by TPIACE@Aug 4 2005, 09:23 PM
sounds like it can make some worthwhile power gains for the money

but am i the only one who thinks 1st is already too short, and my rev limit is 7000. I often start in 2nd bcoz 1st gear below 3000rpm doesnt even get u across an intersection

would still like to see what gains at wheels this mod does on a dyno
[snapback]141838[/snapback]​


It is short but if it was longer it wouldnt pull as hard. Once you've had the car for a while you'll get used to the length and it will seem like its taking ages then you'll want to make it quicker. First gear isnt affected too much with this mod compared to the other gears anyway.

You wont find any dyno results as this is a gear modification. Your better off looking at peoples times or listening to their impressions. zillinois from my350z has dynoed his 3.9 by mapping the old dyno over the new dyno plot using mph instead of rpms. But i dont think he got it printed out and no one else would know to do this.

Quote:
"Actually, you can "see" the gains from final drive ratio change. If you map the old dyno over the new dyno plot using mph instead of rpms the results are quite impressive. I did this with my 3.5 to 3.9."
 

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Did you see the posts from the guy measuring his results with a G-Tech? Found it. Not sure about the 0-60 times because of the shift involved, but the 0-400 is good.

No, I did not notice that before. Those gains measured with the g'tech may very well be correct ... in particluar over 400m. I can't see the 0-60mph improvement as the 3.7 gears will require a 2nd-to-3rd shift to reach 60mph and that alone takes about 0.4sec. So I'd expect the 60mph time to be slower than before. Also, from my experience with g'tech, I saw good 0.4sec variation in my times from one day to another ... in particluar 0-60mph. Main difference between the days was the amount of traction that my car had and hence how well I could launch it. So my suggestion is to do the 'tests' over a few different days and then average the best times from each day ... otherwise you don;t know if you're looking at real gains of just a favourable change in conditions.

ie. on one day I could pull 5.3sec 0-60mph time, while the folling day I could not brake bellow 5.6sec. Also my 400m time was 13.96sec @ 106.4mph.

Though, despite what I mentioned above, a shorter final-drive should improve the 400m time .... ideal gearing for the 400m time would see the 4th gear reach around 167kph (ie. top out just over the finish-line). Though, if you wanted to race over 500m (or any other distance) then 'that' gearing will no longer be idea. That's why I keep on repeating that changing the gearing will only improve the acceleration inb certain increments. In some other increments it will make it worse. If the optimum 400m time is your (or anybody's) goal, then the 3.7gearing would be close to ideal.

For me slightly taller gearing would be ideal ... I'm sure for what I use the car, taller 2nd and 3rd gear would make me quicker. Still, I would idealy do it with just raising the cut-out and keeping the existing gears.
 
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