# 3.9 final drive



## rogerdavis (Feb 16, 2008)

What cars from the skyline family came with a 3.9 final drive? I fear 4.11 might be too low with a R34 gearbox.


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## Vihis (Jan 1, 2008)

None did.

If you need, you could take the diffs from a R34.

Here are calculations based on a R34 GTR box and 265/35/18 tires:

Engine max RPM 7500:

4.111:

Tyre Diameter = 2018.08 mm 
1st Gear = 57.68 km/h 
2nd Gear = 93.6 km/h 
3rd Gear = 130.71 km/h 
4th Gear = 168.63 km/h 
5th Gear = 220.9 km/h 
6th Gear = 279.62 km/h

3.9:1

Tyre Diameter = 2018.08 mm 
1st Gear = 60.8 km/h 
2nd Gear = 98.67 km/h 
3rd Gear = 137.78 km/h 
4th Gear = 177.75 km/h 
5th Gear = 232.86 km/h 
6th Gear = 294.75 km/h

With these ratios, I see no added benefit. I'd like to hear more of your reasons as I'm a curious puppy 

Stock 3.55 final drive:

1st Gear = 66.79 km/h 
2nd Gear = 108.4 km/h 
3rd Gear = 151.37 km/h 
4th Gear = 195.28 km/h 
5th Gear = 255.81 km/h 
6th Gear = 323.81 km/h

---

stock 4.11 5-speed:

Tyre Diameter = 2018.08 mm 
1st Gear = 68.75 km/h 
2nd Gear = 114.78 km/h 
3rd Gear = 169.71 km/h 
4th Gear = 220.96 km/h 
5th Gear = 293.83 km/h

----

Cars with 3.9 dif (R200):

C34 Laurel RB20E MT/AT
C33 RD28 (yep diesel ) MT

A31 Cefiro rb20e MT/AT awd?!

S15 Silvia SR20DET AT

S14 Silvia SR20DET AT

PS13 Silvia SR20DET AT

RPS13 Silvia SR20DET 

These will however have 12mm x 1.25 crown wheel bolts I believe in case you were thinking of transferring the crown wheel and pinion to your R33 GTR, which has M13 x 1.25 bolts. In that case, you'll need NISMO bolts which have a M13 shank and M12 thread, about £50 worth for 10 bolts (38102-RS500).


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## rogerdavis (Feb 16, 2008)

I read on the Canada GTR forum where people were advised to avoid the 4.1 final drive as the ratios are very short.cvI am just doing my own research as to what would be the best final drive


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## Vihis (Jan 1, 2008)

You are a bit out of luck as the front diff is different from the rear so crown wheels are scarce. Unless you went RWD then it's a whole different story altogether.

Tomei made a final gear set with a 3.692 ratio if that helps. Cost is way over $2000 usd.

Mine's also ran the Getrag 6 speed in their R34 with the 4.11 for time attack but I guess yours is a road car ?

Always interesting to hear from a 5 spd to 6 spd conversion  !


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## Adam Kindness (Jun 22, 2002)

i did some calcs on 5sp, 6sp and OS88 using 4.11 (r32 gtr) FD. Revs, speed, rev drop etc

OE 5sp / 4.11









6sp / 4.11 (1st to 5th)









OS88 1-5










The 6sp with 4.11 FD may be a bit too close for motorway only use but it would make the car feel very quick through the gears on any other road.

Cruising in 6th (using a pretty normal sized rolling radius 255/40/17) at 80mph = <3000rpm from memory. 1st is pretty short though. Top speed around 180 in 6th at 8000rpm


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## Adam Kindness (Jun 22, 2002)

also - have a look in here for some of the stuff discussed when I was deciding which box to go for. http://www.gtr.co.uk/forum/167640-getrag-6sp-paired-4-11-diffs-general-questions.html


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## Vihis (Jan 1, 2008)

What is that program called Adam ? would be great to know so I could plan my car's gearing !


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## Adam Kindness (Jun 22, 2002)

just google search 'gear ratio calculator' and there will be quite a few options


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## Adam Kindness (Jun 22, 2002)

edit - double post


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## Vihis (Jan 1, 2008)

I have and haven't seen one which puts out graphs like that, which are useful. Plain numbers are..


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## Adam Kindness (Jun 22, 2002)

ok, i'll search for you then....

:S

http://members.iinet.net.au/~chenglee/GearRatio.xls

http://www.diffsonline.com/techinfo/GearingCalculator.xls

http://www.gearboxman.co.uk/inforatios.html#download

http://www.geocities.com/killer_siller/TransCalc/TransCalc.xls


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## Vihis (Jan 1, 2008)

Many thanks  !


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## R.I.P.S NZ (May 7, 2004)

Adam Kindness said:


> ok, i'll search for you then....
> 
> :S
> 
> ...



Is that you GTR-Glen? :chuckle: opcorn:


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## blue34 (Jul 28, 2005)

4.1s with a getrag 6 speed are great - with 275/35-18s makes 6th gear more useable and livens up acceleration. 8500rpm would still give 200mph..


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