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Location:
Newcastle
Registered:
May 2002
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3TG + W55 + what diff ratio?
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Fri, 21 January 2005 22:26
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I have recently aquired a VS commodore borg warner 8 3/4 inch limited slip diff for use in my TA22. Stock they run 3.08 ratio. I have access to the following ratios 3.45, 3.5, 3.7, 3.9 and 4.11. I was thinking a 3.7 ratio would suit my car (3TG, W55). Although this ratio (pintara) has a harmonic noise at about 86kph, not a problem, just a very closely matched crownwheel/pinion design. My mate who is modifying the diff reckons 3.45 would be the go.
How can I calculate the rpm that the car will do at 100kph (205/45/16 tyres)?
What ratios are other people using and why?
The car will be mostly used on the street, with occasional drag racing.
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Location:
On your mum!
Registered:
May 2002
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Re: 3TG + W55 + what diff ratio?
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Sat, 22 January 2005 07:41
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I use 3.89 gears (I was told by many that it'd be noisy and it isn't).
To get the RPM vs Speed I calculate it in 4th gear (1:1) @ 6000RPM and make all other calculations from there.
I don't know if this is correct OR IF there is a quicker way.
Tyre = 205/45/16 - where 45 = aspect ratio (0.45 x 205) = 92mm sidewall - sidewall x 2 = 184.
Rim = 406mm. 406 + 184 = 590mm (rim + sidwall x 2 = rolling dia - for some reason the true rolling dia is usually bit less - say 10mm)
Pi x dia = circumference OR 3.1416 x 580 = 1822mm (or 0.001822km) of travel per revolution (Tcir)
Gear set = 3.45 - 6000/3.45 = 1739.13 tyre RPM x 60 = 104347.8 tyre RPH (Trph)
Trph x Tcir = 190.122kph @ 6000rpm in 4th gear.
RPM @ 100kmh = 100/190 x 6000 = 3158rpm (4th)
Assuming 14% overdrive for 5th gear = 0.86 x 3158 = 2716
I say that 3.45 is geared too long for your engine and that 3.73 would be better.
373/345 x 3158 = RPM @ 100 in 4th with 3.73 gears (3414)
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Location:
Terrigal
Registered:
May 2002
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Re: 3TG + W55 + what diff ratio?
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Sun, 23 January 2005 04:59
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I've run 4.1 and 3.9 diff on my 3tgte/w55 celica. I'm happy with the 3.9, its comfortable on the freeway and doesn't feel any slower in take off compared to the 4.1 I used to have.
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Location:
Newcastle
Registered:
May 2002
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Re: 3TG + W55 + what diff ratio?
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Sun, 23 January 2005 05:02
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What RPM does it do at 100KPH in 5th? What sort of diff are you running?
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Location:
On your mum!
Registered:
May 2002
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Re: 3TG + W55 + what diff ratio?
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Mon, 24 January 2005 12:18
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For me with 3.89 and 185/60/14 = 3500 (RPM in 5th) I have a Borg Warner (c/w 28 spline axles and 4 pinion LSD FWIW)
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Location:
Newcastle
Registered:
May 2002
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Re: 3TG + W55 + what diff ratio?
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Mon, 24 January 2005 19:10
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Thanks guys, I have decided 3.7 is the ratio to go for. Now to find a pintara to pilage 
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