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what diff Ratio for AU XR8 with T56 

 

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 Post subject: what diff Ratio for AU XR8 with T56
Posted: Thu Oct 14, 2010 8:49 pm 
Stock as a Rock
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Age: 48

Posts: 150

Joined: 6th Nov 2009

Ride: AU2 XR8

Location: waroona
WA, Australia

Hi Guys,

I have just completed a T56 conversion from auto in my AU XR8.

I drives nice, however the standard 3.45 diff ratio is a bit low.

What would you suggest to replace it. A 3.7 or a 3.9.

The T56 ratios are:

1st - 2.97
2nd - 2.07
3rd - 1.43
4th - 1.0
5th - 0.80
6th - 0.62


and I may change from 17" wjeels to 19"

cheers
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 Post subject: Re: what diff Ratio for AU XR8 with T56
Posted: Thu Oct 14, 2010 9:01 pm 
Getting Side Ways
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Age: 28

Posts: 4326

Joined: 30th Oct 2006

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Ride: Envi EF

Location: Grafton
NSW, Australia

3.9s will be doing 2100rpm at 100kmhr.
I wouldnt go much lower than that or the other gears will become too short.

 

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 Post subject: Re: what diff Ratio for AU XR8 with T56
Posted: Fri Oct 15, 2010 12:39 pm 
Stock as a Rock
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Age: 48

Posts: 150

Joined: 6th Nov 2009

Ride: AU2 XR8

Location: waroona
WA, Australia

Thanks krisisdog,

I think you're right. i was leaning towards 3.7.

What difference do you think this would make from the 3.45, and what RPM at 100km/h would the engine be doing with 3.7.

Does the wheel size affect this much - 17" to 19" (depends on overall wheel diameter I guess, and therefore tyre ratio).

What price am I looking at to replace?
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 Post subject: Re: what diff Ratio for AU XR8 with T56
Posted: Fri Oct 15, 2010 3:03 pm 
Stock as a Rock
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Age: 48

Posts: 150

Joined: 6th Nov 2009

Ride: AU2 XR8

Location: waroona
WA, Australia

...actaully speaking to a diff guy, he recommends 3.9

any thoughts?
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 Post subject: Re: what diff Ratio for AU XR8 with T56
Posted: Fri Oct 15, 2010 3:40 pm 
Getting Side Ways
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Age: 34

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Joined: 7th Feb 2005

Ride: AU2 Ute

Location: melbourne
VIC, Australia

Have a look at this:

http://www.malwoodauto.com.au/images/DiffvsOD_RPM.PNG

I dont think 3.45's to 3.7's would feel much different.

I hardly noticed going from 3.23's to 3.45's.
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 Post subject: Re: what diff Ratio for AU XR8 with T56
Posted: Fri Oct 15, 2010 3:58 pm 
Getting Side Ways
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Age: 28

Posts: 4326

Joined: 30th Oct 2006

Gallery: 18 images

Ride: Envi EF

Location: Grafton
NSW, Australia

Well in regards to your rims, 235/45/17s are the same overall size as 235/35/19s, so that doesnt come into play.
Like I said, I wouldnt like gearing much shorter than what I have in my car, T5+3.45s.
T5 ratios:
3.25
1.99
1.29
1
.72

Your 6th gear with 3.9s will be doing 2100 vs 1980 (3.7s) at 100k's. Not much in at cruising speeds, its more so the speeds at which you'll be going through first and second, 50 and 90 odd k's. If you struggle with traction in first as is then going shorter wont really help things.

 

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 Post subject: Re: what diff Ratio for AU XR8 with T56
Posted: Fri Oct 15, 2010 7:31 pm 
Stock as a Rock
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Age: 48

Posts: 150

Joined: 6th Nov 2009

Ride: AU2 XR8

Location: waroona
WA, Australia

thanks for that. that table is useful.

I don't have problem with traction, and in fact its quite good under hard power. Its only when pottering around the streets that I have to ride the clutch on 2nd when turning corners and over speed bumps and such. It does tend to race away. Just seems a little low geared at low speeds. It cruises nice though.

i do have a cam - CompCams 272HR (224/218) which gives slight rough idle. Rev range is around 3500 to 5800. I think this problem might be more to do with the cam, and the engine being unhappy, than actual gearing.

i have been quoted at $1350 to replace diff (supply & fit) with 3.9.

I am now leaning towards 3.9.
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 Post subject: Re: what diff Ratio for AU XR8 with T56
Posted: Fri Oct 15, 2010 8:15 pm 
Getting Side Ways
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Age: 28

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Gallery: 18 images

Ride: Envi EF

Location: Grafton
NSW, Australia

Yeh, 3.9s might be the go if you're after shorter gearing.
I was going off my setup with 245 18s, it struggles for traction in 1st most of the time if I punch it.

 

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 Post subject: Re: what diff Ratio for AU XR8 with T56
Posted: Sun Oct 17, 2010 11:38 am 
Stock as a Rock
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Age: 48

Posts: 150

Joined: 6th Nov 2009

Ride: AU2 XR8

Location: waroona
WA, Australia

...also krisisdog, I notice the T5 has high 1st gear ratio (3.25 as opposed to T56 of 2.97). This may explain your traction problem
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 Post subject: Re: what diff Ratio for AU XR8 with T56
Posted: Sun Oct 17, 2010 1:56 pm 
Stock as a Rock
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Age: 48

Posts: 150

Joined: 6th Nov 2009

Ride: AU2 XR8

Location: waroona
WA, Australia

I have another question.

Would the BA/F XR6T 3.73 diff assy fit AU XR8 setup? Obviously not the whole rear end, but just the diff assembly. Thinking could get one from the wreckers.
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 Post subject: Re: what diff Ratio for AU XR8 with T56
Posted: Wed Oct 27, 2010 2:08 am 
Tyre Shredder
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Posts: 320

Joined: 23rd Nov 2004

Ride: XHII XR8 Ute - Supercharged

Location: Perth
WA, Australia

I have an XH 5.0 that I just fitted a T56 to....

Got 3.7s in the back. "idles' just under 1550RPM @100km/h....

Bloody awesome. Went for a drive down to Margaret river and home (600km round trip) on 1 tank. Trip computer said I used 9.3L/100 :)

I reckon I could almost go for 3.9s, but for economy 3.7s are a good trade off

 

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