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| TKFD |
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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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| krisisdog |
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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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| TKFD |
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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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| TKFD |
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...actaully speaking to a diff guy, he recommends 3.9
any thoughts? |
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| Dansedgli |
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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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| krisisdog |
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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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| TKFD |
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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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| krisisdog |
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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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| TKFD |
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...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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| TKFD |
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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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| xf84 |
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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
_________________ Old - XF with XH XR8 Driveline... http://www.fordmods.com/ford-v8-f2/my-xr8-power-xf-falcon-t20529.html |
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