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post #1 of 41 (permalink) Old 05-08-04, 02:17 PM Thread Starter
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biggrin Diff ratio for good take off

hey people,
seeing as our max speed limit on sydney roads is 110km/h, is there anything i can do to a hydra trac diff to get better takeoff??
I'm Probly gonna look silly but im gonna ask anyway
What is the deal with diff ratio's is higher number better or lower numbers?
what is better for take off/cruising? Please help!!!
Dayne.


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post #2 of 41 (permalink) Old 05-08-04, 02:45 PM
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Re: Diff ratio for good take off

I always get it the wrong way around so feel free to correct me if I'm wrong- Higher is lower numerically and is better for the highway (eg 2.75, 3.00)

Acceleration wise, (eg 3.45, 3.77 or 4.11) give you better punch off the line, but use more fuel, as the engine is doing more revs at hwy speed.

The wheels and tyres you run also have a bearing on the overall rolling diameter, which also have an impact on your final ratio.

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post #3 of 41 (permalink) Old 05-08-04, 04:20 PM Thread Starter
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Re: Diff ratio for good take off

Does anyone know
1.If i can do anything to my hydra track or will i have to swap diffs?
2.What the standard diff ratio is?

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post #4 of 41 (permalink) Old 05-08-04, 04:32 PM
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Re: Diff ratio for good take off

The diff normally has a tag on it advising of the ratio.

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post #5 of 41 (permalink) Old 05-08-04, 04:43 PM
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Re: Diff ratio for good take off

the diff ratio i think for the hydratrak is 3.45:1.

I dont know what mods you can do to the diff to change the ratio. i have 3.9's and it launches bloody hard, but does 2500rpm at 100k's. my fuel usage is only a little higher than it was with an auto, and 3.08:1

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post #6 of 41 (permalink) Old 05-08-04, 05:03 PM Thread Starter
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Re: Diff ratio for good take off

I'd be happy with 2500rpm at 100km. does it throw you back in the seat hard?
Cause thats what im after. With out turbo. Is yours a daily driver OED666?
Did you just use the same year model xr cam? and was it straight bolt in and go?

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post #7 of 41 (permalink) Old 05-08-04, 05:45 PM
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Re: Diff ratio for good take off

well off the mark, with 3.9's is a massive change from 3.08. definitly the pants-O-meter reads quite high...

and yes, its my daily driver...

I have Rollins EB XR cam, and it was a straight bolt on job.

doink1 - What model car do you have???

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post #8 of 41 (permalink) Old 05-08-04, 06:24 PM Thread Starter
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Re: Diff ratio for good take off

97 xh falcon ute. i have droped it 2inchs, resprayed the interior (just need carpet and the seats recovered) so im lookin for a bit of a power upgrade. did you have to do valve springs? and did you get any power increase or did it just smooth out the power delivery?

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post #9 of 41 (permalink) Old 05-08-04, 06:39 PM
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Re: Diff ratio for good take off

I changed from 2.92 to 4.11 and the difference in amazing. Really kicks you in the ass when you take off, but I find when I have the 4.11s I rarely use first gear for regular driving. Alot of people tell you 4.11s are too short for everyday use but I have to disagree. I didnt notice any change in fuel economy and I use it every day.
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post #10 of 41 (permalink) Old 05-08-04, 06:49 PM Thread Starter
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Re: Diff ratio for good take off

Can Anyone suggest a way to get the hydratrac to a higher ratio? What type of diffs did you change to and out of What vehicle did you guys get them out of

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