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Diff Gears, How they affect acceleration

greenfoam

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well I just got my 3.7's fitted and it seems like theres no difference to what it was before...
at 100 it does like 2000 which is what it was doing before I swear. Anyone with manual and 3.7's got any info??

It will be reving at more than 2000 with 3.7s, It'll be on 2400 or so if you really have 3.7s. There nothing really to be gained acceleration wise with a stock cammed 304 by changing diff gears so don't expect to go much faster
 

crewsy

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It will be reving at more than 2000 with 3.7s, It'll be on 2400 or so if you really have 3.7s. There nothing really to be gained acceleration wise with a stock cammed 304 by changing diff gears so don't expect to go much faster

yeh I was cruising on the freeway after I installed it last night and was doing 100 when in actual fact ot was only doing lie 80. I realised today when I was doing 100 and everyone was flying past me hahaha. just needa put my speedo corrector in now.
 

PaulSV6

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For the type of driving you do, the diff ratio in the car at present is probably the most suitable. My reference tells me its 3.08, which is definitely biased towards economy and would account for the sluggish take off.

If you wanted to improve the acceleration slightly without sacrifcing too much economy, your next option would be the 3.46:1 .

I wouldn't recommend going any lower than that.

Calabar, if i went to 3.08, would that make much difference from 2.87 then?

Ive worked out that there is a 7% difference between the two diffs.
 

Calaber

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Calabar, if i went to 3.08, would that make much difference from 2.87 then?

Ive worked out that there is a 7% difference between the two diffs.

Hi Paul,

If you are unhappy with your 2.87, which is a really tall diff, and want better acceleration, the 3.08 won't make much difference - it is still a tall ratio orientated towards economy rather than performance. If you dropped to 3.46:1, you would certainly notice a difference in performance,but also economy and engine noise.

2.87 seems extremely highly geared for an SV6 - are you sure that's what your running at present?
 

PaulSV6

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Hi Paul,

If you are unhappy with your 2.87, which is a really tall diff, and want better acceleration, the 3.08 won't make much difference - it is still a tall ratio orientated towards economy rather than performance. If you dropped to 3.46:1, you would certainly notice a difference in performance,but also economy and engine noise.

2.87 seems extremely highly geared for an SV6 - are you sure that's what your running at present?

Im actually going to buy Andyman's 3.08 out of his VZ wagon, Reading what Danja said earlier about the 3.73:1 7 how much of a difference there was, Thats wat he mentioned earlier, ill double check, but im pretty sure its 2.87:1.
 

dazzah

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Sorry to hijack this thread, but there is a lot of informative posts in this so far, my question relates to diff ratio to tyre sizes, i'm putting a vt v6 engine with the auto gearbox into a 4wd, the original diff ratio for the commodore was 3.08 running about a 22inch (not sure of diameter of stock commy wheel, 16" rim plus 5 or 6 inch of tyre?)...the 4wd will have 4.11 diff ratios and will be running a 33" tyre...Is there a formula to work out what the percentage difference will be.
Thanks
 

greenacc

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yes. The 4.11 diff is 33% lower than the commy.
The 33 inch wheels have a rolling diameter 50% longer than the commy.

The 4WD will be geared 12% higher than the commy. This is probably not what you wanted to hear tho right ?
 

dazzah

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Thanks for the reply, I'm just trying to work out if using the 4.11 diffs and bigger tyres will bring it kind of closer to stock, main concern was that the engine wasn't revving too much...I know if I was using 4.11 diffs and say commy tyre size it will be revving its freckle off and will probably blow the motor up...just wonder how much the 33's would help.
 

greenacc

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what i said above means the engine will be revving 12% lower in the 4WD than in a commy.
You said you are using the commodore auto right ? If the 4WD is heavier than the commo you want it to be geared lower .... not higher or it will be a slug.
 

dazzah

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It's a navara kingcab, so a smallish to med 4wd...and yeh using commodore auto. So run me through this, if it's a 12% difference, say I was cruising along the h/way in a commodore with std diffs at 100klm an hour revs at say 3000 (use this figure as eg)...would the 12% difference mean if I was in 4wd with 4.11 diffs and 33" tyres, revs would be at 2640 or 3360? Did I follow that correctly.
 
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