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diif ratio 

 

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 Post subject: diif ratio
Posted: Mon Aug 13, 2007 5:18 pm 
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i want to change my diff ratio its too high, but i would like to know what a good ratio would be that i will have the good take off but yet a still go the balls on the highway.i have 3.45 atm.
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Posted: Mon Aug 13, 2007 5:27 pm 
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I dont know exactly what you mean by 'go the balls on the highway'

If you mean accelaration at all speeds then stick with your 3.45, or i would personally go 4.11, thats if you dont mind it revving at around 2450rpm @ 100km.

If you want it to drop the revs on the highway and slower acceleration go 3.23 gears, although it would be a complete waste of money imo
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Posted: Mon Aug 13, 2007 5:32 pm 
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3.45 is to slow off the line for me, i think i will change it to 3.23, what did the el xr6 c*m out wit?
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Posted: Mon Aug 13, 2007 6:01 pm 
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ah thats a move backwards.. 3.23 will be slower again maybe look at 3.9's

 

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Posted: Mon Aug 13, 2007 6:02 pm 
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but wouldnt 3.23 be quicker off the line???
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Posted: Mon Aug 13, 2007 6:59 pm 
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can anyone who knows how work out what the 100kmh rpm speeds would be in a 4 spd auto for

3.08 ( i can suply that lol)-- 1850 rpm
3.23
3.45
3.7
3.9
4.11 --2450 rpm


The way I see it if all is pretty linear a 3.7 should be about 2100-2200 on the highway and should boost acceleration well too.

 

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Posted: Mon Aug 13, 2007 7:00 pm 
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GT-01 wrote:
but wouldnt 3.23 be quicker off the line???


No, the smaller the number, the more teeth on the gears, the less rotations of the wheels per rpm which basically means long drawn out gears and sluggish performance.

Standard monts had 3.23 which was still better than the 3.08 the stock models got. The XR6 and the mont ghia's had 3.45 for more performance.

In my opinion, the s**t first gear in the BTR auto calls for a drastic ratio change like 4.11, but like i said, the motor will be revving higher at all given speeds compared to what your used to.

In a T5 manual falcon i wouldnt go higher than say, 3.7 because of the final drive ratios which already make it rev higher than the auto's to begin with......

Last edited by FordFairmont on Tue Aug 14, 2007 7:15 pm, edited 2 times in total.

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Posted: Mon Aug 13, 2007 7:06 pm 
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More Grunt wrote:
can anyone who knows how work out what the 100kmh rpm speeds would be in a 4 spd auto for ......


Just take note of what revs your doing with your current diff ratio and...

(current rpm @100) divided by (current diff ratio) multiplied by (new diff ratio)

eg. It does 1850rpm @100km/h with 3.08 diff and you wanna upgrade to 3.7 so...

(1850 / 3.08) = 600.6 x 3.7 = 2222 rpm @100km/h
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Posted: Mon Aug 13, 2007 7:16 pm 
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Mate get 4.11's I run them and with stock tires sizes you will not be revving at 2450 at 100km you will Rev at 2250 at 100km/h and 2500 at 110km/h

I run them so i would know.... its fukn awesome off the mark and plenty of freeway balls. back to second at 100 and your outa there. you will get about 65 odd outa first and around 115 odd out of second.

 

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Posted: Mon Aug 13, 2007 7:45 pm 
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ebfairmont3.9 wrote:
Mate get 4.11's I run them and with stock tires sizes you will not be revving at 2450 at 100km you will Rev at 2250 at 100km/h and 2500 at 110km/h


I am 99.9% positive he will at least be at 2350 rpm with 4.11 gears. It all depends what hes doing now at 100 and it can be worked out with the formula i posted, and its very accurate as it was spot on with my car when i converted

Didnt you say you havnt recalibrated the speedo yet after your diff swap?
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Posted: Mon Aug 13, 2007 7:50 pm 
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i worked out using net calcs with tires size, gear ratio, etc and it was spot on to where my tacho is when im doing 100, it actually read abotu 2280 or somethin like that on the calc but i cant c that on the tacho. and almost exactly 2500 at 110.

 

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Posted: Mon Aug 13, 2007 8:06 pm 
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second @ 100!

70k's with 3.45:1 and a T5, slap that into second and it screams, after that you have to mother the car... poor gearbox.

 

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Posted: Mon Aug 13, 2007 10:33 pm 
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i sit on 2100 with 3.45 gears in a 4speed.
100 in second, with 4.11's Thats nuts :o
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Posted: Tue Aug 14, 2007 1:00 am 
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yeh. hes right...........

4.11's @ 100km/h will mean 2300rpm
and ~2550rpm at 110.

 

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Posted: Tue Aug 14, 2007 8:43 am 
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moody wrote:
i sit on 2100 with 3.45 gears in a 4speed.


Assuming your 4 speed is a btr auto, then with 4.11's youd be doing 2500rpm @ 100km/h :shock:
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