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Altering diff ratio 

 

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 Post subject: Altering diff ratio
Posted: Sat Jul 14, 2007 10:21 am 
Getting Side Ways
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Location: Castlemaine
VIC, Australia

Hey guys, i have a few really noob questions about diff's:

I think ive got the 3.08 ratio in my EL Futura (gas);
1. Would it be more economical to stick in a lower ratio diff?
2. To do that you could just change the gears inside the diff?
3. Would the extra load on the motor starve the top end of oil or anything like that?

Just thought about it and thought i'd ask :)
Thanks in advance
Matt

 

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Posted: Sat Jul 14, 2007 10:41 am 
Getting Side Ways
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Would definitely change the diff gears, but best left to a diff specialist to do it, as it can be very time consuming to set the correct preload and shimming etc.

I changed to new 3.73 gears and even though it revs higher on the highway, fuel consumption has suprisingly not been affected. The car drives superb and driving around town seems "effortless" and it just gets up and goes without hardly any throttle. Apart from a manual conversion, its the best mod you can do imo

I put this down to, even though it revs higher on the highway, less throttle is needed to maintain those revs.

With an auto i would go a huge jump to 4.11 diff gears, you will notice a massive accelaration increase and revs @ 100km/h will be around 2400rpms which isnt too bad. Nothing worse than spending money fitting diff gears then to wish you had gone shorter.

If your planning on swapping to a manual in the future, then only go as high as 3.73 as the 4.11's will rev way too high.
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Posted: Sat Jul 14, 2007 10:54 am 
Fordmods Junkie
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If you want economy drop some 2.77's in! i got some incredible fuel economy in my old car when i ran them (short time though) was too damn slow. 4 speed auto 2.77's 105 first gear 165 second. But on the highway hmm 1550rpm at 100. about 6.5L Per 100. I went to coolongatta and back from springwood on about 13 litres..

I got 4.11's now it does make economy worse but only on the highway but its not much! prob went from about 8L to about 9.5L it sits on 2250 at 100km/h but its starts to loose economy when u start cruising at 110 which is 2500rpm. I rather a caining lauch then extra economy though.

 

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Posted: Sat Jul 14, 2007 4:30 pm 
Getting Side Ways
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ebfairmont3.9 wrote:
If you want economy drop some 2.77's in!


oops!! i just read his post properly....

To GASMAN, why drop the ratio any further? All you will notice is the car will become more sluggish and will be an unresponsive pig to drive. If anything, just stick with the ratio you have now as it will be as economic as it gets.
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