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What diff ratio is too low? 

 

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 Post subject: What diff ratio is too low?
Posted: Mon Mar 27, 2006 7:08 pm 
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I'm wondering what diff ratio would be too low in order to maintain driveability. I mean I know of cars having 4.11:1 gears.
I mean I want to be able to drive upto around 160 (overtaking while country driving) without going anywhere near the max speed of the car.
At the moment I have 3.23 gears... 3.45 gears are easily obtainable, but for a little extra cost I could have 3.7:1 gears fitted.
Anyone have higher diff ratios or know of ppl that do?

Last edited by AdamN on Tue Mar 28, 2006 11:38 am, edited 1 time in total.

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Posted: Mon Mar 27, 2006 8:06 pm 
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auto or manual?

go too high in a manual and 1st will become useless (wheelspin much??)

go too high in an auto and you'll be revving too high at 100km/h which could impact fuel economy.... ford says the falcon's standard tune is for best economy between 80-120kph, find out what your revs are in top gear at 120kph now and aim for around that amount of revs in top gear @ 100 with the future diff should mean your economy won't suffer much at all
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 Post subject: Re: What diff ratio is too high
Posted: Mon Mar 27, 2006 8:30 pm 
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AdamN wrote:
I'm wondering what diff ratio would be too high in order to maintain driveability. I mean I know of cars having 4.11:1 gears.
I mean I want to be able to drive upto around 160 (overtaking while country driving) without going anywhere near the max speed of the car.
At the moment I have 3.23 gears... 3.45 gears are easily obtainable, but for a little extra cost I could have 3.7:1 gears fitted.
Anyone have higher diff ratios or know of ppl that do?


Go the 3.45's mate.

It'll give you the s**t on the highway if you have 3.7's. Revs will be too high in top gear.

I wouldn't want my 3.45 equipped manual XR6 to rev any higher at 110km than it does now...

If you only drive around town and take her out on the highway once in a blue moon, go for the 3.7. Otherwise 3.45 is your best bet :)
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Posted: Mon Mar 27, 2006 10:24 pm 
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Sorry - your post is a little confusing - are you after a lower ratio or a higher ratio??

If you want a lower ratio - for a 6cyl - I would go for a 3.45:1

I have 3.9:1 in my car, but I wouldnt recommend that unless you have a 6 speed.

I wouldnt go higher than 3.23:1 - it would be an absolute dog to take off.

 

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Posted: Mon Mar 27, 2006 10:45 pm 
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i have 3.45 in my ef, and it sits on 2500rpm at 120kph...
its auto too

 

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Posted: Tue Mar 28, 2006 11:39 am 
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Yeah I got an auto.. and yeah I did mix up high with low.
I have a 3.23:1 at the moment... thing is 3.45:1 doesn't seem like that big a change. Am I wrong?
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Posted: Tue Mar 28, 2006 12:48 pm 
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Pulco wrote:
i have 3.45 in my ef, and it sits on 2500rpm at 120kph...
its auto too

I get the same out of my 3.45, but it's a manual...
Although it's revving a bit high for my liking I still got 9l/100ks driving to canberra and back on the weekend so it's not too bad.

 

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Posted: Tue Mar 28, 2006 6:55 pm 
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if auto 3.73:1 seems to be the go, i have it and love it.

not to sure on manuals, try 3.45?

 

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Posted: Tue Mar 28, 2006 7:06 pm 
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mrnasty wrote:
if auto 3.73:1 seems to be the go, i have it and love it.

not to sure on manuals, try 3.45?


What revs are you doing in 4th gear at 100km/h? 120km/h?
Also, how'd you source a 3.73:1 lsd diff?
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Posted: Tue Mar 28, 2006 7:07 pm 
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I have an auto by the way.
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Posted: Tue Mar 28, 2006 7:23 pm 
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100km/h i sit on 2,300rpm approx. 120km/h without going out and checkin i think its bout 2500rpm.

The diff I actually took from my mates EF that he wrecked with the 3.73's in it. The diff itself was rebuilt and had the LSD center and the gears put in at G&J diffs in dandenong. Most diff centres offer rebuilds and ratio changes, just pop in and ask em. Cost $950 approx for the rebuild/LSD/gears, that was 2 years ago.

 

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Posted: Tue Mar 28, 2006 7:35 pm 
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Yeah that's not too bad :)
Cheers, yeah I was looking at spending just under $1000 if it was fitted.
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Posted: Tue Mar 28, 2006 10:45 pm 
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I've had the thought about upgrading to 3.45.1 but was wondering if it would be really worth it from a 3.23. Auto. and i do a s**t load of country drivin on highways and that.

Anyone know if i would even feel the diffrence?

 

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Posted: Wed Mar 29, 2006 5:06 pm 
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ive heard a few people say they didnt notice when they went from 3.08 to 3.45, hard to say, i definatly noticed a difference, but mine are 3.7's.

 

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