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Best Diff ratio?? 

 

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 Post subject: Best Diff ratio??
Posted: Wed Aug 03, 2011 3:59 pm 
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Ride: 1995 EF Ford Fairmont

Location: Bundaberg, QLD
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Hi guys i was just wondering what would be the best diff ratio for my EF fairmont GHIA, atm its basicly stock but will end up with a cam, extractors and a full exhaust, plus the basic mods.
i was thinking a 3:45 LSD diff would suit alright? ive done some looking around and cannot figure out what i would be better off with. I dont do much highway driving but i dont want to get s**t fuel economy when i do, do some high way driving.
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 Post subject: Re: Best Diff ratio??
Posted: Wed Aug 03, 2011 7:50 pm 
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Hey there, I went from 3.23's in my NF to 3.45's and it does make a good bit of difference without stuffing up fuel economy, my revs went from 2000 at 110k's to 2200 at 110k's with 18' wheels, so not much difference, but noticeable acceleration improvement.

 

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 Post subject: Re: Best Diff ratio??
Posted: Wed Aug 03, 2011 7:55 pm 
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youve omitted the most important factor - auto or manual.

For an auto you can go 3.9's no issues at all. Theres a few people who are using 4.11's too

With a manual you dont want to go any shorter than 3.7.

And the boys with boost generally dont want any shorter than 3.45.

Remember that 3.45 is the stock XR gears so they arent anything 'out there'. Id recommend 3.9s, you wont regret it. But it can be expensive, $200 odd to buy the gears and $500 odd to fit them. It will be much much more if the LSD needs a rebuild.
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 Post subject: Re: Best Diff ratio??
Posted: Wed Aug 03, 2011 8:08 pm 
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OK it is a Fairlane ... so auto! he does highway so imao 3.9's might be too much but there you go what suits one...... :D

 

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 Post subject: Re: Best Diff ratio??
Posted: Wed Aug 03, 2011 8:15 pm 
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he drives a fairmont not fairlane. I was referring to the original question though if thats what you mean. And he said that he doesnt do much freeway.

But most freeways are 100 anyway and you get a decent RPM with very good acceleration gains. There was a good thread on boosted about this.

Facer01 i recommend you join and read this as it should help and contains plenty of first hand info.
http://www.boostedfalcon.net/viewtopic. ... =+3.9+diff

Edit: just realised that it was mainly for manuals but im sure there are others around for autos. Just do a search.
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 Post subject: Re: Best Diff ratio??
Posted: Wed Aug 03, 2011 8:39 pm 
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fairlane6970 drivs a Fairlane, he was talking about his car when he fitted the 3:45 diff.
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 Post subject: Re: Best Diff ratio??
Posted: Thu Aug 04, 2011 12:15 am 
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Thats why I clarified by saying 'I was referring to the original question'

Anyway hopefully this has been a help for facer01
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 Post subject: Re: Best Diff ratio??
Posted: Thu Aug 04, 2011 2:09 am 
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Ride: 1995 EF Ford Fairmont

Location: Bundaberg, QLD
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hmm im starting to think that 3.9s are the go now or even 3.7s anyone know where or what I can get these gears from, also would like lsd
btw the car is auto.
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 Post subject: Re: Best Diff ratio??
Posted: Thu Aug 04, 2011 5:51 am 
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rhys.c wrote:
youve omitted the most important factor - auto or manual.

For an auto you can go 3.9's no issues at all. Theres a few people who are using 4.11's too

With a manual you dont want to go any shorter than 3.7.

And the boys with boost generally dont want any shorter than 3.45.

Remember that 3.45 is the stock XR gears so they arent anything 'out there'. Id recommend 3.9s, you wont regret it. But it can be expensive, $200 odd to buy the gears and $500 odd to fit them. It will be much much more if the LSD needs a rebuild.


If auto, it will be stall and cam dependant.

If manual and boost you're wrong 3.45 are horrible and you don't get to get the car on boost before you've ran out of first gear. Go 3.08's for turbo manual.
If Auto and with boost, again depends on cam and stall but lower ( ie higher no) ratios are not better always.

 

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 Post subject: Re: Best Diff ratio??
Posted: Thu Aug 04, 2011 7:37 am 
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Not correct there The Judge. 3.45's are fine for a manual turbo, it's what Ford put in BA1. 3.73's were fitting to any 6 speed manual turbo.

 

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 Post subject: Re: Best Diff ratio??
Posted: Thu Aug 04, 2011 8:11 am 
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The Judge wrote:

If auto, it will be stall and cam dependant.

If manual and boost you're wrong 3.45 are horrible and you don't get to get the car on boost before you've ran out of first gear. Go 3.08's for turbo manual.
If Auto and with boost, again depends on cam and stall but lower ( ie higher no) ratios are not better always.


actually this is part of the reason why im going auto,
it makes boost in 1st but not fast enough, in my case it starts building boost around 2000rpm but it seems that there is not enough load to boost fast enough in 1st.
by the time it hits 12psi its around 4000rpm with around 1500rpm of full power then its pretty much wheel spin on the limiter, where 2nd gear is awsome and is at 12psi by about 2700rpm.
i can pretty much take off in 2nd and almost accelerate as good as it does with a 1st to second gear change..

67RCE wrote:
Not correct there The Judge. 3.45's are fine for a manual turbo, it's what Ford put in BA1. 3.73's were fitting to any 6 speed manual turbo.


imo thats all dependant on the first gear ratio and what turbo is used.
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 Post subject: Re: Best Diff ratio??
Posted: Thu Aug 04, 2011 12:41 pm 
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Ride: 1995 EF Ford Fairmont

Location: Bundaberg, QLD
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have decided on 3.9s or 3.7s what cars should I be able to get them from
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 Post subject: Re: Best Diff ratio??
Posted: Thu Aug 04, 2011 1:17 pm 
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Ride: 1993 EB XR8

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facer01 wrote:
have decided on 3.9s or 3.7s what cars should I be able to get them from

R31 Skyline or Pintara. Stock up on earplugs though. Mal Wood sell bra new gears to suit the Falcon diff if you are willing to spend the money.

 

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 Post subject: Re: Best Diff ratio??
Posted: Thu Aug 04, 2011 1:28 pm 
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Ride: EF Fairmont Sedan

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67RCE wrote:
......................... Mal Wood sell bra new gears to suit the Falcon diff if you are willing to spend the money.
Around the $650 mark i was quoted for a brand new set...........
Apparently "Strange" make then for Borg Warners

 

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 Post subject: Re: Best Diff ratio??
Posted: Thu Aug 04, 2011 1:45 pm 
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I had 3.9's and an auto. It was a really good setup fuel economy didn't really change either.

 

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