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Please explain diff ratios 

 

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 Post subject: Please explain diff ratios
Posted: Sun Mar 30, 2014 11:59 am 
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Ride: 1994 ford fairmont ED

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Can someone please explain LSD diff ratios, what they do, which ones are better suited to N/A cars.

3:08

3:23

3:45

4:11

They're the ones I hear of a lot there is probably others that I've missed if so list them as well.

Thank you
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 Post subject: Re: Please explain diff ratios
Posted: Sun Mar 30, 2014 12:19 pm 
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Smaller the ratio, less the engine revs to maintain a set speed.

3.08:1 will use less revs to maintain 110km than a 3.45:1 ratio.

Others are

3.27:1
3.7:1
3.9:1

Common sizes.
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 Post subject: Re: Please explain diff ratios
Posted: Sun Mar 30, 2014 2:30 pm 
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Ride: ford falcon au3 xr8

Location: a shit suburb in sydney
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also when you see the ratio 3.45:1 its 3.45 turns of the tailshaft to 1 turn of the rear wheel..
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 Post subject: Re: Please explain diff ratios
Posted: Sun Mar 30, 2014 2:31 pm 
Getting Side Ways
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Standard ratio's from back in the day were 2.77, 2.92 and 3.23, and the odd 3.50.....all Borg-Warner ratio's......and a very rare 4.00 for an XW ute.......IIRC.
Holden had 2.60, 2.78, 3.08, 3.36, 3.55, 3.90 and 4.44.......IIRC.

 

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 Post subject: Re: Please explain diff ratios
Posted: Mon Mar 31, 2014 11:35 am 
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Ride: EF XR6 Wagon, AU2 XR6 VCT

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Which ratio is best suited to your car depends on what you are using it for. A 4.11 ratio would normally be drag use only, as your engine would be revving pretty high on the highway. Also, a Falcon with the BTR 4-speed auto will normally need a higher ratio than a 5-speed manual in the same car as first gear is very long in the auto. Also, a high-stall torque converter with the auto will allow the use of lower ratios (or avoid the need to swap to a higher ratio).

There is no straight answer for N/A vs boosted. An N/A engine with a wild cam will need a higher ratio than an engine with a small turbo that comes on boost at 2000 rpm. Conversely, an N/A engine with a mild cam can use a lower ratio than a drag weapon with a huge turbo that comes on at 4000 rpm+.

Sorry we can't give definitive answers to your question. If you are planning engine mods, let us know what you are looking at doing. Someone on this forum will have had the experience to know what's likely to work best for your combo.

 

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 Post subject: Re: Please explain diff ratios
Posted: Mon Mar 31, 2014 6:26 pm 
Getting Side Ways
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this may help

Code:
            
                  rpm   
      rpm         difference      %
            
2.77      2143.96   356.04   -16.61
2.92      2260.06   239.94   -10.62
3.08      2383.90   116.10   -4.87
3.23      2500.00   0.00      0.00
3.45      2670.28   -170.28   6.38
3.73      2887.00   -387.00   13.40
3.91      3026.32   -526.32   17.39
4.11      3181.11   -681.11   21.41
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 Post subject: Re: Please explain diff ratios
Posted: Mon Mar 31, 2014 8:32 pm 
Fordmods Junkie
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66 coupe wrote:
this may help

Code:
            
                  rpm   
      rpm         difference      %
            
2.77      2143.96   356.04   -16.61
2.92      2260.06   239.94   -10.62
3.08      2383.90   116.10   -4.87
3.23      2500.00   0.00      0.00
3.45      2670.28   -170.28   6.38
3.73      2887.00   -387.00   13.40
3.91      3026.32   -526.32   17.39
4.11      3181.11   -681.11   21.41



can ya explain fa a err 'novice' :mrgreen:
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 Post subject: Re: Please explain diff ratios
Posted: Mon Mar 31, 2014 8:37 pm 
Getting Side Ways
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I had a hq ute with a 308 and an auto with 391 diff gears, she was screaming at 80km/h but shot off the lights like a monster. Theres a few threads on here from guys with specific setups and different diff gears you could check out. I think 3.45 is best with ticky setup and auto as a daily but dont quote me
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 Post subject: Re: Please explain diff ratios
Posted: Mon Mar 31, 2014 8:39 pm 
Getting Side Ways
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Age: 38

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Location: Perth
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66 coupe wrote:
this may help

Code:
            
                  rpm   
      rpm         difference      %
            
2.77      2143.96   356.04   -16.61
2.92      2260.06   239.94   -10.62
3.08      2383.90   116.10   -4.87
3.23      2500.00   0.00      0.00
3.45      2670.28   -170.28   6.38
3.73      2887.00   -387.00   13.40
3.91      3026.32   -526.32   17.39
4.11      3181.11   -681.11   21.41


ok so say your ratio is currently 3.23 and your wanting to know the difference between that and 3.9

therefore look at 1st column, whatever speed you currently doing at 2500 rpm with 3.23 (say 100km/h), you will do the same speed at 3026rpm with 3.9's

the second column just shows the rpm differences between the ratio's based on 3.23 and the third column is just rpm percentages
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 Post subject: Re: Please explain diff ratios
Posted: Mon Mar 31, 2014 9:01 pm 
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 Post subject: Re: Please explain diff ratios
Posted: Tue Apr 01, 2014 1:54 am 
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Ride: 1994 ford fairmont ED

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Thanks for all the replies so far.

The only things done to my car are full exhaust with 4499 pacies and wade 1636 cam. The diff is whatever is standard for a ed mont. I'd like to change it to a LSD but don't know what ratio to go. I enjoy all kinds of driving and do a bit of freeway driving.

The future will hopefully bring a au motor with a bigger cam and different headers so if I change the diff I'd like it to suit the new engine as well.
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 Post subject: Re: Please explain diff ratios
Posted: Tue Apr 01, 2014 7:16 am 
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Ride: NL Fairlane Ghia V8

Location: Geelong
VIC, Australia

I went 3.91's in my NL and it's the best mod i've done. Goes hard off the line, gives better economy around town cause you barely have to touch the throttle, and only uses an extra 300 or so rpm at 100 kph.

Don't bother with 3.45's, it's just too small a step from 3.23's, and the 4 speed autos 1st gear is way tall.
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 Post subject: Re: Please explain diff ratios
Posted: Tue Apr 01, 2014 11:08 am 
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Ride: EF XR6 Wagon, AU2 XR6 VCT

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Agree with NLGHIA5.0: If you are currently running 3.08 or 3.23 with the auto, go to at least the 3.7. Even with 3.45 and only a mild cam, the first gear in the auto is way too tall. I have two XR6s, both with 3.45 and autos. I have a 2800-ish rpm high stall torque converter in the EF (with a mild cam), and it launches great now. But with the stock torque converter, it was a bit of a slouch off the line. If I was starting from a 3.08 or 3.23, I would skip the high stall and go with a 3.7 or even 3.9 diff. Fourth gear is high enough that it won't be revving too bad at 110km/h cruise.

Or you can do what it seems most fordmodders have done: swap in a 5-speed manual. :D

 

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 Post subject: Re: Please explain diff ratios
Posted: Tue Apr 01, 2014 1:10 pm 
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Ride: 1994 ford fairmont ED

Location: perth
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A 3:27lsd from a v8 sprint has popped up on gumtree. How would that go?

I had 3:45 in my v8 ed ghia and that was great
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 Post subject: Re: Please explain diff ratios
Posted: Tue Apr 01, 2014 7:37 pm 
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Ride: 1993 EB XR8

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Would be same as what you have, just just LSD.

 

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