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Old 10-31-2001, 00:35   #1 (permalink)
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Diff Ratio

I started thinking the other day about the effect that a lower ratio diff would have on my XF. At the moment it is 2.77 single wheeler and I would like to get a 3.23 or 3.9 :1.

Would the car go a crap load better with a 3.23 or would i be better with the 3.9??

The car is a 5spd so I would hope that when cruising at speeds its not yelling. Does anyone have any experiences with this ratio change or could someone point me in a direction where i could get some info?? One last question, what revs would the motor do at 120kmh in 5th with both the 3.23 and 3.9?

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Matt
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Old 10-31-2001, 15:11   #2 (permalink)
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Matt,

Some simple arithmetic says that with the 3.23 you revs will rise around 1.2 times and with a 3.9 they will rise around 1.4 times everthing else remaining unchanged.

So if you do say 2500rpm now at a given speed and gear you would be doing ~2900rpm with the 3.23 and ~3500rpm with the 3.9's.

I would suggest 3.23 for an everyday driver with minor engine mods. The 3.9 would be more suited to a very rev happy engine and short sprints (not happy on the highway).

Just my 2cents.
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Old 10-31-2001, 16:30   #3 (permalink)
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From what a guy at work said with his XF, it's doing 2700 somethin at 100km/h. I got a 3.23 in my baby and she turns 1950rpm at 100km/h.

Oh yeah acceleration will be heaps toey with the 3.23, if you want a good compromise get the 3.45 (XR's have got em)stronger takeoff and at 100 you'll be doing 2200rpm.
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Old 10-31-2001, 18:38   #4 (permalink)
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How would you go about getting a 3.45 into an XF?
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Old 11-01-2001, 12:02   #5 (permalink)
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I have a friend who replace his 3.45:1 gear set with a 4.11:1 unit. At 100 km/h on the highway I think he was doing around 2600 - 2700 rpm in fifth gear.
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Old 11-06-2001, 20:08   #6 (permalink)
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Quote:
Originally posted by EF_Falcon_GuY
I got a 3.23 in my baby and she turns 1950rpm at 100km/h.

My 2.92 with a T5 pulls 1900 at 100kmh in 5th. What transmission do you have?
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Old 11-06-2001, 20:30   #7 (permalink)
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Quote:
Originally posted by EA S


My 2.92 with a T5 pulls 1900 at 100kmh in 5th. What transmission do you have?
I've got the BTR T5OD, which is an evolution of the T5, ratio's can vary from gear to gear. By the sounds of things it looks like i've got a taller 5th gear than yours which is offset by the shorter diff ratio.
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Old 11-06-2001, 20:40   #8 (permalink)
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Quote:
Originally posted by EF_Falcon_GuY


I've got the BTR T5OD, which is an evolution of the T5, ratio's can vary from gear to gear. By the sounds of things it looks like i've got a taller 5th gear than yours which is offset by the shorter diff ratio.
Sounds like yours is the one to have for highway driving with 3.23.
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Old 11-06-2001, 20:58   #9 (permalink)
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Quote:
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Sounds like yours is the one to have for highway driving with 3.23.
Yeah she's quite relaxed at highway cruises, and really hauls from 110km/h onwards. A touch of the gas at 110km/h and it will see 140-150km/h.

But i would want it to be alittle nippier off the line to 80km/h. I think a 3.45 would do the trick.
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Old 11-06-2001, 22:31   #10 (permalink)
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Quote:
Originally posted by EF_Falcon_GuY


I think a 3.45 would do the trick.
I was going to go for 3.45 as there's not enough jump from 2.92 to 3.23 to justify it, but I've heard that 3.55 are more readily available and cheaper, but I haven't looked into it yet. Then again, the 2.92 moves pretty well once it winds up a bit and I've started to wonder whether I might leave it in and just put more punch into the donk. Decisions, decisions.
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