Diff Gears, How they affect acceleration

[Calaber]

cheers danja and calaber, useful info there. i've been meaning to do some research on it, cos mine feels sluggish at times off the line, but i dont want to be sacrificing too much top end power cos i do a lot of highway km's every weekend. its easily 400kms highway per weekend, and 100 if i'm luck in town.
my engine is a stock V6, save for a catback 2.5 inch exhaust, and it'll stay almost that way. maybe some extractors at some stage and a CAI.
what diff gears should i be looking at if i want decent acceleration and power up to about 150kmph? and what else should i look at upgrading? what are some of the downsides from this?
apologies to the OP, i feel like i'm stealing the thread. My bad lol
CC

For the type of driving you do, the diff ratio in the car at present is probably the most suitable. My reference tells me its 3.08, which is definitely biased towards economy and would account for the sluggish take off.

If you wanted to improve the acceleration slightly without sacrifcing too much economy, your next option would be the 3.46:1 .

I wouldn't recommend going any lower than that.

 

[GAMBLR]

ok mate thanks for the input, much appreciated.

 

[ozz]

i have a vs v6 which i just got 3.9 gears in

the acceleration is definitely quite a bit better, fuel economy hasn't really been affected, first tank it was even with what i was getting on the old diff, this tank i got 1L per hundred more, but i think my driving might account for that:whistling

i dont do much highway driving though, doing 400kms a weekend on the highway i think it would probably get on your nerves, going through more petrol, and sitting on higher revs. at 100 mine sits on about 2200-2300rpm from memory

the only time i really notice the difference is in 1st and 2nd. the only times it gets into first is when stopped or nearly stopped, but 1st has so much torque, way more acceleration. if you get gears, id get either a spool or lsd as well. i got an lsd, but without it traction would be a big problem in 1st (and lets face it single spinners are embarrassing)

would i reccomend it? **** yeah.

 

[crewsy]

if your doing that much highway driving I wouldnt bother changing them, but as said, if you really want a little more acceleration but dont wnt to compromise your highway driving too much, go for the 3.45's but honestly I dont really see too much point in that

 

[greenacc]

Geez, this thread has gone a little crazy.
The answer to the original question is that lower diff ratio will ALWAYS give faster accelleration...... thats until you hit the red line in top gear doing about 150, and your mate with the stock ratio catches you and fly's right by.

 

[Calaber]

i have a vs v6 which i just got 3.9 gears in

the acceleration is definitely quite a bit better, fuel economy hasn't really been affected, first tank it was even with what i was getting on the old diff, this tank i got 1L per hundred more, but i think my driving might account for that:whistling

i dont do much highway driving though, doing 400kms a weekend on the highway i think it would probably get on your nerves, going through more petrol, and sitting on higher revs. at 100 mine sits on about 2200-2300rpm from memory

the only time i really notice the difference is in 1st and 2nd. the only times it gets into first is when stopped or nearly stopped, but 1st has so much torque, way more acceleration. if you get gears, id get either a spool or lsd as well. i got an lsd, but without it traction would be a big problem in 1st (and lets face it single spinners are embarrassing)

would i reccomend it? **** yeah.

Did you alter your speedo gearing to match the diff? If not, your speedo, odo and trip computer will be giving you false (optimistic) readings.

 

[ozz]

yeah im using the jaycar speedo corrector. the speedo odo and trip all read correctly

 

[crewsy]

well I just got my 3.7's fitted and it seems like theres no difference to what it was before...
at 100 it does like 2000 which is what it was doing before I swear. Anyone with manual and 3.7's got any info??

 

[graemevb]

There may be some confusion here in what is meant by a higher ratio, the original poster rates 3.9 as high and 3.08 as low, where others talk about it the opposite way around. The diff is a speed reducing or force multiplying device so its possible better to refer to diffs that create a lower output speed as lower ratios, that's what is most typical so Ill go with that.

Its been written above that by changing to a lower diff ratio then the acceleration in any given gear will be higher. this is true, but by itself gives the misleading idea that the car will accelerate faster overall, untrue.

The car will accelerate at a higher rate in a given gear with a lower diff ratio, the trade off being that it will be at a lower road speed, and basically the same rate of acceleration as a previous lower gear at the same road speed. There is nothing magical about putting in another diff ratio, no more than putting on smaller wheels.
The only real factor on acceleration at a given road speed is the rpm that the engine is doing which as mentioned by several is just due to the overall gearing created by the whole drive train.

Given that most of us at least have four gears to play with, Choice of diff ratio really is only a consideration for not getting the car bogged down in 1st gear and at the opposite end of the spectrum having the revs low at cruising speed.

 

[danja]

well I just got my 3.7's fitted and it seems like theres no difference to what it was before...
at 100 it does like 2000 which is what it was doing before I swear. Anyone with manual and 3.7's got any info??

What info are you after?