3.25 diff

[DazzyA]

Bit slow getting my head round the diff's, will a 3,25 give good acceleration or top end?

[Andy335Touring]

Nither, it's to tall a ratio for a normal 325, you want either 3.64, 3.73 or 3.91.

The higher the number the better acceleration you get and less top end speed.

The lower you get means less acceleration but more top end speed.

But only to a point !

To tall a dif like the 3.25 will make it slower accerating but it might not gain any top speed due to it not being able to pull the higher gear.

To short a ratio will lose top end speed and you might lose the use of 1st gear. It might not be any quicker because the gears don't last long enough and you will lose time shifting gears.

HTH

[DazzyA]

I see, this diff has come from an M3, or so I'm told.
So one turn of the drive shaft would equal 3.91 turns of the wheels on that diff?

[kam-325i]

I see, this diff has come from an M3, or so I'm told.
So one turn of the drive shaft would equal 3.91 turns of the wheels on that diff?

No, One turn of the driveshaft would give one turn of the wheel !!!

If the Diff is 3.91:1, one turn of the wheel would give 3.91 turns of the propshaft, or the other way round, my head hurts.....

[jmc330i]

I see, this diff has come from an M3, or so I'm told.
So one turn of the drive shaft would equal 3.91 turns of the wheels on that diff?

If the diff came from an M3 then no, because the M3 has a 3.25:1 diff (or 3.15:1 in some cases).

On a 3.91:1 diff, the prop will turn 3.91 times for every 1 turn of the wheels.

[DazzyA]

Oh why am I so thick, I feel like a girl with the offside rule.
If the propshaft turns say 3.91 for one turn of the wheels, then a 3.63 would be quicker on acceleration, surely.
Over 100 turns there would have been 391 turns and 363.
I'm still not sure.

[Eddy]

The best diff for accellerations is a 316i unit that has 4,15 diff ratio... but the most common and usefful is 3,64 or 3,73 with LSD....U get nice get away and a nice top speed....

[Brianmoooore]

It's not quite so simple as a numerically higher diff gives better acceleration.
When I first built my M50 engined touring ( with E36 box), I still had the 3.9 diff (= 4.83:1, in M20 terms), and first gear was totally useless - impossible to put power down without wheelspin, and hitting the rev limiter in milliseconds.

[DazzyA]

I'll check tomorrow what mine is, I must admit I don't seem to have much in first either, a lot more than Brian though.
What about top speed in each gear? Anybody got some figures I can fire at.
Sorry, slightly off topic, but do you need car level to check diff oil?

[johnono]

not worth checking, may aswell change if uԚ´re going to the effort of doing it. havin the car level helps. can be done with the car on the ground. bit fiddly though.. especially if its low

[Brianmoooore]

Loosen the filler plug BEFORE you drain the oil!

[johnono]

top one before the bottom one yep, and dont get it on you