Gearboxes, what's the difference?

[Turbo-Brown]

Anyone know what the difference between the gearboxes fitted to bog standard and 'sport' 325i cars was?

Mine's a bog std one and first gear is irritatingly short when I've become used to close ratio gearboxes over the years!

Cheers!

Alex

[johnono]

change the diff, its probably cheaper, less hasle to fit and will give you a better motorway cruise.
but you probably have a 3.-- lsd anyway so..

[e30_Turbo]

sport boxes have shorter lower ratios, to up acceleration, but not by much...most prefer the std boxes as 60 can be acheived in 2nd with a raised rev limit.

I don't know the exact ratio diff but it is noticable when driving, never had one to compare with but the std one is better for more power I suppose, I like the fact that I can get 120mph out of fourth!

[Turbo-Brown]

They have a SHORTER low 2 gears! Boo! Don't want that!

I was hoping that the 2nd gear onwards would be about the same as the normal one, and that 1st would be higher a-la common close ratio practice.

Cheers for the info guys!

Alex

[Andy335Touring]

Sport boxs have longer 1,2,3 but they are normally coupled with a shorter dif ratio than a standard 325.

325-Dif ratio 3.73

3.83
2.20
1.40
1.00
0.81

sport-Dif ratio 3.91LSD

3.35
2.03
1.36
1.00
0.81

All of these ratios are for face lift car's.

[e30_Turbo]

Andy,

So does that mean I got it right, they are still shorter on the sport box?

And a diff swap would make them longer?

This could be a momment...

[Andy335Touring]

Andy,

So does that mean I got it right, they are still shorter on the sport box?

And a diff swap would make them longer?

This could be a momment...

It's the other way around mate i think ?

Longer closer 1,2,3 on the sport box which is knocked back down by the dif ratio,4,5 is the same so end up shorter because of the dif than in the 325.

I might be wrong though

[Turbo-Brown]

I see, if you multiply the gear ratio by the final drive ratio, you can see that the first three gears on the sport are slightly taller with the last two being shorter.

Also, the first three ratios are closer on the sport, with less of a gap between first and second.

So all I need now is a sport box and LSD.......and for my engine bits to come back from the machine shop.........and to make up the manifolds for these turbos.........and to rewire it for the Emerald........BUT THEN.........the car will be a pile of rust on the drive

[e30_Turbo]

Andy,

So does that mean I got it right, they are still shorter on the sport box?

And a diff swap would make them longer?

This could be a momment...

It's the other way around mate i think ?

Longer closer 1,2,3 on the sport box which is knocked back down by the dif ratio,4,5 is the same so end up shorter because of the dif than in the 325.

I might be wrong though

Andy, I've got the "wording" wrong, seems taller is shorter....I was thinking taller was longer....a proper momment

High diff ratio, short and tall.
Low Diff ratio, Long and close

Same on gearbox....So sport box and 3.73 diff would have a less acceleration than the 3.91??? (Bear with me, I'm trying ) But have better top end?

And the std box mated to a 3.91 diff, would limit it in all the gears? (I can't imagine a shorter 1st! )

[Richy325iTouring]

So what the hell have i got in the touring then?

I got a 3.91 open diff and cant hit 60 in second its more like 55ish


my car fkd up by sound of it

[e30_Turbo]

Richy, I don't think it's poss without a raised rev limiter, mine bounces at 61, just

[Richy325iTouring]

she revs to 6750 and i still cant hit 60

[Turbo-Brown]

fozzymonster, you had it right first time around, taller IS longer.

You're right that a sport box with a std should give worse acceleration, but looked at another way, you'd spend longer in first gear getting the engine up to it's maximum power speed, and then each subsequent change leads to less of a drop in revs so the engine stays in it's power band.

The bigger the number, the better the acceleration for that gear, but of course the less speed it can do.

I'm quite liking the idea of a sport 'box with a std diff.

Wonder if the std crown wheel would fit an LSD though.

[e30_Turbo]

I wonder if tourings had different gearbox ratios then?

[Andy335Touring]

Andy, I've got the "wording" wrong, seems taller is shorter....I was thinking taller was longer....a proper momment

High diff ratio, short and tall.
Low Diff ratio, Long and close

Same on gearbox....So sport box and 3.73 diff would have a less acceleration than the 3.91??? (Bear with me, I'm trying ) But have better top end?

And the std box mated to a 3.91 diff, would limit it in all the gears? (I can't imagine a shorter 1st! )

The high/low/short/tall wording can be a bit

Your two gear box scenario's(sp?) sound right to me.

[Andy335Touring]

So what the hell have i got in the touring then?

I got a 3.91 open diff and cant hit 60 in second its more like 55ish


my car fkd up by sound of it

The tourings are to short geared because of the dif ratio,try a sport box or a differant dif ?

Plenty of cheep 3.73 open difs around or if its got to be an LSD try a 3.64 from a pre-face lift sport ?

Have a play on this gearing calculator to see which set up suits you best.

http://www.unixnerd.demon.co.uk/revs.html

[Richy325iTouring]

well if i use a 3.64 diff as long as my gearbox ratio are standard then i will have amazing topend according to that

[Ant]

I have 3.64 LSD with non sport box and the ratios are loooong, the gearing the way it is sux though because the taller final drive makes the gaping hole in the gearing between 2nd and 3rd mush more apparent, and annoying on a downchange when hooning it .

Sport box please someone ?

[Andy335Touring]

Thats the one down side to that calculator is that i don't think it factors in air resistance or if you have the power to pull the theorectical(sp?) top speed.

It's good for most stuff though.

[Richy325iTouring]

well im after either a 3.64 or or 3.73 lsd

be a few months got some debts and spray to pay for first

[SeamanStaines]

The combo you want is a 3.64 or 3.77 diff with a close ratio Sport gearbox. The number to look for (stamped on the edge of the bellhousing) is a number ending in either HJ or TNN. TNW is a standard 325i box which is the same as the 323i and 325e Eta. It's a wide ratio unit and not that clever.
Many Tourings had the Sport gearbox - my red one did - and they all had the 3.9 diff which is too low.
A point to bear in mind is that 15 inch BBS wheels have a smaller overall diameter (including the tyre of course) than the 14 inch bottle top with the 195/65x14. So a 325i Sport or a Touring with the 15 inch BBS is really revvy at the top end.

The ideal set up would be a 323i dogleg gearbox and an M3 3.25 LSD, but most dogleg boxes are shagged out rubbish and owners are on drugs - they think they're still worth Ԛ£300 when in realisty they all need an overhaul.