Diffs combined with the sports gearboxes

[petroscf]

As I didn't find something on the e21.net, I assume that diff ratio for 323 was 3,45 with all types of gearboxes?
Or did bmw provide other ratios, depending on gearbox type?

[gerrit323]

Nope 323i was always 3.45

[petroscf]

Ok, thanks for the info.

I have the feeling that the car needs to run (or I prefer so) a bit longer.
So, when everything's solved with the engine issues, Ι may look for 3.45 internals, I guess after all the difference from 3.64 I now have won't be that huge...

[petroscf]

Does anyone know, if someone ordered the dog leg gearbox with the 320, did bmw provide a longer than 3.64 diff then perhaps?

[Jeroen]

Noooo again. One diff for each model regardless of gearbox, period. There is a reason for a close ratio gearbox like in the dogleg, and that is optimum performance. Gears closer to each other and no silly overdrive. If BMW were to combine that with a longer diff (effectively making gears longer again) they would undo 99% of the gains achieved with the close ratio box again. What is it that you want? If you want economy, don't get a CR box...

[3771489]

3.36 was possible 323i with cr-box,but it is really ultra-rare. 3.36 crowngear set is still available by Bmw ~600€. Part 33 12 1 209 083.

[petroscf]

Jeroen you're right, first of all I should know what I want.
Truth is I am not sure what I am after
I guess I like to have a faster car, with an engine with enough power, but don't want a totally racing feeling, I know I would probably loose a bit reprise, but wouldn't I gain some max speed? Also, wouldn't acceleration from 0-60mph be quicker if Diff is a bit longer?
And for sure, the engine will gain some life, no? After all the difference is not big I think between 3.64 and 3.45 or is it? The dogleg is always a dogleg with 2nd-3rd and 4th being so close, whatever diff is there to the rear
I really need your opinions here guys, I am thinking of giving it (3.45) a try (and if I don't like it then re swap for 11-40)

[petroscf]

3.36 was possible 323i with cr-box,but it is really ultra-rare. 3.36 crowngear set is still available by Bmw ~600€. Part 33 12 1 209 083.

Maybe there should be a gearbox with the ratios of a dogleg plus a sixth overdrive

[petroscf]

3.36 was possible 323i with cr-box,but it is really ultra-rare. 3.36 crowngear set is still available by Bmw ~600€. Part 33 12 1 209 083.

Maybe there should be a gearbox with the ratios of a dogleg plus a sixth overdrive

You mean they sell crown and pinion something like 11-37?

[Jeroen]

Never saw a 3.36 diff offered as an option, and never came across one either, interesting. Still, that ruins your gearbox ratios. Your acceleration will be fastest with close ratio gears or a short diff, of even both within certain limits. Top speed you gain with longer ratios in gearbox and diff, again within certain limits.

I find that my 323i with eco overdrive gearbox is a bit too long, could be a little better if the gears were slightly closer, especially in the mountains. I am going to achieve that by using a shorter diff behind that overdrive box. Going one step shorter from 3.45 (323i) to 3.64 (320/6). On the track I used a 3.91 LSD with my 323i (decades ago haha) which really makes things short. You keep shifting and you can only do this on a relatively slow track as you run out of top speed rather quickly. Can't recall what the top speed was back then but probably around 170 kmh.

[petroscf]

Never saw a 3.36 diff offered as an option, and never came across one either, interesting. Still, that ruins your gearbox ratios. Your acceleration will be fastest with close ratio gears or a short diff, of even both within certain limits. Top speed you gain with longer ratios in gearbox and diff, again within certain limits.

I find that my 323i with eco overdrive gearbox is a bit too long, could be a little better if the gears were slightly closer, especially in the mountains. I am going to achieve that by using a shorter diff behind that overdrive box. Going one step shorter from 3.45 (323i) to 3.64 (320/6). On the track I used a 3.91 LSD with my 323i (decades ago haha) which really makes things short. You keep shifting and you can only do this on a relatively slow track as you run out of top speed rather quickly. Can't recall what the top speed was back then but probably around 170 kmh.

Exactly: not being interested in track day use (at the moment), I am however interested in mountain driving, and, unfortunately, to get there you need to pass from motorways.
If we assume that the h/power of my m10 is almost this of a 323i, then you can see my ratio is rather close: You are going to step shorter from 3.45 to 3.64 because you have an overdrive gearbox.
I was thinking the same way (to step a bit longer to 3.45) because the c/r makes the things now just a small bit longer than when you had the 3.91 (top speed I saw so far is 192 but with the car ready to burst-rpm were almost at red-I don't like pushing the engine so much)
2nd-3rd and 4th are so close that in the city you change them all and move in the traffic with 5th

[petroscf]

... Also, wouldn't acceleration from 0-60mph be quicker if Diff is a bit longer? ...

I mean, I have a feeling that, accelerations from 0, if I am guessing right, would be quicker with a bit longer diff as you probably might be one gear change less

[Jeroen]

1. What combo to choose depends on your current setup and wishes. But if you installed a CR gearbox and now want to make this shorter effect undone with a longer diff then why did you install a CR box? That was my question.

2. What do you want, faster acceleration or better numbers? If you measure a 0-100 kmh an extra gearchange may affect your time negatively, but it doesn't necessarily make your car slower. Like with my E30 320iS compared to the E30 M3: the M3 has a faster 0-100 time as it can reach 100 in 2nd, the 320iS has a shorter diff which requires a change to 3rd to reach 100. However, because of the shorter diff the 320iS is seconds faster up to 200. The short diff makes the car faster (for example also on 0-80) but if you just focus on a 0-100 time you want a longer diff.

[petroscf]

Yes, I understand what you mean

Of course I am not changing anything at the moment, I want first to live some time with the set up as is, before I decide what I really need. And of course nothing should be decided before the engine makes some kms (I don't know what term is used in English for this, when an engine is new and needs to "soften" a bit first)

However, for instance, on your 323 you would like to shorten it a bit, for a quicker feeling, right? So you would go for a 3,64 ratio, as you have an OD gearbox.
But would you go for a C/R gearbox after that? I mean WITH the 3,64 ratio diff? Or would you consider (in such scenario) re fitting your 3,45 again?

I am not insisting at all, and I am not sure about all this! I am making all these questions, in order to understand what to expect before I do any move

By the way, this 3,36 really exists, I checked it, 3771489 is right! It is 11-37 indeed, and seems to me a very interesting option for a 323i with c/r gearbox!

[Jeroen]

I would not do both on a street car, that would be too short. My point is, once again, why fit a shorter CR gearbox and then make it undone with a longer diff. Then you are almost back where you started (approximately) so that is why I can't think of any reason to go for that combo, unless you now have a diff that is already too short which may be the case with your car at the moment(?). That is why you need to decide what your current setup needs adjustment for. For me it would be -now I find I want a slightly shorter driveline- either a CR box or a shorter diff. Since most times the CR doglegs have slightly more notchy gearchanges and are less fool proof as others hardly can drive with the shift pattern, my choice is to go the easy way and fit a shorter diff instead.

I never contested the fact the 3.36 exists, but as I stated I never ever saw this in any options list. So what particular situation or application was this meant for? The brochures I have all list the dogleg as a separate option without a diff change, and a longer diff isn't listed either. Still I would not have any clue when you would want this. Funny that, as far as I'm aware, it was never used by Alpina. And if there's one car that benefits from a longer diff it would be a M30 powered B6. As far as my information goes the B6 gearbox had modified ratios to compensate for this, but that seems like going for the most difficult option. But perhaps gearbox manufacturer Getrag was more willing to do small scale modifications than diff producer ZF. Still puzzled!