Diff ratio for M30 conversion

[m10man]

I dont know if this has been covered yet or not but here goes - I have a 3.46 ratio in mine and it just feels like it needs another gear at highway cruising speeds and it doesnt quite get to 100km/h in 2nd gear.

The guys in Germany reckon the 3.25 ration is the best - has anyone used a higher ratio than 3.46 - if so what is your opinion?

I know where I can get a 3.25LSD, so I should whack it in and try it.

[Gunni]

what are the trans ratios

[bigdek]

3.46 is the optimum diif if you are using an e34 5 speed box

[bigdek]

evodan runs a 3.25 in an m30 touring

[m10man]

I am using the E34 260/6 5 speed. The ratios are: 3.83, 2.2, 1.4, 1.0, .81. Once I get a chip that raises the limiter I should hit 100km/h in second just.

[Gunni]

what is the current max revs?

what you want is to USE the revs , not just run trough them,

60-65kmh in first
95-105kmh in second ,
150kmh in 3rd and so on.

you need a 3,25 if your revving it to 6,4k

[m10man]

I dont know the revs as I still cant get my tacho to work (reading too fast) but I hit the limiter before reaching 100km/h. What is the limiter set at on the 535i?

[Gunni]

My M30 is at 6400rpm

[m10man]

Ok, I have just done the maths. This applies to a car (mine) that has 16 inch wheels with 225/45 tyres on the rear.

With a 260/6 5 speed and a 3.46 ratio diff this is what you get in 2nd gear:
59.9mph (96.4km/h) @ 6400rpm. So with the stock limiter you dont reach 62mph or 100km/h.
63.6mph (102.3km/h) @ 6800rpm. So with a raised limiter it is possible.

With a 3.25 ratio diff you get:
64mph (103km/h) @ 6400rpm. So with the stock limiter 62mph or 100km/h is reachable in 2nd gear.

Just for interest the top speeds would be:
3.46 diff @ 6000rpm = 165mph or 265km/h
3.25 diff @ 6000rpm = 176mph or 283km/h

I can get my hands on a 3.25 LSD so I might bolt it in and try it. I will do 0-100km/h, 1/4 mile and 0-160km/h times with both diffs and see what the difference is. (Honestly officer, this is an official scientific test )

[DRIFTBOY]

I have a chipped M30 (limiter at 6700 rpm, I think) with 205/50 x 15" tyres and a 3.73:1 diff and I want a longer ratio. My speedo shows 67mph at 3000 rpm in 5th gear. I keep going for 6th! And 1st is useless! I normally pull away in 2nd. It will still lay rubber pulling away in 2nd too, even with the engine running badly! I'm looking out for another lsd diff!

[m10man]

I have a chipped M30 (limiter at 6700 rpm, I think) with 205/50 x 15" tyres and a 3.73:1 diff and I want a longer ratio. My speedo shows 67mph at 3000 rpm in 5th gear. I keep going for 6th! And 1st is useless! I normally pull away in 2nd. It will still lay rubber pulling away in 2nd too, even with the engine running badly! I'm looking out for another lsd diff!

Yes I imagine you would - with my 3.46 diff it stills feels like I could use a another gear on the highway. What ratio do you think you want then? I am leaning toward changing mine to a 3.25 for good. Will wait and see what it feels like though - but I really want to be hitting 100km/h in 2nd gear.

[DRIFTBOY]

I think the low revving grunt of these engines can make good use of a long diff. I'd like to have about 60mph in 2nd gear. Not too fussed about top speed but I do do like to hit 150 odd on the speedo now and then!

I like a good shove of acceleration too but it defeats it if you have to change change gear every 3 seconds!

[ric325i]

all this talk gets me VERY excited about getting my conversion done!

just need to find the car and and away.

[Andy335Touring]

Have a play with this mate

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

I have an E34 g/box, 3.64LSD, standard sized wheels/tyres and a rev limiter set to 6.3k(?). It will show 60mph in second on the dials but it won't reach a true 60mph in second according to my old style G-tech.

I want to change to a 3.46LSD and ideally i want the gears from a 325 Sport built in to an E34 box, but i don't know for sure if this is possible but it is very likely.

I have tried a 3.25LSD and it's nice in the first three gears but bogs down/ blunts the pull in 4th and 5th unless you keep the revs up. I didn't top it out properly but i got an indicated 150mph @ 5.5k according to the speedo.

The 3.64 tops out at 150-155mph at about 6-6.1k.

[DRIFTBOY]

I have tried a 3.25LSD and it's nice in the first three gears but bogs down/ blunts the pull in 4th and 5th unless you keep the revs up. I didn't top it out properly but i got an indicated 150mph @ 5.5k according to the speedo.

The 3.64 tops out at 150-155mph at about 6-6.1k.

Going by that I think I'd be happy with a 3.64 or 3.46.
It's not a priority at the moment though, got to get other things up to scratch, with little money to do it!

[nickso]

3.46lsd is good in mine although i still feel it revs too high in 5th when cruising at 70-90mph.

its great for 1st to 4th though.

2nd and 3rd gears are immense

you made the right choice there derek

[m10man]

Thats a great site Andy - would have saved me the headache of working it all out manually
It it good to hear your feedback about the 3.25 ratio also.. You're right nickso about 2nd and 3rd being awesome - just a smigeon behind an E46 M3 in the 60-80mph test in 3rd!

[nickso]

Thats a great site Andy - would have saved me the headache of working it all out manually
It it good to hear your feedback about the 3.25 ratio also.. You're right nickso about 2nd and 3rd being awesome - just a smigeon behind an E46 M3 in the 60-80mph test in 3rd!

i followed an e46 m3 off a roundabout....i was right up his arse to try and get him to floor it....he did and i was quite happy that i wasnt too far behind him in 2nd and 3rd

he was pulling away but i think i surprised him in my crappy old touring

[m10man]

i followed an e46 m3 off a roundabout....i was right up his arse to try and get him to floor it....he did and i was quite happy that i wasnt too far behind him in 2nd and 3rd

he was pulling away but i think i surprised him in my crappy old touring

Cool! I am lucky to be about 150kg or so lighter than you touring guys so I should be able to give one a right old scare. Is there any way you can get the tourings lighter without going stupid? Improving the power to weight really helps.

[ant2]

i have a 3.6 diff and an m3 dogleg so mine is even worse, i really need a 2.93 or something as it does about 130 flat out in 5th

[nickso]

i followed an e46 m3 off a roundabout....i was right up his arse to try and get him to floor it....he did and i was quite happy that i wasnt too far behind him in 2nd and 3rd

he was pulling away but i think i surprised him in my crappy old touring

Cool! I am lucky to be about 150kg or so lighter than you touring guys so I should be able to give one a right old scare. Is there any way you can get the tourings lighter without going stupid? Improving the power to weight really helps.

to be honest the touring is a comfort and speed car for me so im not too fussed about losing some weight....in fact when i can finally get some leather for it im going to be adding weight lol

ive already decided on the e30 project im hopefully going to start early next year....now that car is going to be lightweight

[Brianmoooore]

Easiest weight saving on a car is to remove all the junk that collects in it over time, and for the driver to diet.

[nickso]

Easiest weight saving on a car is to remove all the junk that collects in it over time, and for the driver to diet.

tourings are way too easy to load up with crap in the boot....mine is

[gareth]

the only extra bits mine has kicking about is the bmw tools and a windscreen demister pad!

mine has a 3.91:1 diff at present which is amusing! i can do donuts in 3rd in the dry

[m10man]

mine has a 3.91:1 diff at present which is amusing! i can do donuts in 3rd in the dry

[ant2]

hah try that with a 5th 1:1 box and you can pull 4th i should know

[gareth]

[evodan]

Each to there own I suppose, deppends what you want the car for, I run an every day car with mostly motorway miles so I use a 3.25, cruises at 70 @ 2500 or 100 @ 3500
But would guess that Bigdek is right and 3.46 would be best as this is how BM designed it. although this is a rare ratio to find.

[Ziggy]

I have a chipped M30 (limiter at 6700 rpm, I think) with 205/50 x 15" tyres and a 3.73:1 diff and I want a longer ratio. My speedo shows 67mph at 3000 rpm in 5th gear. I keep going for 6th! And 1st is useless! I normally pull away in 2nd. It will still lay rubber pulling away in 2nd too, even with the engine running badly! I'm looking out for another lsd diff!

PM me when you find one & want to shift the 3.73! Just what my lowly 2.5 (with a noisy 3.91lsd at the mo!) needs...

I'll send you details on one I've found that you may be interested in...

[oze30]

Ive got a 3.73 lsd in mine with an e34 box. Tops out about 125, but i havent really tried to push it. hopefully I will be bringing my touring back when I go, so will be able to have a little 335 meet in Oz!

[orr]

Sorry to jump in, but can anyone explain to me how diff ratio is worked out/or how it works. Thankyou.

[DRIFTBOY]

Very basically, there are two cogs in a differential (final drive).

The (final drive) ratio is how many times the propshaft turns one cog compared to how many times the cog that links to the driveshafts turn.

In say a 3.46:1 diff, the propshaft will turn 3.46 times for every 1 revolution of the driveshafts.

It's a bit like a one speed gearbox, but of course the diff is also there to enable the wheels to rotate at different speeds when the car is turning a corner, as the inside wheel has less distance to travel than the outer wheel.

Martin.

[orr]

Thanks for that but how do you work out the last two numbers eg 46 is it like a clock face,46 meaning 3 quarters of a turn.

[e30world]

swap gearbox

[Brianmoooore]

Thanks for that but how do you work out the last two numbers eg 46 is it like a clock face,46 meaning 3 quarters of a turn.

No, 0.46 is just under half a turn.
3.46 diff should need 346 turns of the input shaft for 100 turns of both output shafts together.
200 turns of the output shaft if the other output shaft is held still on an open diff.