diff ratios

[Jonty m50e30 0]

gidday folks I'm looking for a bit of advice, the m50 engine is going in the car this week and I guess I have to start thinking about diff ratios, I can't find a LSD and I expect no one else can either, so I need to consider the appropriate open ratio the diff in the car currently is a 3.64 I am running a getrag 260 on 205/50/15's the engine should produce about 230-240bhp with LINK and induction, exhaust mods etc and I will be looking for good performance between 80kph and 180kph as that will be the speed range on the circut, revs I am not concerned about at this point, I have lightened the flywheel heaps so it should gain revs pretty quick, probably want to be in 3rd 4th and 5th most of the time so I need to figure out what ratio will best suit, any advice would be appreciated as I have no idea. :banghead:

Cheers

[bumpstop325 0]

there are always LSD's on ebay.

import it and get it recon

[E30-323ti 66]

What gearbox are you running??

If it is a 5spd from the E36 it will have a 1:1 5th so you'll want a 3.25 or 3.46 (3.73 at the shortest).

It is more economical to get a quaife centre for your open diff than to import a 2nd hand LSD from the states and then get it recon'd.

my $0.02

[Jonty m50e30 0]

cheers guys yes thought about importing, however I like the sound of the quaife centre, who in NZ does this? I am running the 260 out of a e28 525, I am pretty certain that it does not have the 1:1 ratio 5th what ratio should I use with this?

[E30-323ti 66]

I'd be inclined to stick with the 3.64 on a M50B25.

Palmside in Chch are the quaife dealer, last time I asked they were ~$1600.

[Carl 3]

I have a 3.25 open diff that I would love to swap for your 3.64

kph when running a Getrag 260 with a 3.25 diff on 205/50/15's @ 6500rpm:

1st = 60

2nd = 105

3rd = 165

4th = 230

5th = 285

Hope that's of some use

Edited October 27, 2004 by ///Carl

[Guest Andrew]

cheers guys yes thought about importing, however I like the sound of the quaife centre, who in NZ does this? I am running the 260 out of a e28 525, I am pretty certain that it does not have the 1:1 ratio 5th what ratio should I use with this?

The 4th is 1:1 .. 5th is slightly overdriven.

[Jonty m50e30 0]

Thanks e30-323ti I will check them out, ///carl what engine are you running to get 285kph obviously not a m20, I will try the 3.64 and if it is crap I will give you a shout re the 3.25, thank Andrew for clearing up the gear ratio in 4th probably means I wont hit 5th on the track, I guess i will have to learn as I go and see how it pans out.

Cheers

[Carl 3]

M20B20, I completely destroyed my 3.45 diff so am using a 3.25 interim, the 3.45 was a good ratio but the 3.25 is too long for my engine, although it's bloody economical with 100kph being 2200rpm in 5th.

E: I should also point out that I was running a 4.45 for a while before dropping a whole ratio because it was way too short with a top end of 205kph redlining in 5th and 1st being completely impractical and 100kph being 3300 rpm in 5th.

Edited October 27, 2004 by ///Carl

[Grant 4]

I have a 3.25 open diff that I would love to swap for your 3.64

kph when running a Getrag 260 with a 3.25 diff on 205/50/15's @ 6500rpm:

1st = 60

2nd = 105

3rd = 165

4th = 230

5th = 285

Hope that's of some use

Carl, I assume that your speeds in different gears are theoretical only. I strongly doubt that a 320i (M20B20) would ever hit 230, or 285 km/h.

Cheers

[Guest Andrew]

Thanks e30-323ti I will check them out, ///carl what engine are you running to get 285kph obviously not a m20, I will try the 3.64 and if it is crap I will give you a shout re the 3.25, thank Andrew for clearing up the gear ratio in 4th probably means I wont hit 5th on the track, I guess i will have to learn as I go and see how it pans out.

Cheers

I think 5th is 0.81 .. we were hitting 5th gear down the back straight at pukekohe @ ~ 220 kph.

Take heaps of photos of the swap.

[Carl 3]

Grant, they are theoretical although I can back most of them up with exception to the 280 odd in 5th

I've got a spreadsheet which calculates the speeds for a given RPM and wheel size and so far it's been extremely accurate as I tested it using all three diffs I had (4.45, 3.45, 3.25) around the 100kph mark so the s/s has been quite valuable.

In regards to my engine when I had the opportunity to get up to speed to test the engines pulling power with the different diffs, with the 4.45 my B20 engine had no probs pulling from 45kph in 5th right up to redline at 205kph.

With the 3.45 it would pull from 50kph in 5th but struggle to get past 3500 rpm which was around 150-160kph from memory, after dropping it into 4th and booting it then changing into 5th it would start to pull away but I didn't have enough track to test how much horsies the B20 had.

I have yet to test the 3.25 for lack of track or private road.

It's really interesting though to note how the motronic engine does fancy stuff to get power/torque from below 4000rpm but once it hits 4k it just dumps fuel and the engine goes like snot - hence why my engine can't pull the 3.25 and 3.45 in 5th gear around the 3500rpm mark but once it hits 4k it has enough horsies to pull away.

[Grant 4]

Is that Ove's spreadsheet?

Also remember that your speedo is wildy out at those speeds and tends to read speeds way over what you are actually doing.

Realistically I doubt whether the M20B20 is cabable of getting over 200km/h at all (regardless of what diff is used), there just simply isn't enough power at high speeds to counter the terrible aerodynamics that the E30 has.

[Carl 3]

Is that Ove's spreadsheet?

Also remember that your speedo is wildy out at those speeds and tends to read speeds way over what you are actually doing.

Realistically I doubt whether the M20B20 is cabable of getting over 200km/h at all (regardless of what diff is used), there just simply isn't enough power at high speeds to counter the terrible aerodynamics that the E30 has.

I can email you the spreadsheet if you like, I don't know who created it but I got it off Glenn so it also has the supra gearbox ratios aswell, pm me your email address and i'll flick it off tonight.

As for my speedo being wildly out, can I point out that i'm running 205/55/15's so my actual speed is more than what my speedo says. I have tested this with Ali and Jamahl's cars while down south as we had the radios, my speedo says 97kph when i'm actually doing 100kph which can be dangerous as doing the standard 105-110 on the open road is actually more like 110-115...in the ticket zone

I can testify that my M20B20 has done over 200kph, it redlined with the 4.45 in 5th @ over 205kph on the speedo, so taking the speedo *wildly out* into account that would be in excess of 210kph.

Note that I have twin coby's (1 for each pipe) instead of a cat so that may make a diff.

[Gus 5]

the terrible aerodynamics that the E30 has

what?!?! bricks have feelings too

[Gus 5]

and as for speedo error....i passed one of those sign thingys doing "50" it told me i was doing 44

schooled...then it went up to 80

[Guest Spargo]

They had one of those on the onramp coming out of akl city once, it took me a few goes to get a high score

Jonty, can you go into extreme detail your brake setup? Are you going hydraulic or vaccuum? Remote booster or none? Twin masters? I want to know it all.

[Grant 4]

As for my speedo being wildly out, can I point out that i'm running 205/55/15's so my actual speed is more than what my speedo says. I have tested this with Ali and Jamahl's cars while down south as we had the radios, my speedo says 97kph when i'm actually doing 100kph which can be dangerous as doing the standard 105-110 on the open road is actually more like 110-115...in the ticket zone

I can testify that my M20B20 has done over 200kph, it redlined with the 4.45 in 5th @ over 205kph on the speedo, so taking the speedo *wildly out* into account that would be in excess of 210kph.

Note that I have twin coby's (1 for each pipe) instead of a cat so that may make a diff.

Believe me, at speeds in exces of 120km/h, the speedo on an E30 is wildly out, and will read at a speed much higher than you are actually doing (regardless of what size wheels you have).

[E30-323ti 66]

Sam (E34-535ti) and I made the spread sheet.

Dam website won't let me upload the excel file!!

Sorry folks

Here is a screen shot for you Jonty, getrag 260 w/3.64:1 & 205/50 R15's

And funnily enough you get the same speeds w/3.91:1 & 245/40 R17's Like mine!!!

[Guest Andrew]

Carl I wouldn't be suprised if the speedo was 20 K out at those speeds.

Motronic doesn't do any of those fancy things. It has a partial throttle map and a WOT map. It can advance/retard timing.

[Ghost 0]

Speedo out in an e30- nah

We WERE doing 247... dont knock it back

[Carl 3]

Carl I wouldn't be suprised if the speedo was 20 K out at those speeds.

Motronic doesn't do any of those fancy things. It has a partial throttle map and a WOT map. It can advance/retard timing.

WOT map, advancing/retarding, I consider that to be doing something fancy.

As for the speeds, when I redlined the 4.45 at just over 200kph, I checked the s/s for the theoretical top end and the speeds matched up...so go figure, perhaps your pickups are a little funny, you may want to check that your banana skins haven't messed things up

[Guest Andrew]

Carl I wouldn't be suprised if the speedo was 20 K out at those speeds.

Motronic doesn't do any of those fancy things. It has a partial throttle map and a WOT map. It can advance/retard timing.

WOT map, advancing/retarding, I consider that to be doing something fancy.

As for the speeds, when I redlined the 4.45 at just over 200kph, I checked the s/s for the theoretical top end and the speeds matched up...so go figure, perhaps your pickups are a little funny, you may want to check that your banana skins haven't messed things up

OK so maybe you got 200 .. but let us know if that 60 kW can push it any more

[Jonty m50e30 0]

cheers e30-323ti thems some interesting figures, possibly pretty good for the circut, should hit those speeds fairly quickly with the m50 I think I'll stick with the 3.64 until I find or create a lsd.

CiLK WuRM I have biffed the vacum booster, it gets in the way of the inlet manifold anyway welded a plate over the hole and re mounted the original master cylinder, just fabricated a push rod that fits nicely into the linkage in the car and straight into the master cylinder. I considered twin masters and a bias bar and this is what I will do eventually just needed it out of the way for now.But I feel that the booster gives a bit of a false feel on the track so I will be sticking with hydro - besides who doesn't want thighs of steel , I will get some photos up of the brake system.

Put the engine in the hole today every thing just bolts right in - - Everything but the exhaust manifold that is - - that gets nice and stuck on the steering column - Oh well kinda figured that so here comes some new hand made extractors - fiance's gunna spew oh well I'll get some pics of the install up soon, very simple in a circut car with no ECU to match up etc.

[Carl 3]

Haha, Glenn, if I use 7000 as the max rpm my car theoretically can do 300kph

I think it actual rev limits at something more like 6800, just not quite getting there