dif upgrade

[Lee]

I have finally found a 3.73 crown,wheel and pinion and LSD which fits the MC and at a brilliant price of $273 (£150ish) Bargain :!:

'Yes sir, ofcourse we can ship to the UK, that will be $400 for shipping'

Bugger :!:

keep searching.

but I guess even at £380 thats a cheap performance mod for a NA car

[khooni]

I have family in the US, If you tell me who is selling it I might bring it back

[Lee]

I have family in the US, If you tell me who is selling it I might bring it back

you might look silly with a 45kg dif under your arm :shock:

and I reckon the airline might want to charge you for another flight!

[Lee]

thought I would revive this as I have ordered my 3.64 LSD

will be delivered on wednesday and it is booked in to be fitted in 2 weeks.

I have a sneaking suspicion that another member is going to beat me to it though :wink:

[physco johnson]

Would be interested to here how much difference the new diff makes to the acceleration. Would also be good to know how much difference (worse I guess) it makes to your MPG on a long Motorway journey.

[chippy]

I have a sneaking suspicion that another member is going to beat me to it though :wink:


Hopefully be fitted by the weekend :twisted:

[c_w]

Whats the standard diff ratio? I must admit it would be nice to have shorter intermediate gears by lowering the diff and making them closer together. Only concern would be top gear on motorway which boarders on being lowish already for this kind of car/engine.

[Lee]

Whats the standard diff ratio? I must admit it would be nice to have shorter intermediate gears by lowering the diff and making them closer together. Only concern would be top gear on motorway which boarders on being lowish already for this kind of car/engine.

3.15

check out this calculator... put in the final drive/diff ratio you want and it will give you the speeds/revs per gears

you can change the tyre/wheel size also... is a good tool

http://www.368s.com/tools_rpm.php

Lee

[chippy]

Fitted my 3.46 multiplate LSd yesterday and am really pleased with the improvement 8)

The car now feels more urgent everywhere, especially 3rd-5th, almost as if the car has suddenly gained 30hp :twisted:

Also really pleased to report that it doesn't feel over revvy in top gear. 3000rpm in top gear was 71.5mph (Im running 265/35/18rears) and is now 65.5mph,a difference that i can honestly say hasn't changed the smoothness of the car at all 8)

Lee and i have spent a lot of time researching this swop and we decided that i would try the 3.46 ratio and Lee will try the 3.64(should be bonkers :twisted: )so we can evaluate the best ratio :idea:

The swop is reletively simple if you have a ramp and axle lift as it is mainly just unbolting and re bolting lots of bolts. It took me about 5 hours but having done it once rekon 4-4.5 hours is about right.

Once Lee has fitted his we will do some comparitive tests and post an article on it.

[maahny]

Look forward to hearing the results. I am very interested in doing this upgrade. It makes more sense than trying to gain BHP improvements.

[chippy]

Look forward to hearing the results. I am very interested in doing this upgrade. It makes more sense than trying to gain BHP improvements.

They refer to the diff swop in the US as....'The poor mans supercharger' :wink:

Very true! 8)

[chippy]

Look forward to hearing the results. I am very interested in doing this upgrade. It makes more sense than trying to gain BHP improvements.

They refer to the diff swop in the US as....'The poor mans supercharger' :wink:

Very true! 8)

[Lee]

Mine is booked in for wednesday, I brought it forward as I was excited at Tonys results :D

well done Tony, see you this afternoon

Lee

[maahny]

More reliable too I bet :D

My friend spent a vast amount of money on tuning his e30 m3 (now has about 280BHP from NA 2.3 litre engine) and he said the diff upgrade was the best value.

[chippy]

Mine is booked in for wednesday, I brought it forward as I was excited at Tonys results :D

Lee

Best i book off some time next weekend for a bit of back to back testing :wink: :twisted:

[Lee]

Mine is booked in for wednesday, I brought it forward as I was excited at Tonys results :D

Lee

Best i book off some time next weekend for a bit of back to back testing :wink: :twisted:

sounds like a good idea :idea:

I reckon you must know an ideal place Tony :!: shooosh :twisted: :D

lots of testing!

[chippy]

I reckon you must know an ideal place Tony :!: shooosh :twisted: :D

lots of testing!


:wink:

[khooni]

3.64 diff is from which model? Will the M3s 3.62 diff fit?

[Lee]

3.64 diff is from which model? Will the M3s 3.62 diff fit?


Khooni my 3.64 diff gets fitted tomorrow when my car gets serviced

the diff is from a e30 325 sport which had a limited run with LSD

I drove Tony's car (chippy) at the weekend and I can honestly say that I wish I had changed my diff ages ago!

[luke]

what was the cost for the 2 diffs? and where did you get them from?

Thanks


Luke

[brady]

well lee hows the diff?

[chippy]

well lee hows the diff?

Brady

Lee has been a bit manic with work so car didn't go in for the work yesterday. He's hoping to get it dropped off today and picked up tonight or friday.........watch this space :wink:

[brady]

cheers

[Lee]

well lee hows the diff?

Brady

Lee has been a bit manic with work so car didn't go in for the work yesterday. He's hoping to get it dropped off today and picked up tonight or friday.........watch this space :wink:

Cheers Tony :D

will defo have the car back on saturday latest

Im having the VANOS filters changed whilst shes in so not sure if it will be ready tomorrow

also am off out tonight with customer for a heavy night out in London so wont be fit for much tomorrow :? :D

[chippy]

also am off out tonight with customer for a heavy night out in London so wont be fit for much tomorrow :? :D

Lightweight :roll: .........you'd best get some practice in for Le Mans :shock: :lol:

[Lee]

DO IT DO IT DO IT :!:

excellent!

its harder to get the traction down in 1st but the acceleration is far more extreme

Violent comes to mind!

accelerating in 2nd from about 40mph/4000rvs is neck snapping

power is much more available from lower down the revs, no wait at all just force!!

in 5th at 70mph I am doing 3500rvs so about 500 more

dropping a gear to 4th is just not necessary any more, hit the throttle and watch the needles climb

its a rev hungry monster!! :D

this is how it should have been as standard!

[p 5ary]

DO IT DO IT DO IT :!:

excellent!

its harder to get the traction down in 1st but the acceleration is far more extreme

Violent comes to mind!

accelerating in 2nd from about 40mph/4000rvs is neck snapping

power is much more available from lower down the revs, no wait at all just force!!

in 5th at 70mph I am doing 3500rvs so about 500 more

dropping a gear to 4th is just not necessary any more, hit the throttle and watch the needles climb

its a rev hungry monster!! :D

this is how it should have been as standard!

sounds the business lee, what was the grand total?

[c_w]

DO IT DO IT DO IT :!:

excellent!

its harder to get the traction down in 1st but the acceleration is far more extreme

Violent comes to mind!

accelerating in 2nd from about 40mph/4000rvs is neck snapping

power is much more available from lower down the revs, no wait at all just force!!

in 5th at 70mph I am doing 3500rvs so about 500 more

dropping a gear to 4th is just not necessary any more, hit the throttle and watch the needles climb

its a rev hungry monster!! :D

this is how it should have been as standard!

Yep but only if it had a 6th cog to drop the revs on a long cruise. 3500rpm at 70mph is too high IMO for this kind of car, it was even commented in road tests that the standard 5th was a little undergeared to start with compared to the high speed cruising potential of a 6 speed M3.

But I bet if you don't do much long motorway journies then this modification is excellent, I know from experience with my 205GTI just how much difference lowering the final drive makes, it makes the car feel lighter, and the engine more powerful and torquey.

[Lee]

DO IT DO IT DO IT :!:

excellent!

its harder to get the traction down in 1st but the acceleration is far more extreme

Violent comes to mind!

accelerating in 2nd from about 40mph/4000rvs is neck snapping

power is much more available from lower down the revs, no wait at all just force!!

in 5th at 70mph I am doing 3500rvs so about 500 more

dropping a gear to 4th is just not necessary any more, hit the throttle and watch the needles climb

its a rev hungry monster!! :D

this is how it should have been as standard!

Yep but only if it had a 6th cog to drop the revs on a long cruise. 3500rpm at 70mph is too high IMO for this kind of car, it was even commented that the standard 5th was a little undergeared to start with compared to the high speed cruising potential of a 6 speed M3.

But I bet if you don't do much long motorway journies then this modification is excellent, I know from experience with my 205GTI just how much difference lowering the final drive makes, it makes the car feel lighter, and the engine more powerful and torquey.

i get your point but I am not sure if it is just me but I like to drive fast everywhere with bags of power on tap(where conditions permit)

I have tested the car on a long drive and I really can not notice the difference apart from having much more power immediately available.

if i didnt expect the car to rev higher I would not have noticed it!

I think the only real difference for me will be the dip in fuel economy but if you want a economic car you do not buy an MC :D

[exdos]

Lee,

Sounds like a very cool mod. We'll all have to follow you on the Welsh Weekend meet otherwise, we'll all be holding you up :wink: :twisted:

[Lee]

Lee,

Sounds like a very cool mod. We'll all have to follow you on the Welsh Weekend meet otherwise, we'll all be holding you up :wink: :twisted:

John

your welcome to try out car and see what you think of the diff upgrade.

we are really looking forward to the weekend :D

I have taken Dale out in the car since the diff change, I will let him post his thoughts when he is next online.

Lee

[exdos]

John

your welcome to try out car and see what you think of the diff upgrade.

we are really looking forward to the weekend :D

I have taken Dale out in the car since the diff change, I will let him post his thoughts when he is next online.

Lee

Lee,

I'd like to try it :P

I'm currently working on another Exdos mod (nothing to do with air intakes) at the moment which seems promising. I'll let you see what it's all about at the Welsh Weekend meeting. 8)

[dalecan]

After a small drive in Lee's car I can report that it is BALLISTIC :lol:

The acceleration is neck snapping and wheel spin is even more on tap. It will be good to see the 50-70 mph time. It will be even more fun in the wet :shock:


Lee, you will have to let us know what the fuel consumption is like (not that it is that important).

[chippy]

I think Lee and i will have to do some comparative tests with regard to the fuel consumption between my 3.46 and Lee's 3.64 diffs.

Actually, perhaps we should invite Dale along to do a test between 3.15(OEM) and the upgraded diffs :idea:

Any excuse for a run out :twisted:

[agikellodom]

I need a design for my website, who can do it?

[Greenbat]

I need a design for my website, who can do it?

http://i26.photobucket.com/albums/c102/kyeikofi/offtopic1.gif

[dalecan]

Chippy,

I'm up for that. Although, I think I will struggle to keep up :?

[exdos]

chippy and Lee,

Since the OEM diff has a ratio of 3.15, then the 3.46 diif is working with a mechanical advantage of 9.84% over OEM and the 3.64 diff is working at a MA of 15.5% over OEM, respectively.

Since the mechanical advantage is to the engine, then these figures roughly equate to an effective increase in power output of 31.59bhp for chippy's 3.46 diff and 49.52bhp for Lee's 3.64 diff. A cheap "power increase" mod.

One would estimate that there would be a 9.84% (3.46 diff) and 15.5% (3.64 diff)decrease in acceleration timing and fuel economy will also be increased by a similar percentage and the top speed of the cars will also be reduced by the same percentages, respectively.

In the case of the 3.64 diff, particularly, if it's at all possible, I'd be inclined to put a longer 5th gear into the gear box to restore the engine rev/ speed to OEM ratios which will preserve fuel economy when cruising and motorway driving. You'll have more than enough acceleration in the first 4 gears to see off just about everything you meet on the road. :twisted: :twisted: 8) :D

[chippy]

chippy and Lee,

Since the OEM diff has a ratio of 3.15, then the 3.46 diif is working with a mechanical advantage of 9.84% over OEM and the 3.64 diff is working at a MA of 15.5% over OEM, respectively.

Since the mechanical advantage is to the engine, then these figures roughly equate to an effective increase in power output of 31.59bhp for chippy's 3.46 diff


Ha Ha......so i wasn't too far out when i said the car felt like it had gained about another 30bhp :lol: :wink:

[physco johnson]

So if EXDOS is correct then assuming 0-60 of standard car is say 5 seconds and the acceleration should be 15% better then the 0-60 should now be 4,25seconds assuming:-

- You can get the power down
- Timing of 1st to 2nd gear change is consistent
- Engine torque / power curve at given speed vs drag does not come into play.

Unfortunately, being a sad mathmetician type person I would guess the acceleration gains will not be linear as there are a high number of non linear effects that would need to be accounted for.

However, I am sure it does make a bloody big difference, and I would be VERY interested to do the same mod to my MC provided I could source a longer 5th gear as I wouldnt be able to afford the higher fuel costs as I do a lot of motorway journeys.

[exdos]

chippy and Lee,

Since the OEM diff has a ratio of 3.15, then the 3.46 diif is working with a mechanical advantage of 9.84% over OEM and the 3.64 diff is working at a MA of 15.5% over OEM, respectively.

Since the mechanical advantage is to the engine, then these figures roughly equate to an effective increase in power output of 31.59bhp for chippy's 3.46 diff


Ha Ha......so i wasn't too far out when i said the car felt like it had gained about another 30bhp :lol: :wink:

chippy,

You must have a pretty accurate "butt-dyno". Smart arse :lol: :lol:

[exdos]

Unfortunately, being a sad mathmetician type person.

However, I am sure it does make a bloody big difference

So, please do the maths and tell us what the "bloody big difference" is.....

TBH, the actual improvements on "official" timings are irrelevant, what is important is that in either chippy's or Lee's hands, their cars, with uprated diffs, will accelerate faster than they did before with OEM diffs, therefore, there will be real and very significant decrease in time in getting to any given velocity. I assume that their gear-changing skills will remain constant.

[THE ANIMAL]

The problem you might get though with just increasing 5th is that if you end up putting a too tall gear the change between 4th and 5th becomes larger and will drop you out the power band on change and take longer to wind it back up into the rev range.

But a small increase might be ok.
Cars with good flat torque curves this doesn’t effect as much.

It also makes it far easier to accidentally over rev the engine on down change when heal and toeing.

as exdo has pointed out unless your a total monkey at the wheel you will very easily see and feel the performance gain in acceleration, with the sorter diff.

Depending on how sensitive you are as a driver you can even tell the difference between brand new rear tyres on a car and very worn ones the worn ones have a smaller diameter which will have a similar effect to the diff shorter gearing faster acceleration.

[exdos]

THE ANIMAL,

I agree with your comments. The way that I am looking at this though is that unless you get to use your car much at speeds in excess of 120mph then the first 4 gears, used with a higher ratio diff, should be plenty to make you more than "street competitive" up to 120mph. Therefore, by making the 5th gear "taller", to restore the revs/speed relationship to OEM proportions, 5th gear could be considered as a kind of "overdrive" cruising gear, although it could still take you to top speed at the same rate of acceleration as exists with OEM gear/diff ratios. (which is still quite quick :wink: )

It will be paramount that chippy and Lee learn the precise speeds for each gear change-down to avoid over-revving. IIRC Racing Rod blew the Hawthorn's engine with a muffed gear change (was this after they changed the diff??).

I know that chippy wants to take his MC to the Nurburgring, so with his 3.46 diff, he is theoretically reducing his restricted top speed of 155mph (7500rpm in 5th) to 139.75mph. Therefore, if he is wanting to put in a very fast time, what he gains in acceleration may well be lost by having a relatively low top speed. Swings and roundabouts. As I see this, he'd be far better to get to the highest speed he can in 4th gear then accept whatever rate of acceleration the conventional 5th gear ratio might give in order to achieve a top speed of greater than 139.75mph. The alternative would be a 6 speed box with the right cogs to benefit from the 3.46 diff and the 6th gear could then take over where a 5th gear restricted to 139.75mph leaves off.

In the case of Lee and his 3.64 diff; his top speed is now reduced to 131mph and he'll be revving the nuts out of his engine in all gears to get there. I would think that if he can get to, say, 110mph in 4th quicker, then he can afford to coast in 5th gear thereafter to take him on to 155mph should he ever need it. Likewise on motorways the lower revving in 5th gear would save some engine wear.

The higher revving will also increase engine wear rates proportional to their percentages calculated, and also their servicing intervals will also be shortened in similar proportions. No such thing as a "free lunch".

[Lee]

THE ANIMAL,

It will be paramount that chippy and Lee learn the precise speeds for each gear change-down to avoid over-revving. IIRC Racing Rod blew the Hawthorn's engine with a muffed gear change (was this after they changed the diff??).

:

absolutely!, I have been very concious of this!

with regards to my top speed, I have gone quite close to the speed which you have quoted and I have the impression that it will definitely go past this.

I cant remember what the calculator says on 368s.com

i will check

regards

p.s a 6 speed box may be on the cards

[chippy]

How is the coupe restricted to 155mph.......number of revs in 5th, actual speed??

From my research a standard m-coupe(3.15 diff) should be doing about 6650rpm in 5th to reach 155mph.
With my 265/35/18 wheels and 3.46 i would need to be doing 7150rpm to reach 155mph.

So if the m-coupe's limiter is based on actual speed rather than revs in 5th gear, I should still have a top speed of 155mph :?:....not that you would want to hold the car at those sort of revs for long mind :shock:

Just waiting for Prof. Exdos to show me the flaws in my reasoning :oops: :P

[Lee]

the RPM tool says the following for 3.64

7000 revs =141.4mph
7500 revs =151.5mph

is this wrong :?:

[c_w]

I know that chippy wants to take his MC to the Nurburgring, so with his 3.46 diff, he is theoretically reducing his restricted top speed of 155mph (7500rpm in 5th) to 139.75mph. Therefore, if he is wanting to put in a very fast time, what he gains in acceleration may well be lost by having a relatively low top speed. Swings and roundabouts.

If you could ever see 7500rpm in 5th with a standard diff you will be hitting 175mph, 155mph should be around 6650rpm (based on 23.3mph/rpm). The eletronic speed limiter seems to bit a bit random as most figure the M Coupe at 160mph top speed.

The lower diff will suit the Ring better than the longer standard gearing as I found 3rd too long on some parts (the gear you mainly use on the twistier parts), where shorter intermediate gearing would have made it much more punchier, but even with the shorter gearing I don't think you'll run out of gearing in 5th on the Ring.

Generally with lower gearing the car feels more accelerative, often MORE accelerative than it actually is (I wouldn't use hard maths to calculate differences), the main real benefit is much more flexibility in-gear and a more sporting nature of the engine and drive. I would bet that the 0-60 is not lowered much (if at all) by reducing the gearing, the 2nd gear as standard makes a touch under 70mph anyway and for 300bhp this should be fine. When you start getting bigger power they tend to stretch the lower 2 gears to aid traction, and often have 1st gear making 60mph.

A 15% reduction in acceleartion times, lets say 0-100 is 11seconds that would mean 9.35seconds, which goes from very quick, to current supercar quick which isn't going to happen, plus you need an extra gear change to make 100 (in 4th).

However if you reduce it so much that you can't make 60mph in 2nd then you'll increase the 0-60 time (and a 15% reduction DOES do this).

I would go as far as saying a straight line drag would result in little difference in acceleration, but in-gear flexibility would be hugely better with the lower diff ratio making it hugely nicer to drive and more potent on a twisty road where the right gear is always there instead of the "universal" 3rd gear as standard.

[MrMicko]

THE ANIMAL,

I know that chippy wants to take his MC to the Nurburgring, so with his 3.46 diff, he is theoretically reducing his restricted top speed of 155mph (7500rpm in 5th) to 139.75mph. Therefore, if he is wanting to put in a very fast time, what he gains in acceleration may well be lost by having a relatively low top speed. Swings and roundabouts.

I have no knowledge of chippys driving skills, but the Ring is so bumpy track that high speeds with M Coupe is pretty frightening without modifications to aerodynamics and suspension, and maybe even after those modifications. You can watch ring videos from our trips to ring from http://www.carfreaks.net/. I've been driving there also, but my M Coupe is still "ring virgin". Many of you may have seen our M Coupe video clip, that tells a lot about the Ring and its bumpy ride :)

So my point is that 3.46 differential might be ideal for ring, because there is very few places that you achieve speeds like 155mph if you aren't totally insane :)

I recommend watching "Incar: BMW M5 at Nordschleife" from carfreaks.net, M5 driven by skilled driver and you can see what speeds he is going. And track-challenge.com is a great place for information about ring speeds too.

[BEN]

i have seen 165mph before, and 170mph in the roadster

[THE ANIMAL]

I have the answer to all your problems for the ring

http://www.racecarsdirect.com/cars/details.asp?id=34696&cat=5

[BEN]

what about this one!!!!!!

http://cgi.ebay.com/ebaymotors/BMW-Limited-Slip-Differential-LSD-3-91-Rebuilt_W0QQcmdZViewItemQQcategoryZ33731QQitemZ805 5895025QQrdZ1QQsspagenameZWD2V

[chippy]

I chose the 3.46 with the Ring in mind, so will let you know as i hope to get over in July and August.

I have abit of a love/hate relationship with the Ring having done around 130 laps there(mainly on 2 wheels 8) ) which 129 were just motoring nirvana :twisted: and the other one involved a broken neck, blood clots on the brain etc :shock:

It just keeps under your skin......literally :roll:

[BEN]

do you think a 3.91 ratio would get the car under 4 secs?

i have now already started a list of mods if a get the MC back!
dif is number one!

[THE ANIMAL]

I chose the 3.46 with the Ring in mind, so will let you know as i hope to get over in July and August.

I have abit of a love/hate relationship with the Ring having done around 130 laps there(mainly on 2 wheels 8) ) which 129 were just motoring nirvana :twisted: and the other one involved a broken neck, blood clots on the brain etc :shock:

It just keeps under your skin......literally :roll:



Arghhhh ouuch

[chippy]

do you think a 3.91 ratio would get the car under 4 secs?

i have now already started a list of mods if a get the MC back!
dif is number one!

The guys in the states have been doing the diff swop thing for a few years now and the general thinking is that 3.73 is the shortest and most extreme(trackday only) gearing for the coupe :shock: ,all the guys who fitted a 3.91 have changed back to either a 3.46 or 3.73 :wink:

[BEN]

but if you had a 6 box, it could be used?

[Lee]

I have to say that on a non technical level it feels much easier to drive around town and is no way a hinderence on the motorway, but I will do some more high speed testing and report my findings

[c_w]

do you think a 3.91 ratio would get the car under 4 secs?

i have now already started a list of mods if a get the MC back!
dif is number one!

No chance, what you need is a lot more power & traction (and/or less weight), the standard gearing is probably best as it is for quick 0-60 times. Reducing the gearing by putting such a low geared diff on would hinder it IMO unless you have massively stickier tyres but even then you wont make 60mph in 2nd anyway. Not much on the road gets below 4 seconds. The only car you could reasonabley compare to is the TVR Cerbera which does mid 4seconds and is rocketship in a straightline with almost 400bhp and 1100kg (I think it makes 60mph in 1st gear too). Everything else is pure supercar and most of those won't see below 4 seconds.

[exdos]

How is the coupe restricted to 155mph.......number of revs in 5th, actual speed??

From my research a standard m-coupe(3.15 diff) should be doing about 6650rpm in 5th to reach 155mph.
With my 265/35/18 wheels and 3.46 i would need to be doing 7150rpm to reach 155mph.

So if the m-coupe's limiter is based on actual speed rather than revs in 5th gear, I should still have a top speed of 155mph :?:....not that you would want to hold the car at those sort of revs for long mind :shock:

Just waiting for Prof. Exdos to show me the flaws in my reasoning :oops: :P

chippy,

In doing my calculations of your theoretical top speeds I inadvertently assumed that the 155mph was rev limited rather than speed limited :oops: :oops: (typing fingers in gear, brain minus differential)

I do actually know that the MCs speed limiter must work on speed rather than engine revs because MCs have been proven to go to speeds of at least 172mph (gps based recording).

Using your information that with an OEM diff, the speed is limited to 155mph is achieved at 6650rpm, then this equates to 42.9 rpm per mph in 5th gear (6650/155=42.903). Therefore the theoretical maximum speed of an OEM MC is 174.81 mph (7500/42.903 = 174.81). The theoretical and actual attainable figures are thus very close.

In your case with a 3.64 diff where you achieve 155mph at 7150rpm, this equates to 46.13 rpm per mph in 5th gear (7150/155=46.129). Therefore your theoretical top speed at 7500rpm must be 162.59 mph (7500/46.129=162.587). That's with OEM 17' wheels.

I know from using gps on my own MC that the MC's speedo under-records by approximately 7% (100mph when actually doing 93mph) and that when I changed to the same size 18" tyres that you have, the speedo under-records by just 3% (100mph when doing 97mph) therefore your 18 inch wheels will increase your theoretical top speed by just over 4% so you should actually be capable of getting 169mph with your 3.64 diff. :D 8)

Likewise Lee's theoretical top speed will be higher than I earlier suggested it will be approximately 15% less than 174.81mph

[Lee]

I know I can make over 60 in 2nd gear so if I can get the traction down in 1st it should be improved.

I am going to research some really sticky tyres for this summer.

Are the racelogic systems which measure your 0-60 any good?

[exdos]

Generally with lower gearing the car feels more accelerative, often MORE accelerative than it actually is (I wouldn't use hard maths to calculate differences), the main real benefit is much more flexibility in-gear and a more sporting nature of the engine and drive. I would bet that the 0-60 is not lowered much (if at all) by reducing the gearing, the 2nd gear as standard makes a touch under 70mph anyway and for 300bhp this should be fine. When you start getting bigger power they tend to stretch the lower 2 gears to aid traction, and often have 1st gear making 60mph.

A 15% reduction in acceleartion times, lets say 0-100 is 11seconds that would mean 9.35seconds, which goes from very quick, to current supercar quick which isn't going to happen, plus you need an extra gear change to make 100 (in 4th).

However if you reduce it so much that you can't make 60mph in 2nd then you'll increase the 0-60 time (and a 15% reduction DOES do this). etc.

c_w,

I totally agree with what you are getting at here. Increasing the ratio of the diff will make the car more "accelerative". In otherwords, the car will accelerate faster in each gear. However, a more accelerative car might not beat any of the conventional acceleration times (0-60mph, 0-100mph etc.) dependant upon the points at which gear shifting are required. Obviously, there are limits as to how fast you can change gear manually. Therefore any increase in acelerativeness of a car in all gears is not matched by the human hand. Manufacturers deliberately gear their cars to achieve specific performance figures which they can boast about and keep the human element (gear changes) to the minuimum to do so.

As yet, I haven't spent a penny on trying to extract more "juice" out of my MC; all my efforts have been directed at improving the handling of the car, where preservation of speed around corners is my priority. I will be really interested to see first hand, precisely how the diff change improves the performance of Lee's MC at the Welsh Weekend meeting, and I hope he will drive some sections of the route paired with me, if I can keep up with him :?:

[THE ANIMAL]

If you want to have a sorted car for the ring don’t spend the money on the diff. There are far better ways of making your car fast with that money for the ring.

(But id have to agree with the diff being great fun in every day driving for the increases acceleration through the gears if you didn’t mind having a max of 155 or maybe lower via gearing).

Id put the diff on as one of last options id do the suspension first Kw3 and the roll bars and strut braces then get another set of wheels with slicks on them or semi slick special track tyres. Large 4 or 6 pot breaks with some nice big 355mm discs then have the car set up nicely on a flat patch with some corner weights then you’ll be nicely set for the ring. One really good value for money upgrade is powerflex bushes all-round and have the rear end converted so you can adjust it set up wise. With the rear end set up properly you get a good increase in rear end grip from the tyres. You’d be amazed.

As exdo pointed out its all about entry speed baby huge entry speed

When you get increase in grip and have higher cornering speeds your going to end up wanting maybe longer gearing as you find yourself in wrong gears with the engine having the balls revved out of it if your too short the art is finding the right set up and balance for what you want with it or the circuit.

[c_w]

I know it's slightly off topic but yea uprated brakes are a must for the 'Ring (or trackdays in general), my standard setup with DS2500 pads faded and juddered badly. Road-legal semi slicks are as far as you can go with tyres at the ring as the car has to be road-legal.

I keep reading a lot of conflicting opinions on ARBs, about stiffer ones reducing grip etc.

The more I think about a lower diff on the Coupe the more I want one (I know just how much more enjoyable my 205GTi drove after lowering the final drive by 10%) but reducing the already borderline 5th gear cruising is a big negative for me.

[exdos]

As exdo pointed out
I am actually plural i.e. exdos :wink: :lol:

[exdos]

I keep reading a lot of conflicting opinions on ARBs, about stiffer ones reducing grip etc.


c_w,

I've said it before, my car's handling with KW3 suspension was awesome. With H&R ARBs, even on their lowest setting, the handling has gone to stupendously awesome. I'm running with some negative camber at the front, which also helps to increase turn-in but it also increases front end grip too.

My bravery is now the limiting factor to the car's performance, and that is getting better each time I drive, because I now believe that the car will stick to the roads at speeds which I wouldn't have previously thought possible. I keep pushing at the "envelope" and I am just amazed at the grip, but then when I reflect on how the grip is being achieved, it all simply boils down to the theory of car stability working out in practice.

If you can keep both left and right tyres maintaining a contact patch with the road during cornering, then you get a considerable increase in lateral friction resistance over what you are used to experiencing when the car normally rolls to the outside with softer OEM suspension and ARBs. It works the same on both wet and dry roads. It's that simple.

I'm going to try the stiffest settings on the ARBs soon. if I fail to post again then you'll know that the softer settings are the best :wink: :lol:

If you want to see these things in action, bring your MC down here and come and drive with 3 of us who have all uprated to H&R ARBs. Are you free any weekdays next week or Sunday 30th April? We're having a "mini-meet" provided we have a decent weather forecast.

[Greenbat]

I know I can make over 60 in 2nd gear so if I can get the traction down in 1st it should be improved.

I am going to research some really sticky tyres for this summer.

Are the racelogic systems which measure your 0-60 any good?

Lee I have got an AP22 unit

http://www.race-technology.com/WebPage2/Products/AP22/AP22Home.html.

We can do some test runs if possible during the Welsh weekend or you can borrow it for a trial. I haven't actualy tried it on the MC but did quite a bit on my old car. I was getting 5.82 to 60mph and 15.08 to 100 in my 3.0ltr M3

Greenbat

[chippy]

If you want to have a sorted car for the ring don’t spend the money on the diff. There are far better ways of making your car fast with that money for the ring.

(But id have to agree with the diff being great fun in every day driving for the increases acceleration through the gears if you didn’t mind having a max of 155 or maybe lower via gearing).

Id put the diff on as one of last options id do the suspension first Kw3 and the roll bars and strut braces then get another set of wheels with slicks on them or semi slick special track tyres. Large 4 or 6 pot breaks with some nice big 355mm discs then have the car set up nicely on a flat patch with some corner weights then you’ll be nicely set for the ring. One really good value for money upgrade is powerflex bushes all-round and have the rear end converted so you can adjust it set up wise. With the rear end set up properly you get a good increase in rear end grip from the tyres. You’d be amazed.

As exdo pointed out its all about entry speed baby huge entry speed

When you get increase in grip and have higher cornering speeds your going to end up wanting maybe longer gearing as you find yourself in wrong gears with the engine having the balls revved out of it if your too short the art is finding the right set up and balance for what you want with it or the circuit.

Totally agree with you, the diff shouldn't be the 1st mod to think about, but my car isn't totally standard :wink:

One of the reasons for changing the diff was that i was able to get hold of a converted 'racing' multi-plate LSD which has given me more traction on exit. Also as i did the work myself the cost including service items was less than £350 :wink:

If there's one circuit that will show any weakness in your car then its the Ring especially brakes! The only brakes i've had that were up to the task were a set of AP's finest 6 pots.

Talking about suspension, does the KW3 have seperate high and low speed damping as this made a massive difference one my race bike? The dual damping unit i had on my race bike was made by Penske and i have e-mailed them about options for the coupe.

[exdos]

Talking about suspension, does the KW3 have seperate high and low speed damping as this made a massive difference one my race bike? The dual damping unit i had on my race bike was made by Penske and i have e-mailed them about options for the coupe.

chippy,

No. There is bump/compression, rebound and height adjustment only. I've not seen or heard of any suspension for the MC with anymore adjustment possibilities than that. You'd have to set up your suspenion with the best compromise.

I've just done some further calculations (I hope I'm using the right numbers this time :oops: :wink: ) The front track width is 1422mm and with OEM suspension set up there is approximately 75mm of compression, this translates to approximately 3 degrees of bodyroll. With KW suspension the compression can be reduced to about 25mm and this approximates to 1 degree of bodyroll. As you know, the H&R ARBs adjust the rate at which the body rolls, so in the case of KW suspension the lateral rolling can be pretty well controlled. In any case, it's not always the rolling on entering corners that's the problem, it's sometimes the unloading of the roll on straightening out from the corner that can catch you out. Therefore, as I see it, the less bodyroll and the more it can be controlled, the better.

[Lee]

I know I can make over 60 in 2nd gear so if I can get the traction down in 1st it should be improved.

I am going to research some really sticky tyres for this summer.

Are the racelogic systems which measure your 0-60 any good?

Lee I have got an AP22 unit

http://www.race-technology.com/WebPage2/Products/AP22/AP22Home.html.

We can do some test runs if possible during the Welsh weekend or you can borrow it for a trial. I haven't actualy tried it on the MC but did quite a bit on my old car. I was getting 5.82 to 60mph and 15.08 to 100 in my 3.0ltr M3

Greenbat

thanks for this Greenbat!

will be very interested to see!

am hoping to have my car running new wheels/tyres by the welsh weekend so should be putting traction down a little better!

also my new brakes may be available to me so will be stopping pretty quick too :D

[chippy]

Priceless............was just reading the last post from Exdos, when the wife shouts up the stairs..."Where are you?"
To which i replied..."Just reading some stuff on suspension for the BMW"
Bless her she then says..."Why, it just goes up and down right....what more is there to it!" :shock: :roll:

Don't think she'd enjoy most of your post's Exdos :lol:

[exdos]

:lol: :lol: :lol: :lol:
I can talk about all manner of other things if she prefers ....

[THE ANIMAL]

Ahhh now a race diff is a whole different ball game they are certainly worth it. The best point of the diff your talking about a race diff which should have lots of adjustments to it as in your able to loosen or tighten the diff up also you should be able to change the ramp angle as well now setting this form off diff up is a black art and can have huge implications on how your car will handle especially in the corners on entry and exit when your braking on entry into the corner and braking all the way into the apex and then when you start coming of the breaks onto the throttle these type of diffs set up well can make a huge difference.


Oh if you want a 3 way adjustable set up then Leda can supply you with this probably running on remote dampers as well but this is not needed as setting your car up on a 3 way you can very easily get lost.

[gcomm]

The best suspension or these cars is made by:

1. Sachs
2. http://www.jrzsuspension.com
3. http://www.motonsuspension.com/

JRZ even do a 4 way adjustable damper if you have a spare £5,000 lying around.

[Lee]

after well over 100miles of testing today I can report that I have done around 120miles on £20 of fuel, mostly motorway.

is this good/bad?

the performance is outstanding :!: and continues to impress me :!:

the car is just so easy to drive fast and always seems 'on cam'

from standing start it is blistering and I feel as if I am getting to 60mph a good deal quicker

from 60 to 120 is so mouch quicker also

this really is how this car should have been in my eyes, I would much rather have the power how it is now :D

[exdos]

after well over 100miles of testing today I can report that I have done around 120miles on £20 of fuel, mostly motorway.

is this good/bad?

the performance is outstanding :!: and continues to impress me :!:

the car is just so easy to drive fast and always seems 'on cam'

from standing start it is blistering and I feel as if I am getting to 60mph a good deal quicker

from 60 to 120 is so mouch quicker also

this really is how this car should have been in my eyes, I would much rather have the power how it is now :D

If I assume £1 per litre for fuel then you've used 20 litres of fuel = 6miles per litre (120/20=6)
Fuel consumption in MPG = 6 x 4.54 litres = 27.24mpg
That's as good as anything I've ever returned :D

You've now got the power capabilities of the engine at useable speeds rather than at an almost academic top speed you'll hardly, if ever, use.

[Broccers]

I wish mine did 27 mpg - are you sure Lee :D

[Lee]

You've now got the power capabilities of the engine at useable speeds rather than at an almost academic top speed you'll hardly, if ever, use.


I have only ever really travelled at silly speeds a couple of times!

surely it is better to have the power where you can use it!

you can report your own finding after the welsh weekend Exdos :)

regarding fuel economy...

the red light had just come on so I put £20 in and reset the odemeter, when the light came back on to inicate I need to put more fuel in, I had done 119 miles

a rough way of working I know! but surely there or thereabouts?


Lee

[exdos]

you can report your own finding after the welsh weekend Exdos :)


Very much looking forwards to trying it :twisted: 8)

I've just been reading about a guy in the US who turbocharged his MC and gets 450bhp at the wheels and had to go the opposite way and fit a 2.79 diff because he was getting too much wheel spin and finding the gearing too short until he got to 4th!
http://activeautowerke.com/mags/bmwcar-sept01/default.asp

[Lee]

you can report your own finding after the welsh weekend Exdos :)


Very much looking forwards to trying it :twisted: 8)

I've just been reading about a guy in the US who turbocharged his MC and gets 450bhp at the wheels and had to go the opposite way and fit a 2.79 diff because he was getting too much wheel spin and finding the gearing too short until he got to 4th!
http://activeautowerke.com/mags/bmwcar-sept01/default.asp

porsche turbos & ferraris could not keep up!!! the only thing that did was a diablo :!: :D

[exdos]

porsche turbos & ferraris could not keep up!!! the only thing that did was a diablo :!: :D

The cost of the turbo conversion work for the US turbocharged MC was $31,800 (£17,865) including all engine, transmission and suspension parts. This sounds a lot less than Birds' Hartge conversion to the e39 M5 engine.

[Lee]

porsche turbos & ferraris could not keep up!!! the only thing that did was a diablo :!: :D

The cost of the turbo conversion work for the US turbocharged MC was $31,800 (£17,865) including all engine, transmission and suspension parts. This sounds a lot less than Birds' Hartge conversion to the e39 M5 engine.

agreed the Hartge option sounds very expensive, but it is based on the new M5 motor!

I would personally buy a trashed (rear ended) e39 M5 and get Racing Technologies to carry out all of the work :D

[BEN]

should we all keep our eye out then?

[Lee]

done 40 miles of testing with an e46 M3

I was nearly pushing him down the mostorway :D

[maahny]

I think you need to get down to santa pod and see what 1/4 mile time you can get :D

[chippy]

done 40 miles of testing with an e46 M3

I was nearly pushing him down the mostorway :D

My friend with an e46 m3 complete with full exhaust and intake mods is 'gutted' how quick the coupe is now with the new diff :lol: :twisted:

[M3 Compact]

Great Mod Lee. 8)

There's no way to change the ratio of the 5th gear, it drives directly. (1:1)

I use a 4.45 with 6 speed and don't use first, 147 MPH on the rev limiter in 6th. (Overdrive 6th at 0.83 : 1, the first 5 gears are virtually the same ratio in the 5 speed box and the 6 speed box.)

Time to uprate the locking characteristics now Lee. :wink:

[c_w]

When people are talking about changing the diff, do they mean the whole lot in the casing or do you brreak apart the original diff casing and fit the shorter one?

[Lee]

When people are talking about changing the diff, do they mean the whole lot in the casing or do you brreak apart the original diff casing and fit the shorter one?

completely new diff with different ratio, re using the existing finned cover from the MC diff.

it is essentially a bolt on/bolt off job so you can change back easily :!:

[BMWboy]

http://www.fabdirect.com/index02.htm

new m5 lump anyone?

[Greenbat]

done 40 miles of testing with an e46 M3

I was nearly pushing him down the mostorway :D

My friend with an e46 m3 complete with full exhaust and intake mods is 'gutted' how quick the coupe is now with the new diff :lol: :twisted:

Are you saying the E46 M3 even with your new diff is quicker than the mC?

Greenbat

[Lee]

no greenbat

I always had the edge over E46 M3's but now it is so much more exagerated!

I had to keep backing off or I would have been in his boot :D

[Greenbat]

no greenbat

I always had the edge over E46 M3's but now it is so much more exagerated!

I had to keep backing off or I would have been in his boot :D

I feel better now Lee

Greenbat

[chippy]

done 40 miles of testing with an e46 M3

I was nearly pushing him down the mostorway :D

My friend with an e46 m3 complete with full exhaust and intake mods is 'gutted' how quick the coupe is now with the new diff :lol: :twisted:

Are you saying the E46 M3 even with your new diff is quicker than the mC?

Greenbat

NO :!:

My friend was rather upset that after spending £2000 on mods, my m-coupe would pull out a good gap on his e46 m3 despite his best efforts 8) :twisted: