M42club.com - Home of the BMW E30/E36 318i/iS
DISCUSSION => Engine + Driveline => Topic started by: 92BMW318is on April 30, 2010, 02:32:24 AM
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I have a 92 318is
I need to know what kind of diff would be the best for my car, i want acceleration more then i want top speed. I need Some one to school me on the different gear ratios and what would be best for my car.
Whats the difference between an open diff and a lsd
Ive tryed to look at the threads as well as google but couldn't find what i was looking for.
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I have a 92 318is
I need to know what kind of diff would be the best for my car, i want acceleration more then i want top speed. I need Some one to school me on the different gear ratios and what would be best for my car.
Whats the difference between an open diff and a lsd
Ive tryed to look at the threads as well as google but couldn't find what i was looking for.
An open diff delivers torque to both rear drive wheels, and also allows the wheels to turn at different rates for going around corners smoothly.
http://en.wikipedia.org/wiki/Differential_%28mechanical_device%29
An open differential delivers equal torque to both wheels, no matter what. This means that when one wheel loses traction, and only needs a small amount of torqure to spin, then the other wheel simply gets that same small amount of torque. The sum total torque delivered to the road therefore shrinks the less traction either of the tires have. On ice, the total torque delivered might approach zero. If you have one tire up in the air on hard cornering, the other tire gets zero torque.
The limited slip differential is designed a bit differently. It will always send a useful amount of torque to the wheel with the better traction. So you get a benefit from the limited slip feature in situations where one wheel loses grip, during racing or on loose surfaces for example.
There are different kinds of limited slip diffs, but the most common in the E30/E34 world is the clutch (plate) type. A few owners have installed helical gear differentials (torsen, Quaife, etc.) as well.
If you want more acceleration in a straight line in a 318, then an LSD probably won't help. However, if you have additional power, or if your tires are not great, or if you want that acceleration on loose surfaces (all situations where you might spin your rear wheels) then an LSD would be a significant help. If you want more acceleration during hard cornering, then absolutely an LSD will help.
As for gear ratios, there are a few to choose from in the BMW world. I'm familiar with E30 ratios, but not so much E34 ratios. In my car, which is a '91 318is with M42 motor and Getrag 240 transmission (which is stock for my year), I run a 4.27 rear end. In fact the 4.10 that was stock in my car was also pretty good. The effect of the gear/diff ratio is a torque multiplication. The higher your total gear ratio, the more torque you feel at the wheels. And since torque is what makes your car get up and go from a stop, improving your torque multiplier is a good thing.
Here's some reading:
http://www.team-integra.net/sections/articles/showArticle.asp?ArticleID=707
In my case, I only improved my torque multiplication factor by about 4% by going from a 4.10 to a 4.27 ratio in the rear end.
One other thing that really helped my car accelerate better was to change to a lightweight flywheel+clutch assembly. I also mounted the lightest wheels and tires that I could. These two things reduce the rotational mass that the engine has to accelerate. Accelerating rotational mass takes more power from the engine than accelerating static mass, pound for pound that is, mainly because the rotating mass has to move faster than the static mass. So lighter wheels and tires plus lighter flywheel should theoretically allow your engine to spin up faster. In practice, the flywheel is rotating a lot faster than your wheels are from a start, so lightening that has a large effect in first and second gears and less effect once you get beyond second. Lightening the wheels has a more subtle effect, and assists handling dynamics in other ways too, so it is good thing to do, but does not give you much of a boost in acceleration.
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And now in plain english...
Open Diff: Standard on most BMWs.
Sends power equally to both wheels, regardless of whats happening on the road (dry,wet,icy).
LSD: An optional extra on non-M models. Standard on M models.
Sends a set percentage of power to the wheel which has the most grip.
I.e. put your foot down on a left hand corner, and the wheel with the most grip (in this case the right-rear) will be fed a pre-determined percentage (usually 25%) of the inside wheels power. Basically the power will always go to the wheel with the most traction, to help increase and/or maintain cornering speed.
Simples ;)
And on a side note, the iS came with a 4.10 Open Diff as standard. I changed to a 4.10 LSD and it has transfromed the car :) There isnt too much in it, performance wise, between the avaliable LSD ratios. I'd have liked a 4.27 if all the car saw country B roads more often, but it doesnt.
Scott.
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it's probably a waste to buy a brand new lsd (whether pumpkin or just rebuild kit) unless you're trying to be the drift king. or you're completely restoring the rest of your car as well.
just buy a used one, hopefully low miles, but it's more important how it was driven (rainy day antics or just a commuter to work) and whether there was fluid in it. don't pay attention to the ratio since you're trying to get your car running, if you find what you wanted later you can always swap and resell. because it's not always easy to find the one from your trim which will just swap in without any additional work (or parts), as there's small case (e30 318), medium (6cyl) and large (5series?), and small differences in all of those.
http://www.youtube.com/watch?v=zDXMOnYiMa8
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E30 Diffs only came in Small and Medium case flavour. Although one is larger than the other, thats it - there was no 'large case' diff as such. Its just Small or Medium case :) The Medium case'd diffs were found on the 6cyl models, and are capeable of withstanding higher torque output. My own 4.10 LSD (rare) is a Medium case (so extra rare :D) I think it was from a US spec 318i convertable.
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i called bulvarian yesterday and they said that the normal gear ratio for my car was somthing like 3.65
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So you're ok with "bulvarian" telling you it's something like? Yeah...I'd buy from them.
Your car has a 3.45 stock ratio.
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And now in plain english...
Open Diff: Standard on most BMWs.
Sends power equally to both wheels, regardless of whats happening on the road (dry,wet,icy).
LSD: An optional extra on non-M models. Standard on M models.
Sends a set percentage of power to the wheel which has the most grip.
I.e. put your foot down on a left hand corner, and the wheel with the most grip (in this case the right-rear) will be fed a pre-determined percentage (usually 25%) of the inside wheels power. Basically the power will always go to the wheel with the most traction, to help increase and/or maintain cornering speed.
Simples ;)
And on a side note, the iS came with a 4.10 Open Diff as standard. I changed to a 4.10 LSD and it has transfromed the car :) There isnt too much in it, performance wise, between the avaliable LSD ratios. I'd have liked a 4.27 if all the car saw country B roads more often, but it doesnt.
Scott.
So the bigger the number the more speed you will have and the lower the the number the more acceleration?
should i go up from the stock of 3.45, or should i stay at it.
id rather have acceleration then top speed
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it's probably a waste to buy a brand new lsd (whether pumpkin or just rebuild kit) unless you're trying to be the drift king. or you're completely restoring the rest of your car as well.
just buy a used one, hopefully low miles, but it's more important how it was driven (rainy day antics or just a commuter to work) and whether there was fluid in it. don't pay attention to the ratio since you're trying to get your car running, if you find what you wanted later you can always swap and resell. because it's not always easy to find the one from your trim which will just swap in without any additional work (or parts), as there's small case (e30 318), medium (6cyl) and large (5series?), and small differences in all of those.
http://www.youtube.com/watch?v=zDXMOnYiMa8
thanks man for the help thank all of you guys actually,
ill most likely just buy the stock and figure the rest out at a later date
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good, you can always weld the diff :D
when i bought my car i drained the fluid and there was plenty of metal that came along, so i figured there wasn't much locking ability left and to save money I would continue to drive it, not dealing with it until it became undriveable. couple years later still hasn't.
info on this topic is confusing. you'd have to deal with more cars than just one 318 to see the whole picture. if i was you i would go to a bmw/german auto dismantler, especially the ones you can walk through and see stacks of transmissions and diffs, to see what will fit (same pumpkin), and what could fit with some small alterations (changing the case,etc). you don't have to worry about swapping internals due to your damaged unit, unless you're buying more than one new diff. look at the stickers and tags for ratios.'
(http://img196.imageshack.us/img196/2541/diffh.jpg) 41:10 = 4.10
Would help if the broken diff was in the car to compare before i buying anything. places like that usually have lousy return policies, only if its fked up they'll begrudgingly let you bring it back, they won't refund your labor cost ofcourse. so do the work yourself
http://www.r3vlimited.com/board/showthread.php?p=1498642
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http://forums.bimmerforums.com/forum/showthread.php?t=339548
so large case diffs are from the 7 & 8 series o_o ? (for the 8 or 12 cylinder?)
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http://forums.bimmerforums.com/forum/showthread.php?t=339548
so large case diffs are from the 7 & 8 series o_o ? (for the 8 or 12 cylinder?)
Yes the large 210's are from the 8 & 12 Cyl's.
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So the bigger the number the more speed you will have and the lower the the number the more acceleration?
should i go up from the stock of 3.45, or should i stay at it.
id rather have acceleration then top speed
Other way round fella, the bigger the number the quicker the acceleration.
E.g. for a 4.10 ratio, the rear wheels will turn 4.10 times for every 1 engine revolution. So if you increase that 4.10 number (so the wheels turn more, compared to the engine's own revolutions) then you'll have greater acceleration. Get it? :D
BTW as far as I know (and im 99% on this), the E30 318is came with a 4.10 ratio'd Diff (either in Open or LSD flavour). There wasn't a 3.45 avaliable on any of the models. The closest was a 3.46 on a few pre-facelift models :
http://www.e30zone.net/e30zonewiki/index.php/E30_Differentials
^ From the UK's E30 Zone Wiki :cool: ^ A great resource.
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BTW as far as I know (and im 99% on this), the E30 318is came with a 4.10 ratio'd Diff (either in Open or LSD flavour). There wasn't a 3.45 avaliable on any of the models. The closest was a 3.46 on a few pre-facelift models :
http://www.e30zone.net/e30zonewiki/index.php/E30_Differentials
^ From the UK's E30 Zone Wiki :cool: ^ A great resource.
His 1st post said that he has '92 318is. 3.45 in manual 92-93 318i/is. The 3.46 was in the 5 series.:)
Cheers,
~Ralph
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I see ;)
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something not mentioned yet in this thread is that several non-M 6-cyl Z3s came with torsen (not clutch-pack) LSDs.
i swapped my 4.10 med-case clutch-pack out for a 4.10 torsen from an auto Z3 a few months ago and i love it. it just knows where the grip is, and in the wet where a clutch-type would just spin both wheels, i can feel the ass end of the car wiggle ever so slightly as it sends power to whichever wheel has more traction. they also don't wear out like a clutch-type does. (well, they will eventually, but the diff is likely to outlive most of the rest of the car.)
i'm pretty sure they were available in 3.73 also, and if i had an e36 m42 car, that's the ratio i'd look for.
as a side note, US-spec 318i convertibles came with a 4.27 open small-case. i still have the one that came out of my car, if anyone wants it.
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i have a question again..
I just bought a diff from pull a part, it came off a 93 325i same exact diff case, even asked the ladie she said it was interchangeable. so i go out there take the Diff off the 325i. So i get back and take my old diff off and put the 325i on my 318is, everything fit well, nothing went wrong.
until i drove it and it has a lower gear ratio, it seems. at 65mph Im buried at 4rpm. with the old one i was close to 3rpm at 65mph.
What i dont get is the engine in the 325i was the same engine as mine,
same engine block, same intake, the only thing i seen that was differnt was the fuel injectors which i took, want to know if the fuel injectors for the 325i will work with my car.
but the biggest thing i want to know is why there is such a big difference in rpms, i thought the guy that use to own the 325i had some 17inch rims or somthing. is there a difference if the car was automatic or Manuel?
ha if i did go and buy some bigger wheels would this lower the rpms?
Also is 65 at 4rpms bad for my engine, i dont want to blow my motor
thanks for your help
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Dude,
You have major conflicting information so it makes it very hard to give you the correct advice.
E36
325i/is 1992/93 3.15 (M) 3.15 (M) 3.19 (A) 3.19 (A)
318i/is 1992/93 3.45 (M) 3.45 (M) 4.45 (A)
325ic 1994 3.15 (M) 3.64 (A)
Those are the ratios available. You don't have a lower gear ratio in your car now, you have a higher one. Higher ratio has quicker pick up which makes you run out of gear faster which makes you run higher RPM.
Clearly the 318 ratios are higher than the 325's. This would mean that you have a completely different diff in your car NOW that you have no idea what it is, OR you didn't have the correct diff in your car to begin with:-) What if the junker car's previous owner was an enthusiast and changed the diff?
Just as an example with tire change, you can take a 4.10 and switch from a 225/50 tire to a 225/45 and it will effectively change your diff to a 4.17
Do you have a 318 or a 325? You said the 325 junker has the same motor, engine block and intake as your car which means you don't have a 318 unless you or someone else did a motor swap on your car.
Let's start with do you have a 4cyl or a 6cyl?
How many fuel inj's did you take from the junker? And how many do you need for your car?
What does the lady at this place really know? Yeah the "size" of the case may fit but not the ratio. Something is a miss and it's hard to help if all the info is not complete and correct.
I would not run a diff that put me at 4K @ 65mph. It will shorten the life of the motor. It won't blow up but I think that it's way too high of a ratio that you have now.
~Ralph
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Keep in mind that auto trannys & manual trannys carry different diff ratios too. and a 'vert will always have a much lower (bigger number) diff because it's hundreds of pounds heavier than the hardtops. You can look for a metal tag on the diff case that will have the ratio stamped on it. The cases can all swap easily, but the ratio might be totally wrong for your car.
The diff and the wheels will combine to produce your final drive ratio...so say you have a 4.10 - the diff divides the driveshaft revs (not the engine RPM) by 4+, then the wheels multiply each rev by their circumference to get mileage. So the smaller the tires, the faster the car will run. It's a lot of math, but it's not hard to do.
Don't worry about 4k RPM...I run mine there often. It'll shorten the engine life if you do it all the time though. I'm pretty sure the injectors are physically the same but can vary on flow rate. There are a few detail differences but they're all Bosch designs. You'll have to check the part numbers to be sure how much fuel they flow. Going to slightly larger injectors usually helps with idle and might give you a few more HP.
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Keep in mind that auto trannys & manual trannys carry different diff ratios too. and a 'vert will always have a much lower (bigger number) diff because it's hundreds of pounds heavier than the hardtops. You can look for a metal tag on the diff case that will have the ratio stamped on it. The cases can all swap easily, but the ratio might be totally wrong for your car.
The diff and the wheels will combine to produce your final drive ratio...so say you have a 4.10 - the diff divides the driveshaft revs (not the engine RPM) by 4+, then the wheels multiply each rev by their circumference to get mileage. So the smaller the tires, the faster the car will run. It's a lot of math, but it's not hard to do.
Don't worry about 4k RPM...I run mine there often. It'll shorten the engine life if you do it all the time though. I'm pretty sure the injectors are physically the same but can vary on flow rate. There are a few detail differences but they're all Bosch designs. You'll have to check the part numbers to be sure how much fuel they flow. Going to slightly larger injectors usually helps with idle and might give you a few more HP.
so is there anyway to fix the ratio, like going up tire sizes,
how hard is it to change out the guts?
also the whole tranny was taken out of the car i took the diff off of it looked like it it might of been a Manuel but the clutch wasn't there ither
also the person asked me if the diff i had was a locking differential. im sure it isnt but, whats the diffrence
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The easiest way to change the ratio is to find the right diff and swap it in. Changing wheels and tires can be another way to change the effective ratio.
You could change out the ring & pinion gears and even bolt a limited-slip pack into an open diff, but it's always cheaper to buy a used unit. A mechanic needs to set the front flange pre-load properly, or the diff will burn itself up quickly.
BMWs can be tail-happy, so they sometimes come with "locking" or "limited-slip" (LSD) diffs. They usually have a big "S" painted on the case. The opposite of an LSD is an "open" diff. A quick way to check is to spin one of the wheels or output flanges and see which way the other one goes. If it spins the opposite direction, you have an open diff. If it spins the same way, you have an LSD. They're also usually about twice as expensive as the open units.
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Dude,
You have major conflicting information so it makes it very hard to give you the correct advice.
E36
325i/is 1992/93 3.15 (M) 3.15 (M) 3.19 (A) 3.19 (A)
318i/is 1992/93 3.45 (M) 3.45 (M) 4.45 (A)
325ic 1994 3.15 (M) 3.64 (A)
Those are the ratios available. You don't have a lower gear ratio in your car now, you have a higher one. Higher ratio has quicker pick up which makes you run out of gear faster which makes you run higher RPM.
Clearly the 318 ratios are higher than the 325's. This would mean that you have a completely different diff in your car NOW that you have no idea what it is, OR you didn't have the correct diff in your car to begin with:-) What if the junker car's previous owner was an enthusiast and changed the diff?
Just as an example with tire change, you can take a 4.10 and switch from a 225/50 tire to a 225/45 and it will effectively change your diff to a 4.17
Do you have a 318 or a 325? You said the 325 junker has the same motor, engine block and intake as your car which means you don't have a 318 unless you or someone else did a motor swap on your car.
Let's start with do you have a 4cyl or a 6cyl?
How many fuel inj's did you take from the junker? And how many do you need for your car?
What does the lady at this place really know? Yeah the "size" of the case may fit but not the ratio. Something is a miss and it's hard to help if all the info is not complete and correct.
I would not run a diff that put me at 4K @ 65mph. It will shorten the life of the motor. It won't blow up but I think that it's way too high of a ratio that you have now.
~Ralph
i have a 4cylinder 318is the 325i had a 4cylinder, i got 4 injectors from it from it. a ICV and a bumber strip. the 325i at the yard had the same intake the same fuel rail the same engine the same throttle body, ect.. i looked up the 325i motor yesterday i couldnt find anything that said they made 4cylinders which is confusing me.
so same motor same body e36... i dont see why the diff would be geared so diffrently if the 325i has a lower gear ratio like you stated then my car shouldnt be running at high rpms, unless the diff was swaped into the 325i before it was scrapped.
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you have not made this any less confusing :P
only explanation i have is that the j-yard car was a 318i/s rebadged as a 325i, because every e36 other than the 318i/s had a 6-cylinder.
btw i just drove from sacramento to LA... i'm at 4000rpm right at 80mph and i sustained that speed the whole way. if you usually cruise at 65, i wouldn't be that worried about sustaining that RPM continuously. my vote is change your oil frequently, enjoy that quick acceleration, and get some other modifications to accentuate it. :)
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you have not made this any less confusing :P
only explanation i have is that the j-yard car was a 318i/s rebadged as a 325i, because every e36 other than the 318i/s had a 6-cylinder.
btw i just drove from sacramento to LA... i'm at 4000rpm right at 80mph and i sustained that speed the whole way. if you usually cruise at 65, i wouldn't be that worried about sustaining that RPM continuously. my vote is change your oil frequently, enjoy that quick acceleration, and get some other modifications to accentuate it. :)
im reallllllly sorry guys but it came off of a 320i not a 325i :/
so i guess the diff i have is a 2.73.... :/
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stop doing drugs. then work on your car or post on this forum
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deekay and PumpItUp are both right, but PumpItUp takes the cake on this one!!
You have no clue what the hell you're talking about. If you did then you wouldn't have made such a ridiculous statement.
Now I know you're wasting everyone's time here. Go read and learn about what you think you might have and might fit and then get back to us with an educated, sensible, logical, and realistic view point that really needs attention.
~Ralph
im reallllllly sorry guys but it came off of a 320i not a 325i :/
so i guess the diff i have is a 2.73.... :/
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yup, e36 320i is still an inline-6 car.
as has been said, what you have in the car now is a numerically high diff if you're turning 4Krpm @ 65mph- it HAS TO be something 3.73 or above.
come to think of it, i think i am turning about that much rpm @ that speed in 4th gear (1:1), so you may very well have found a 4:10. who knows.
either way there should be a tag on the rear cover of the differential that says the ratio and can end all of this conjecture immediately.
at the end of the day you've got a nice short-geared setup that's well suited to the peaky little 4-banger under your hood, and you said you wanted acceleration at the expense of top-speed. now you've got it. stop worrying about it and start researching what suspension and tires you might want.
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Yes the 320i is a 6cyl (my cousin has one in Germany) but was not imported to the USA. However, 3 cars were donated to the Georgia State Police in 1996 for the Olympics in Atlanta and were tagged "1" "2" and "3" on the license plates. After the games they were put into regular service for patrol. 2 were hit and crashed (not by the officers) and not sure what happened to "3".
MPH= (RPM)(TIRE DIAMETER in inches) [divided by] (GEAR RATIO)(336)
Now 92BMW318is can go figure it out for real.
~Ralph
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Yes the 320i is a 6cyl (my cousin has one in Germany) but was not imported to the USA. However, 3 cars were donated to the Georgia State Police in 1996 for the Olympics in Atlanta and were tagged "1" "2" and "3" on the license plates. After the games they were put into regular service for patrol. 2 were hit and crashed (not by the officers) and not sure what happened to "3".
MPH= (RPM)(TIRE DIAMETER in inches) [divided by] (GEAR RATIO)(336)
Now 92BMW318is can go figure it out for real.
~Ralph
I dont know what to tell you guys, the fucken 320i had a 4 cylinder same exact setup as mine, engine wise.
my bad i said it was a 325i.
i dont do drugs.
if bmw didn't make the 320i in a 4 cylinder then why are they selling them online.
http://market.autopartsfair.com/used-parts-leads/bmw-320i-air_conditioner_compressor-request-1272319.html
(http://m42club.com/forums/picture.php?albumid=133&pictureid=779)
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i think we're all done arguing with you. good luck.
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i think we're all done arguing with you. good luck.
what ever man.no one can possibly know everything.
at least i have the balls to admit when im wrong :)
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read your questions, they're ridiculous.
so are your facts.
320, 325, 4 cylinder, 6 cylinder, automatic, manual, whats the difference right.
GET YOUR FACTS STRAIGHT. If the transmission is missing it's flywheel, etc, then look in the F00king cabin to see if it has a stick shift or a thing with P/R/N/D on it
If there is no cabin, look at the thing sticking out the transmission itself. Does it shift like a 5-speed or only up & down like an automatic. Ask someone. USE YOUR HEAD. If you can't remember anything, use some paper and a pen.
What car it came off doesn't even matter now, since it works on your car. But now you're asking about ratio?? Clean the yellow sticker on the diff, it will say the ratio on it as I previously posted. Oh right, you don't read previous posts.
No driving at 4k rpm (vs 3k) will not kill your engine. Technically it will put more "wear" on it, but "technically" a well lubricated motor will sustain no damage once it has warmed up. At the same time if you have more power at low speeds, you won't have to rev as high on the street. What do you think is better for a engine, continuous 4,000 rpms, or erratic redlining. As long as you do your oil changes it will be fine. Over the course of a decade, I don't know. In a more realistic context, it will be fine.
I had a 2002, without the 5-speed swaps they're like humming birds anything above 55mph. Didn't stop me from doing 100 all the time. If in 5 years you still have the car and the engine needs to be rebuilt, then so be it. It's not like it's cheaper to be playing around with diffs or buying bigger wheels. You might waste some mpg on the highway, but save it on the street. Just don't be anal. Don't listen to conventional wisdow, or some redneck telling you "son, you're going to blow your engine". That's all outdated nonsense. How many people have you heard blowing their engines? They might overheat it, and throw it out because it got damaged or blew the headgasket, they might run into a tree, need a new transmission, whatever. In much of Europe people drive 100mph in the left lane with their VW Polos, much faster in Germany, and here you're afraid of the effects of going the speed limit. Don't be afraid to rev a BMW. And if you have a 4 cylinder and don't rev it... well that's no way to live.
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I'm sorry for reviving this thread, but it's my birthday, and this is one of my favorites. PumpItUp is my hero of the day. I promise I will hit red on the tach today. I wonder if this guys car still runs? We should have started a pool...
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wtf is this guy talking about?
the only car i ever heard of have something lower than a 3.46 was an eta which came with a 2.93...
either way how the FUCK are you at 4k at 65? i had a 4.27 and a rebuilt race tranny in my first 318is and i was still able to do 55in 2nd gear and only at like 3k at 65 MPH
less shrooms and maybe you will be able to read ur TACH and MPH a little better...
also if your having this much trouble with you car maybe its time for u to take it to the dealer because mechanics just isnt working for you...
sorry if im pissing anyone off but i just went through this whole thread and i read one of this guys statements sayin it was a 325 with a 4cyl? WTF