Are higher diff ratio's bad for sc'd cars?

[Mteknic330ci]

I was having a discussion on wether a high or low diff or lsd ratio is better for FI/sc'd cars? Can an expert intervine please?

[vmwerks]

Not really but the extra torque makes the higher diff ratio moot. I am running a 3.46 non-lsd and an SK1, my 1st gear is worthless. Super sweet car BTW!

[Mteknic330ci]

Not really but the extra torque makes the higher diff ratio moot. I am running a 3.46 non-lsd and an SK1, my 1st gear is worthless. Super sweet car BTW!
Thanks.. moot?

[vmwerks]

moot=pointless (I think...) :P

A lower ratio diff will give you more useable torque since the engine has a higher mechanical advantage over it's weight. With FI, at least in my case, the diff is too low and 1st gear runs out way too fast. I am running a 6 speed trans so I really don't give up anything at the top end either.

[iLLM3]

In an M3 stage 1+ its worthless to have anything higher than stock. I had a 3.91, and 1st and 2nd a stock M3 could keep up with me, it would rev so fast hardly any boost was being produced, the M3 loves its tall gears, that's what makes it pull like an animal, same with 330ci, taller is better :thumbup:

[Mteknic330ci]

In an M3 stage 1+ its worthless to have anything higher than stock. I had a 3.91, and 1st and 2nd a stock M3 could keep up with me, it would rev so fast hardly any boost was being produced, the M3 loves its tall gears, that's what makes it pull like an animal, same with 330ci, taller is better :thumbup:
Taller, as in higher or lower diff ratio?

[K-DOG]

I think a 3.15 is probably the best all around ratio for our cars.

[iLLM3]

Taller, as in higher or lower diff ratio?

Lower diff ratio :thumbup:

[samir@technik]

Turbochargers need longer gears to "build" boost. Superchargers are like naturally aspirated engines (linear power delivery), so they will benefit from shorter gearing since more torque is generated to the wheels at a lower RPM. However, too short of a gear will cause traction issues in addition to frequent gear changes (which kills your acceleration/quarter times).

[samir@technik]

it would rev so fast hardly any boost was being produced

You were still making just as much boost as before. It doesn't matter if you're running a 2.93 or a 4.10...a supercharger will always make the same amount of boost at a given RPM because it is <u>belt driven</u>, not exhaust driven.

[thekubiaks]

I think a 3.15 is probably the best all around ratio for our cars.

Agreed, 3.15 is about the best compromise.

[Mike Benvo]

You were still making just as much boost as before. It doesn't matter if you're running a 2.93 or a 4.10...a supercharger will always make the same amount of boost at a given RPM because it is belt driven, not exhaust driven. I was just about to say that.

I went with a 3.64 diff with my setup and couldn't be happier. Yes first gear is a little crazy, but then again I don't really launch my car.

Usually with a turbo you want longer gearing, and with a supercharger you want shorter gearing. There is a point of diminished returns though. Grip is a huge factor in this. I am shifting a lot more than I want to, but I don't really care that much. The pull on the highway with this gearing is absolutely amazing. I've hit 140-155mph a few times in the last week and it's just amazing how fast the car gets up there.

[Mike Benvo]

Agreed, 3.15 is about the best compromise.
For a 5 speed yes, but for a six speed I would opt for something a bit more agressive. :thumbup:

[Mteknic330ci]

For a 5 speed yes, but for a six speed I would opt for something a bit more agressive. :thumbup:
I agree also, my bro has a 3.46 and a five speed, bad idea, redlines around 130 in fifth. I have a 3.46 with an m3 6-speed I could still hit 160-170 If I had the room. I need to get my cams!!

[Mike Benvo]

I agree also, my bro has a 3.46 and a five speed, bad idea, redlines around 130 in fifth. I have a 3.46 with an m3 6-speed I could still hit 160-170 If I had the room. I need to get my cams!! My car is at the shop for cams now http://forum.e46fanatics.com/images/smilies/woot.gif I can't wait.

Before I got my 3.64, I had a 3.07 with the 6 speed, which could hit 198MPH in 6th Gear at 7k RPM. Now that's fast! (Don't know if the car had the power to get up there though, so lets say I was rolling down a steep hill).

[Mteknic330ci]

I don't even have zhp cams, Are you getting the technik cams for FI? Thats what I'll eventually get.

[Mike Benvo]

I don't even have zhp cams, Are you getting the technik cams for FI? Thats what I'll eventually get.
Right now I have the ZHP cams.

Going in are the technik FI cams http://forum.e46fanatics.com/images/smilies/smokin.gif

[iLLM3]

You were still making just as much boost as before. It doesn't matter if you're running a 2.93 or a 4.10...a supercharger will always make the same amount of boost at a given RPM because it is <u>belt driven</u>, not exhaust driven.

I heard different from many, many different sources. It was a night and day difference between stock gears and 3.9 :dunno:

[Solid]

All the DTMpower FI guys say the same thing. Longer for turbo, shorter for SC.

[Mike Benvo]

I heard different from many, many different sources. It was a night and day difference between stock gears and 3.9 :dunno: Correct, that is because you lost traction, causing the RPM's to shoot up. THere is a direct coorelation between the wheels and the RPM that you at, at any given time. Because you lost traction, the engine reved almost freely, making it seem like the car was not as quick. In reality though, traction was your enemy, and most likely the traction was lost because of the taller gearing.

With a supercharger, under WOT conditions, you will make a certain amount of boost "x" depending on the RPM you are at. This is a static value. For example, I will read 9.5PSI at 6500RPM whether I have 10.0 gears or a 1.00 (just as an example). As Samir said, becasue a supercharger is driven by the crankshaft (which is eventually mechanically linked to the wheels, though the tranny, driveshaft, and diff), and not by exhaust gases, the amount of boost you are making is dependant on pulley size, and RPM. With a turbocharger, the amount of boost at any given RPM can be different with different gear ratios, because turbos rely on exhaust gases.

[samir@technik]

I heard different from many, many different sources.

A supercharger builds boost based on engine RPM and makes maximum boost pressure at redline, right? Does your gear ratio affect your ability to hit redline? No. Therefore, "boost" is generated irrespective of gear ratio.

Whoever started this misnomer about a supercharger needing a lower gear ratio "to build boost" doesn't know what they're talking about. They made the mistake of confusing the way a turbo builds boost with the way a supercharger builds boost. They are totally different.

For a supercharged car, gear ratio has no effect on boost whatsoever.

It was a night and day difference between stock gears and 3.9 :dunno:

Yes, because you had to shift more frequently due to the amount of power you are making (or due to traction, or both), which kills your acceleration. Not because you weren't making the same boost as with your 3.62. The only way to alter boost on an SC is via the pulley.

[steelgrey330ci]

I have a 3:15 gears and I find that not bad. It does help with the torque but again first gear off the light forget about it. I do notice a shorter top end but how many times do you go that fast. Whats good about it is you can still hit stop speed and pull to redline very easy.

I also have the uuc setup with the 12lb flywheel, that helps with any lag through the rpm band.

[steelgrey330ci]

sorry 8.5lb flywheel

[Mteknic330ci]

I started this thread because someone was trying to agrue with me that lower diff ratios are are better on sc'd cars.. I believed the opposite but still thought I could get some expert advice. Turns out I was right though, higher ratios are great for sc'd cars. It keeps you in the high rpm's were boost is throughout all gears, (all 6).

[Mteknic330ci]

I have a 3:15 gears and I find that not bad. It does help with the torque but again first gear off the light forget about it. I do notice a shorter top end but how many times do you go that fast. Whats good about it is you can still hit stop speed and pull to redline very easy.

I also have the uuc setup with the 12lb flywheel, that helps with any lag through the rpm band.
Learn how to drop the clutch proporly at a low rpm so you can get traction in 1st.

[steelgrey330ci]

well trust me I've tried, its hard cause every day is different, road temp and everything.

with the clutch kit and flywheel it grabs hard and I'm running 265 in the rear.

If I pop it at 2500rpm it goes to red, if I go any lower it bogs out so I try to ride first out and then beat the piss out of it.

[Mteknic330ci]

well trust me I've tried, its hard cause every day is different, road temp and everything.

with the clutch kit and flywheel it grabs hard and I'm running 265 in the rear.

If I pop it at 2500rpm it goes to red, if I go any lower it bogs out so I try to ride first out and then beat the piss out of it.
Mine does the same.. Try not to pop let it half way out for a split second so you start rolling then dump it at like 10. I have the same power and it works great. I chirp through 1st but it's better than breaking loose.
I'm only running 235's. Soon to be 9.5 in the back though.

[Mteknic330ci]

Maybe you need better tires?

[steelgrey330ci]

my tires are yokohammas avs sport which i think are not the best.

I do have 19 x 10 in the rear.

[steelgrey330ci]

what i need is a lsd, i have 3:15 but 3:15 lsd is a different story. Do you know who makes one

[bernstem]

Right now I have the ZHP cams.

Going in are the technik FI cams http://forum.e46fanatics.com/images/smilies/smokin.gif

:ben: Damn you, I'm still waiting on my head before I can install mine. :ben:

[samir@technik]

steelgrey330ci: Try...

http://www.performancegearing.com/index.asp
http://www.metricmechanic.com/

[samir@technik]

:ben: Damn you, I'm still waiting on my head before I can install mine. :ben:

Head is almost ready, I think it can ship tomorrow.

[bernstem]

Head is almost ready, I think it can ship tomorrow.

:evil: thanks - looking forward to it :evil:

I'll stop jacking this thread now.

[iLLM3]

A supercharger builds boost based on engine RPM and makes maximum boost pressure at redline, right? Does your gear ratio affect your ability to hit redline? No. Therefore, "boost" is generated irrespective of gear ratio.

Whoever started this misnomer about a supercharger needing a lower gear ratio "to build boost" doesn't know what they're talking about. They made the mistake of confusing the way a turbo builds boost with the way a supercharger builds boost. They are totally different.

For a supercharged car, gear ratio has no effect on boost whatsoever.



Yes, because you had to shift more frequently due to the amount of power you are making (or due to traction, or both), which kills your acceleration. Not because you weren't making the same boost as with your 3.62. The only way to alter boost on an SC is via the pulley.

Hmm yea your right!! I just thought since it was rtevving so damm quick it was like skipping LOL, hard to explain. When i had the 3.9 in my car also wasnt on the good tuning, 7.5 pulley and ran like shlt, still was a night/day difference bewteen stock diff and that, but it could have also been numerous other things causing a stock M3 to be right by my side throughout 1st and 2nd gear LOL! :ben:

Oh well, now its an animal!! :bump:

[Mteknic330ci]

what i need is a lsd, i have 3:15 but 3:15 lsd is a different story. Do you know who makes one
Oh damn, thats the problem!! I have an lsd, it must make a huge difference.

[vmwerks]

Just got back from the dragstrip.. the car leaps so hard in 1st and spools so quickly that I had a hard time shifting b4 hittng the rev limiter :rolleyes: No I am not going to post 1/4 times....

[GBX330ci]

Agreed, 3.15 is about the best compromise.

I have a 3.38 in my blown 5 sp 330 and i think its perfect :evil:

[steelgrey330ci]

I wanted that one as well but how is your first gear off a light. Do you have lsd ?

[GBX330ci]

I wanted that one as well but how is your first gear off a light. Do you have lsd ?

First gear goes by real fast, almost too fast, but i still have plenty of traction off a light. I'm running 255's in the rear which probably help.

no lsd!

[drhendrix]

I have a 3.38 in my blown 5 sp 330 and i think its perfect :evil:

I'm getting a 3.38 installed tomorrow :woot:

[rana]

these types of threads make me wish I had a manual transmission :bawling:

after this car, i swear to god, all my other cars will have a Manual Tranny. Screw AUTOMATIC and Screw F1 paddle shifters :ben:

[K-DOG]

Can anyone tell me where I can get a Kaaz diff?
I tried to contact these "rebuild" shops that technik linked, but they want about $3000-2500 for a conversion if you provide the core....even more if you dont provide the core....WAY too high imho. Might as well get a new LSD with a custom ratio for that price.

[MrBlonde]

I've run a 427 and a 391 diff in my M Coupe. The shorter difs are much better for drag racing. Taller diff ratios are good for highway busting or for those who can't launch or change quickly.

[kvcicca]

Can anyone tell me where I can get a Kaaz diff?
I tried to contact these "rebuild" shops that technik linked, but they want about $3000-2500 for a conversion if you provide the core....even more if you dont provide the core....WAY too high imho. Might as well get a new LSD with a custom ratio for that price.

www.diffsonline.com

Hands down the best around for Kaaz.

[meel330]

i have 3.46 in my six speed and 1st will throw you back but i feel like my car is being robbed of power 1 and 2nd i dont know why? maybe AA sucks ballz :dunno:

[iLLM3]

i have 3.46 in my six speed and 1st will throw you back but i feel like my car is being robbed of power 1 and 2nd i dont know why? maybe AA sucks ballz :dunno:

Dunno b, i say swap out your diff to stock, your kit was honestly built for stock diff just like mine :dunno:

[Mteknic330ci]

i have 3.46 in my six speed and 1st will throw you back but i feel like my car is being robbed of power 1 and 2nd i dont know why? maybe AA sucks ballz :dunno:
I have the same setup with M3 6-speed. First rips, but second? Higher diff ratios leave you in higher rpms after you shift. Thats were boost is so you benefit power but have a shorter gear. Sc'd cars benifit higher diff ratios and since your a 6-speed you dont have to worry about ruining your top speed. I think your stock ratio is 2.93 . Don't go lower go higher :thumbup:

[samir@technik]

I think your stock ratio is 2.93 . Don't go lower go higher :thumbup:

Agreed. 2.93 is way too tall for these cars.

[MarvelPhx]

I went from the stock 3.07 ZHP open diff to a 3.38 Limited Slip Diff with 90/10 slip angles. And I love it. Boatloads of fun to have.

On the street, it is tall enough to maintain about 3100rpm at 80mph in 6th and short enough to strip 0-60 times without needing to shift to 3rd. LSD makes for some interesting burnouts, donuts, and drifts as well if that is your thing.

On the track, the LSD slip angles are agressive enough to straighten the car out of turns by simply adding gas pedal, but quickly roll back to allow easy turn-in and transition. BMWs have great chassis for track surface transitions and irregularities. If you have ever taken turn 1 at Phoenix, you know what I mean.

I still firmly believe that any "performance package" or similiar BMW should come with a factory LSD or at least the option to add one. Shall we look at competitors? Lexus, Infiniti, Nissan Sentra for god's sake.... come on...

As for ratios, you want one that will quicken the car and maximize your engine's torque curve without adding too much shifting. BMW is going to put a rear gear in that will provide reasonable acceleration and very good gas mileage to meet EPA regulations. Once you own the car, screw those limitations. Someone asked me once, hey with your 3.38, didn't you lose top speed.... yeah, I did... I went from being able to hit 185 to being able to top out at 175... And my answer: Do you know how many times I hit 175 much less 185? Now, how many times do I go 0-80? I'll take the shorter gears.

[crazy01]

Ok so what gears would you guys recommend if you have a 5 speed? My stock is a 3.15. Should I get a 3.23?

[vmwerks]

I've run a 427 and a 391 diff in my M Coupe. The shorter difs are much better for drag racing. Taller diff ratios are good for highway busting or for those who can't launch or change quickly.

You mean me right? :P

[Mteknic330ci]

Ok so what gears would you guys recommend if you have a 5 speed? My stock is a 3.15. Should I get a 3.23?
A 3.46 will leave your top speed at about 130, and a 3.38 will leave it at 140 ish, go as high as you can. (3.38 or higher) :woot:

[vaio76109]

Can anyone tell me where I can get a Kaaz diff?
I tried to contact these "rebuild" shops that technik linked, but they want about $3000-2500 for a conversion if you provide the core....even more if you dont provide the core....WAY too high imho. Might as well get a new LSD with a custom ratio for that price.
http://www.overboost.com/obs/product.asp?pid=21314&cat_id=11&cat_name=&sc_id=&sc_name=

[K-DOG]

http://www.overboost.com/obs/product.asp?pid=21314&cat_id=11&cat_name=&sc_id=&sc_name=

Holy crap is that for the entire unit??? Or just for a kit that will allow you to convert it into an LSD?

[vaio76109]

Holy crap is that for the entire unit??? Or just for a kit that will allow you to convert it into an LSD?
That is just the LSD unit. It only fits in certain 3.46 carriers tho, not 2.93's or 3.15's or.....etc

Look for a thread by BMWDON

[dystynkt]

bringing this thread back from the dead (rather then starting a new one), what would be the best gear ratio for me to go to running a vf charger on a 99 323i??

[Casanova]

my bro has a 3.46 and a five speed, bad idea, redlines around 130 in fifth.

*sigh*

I have the same problem :(