Gear ratio change?

[Dathaeus]

This may be something totally dumb as someone who loves to drive hard but has never raced professionally or messed around with cars much internally....

But I always thought my gear ratios were not "pleasing to me"... even worse than my old 1997 328i. I didnt think much of it before I read this

Project E46 330i ZHP (http://www.turnermotorsport.com/t-project-e46-330i-zhp.aspx)

Shortening the ratios would really feel like something I think I want... I hardly approach high RPM's in 6th so I wouldn't care about that. Shifting is definitely my weakest driving skill, but this is worth a try only if I dont have to spend thousands on parts... is it just settings that can be easily modified under the hood or should I just let it be? I am sure someone here has done something like this........ ya?

[az3579]

Gear ratios involve a differential swap. You can change to an open diff which is cheaper, or you can get a LSD, which runs a few grand.

Sent from my DROID RAZR HD using Tapatalk 4

[Hermes]

Gear ratios involve a differential swap. You can change to an open diff which is cheaper, or you can get a LSD, which runs a few grand.

Sent from my DROID RAZR HD using Tapatalk 4

This... It's not gonna be a cheap and easy under the hood fix. You can try to find a finned shorter ratio open from an auto, it will be cheaper than a LSD but will still cost you multiple hundreds and require getting under the car to install

[Vas]

So where is the best place to get a 3.46 rear end ?

[JupiterBMW]

So where is the best place to get a 3.46 rear end ?

+1


iPhone 5S. Tapatalk Pro. BOOM

[derbo]

OP,

Having shorter gear ratios, mean you shift MORE through the gears as the gears have a smaller range of mph.


If you still want a shorter gear ratio, a 3.46 from the auto 3series (nonZHP) is the most popular. SalvageYards, forums are common places to find these differentials. The input flange and the output flanges may need to be exchanged with your existing ones to match your half-shafts and driveshaft.

[wsmeyer]

As far as I can tell no 330i's came with the 3.46. 325i's, 325xi's, and 330xi's came with the 3.46 rear end but are the internals interchangeable?

[derbo]

As far as I can tell no 330i's came with the 3.46. 325i's, 325xi's, and 330xi's came with the 3.46 rear end but are the internals interchangeable?

Oops, I'm sorry. 323/325i were the ones with the 3.46. Thanks for the correction.

330i autos came with 3.38.

:)

[BCS_ZHP]

The input flanges are different from a 325 to a 330, 4 bolts vs. 6 bolt to attach to the driveshaft. I have been told changing that input flange can be troublesome, save yourself the headache and look for a 3.38 vs. the 3.46, the gear ratio difference is negligible. The output flanges you can reuse from your existing differential, they pop right out with a little leverage to the side of them. And then don't forget to procure a couple of output shaft seals as you don't want to have to do this twice to replace the $5 seals.

[wertyu78]

This... It's not gonna be a cheap and easy under the hood fix. You can try to find a finned shorter ratio open from an auto, it will be cheaper than a LSD but will still cost you multiple hundreds and require getting under the car to install

I picked up a Z4 3.64 differential with finned cover for $25. I did have to swap the flanges, but no issues at all!

[Vas]

I picked up a Z4 3.64 differential with finned cover for $25. I did have to swap the flanges, but no issues at all!

What year z4?

I would love to do this and then swap in a clutch pack lsd unit.

[az3579]

What year z4?

I would love to do this and then swap in a clutch pack lsd unit.

I would assume E85 body style, any year of that range... pre-2009.

[wsmeyer]

There's a 3.46 from a 325 on e46f right now if someone is feeling adventurous

http://forum.e46fanatics.com/showthread.php?t=1007697

Only $185.00

[Avetiso]

I have a 3.38 from my parts car.
Sent from my SPH-L720 using Tapatalk 2

[PirateZHP]

Sooo... what do these all really help with? And do you lose 6th gear?

[Avetiso]

Sooo... what do these all really help with? And do you lose 6th gear?

No, differential doesn't affect your transmission directly.

Sent from my SPH-L720 using Tapatalk 2

[Hermes]

Well... it does in a sense. You will gain acceleration with the shorter gearing, but lose some top speed in each gear. You will not lose an entire gear, just speed vs rpm in each gear will change vs now

[az3579]

An important thing to note is that your gas mileage will suffer because of the higher revs at cruising speed. This site will calculate what the revs will be at any given speed:

http://www.bokchoys.com/differential/e46_gear_ratio_calculator.htm

This may not matter to some, but just having higher revs while on the highway can be irritating depending on the circumstances.

[derbo]

An important thing to note is that your gas mileage will suffer because of the higher revs at cruising speed. This site will calculate what the revs will be at any given speed:

http://www.bokchoys.com/differential/e46_gear_ratio_calculator.htm

This may not matter to some, but just having higher revs while on the highway can be irritating depending on the circumstances.

Im losing 2-3mpg difference with my 3.62. Used to get 29-30mpg consistently, I'm getting closer to 26-28 depending on how hard i drive, which happens more often since I'm in the powerband quite more often..


IMO, as long as the RPM for 70mph in 6th gear is near 3000rpm, you should have minimal impact on mpg unless you drive it harder.

[JupiterBMW]

...70mph in 6th gear is near 3000rpm, you should have minimal impact on mpg unless you drive it harder.

What if your highway cruising speed is typically 85-ish...? :shifty

[midlandtech]

I've been wanting to do this for awhile. Need to find the right price as I'm sure shipping would be expensive

[alexandre]

I'm running a 3.46 from an auto 325. PO's bill shows about 250$ for the diff from their local yard and 2h labor for install.

I love the setup, it fits the 330 motor and 6 speed beautifully - although I've never driven a 3.07 ZHP so I can't compare.

[BCS_ZHP]

EDIT: Didn't intend to insult anyone's intelligence with the below post, just decided to add it after there seemed to be some earlier questions in this thread on what a differential gear change would do and how it would affect the car's performance.


So our manual transmissions have the following gear ratios:
1-4.35, 2-2.5, 3-1.66, 4-1.23, 5-1.00, 6-0.85

Now couple that to your stock 3.07 differential gear ratio and you get final drive ratios (multiply each transmission gear ratio by the differential gear ratio) of:
1-13.35, 2-7.68, 3-5.10, 4-3.78, 5-3.07, 6-2.61
What this means is your engine has to make 13.35 rotations when in 1st gear to rotate your rear tire once, 7.68 engine rotations in 2nd gear to rotate your rear tire once, and so on.

Now do the same exercise for a 3.38 differential gear ratio which was in any 330 with an automatic:
1-14.70, 2-8.45, 3-5.61, 4-4.16, 5-3.38, 6-2.87

So after a swap to a lower differential gear ratio, you have to make more engine rotations in any of the 6 gears to get the same one rotation of your rear wheel. At any given speed, more engine rotations means you're higher up the rpm band. Climbing up the rpm band is where your HP and torque start to increase (there is a limit up near the top of the rpm band where both HP & torque gains flatten out).

So changing to a lower differential gear ratio changes your final drive ratio and should move you up the power and torque band sooner. How much you want to jump is up to you, some guys even go above the 4.00 ratio level to get even more power & torque sooner but as BP & others noted it negatively affects fuel economy.

On fuel economy, how much will it negatively affect it. All things being equal, a 3.38 or 3.46 differential gear ratio change should decrease your fuel economy about 10-12%. There are more intricate calculations you can use but try this one:

3.38 - 3.07 = 0.31, then 0.31 / 3.07 = 10.09%; 3.46 - 3.07 = 0.39, then 0.39 / 3.07 = 12.7%

And use the same for figuring out your new cruising speed rpms. If your car cruised at 55 mph at 2500 rpms, after the differential gear ratio change your rpms at 55 mph should be about 10% higher or around 2750-2800 rpms.

Hope that clears up some of the mystery behind a differential gear change. Drag racers do it all the time, we used to do it back in the day on the street with the 60's/70's muscle cars too.

And costs, I picked up a used 3.38 differential for $200 and new output seals & diff fluid from ECS for another $40. Just waiting for Stuart to get his lift installed :) so we can make this swap happen the easy way, he tells me its about a 2 hour evolution to swap the diff on our cars.

[az3579]

Also note that by cruising at higher RPMs, you're wearing your engine a slightly more accelerated rate as well. The difference between the stock diff and the lower ratio diff is negligible with daily driving, but it is still a difference nonetheless. This is one of the reasons why race engines' lifespans are measured in hours not by miles; they are constantly revving off the charts. A street car's engine will typically last longer the lower you keeps the revs on average. That's one reason why in the E30 world, the 325e's are slow as balls and only rev to 4.5k redline, but they last forever (mileage in the 300's and 400's is not unheard of). Same story with diesels; low revs but are bulletproof.

Personally, unless I'm at the track, I'd prefer to keep the revs as low as possible so 1) I don't have to visit the pump more often, and 2) my engine lasts longer when I'm not pushing it. Unless you auto-x frequently, I personally don't see too much of a benefit unless you don't care about either of those things. In that case, it sure is a helluva lot more fun with a (different) diff!

[derbo]

Reason I put it is was for LSD and the upp gear ratio. Its going to be funnnn

sent from my mobile device

[az3579]

Reason I put it is was for LSD and the upp gear ratio. Its going to be funnnn

sent from my mobile device

Well now that you have a douche buggy, you don't have to worry about wearing out your ZHP nearly as fast. :biggrin
(self proclaimed douche buggy, before anyone bites my head off here!)

[derbo]

its okay. I love my douche buggy. Remember that article about Prius drivers and bmw drivers are the worst dbags. I bet I get double since I own both. Hahahah

sent from my mobile device

[az3579]

But you're neither... right? lol

[derbo]

But you're neither... right? lol

Two wrongs make a right?

two negatives together make a positive?

LOL

BP has good points on the gear ratio change. Higher RPM definitely will wear the engine faster. How much? Can't really say, but I highly doubt its enough to make a problem out of it.

[Hermes]

Engine wears out, put in S54. Problem solved

[derbo]

Engine wears out, put in S54. Problem solved

I know thats my solution :)

[Dathaeus]

Thanks guys for the outstanding info as always... for some reason I didn't get email alerts even though I was subscribed for instant notification as I usually do, hence my late response.

Yes, my whole goal was

1. Make it more fun to drive at under 60mph where most of my driving is done. I like to drive more with my shift knob than brakes, and wouldn't mind using the higher rev end more... I just need to improve my shifting skills.

2. I get on long drives on the highway (over 15 minutes) maybe a few times a month, if that. Also if this were a 5 speed, no way would I even think about this. With 6, it makes the shorter shifts and slightly higher cruising RPM fine with me.... I don't need to break 160mph very often and don't plan on taking this baby to Nurbergring or anything.

3. I don't drive that often so paying 10% more in fuel probably means less than a few bucks a months or me, so that and engine wear, not really a concern.

4. Some roads I feel like I should be able to ride in 2nd or 3rd, but right now (due to posted speed limits), I feel like I am "in between"... just feels wrong, if that makes sense.

5. 2nd gear seems to barely reach 60mph almost near redline I think... so shorter ratios would make me feel better in getting into 3rd to make it up there... this may not be relevant to anything, but I still like to do the 0-60 test when I can.
__________________________________

So it seems I need to get the 3.38 differential (altho that 3.46 on the other forum is tempting)... anyone who installed with the 3.46 also think its more trouble or is the overall install process pretty similar in labor difficulty?


I'm running a 3.46 from an auto 325. PO's bill shows about 250$ for the diff from their local yard and 2h labor for install.
I love the setup, it fits the 330 motor and 6 speed beautifully - although I've never driven a 3.07 ZHP so I can't compare.

So alexandre, you concur that the 3.46 is the way to go for this, that I am not just imagining it might be better with all my points above, anything else you can add?

[az3579]

If you wanted to do 0-60 faster, then keeping the stock diff is better for that one particular thing. You can get a touch over actual 60 in 2nd gear if you rev it out to 6700 RPM. Shifting wastes time in that regard, so the advantage you get from quicker acceleration is home the moment you go to shift into third.

For everything else - either of those ratios will do well for you!

Sent from my DROID RAZR HD using Tapatalk 4

[Dathaeus]

For my final decision,

3.38 vs 3.46

Any strong opinions on this from experience or the like, especially on the type of result I am looking for? If there is negligible difference, then I'll just go with the cheaper and/or newer one thats a better value. I just dont want to get one and then find out the other was more optimal for......... You know how it is.... I think both are available for sale right now so I'd like to take advantage.



If you wanted to do 0-60 faster, then keeping the stock diff is better for that one particular thing. You can get a touch over actual 60 in 2nd gear if you rev it out to 6700 RPM. Shifting wastes time in that regard, so the advantage you get from quicker acceleration is home the moment you go to shift into third.

For everything else - either of those ratios will do well for you!

Really? I always feel like I lose some power when it reaches about 50-55, gets me a little frustrated, but maybe I'm just imagining it. Ya but thats fine, 0-60 time is not one of my top 3 reasons for doing this so if I can get the other satisfactions, I think I am pretty much set on doing it.

Thanks!

[alexandre]

Very happy with the 3.46. Fits the car perfectly. Either will cost the same but 3.46s are much more readily available.

[Dathaeus]

Very happy with the 3.46. Fits the car perfectly. Either will cost the same but 3.46s are much more readily available.

There is some other guy selling the 3.38 which is why I was asking... I think I'll be fine either way but... again, JUST in case....

Also, followup on the 0-60, tested just now, and I lose a ton of power after 5500 rpm... it finally reaches 60 at like 6200+ rpm, so unless I am doing something fundamentally wrong, I dont see how the optimal 0-60 can be in 2nd gear.

[derbo]

:whistles: 3.62 ;)

sent from a Moto X

[Hornung418]

BP your concerns about engine speed at cruising speeds is kinda silly. This car has an OD gear (6th.) So what about the cars that have the 2.93 and cruise perfectly fine at 3000 rpm in 5th? The engine is not wearing out any faster than the ZHP cruising at 80mph and 2600 rpm. Now if you are going to be redlining it and racing I can completely understand...but to be concerned about cruising speeds and economy is silly when anything over 55 is highly unefficient. Drag takes over and is actually more work to keep her going 80 mph.

Cheers to the swap. Wake up the beast :-)

Sent from my GS3.

[Vas]

3.62 gets my vote

[PirateZHP]

Here is a question...

I know everyone is saying go with 3.46 or 3.62 which are good jumps from our diffs, HOWEVER if I can get a 3.15 LSD for cheap, wouldn't that be worth it just to get the LSD? I realize it won't do much as far as adding quickness/speed/acceleration, but it will at least have LSD... amiright?

[Avetiso]

Here is a question...

I know everyone is saying go with 3.46 or 3.62 which are good jumps from our diffs, HOWEVER if I can get a 3.15 LSD for $150, wouldn't that be worth it just to get the LSD? I realize it won't do much as far as adding quickness/speed/acceleration, but it will at least have LSD... amiright?

Where will you find one that fits the E46?

[PirateZHP]

Where will you find one that fits the E46?

Isn't that what comes in a 325?

[derbo]

Manual 325i.

[derbo]

Here is a question...

I know everyone is saying go with 3.46 or 3.62 which are good jumps from our diffs, HOWEVER if I can get a 3.15 LSD for cheap, wouldn't that be worth it just to get the LSD? I realize it won't do much as far as adding quickness/speed/acceleration, but it will at least have LSD... amiright?

for $150, You can't really go wrong with that. gear ratio-wise you wont really notice a difference, but the LSD you will notice the handling characteristics change.

[PirateZHP]

Right...

Derek, you have done a lot of research. Is this worth it at all?

Edit: Sorry, just saw your answer...

[Avetiso]

How have I not heard of this? !

[Hornung418]

E46 M3 differential/ subframe swap with the e39 M5 ring and pinion. That will give you an OEM LSD with a manageable first and second gear.

Sent from my GS3.

[derbo]

How have I not heard of this? !

You should buy a wrecked M3 and I can take the engine/transmission ;)

[derbo]

E46 M3 differential/ subframe swap with the e39 M5 ring and pinion. That will give you an OEM LSD with a manageable first and second gear.

Sent from my GS3.


1st/2nd Gear are useless anyways. Its all about 3rd and 4th and 5th on the track :). Funny cause the E39 guys love to switch to the M3 3.62 ring n pinion.

[Hornung418]

Track yes...as a DD however, you would want something sane. Why don't yiu out the 4.10 LSD in your ZHP?

GS3 + TT4

[derbo]

Track yes...as a DD however, you would want something sane. Why don't yiu out the 4.10 LSD in your ZHP?

GS3 + TT4

I thought about it and it may come around in the future. I like to get use to the 3.62 first.


IMO the 3.62 is amazing in the city :)
sent from a Moto X

[PirateZHP]

No dice on the 3.15lsd for me... just an update.

[derbo]

No dice on the 3.15lsd for me... just an update.

What happened?

Sent from a Moto X

[PirateZHP]

What happened?

Sent from a Moto X

Sold out from under me. There will be more. I will wait and find another diff...

[derbo]

It's almost too good to be true with a 3.15 LSD for that low of a price.. Well, heres toa 3.46 ;)

[PirateZHP]

It's almost too good to be true with a 3.15 LSD for that low of a price.. Well, heres toa 3.46 ;)

Maybe a 3.62?... or 4.10?...

[derbo]

Maybe a 3.62?... or 4.10?...

Beast. I don't even know what 4.10 would be... Never use 1st ever?

Sent from a Moto X

[PirateZHP]

Beast. I don't even know what 4.10 would be... Never use 1st ever?

Sent from a Moto X

1st would probably be fairly pointless. But just think about what 3rd-5th would feel like!

[Hermes]

Manual 325i.

I was under the impression this (E36 diff) takes massive modification to make it bolt up. Not a bolt in mod like E46 M3 rear end

[derbo]

1st would probably be fairly pointless. But just think about what 3rd-5th would feel like!

feels like we might be out of the powerband too often. You just have more chances to mis shift :)

[PirateZHP]

feels like we might be out of the powerband too often. You just have more chances to mis shift :)

You are running 3.62, right? I thought I remember you saying that you love it. I realize it isn't the 4.10... so maybe I should go with the 3.62...

[Avetiso]

Ahem, there's a 3.38 in me garage. What do you guys honestly think the overall hit to MPG will be? Might just toss it in myself.

[PirateZHP]

Ahem, there's a 3.38 in me garage. What do you guys honestly think the overall hit to MPG will be? Might just toss it in myself.

3.38 LSD? Do it, Dario... or fly it out here and put it in my car... I will be the guinea pig! :rofl

[derbo]

You are running 3.62, right? I thought I remember you saying that you love it. I realize it isn't the 4.10... so maybe I should go with the 3.62...

Matt,

I do run 3.62 yes. Around 45mph I'm already in 4th for normal 3k shift driving..LOL.

3.07
MPH @ 3000RPM
1st gear 17mph
2nd gear 29mph
3rd Gear 44mph
4th Gear 59mph
5th gear 72mph
6th gear 85mph

3.62
MPH @ 3000RPM
1st gear 14mph
2nd gear 25mph
3rd Gear 37mph
4th Gear 50mph
5th gear 62mph
6th gear 72mph

4.10
MPH @ 3000RPM
1st gear 13mph
2nd gear 22mph
3rd Gear 33mph
4th Gear 44mph
5th gear 54mph
6th gear 64mph

I think this chart helps you figure out some stuff.

http://www.bokchoys.com/differential/Speed.htm

This calculator helps too. I set the redline to the RPM you want to see the MPH in each gear. :)

http://www.bokchoys.com/differential/e46_gear_ratio_calculator.htm


Driving to the track with the car running at 65mph at 3000RPM, seems a little bad for daily-driving..

[PirateZHP]

Oh, great info, Derek! Yeah... I guess since I am still having to DD my ZHP, I should think about that as well.

[Avetiso]

Matt,

I do run 3.62 yes. Around 45mph I'm already in 4th for normal 3k shift driving..LOL.

3.07
MPH @ 3000RPM
1st gear 17mph
2nd gear 29mph
3rd Gear 44mph
4th Gear 59mph
5th gear 72mph
6th gear 85mph

3.62
MPH @ 3000RPM
1st gear 14mph
2nd gear 25mph
3rd Gear 37mph
4th Gear 50mph
5th gear 62mph
6th gear 72mph

4.10
MPH @ 3000RPM
1st gear 13mph
2nd gear 22mph
3rd Gear 33mph
4th Gear 44mph
5th gear 54mph
6th gear 64mph

I think this chart helps you figure out some stuff.

http://www.bokchoys.com/differential/Speed.htm

This calculator helps too. I set the redline to the RPM you want to see the MPH in each gear. :)

http://www.bokchoys.com/differential/e46_gear_ratio_calculator.htm


Driving to the track with the car running at 65mph at 3000RPM, seems a little bad for daily-driving..

Wow, I'd still hit 60 in 2nd, as opposed to 67. I think I'm going to do it. Derek, how much quicker would you say the car feels?

[derbo]

I was quoted an 18% change in acceleration for the 3.64 (close to the M3 ratio) and 12% for the 3.46 from Jim Blanton. (http://www.performancegearing.com/)

[derbo]

Wow, I'd still hit 60 in 2nd, as opposed to 67. I think I'm going to do it. Derek, how much quicker would you say the car feels?

Dario, what do you mean 60 in 2nd? I hit 55mph at redline in 2nd and I have to shift...


I suppose if I can make it out to the meet, you can give it a whirl.

[PirateZHP]

Dario, what do you mean 60 in 2nd? I hit 55mph at redline in 2nd and I have to shift...


I suppose if I can make it out to the meet, you can give it a whirl.

I assume he means with the 3.38 he has in his garage... that should still get to 60 in 2nd...:dunno

[Avetiso]

Dario, what do you mean 60 in 2nd? I hit 55mph at redline in 2nd and I have to shift...


I suppose if I can make it out to the meet, you can give it a whirl.
3.38. Also, made a mistake and calculated it at a 7,000rpm redline, when it should be 6,800rpm. I suppose a tune would fix that...

I assume he means with the 3.38 he has in his garage... that should still get to 60 in 2nd...:dunno
This.

[Avetiso]

Correction: 57.25mph at 6,800rpm in 2nd gear with a 3.38 vs 63.03mph with a 3.07.

[Hermes]

I don't like running my engine past 6000, too much stress on the oil pump nut

[derbo]

I don't like running my engine past 6000, too much stress on the oil pump nut

The ZHP have an upgraded oil nut, don't they?

[Hermes]

Supposedly, but they supposedly still back off

[Vas]

The ZHP have an upgraded oil nut, don't they?

Yes they do.

[terraphantm]

The ZHP have an upgraded oil nut, don't they?

As far as I can tell, the only difference is that it comes with some thread locker. There have been failures reported with red loctite, so it's still something to worry about.

That said, the crank damper for 2001/2002 and 2003+ models is different. Fewer failures reported for the latter.