3.23 to 3.73 differential swap DIY AKA poor man's supercharger

[Suprgnat]

Originally Posted by Bimmer-Bob

Just FYI there is minor modification required to make the E60 cover fit our cars - like a spacer and a longer bolt. I don't know exactly because I bought the diff already built by Jim Blanton.

From my earlier thread:

Originally Posted by Suprgnat

So I sent an email to Jim at Performance Gearing asking about the finned differential cover and spacer and whether I could buy it from him as a stand-alone option. I explained to him that I've already committed to purchasing from someone else (been talking to Dan at Diffsonline for over a month). Jim at PERFORMANCE GEARING http://performancegearing.com/ confirmed that the E60 finned diff cover P/N 33117516280 is the correct part number and generously gave me consent to share this information with the 1addicts community:

"Paul,

No, just an option for the complete rebuild.

That's the correct rear cover part number, you will need a longer rear mount bolt:

33 17 6 760 336

and a 15-16mm thick spacer , ID =14mm, OD= approx 32mm

or 3 of these:

33 17 6 779 816 (5mm thick aluminum spacers)"

[Bimmer-Bob]

Originally Posted by Suprgnat

From my earlier thread:

Don't forget the drain plug! (p/n 33117525064)

Although I guess in a pinch you could re-use the original.

Jim is a solid guy to deal with. Must've missed that post of yours; I was curious about the specifics. Thanks.

[Suprgnat]

Originally Posted by Bimmer-Bob

Don't forget the drain plug! (p/n 33117525064)

Although I guess in a pinch you could re-use the original.

Jim is a solid guy to deal with. Must've missed that post of yours; I was curious about the specifics. Thanks.

You're welcome! You were instrumental, through your posts, in my seeking out and getting the information.

FWIW, I bought Dimple magnetic drain plug(s) for my diff, transmission, and engine.

[gixracer]

A quick FYI there are now 2 of 33117516280 left in the country.

I just ordered mine today

[MightyMouseTech]

Originally Posted by The Wind Breezes

1. The car needs more power. Gears really won't help you that much.

2. If short on $ don't get a LSD weld the diff. That's what I did and it's awesome.

That is all.

Weld the rear diff? That is just terrible advice.

[E91WAG3N]

Originally Posted by Bimmer-Bob

Just FYI there is minor modification required to make the E60 cover fit our cars - like a spacer and a longer bolt. I don't know exactly because I bought the diff already built by Jim Blanton.

Originally Posted by Suprgnat

From my earlier thread:

Thanks for bumping over the info! I recalled seeing it in Bob's thread way back when.

Originally Posted by gixracer

A quick FYI there are now 2 of 33117516280 left in the country.

I just ordered mine today

I think I'm about to pull the trigger, would hate to see it go NLA.

[minirips2]

I'm curious about the 3.73 diff swap, as well. I'm wondering if the speedometer reads high as a result of changing ratios? Next to CDV delete, this is probably number one on the "bang for the buck" mods list. it would be a great excuse to swap out the RSF bushings, too.

[Suprgnat]

Originally Posted by minirips2

I'm curious about the 3.73 diff swap, as well. I'm wondering if the speedometer reads high as a result of changing ratios? Next to CDV delete, this is probably number one on the "bang for the buck" mods list. it would be a great excuse to swap out the RSF bushings, too.

Diff has no affect on the speedo. The speedo is "driven" by the pulse generators in the wheel carriers, the same ones used for the stability and braking control.

[desertman123]

Originally Posted by minirips2

I'm curious about the 3.73 diff swap, as well. I'm wondering if the speedometer reads high as a result of changing ratios? Next to CDV delete, this is probably number one on the "bang for the buck" mods list. it would be a great excuse to swap out the RSF bushings, too.

Yeah as said before speed is read off the ABS tone rings.

Also it would be a good opportunity - I already have Whiteline RSFB inserts so I didn't need to do anything. I don't drive this car hard enough to justify anything more.

Sidenote: I have both a muffler delete and the shorter diff, so when I'm on the highway the exhaust is a little bit louder at any given speed - keeping speed with rural I-4 traffic ( ) can introduce a small bit of drone.

[gixracer]

I finally had a chance to get mine in........ I was very frustrated because the front left bolt did not want to spin out easily. the e-brake cable is in the way of the socket so a ratched cresent wrench was the best option. make sure the drive shaft is off so it doesn't take 10x as many movements. Then the rear one decided to hang up and take forever. Even with the diff supported it did not want to come out. I recommend taking the rear one out first before the front two. make sure to also break free all three before removing them. Those two wasted an extra 45 minutes of time. the 16 torx head, 12 half shaft and 4 drive shaft were easy. I only had to get up to the car twice to release the e-brake and get it out of gear.

Next issue was the finned diff cover did not want to fit. I had pre-installed and filled the diff to make life easier. The cover was against the oem section of my exhaust and I had to trim out a fin and a half to get the diff cover off the exhaust.

Results. 3.73 is in. It winds up noticeably faster. I hope that the shorter gearing will work for the tracks, Grattan, Waterford and Gingerman(when I get time). Dont know when the next time I get to the Dragon with this car but it will be fun but still would want the LSD there= more $. I was pleased because the the engine got into the power band faster and was just as happy to rev. At the tracks I'm at 130 it's about maxed out as top end. Now I will be able to use 5th on a regular basis.

[Suprgnat]

Originally Posted by gixracer

Next issue was the finned diff cover did not want to fit. I had pre-installed and filled the diff to make life easier. The cover was against the oem section of my exhaust and I had to trim out a fin and a half to get the diff cover off the exhaust.

A little late, but this may have been helpful to you.

Originally Posted by Suprgnat

So, reviewing innumerable posts it was obvious I'll need to machine the cover to clear the stock/BMWP exhaust. The Quaife/Birds cover is clearly a modified OEM BMW part and it looks to be machined on the last two fins about even to the thickness of the cover proper which is about 45mm. I've decided, after spending too much time under my car following getting back from a 16 hour delta-t, to machine as follows in the attached picture:

[gixracer]

Originally Posted by Suprgnat

A little late, but this may have been helpful to you.

I had seen that, was under the impression that it was for the 135’s oh well. when looking at BimmerBobs pic there were no fins missing. I’ll do the dremel thing and get it done so it look ascetically pleasing.

[Bimmer-Bob]

Clearance doesn't seem to be an issue with the MagnaFlow cat-back - plain dumb luck on my part:

I had wondered if a stock 128i exhaust would clear, since I knew the cover required trimming on the 135i. Bummer that you guys found out the hard way that it does not. But, at least its still workable with a little bit of elbow grease, rather than a total no-go.

Anyway, lookin' good, guys! I always get a kick out of seeing those fins poking out the backside. It's just such a nice little detail and finishing touch.

[Suprgnat]

Originally Posted by Bimmer-Bob

Clearance doesn't seem to be an issue with the MagnaFlow cat-back - plain dumb luck on my part:

Attachment 1696262

I had wondered if a stock 128i exhaust would clear, since I knew the cover required trimming on the 135i. Bummer that you guys found out the hard way that it does not. But, at least its still workable with a little bit of elbow grease, rather than a total no-go.

Anyway, lookin' good, guys! I always get a kick out of seeing those fins poking out the backside. It's just such a nice little detail and finishing touch.

The cool part is that I had/have access to a machine shop for both the cover mod and to make the spacers for the cover.

[gixracer]

Originally Posted by Suprgnat

The cool part is that I had/have access to a machine shop for both the cover mod and to make the spacers for the cover.

Spacer was easy, quick phone call with dimensions and I had it the next day. I did notice that the bushings are very flexible. Anybody have ideas for alternatives, are the M's worth it? I have M sub frame bushings in already.

Quick notes from driving into work to with the car, first is short and definitely find myself in 5 more on two lane road, lots more shifting. Observation on the math from the tach /speedo in 6th 500RPM per 10mph +/- nets about 3500 at 80. I have yet to take it on the highway. It will be at the track on Saturday and it will be in storage for the winter on Sunday. The fall fun driving will be in the wife's X1 35i Msport, mmmm love N55 turbo.

[Bimmer-Bob]

Originally Posted by gixracer

Spacer was easy, quick phone call with dimensions and I had it the next day. I did notice that the bushings are very flexible. Anybody have ideas for alternatives, are the M's worth it? I have M sub frame bushings in already.

I did the ///M diff bushings at the same time. I din't install the diff myself, so I wasn't able to compare against the stock bushings, and I also had a rear sway bar installed at the same time - but overall, the rear end feels very buttoned down and predictable now.

[gixracer]

track day is complete

damn that thing revs up fast and the diff needs a LSD so badly

On the highway if you turn up the music its not so bad. my milage at 80 on cruise control was 25mpg. I think if I am going to keep the car as a street car it will be changed to a 3.64 with LSD. The difference from 3.23 will be noticeable but not to the point where it will be super tight with the 3.73.

There were a few situations where I could not downshift because the spread was so minimal, but that is dependent on what track your at. The main place was a 110 degree left that transitioned into a uphill right. I was too high in the rev range to make it effective because the inside wheel would spin and the amount of time in the gear was to short to justify the shift vs trying carry the corner speed.

Dedicated track car = great mod
Daily driver= too much time shifting
split duty= not bad unless on the highway(limited time)

[Bimmer-Bob]

Originally Posted by gixracer

Dedicated track car = great mod
Daily driver= too much time shifting
split duty= not bad unless on the highway(limited time)

I think it took me a few days to get used to the changed shift points, but I don't even notice it now (i.e., it could have come this way, and I wouldn't have found it odd).

I will say that before the mod, it was very common for me to drive around in 3rd & 4th most of the time, and almost never in 6th. Basically only used 6th for long-distance, sedate interstate driving. So I really didn't feel like I was giving up too much at the top end. Now I'm in 5th a lot more often.

6th is still rarely used, but I live on an island now with nothing larger than a two-lane road and mas speed-limits of 50-55mph (often lower). I'd say I rarely exceed 60-65mph, unless I drive over to the mainland and get on the interstate, which isn't very often in this car.

But, like I said, totally subjective. Depends on personal tastes, driving styles, etc. It's good that you tried the 3.73 with an open diff first, rather than paying big bucks for the LSD and regretting it.

[desertman123]

OP updated with video

I've been dailying this for a bit now and I still love it. Yeah it's a lot of shifting but you get used to it, and with skipping gears occasionally. Highway isn't bad, it's nice to have some more power but the RPMs do climb quickly.

[Suprgnat]

Originally Posted by desertman123

OP updated with video

I've been dailying this for a bit now and I still love it. Yeah it's a lot of shifting but you get used to it, and with skipping gears occasionally. Highway isn't bad, it's nice to have some more power but the RPMs do climb quickly.

A lot of shifting? With a 3.73, 3rd is good from 33 MPH@2750 RPM (peak torque) to 81 MPH @6800 RPM (or a little higher). That's a 50 MPH spread!

Hold the go-pedal down longer!

For Reference: 3.64 Diff Chart

[Bimmer-Bob]

Originally Posted by Suprgnat

A lot of shifting? With a 3.73, 3rd is good from 33 MPH@2750 RPM (peak torque) to 81 MPH @6800 RPM (or a little higher). That's a 50 MPH spread!

Hold the go-pedal down longer!

+1

So long as the engine is warm you can rev, rev, rev an N52 all day. I almost never use 6th, even with a 3.73. Hell, 5th gear sees rare use.

[Eins Suchtig]

[IMG][/IMG] don't hear the OP . He's bad influence... 3.73 arrived!!!!