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      04-08-2013, 12:44 AM   #1
N111CUK
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M3 Rear Subframe in 335i conversion

335i project M3

Now before I start let me just answer the question most people put to me. Why dont you just buy an M3? Well because I prefer the N54 engine the 6AT transmission and how it drives daily. I also believe this car can make a great weekend arrive and drive track car and overcome its heating issues.
What mods on my the 2007 335i 6AT M Sport

Vishnu Procede V5 500
Vishnu PWM Methanol Injection trunk mounted 800
PLM 3 De cat Down Pipes 200
Custom cat back exhaust using OEM back box 400
Injen Dual Cone Intake 200
Spearco FMIC 300
HEL braided brake lines 95
M3 Rear sub frame including disks brakes hubs etc.. 500
M3 Front brakes with M3 hubs and carriers 150
KW V3 coilovers M3 spec 1450
H&R Anti Role Bar Front 75
Original Cost of Car 14,000

Total spend 18,670

The main mod which is of most interest is my M3 rear sub frame transplant
The complete M3 sub frame fits 100% into the 335i and requires a modification to the Prop shaft.

Why use an M3 rear instead of the Quaife? Well this route IMHO is better as I get all the clever suspension bits from the M3, stronger axles and prop including better brakes and for less money.

I must offer my gratitude to another e90post member IDNAN who had already completed this conversion before and helped me overcome some major questions. THANKS!

ALSO a big thanks you to MVG Engineering in Dartford Erith for all their help in getting this Installed. 01322 342699 speak to John he is very knowledgeable

Combinations of parts for the M3 Differential install

M3 E92 DCT Rear sub frame with FD of 3.15
M3 E92 DCT Prop shaft
335i 6AT Prop Shaft

As I mentioned before the sub frame is a straight fit. The considerations you will have to take into account are the final drive of the differential you choose.

335i gearbox transmission ratios
335i 6MT OEM Diff gearing FD 3.08
335i 6AT OEM Diff gearing FD 3.46
335i DCT OEM Diff gearing FD 2.56
M3 gearbox transmission ratios
M3 6MT OEM Diff gearing FD 3.85
M3 DCT OEM Diff gearing FD 3.15

Now armed with this information you can decide what FD you end up with. Choosing a lower number than your OEM setup will give you longer gearing and picking a higher number than OEM will shorten you gearing. This will not throw up any CEL codes but will be important to overall performance output.

I picked the DCT M3 diff as this would lengthen my first gear which was a little short IMHO and means my 1 gear launches are more usable with all the performance mods. I also can cruise on the motorway freeway at lower revs and higher speeds improving MPG.

If you have a DCT 335i and install a 6MT M3 diff you would be way out and you could take off in 3rd gear which would be crazy. I would go with as close a ratio as OEM and maybe go longer if you have mods making the car more powerful with more torque.

Now once you have the Diff you need to modify the prop. You could get a new prop built but so long as you have the M3 prop you can use this with your OEM prop and create a new prop for this application.

The best way to create the new prop is to combine the 335i prop and the M3 prop. Use the 335i tri bolt flange plus gimbal plate (rubber bushing with 6 holes) and the 335i centre bearing(this is vital to keep everything in line as intended by BMW OEM). You then mate this to the M3 prop creating a very strong custom prop which is mostly M3 but is 100% OEM fit.

Measuring this was simple. The measurements are split into two parts.
1. Diff to Centre bearing
2. Centre bearing to Transmission

The first measurement on the M3 prop is spot on. This part of the M3 prop remains constant because we share the same monocot chassis as the M3. What we need to measure for cutting and attaching is the second measurement. This measurement is from Centre Bearing bolt hole to rear side of the tri bolt flange. To get this absolutely right you should provide the prop builder both of the measurements because they will need to remove the centre bearing and attach the 335i bearing and therefore they need to know where all three points will be in relation to each other.

What I did was to attach the 335i prop to the transmission (make these bolts tight) and centre bearing (locate only one bolt) and take a measurement from the centre bearing bolt hole (one without the bolt) to the face of the flange attached to the 335i prop (your tape measure will be at an angle thats OK). Then once you have this take it off and attach the M3 prop to the diff and then to the centre bearing again put all 6 bolts tight on the diff and only one bolt in the centre bearing. Then take another measurement. You now have both measurements for the Diff builder. Get a good shop to make this up for you. I used JW Engineering in Erith Dartford, they build racing props for kit cars and touring cars so they know there stuff.

NOTE: It is important to understand at this point that any prop has expansion movement at one of its halves; the 335i prop has movement at the front portion near the transmission where by the M3 prop has its movement at the rear at the diff. You should only keep one movement when building a prop
Some other challenges and choices that comes to light when doing this.

1. The M3 rear sub frame comes with all the M3 suspension arms etc.. (GREAT!!) but this also means you need M3 shocks and Springs as the 335i shocks wont fit . At this point I decided to get new coil overs and opted for KW V3. I ordered the M3 version.

2. Now you have M3 rear brakes they are actually bigger in diameter than the 335i fronts and also drilled. You could just keep the 335i fronts but I opted to keep the OEM theme here and get some cheap M3 front Disks Callipers hubs and Carriers. This also makes the M3 KW coil overs fit. So Im stopping a lot better now.

3. Depending how your sub frame turns up you may need some extra bits from the dealer. Bolts were the main bits that I needed. Prop bolts, Calliper carrier bolts, M3 Rear spring lower bushings, M3 Front strut plates etc.
The whole project took a week but with better planning and this info Im providing you could get this done in two days tops. I had a lot of stop starts as I would run into a parts shortage or the above challenges and I needed to stop working.

Whats she like to drive. Well I can say that its better than the OEM M3 and very committed into corners. Traction is never an issue and no noises or issues with the conversion. If I had gone the Quaife route I would have not gained better breaks suspension and M3 components so I think I got a better deal and car in the long run.

The car is no wider at the rear than with the 335i rear sub frame so no concerns with wheel clearance.

Ill try and help any of you guys with this conversion you may want to take your own route to complete this.

Thanks for reading my post all the best
Adam




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      04-08-2013, 01:14 AM   #2
scaryprowler
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Wow! Great info, thanks for sharing.
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      04-08-2013, 02:27 AM   #3
Josh1a1h
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You a F****** legend!!!

Thank you for this detailed write up! I have wanted to go this route for ages over the quaife!

I heard the stock LSD is much better and smoother than a quaife too!

THANK YOU SO MUCH
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      04-08-2013, 02:43 AM   #4
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Congrats - awesome job.

Like Idnan you've got a better final result really with all the M3 rear bits.

Good job. Wish I had the time/skills to do it......
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      04-08-2013, 03:14 AM   #5
Josh1a1h
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How much did the prop set you back mate?
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      04-08-2013, 04:22 AM   #6
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Congrats mate, glad I could help you out. You got the m3 subframe dirt cheap so it was much cheaper than the quaife swap. Those m3 rear end bits are so much stiffer than the non-m equivalents.
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      04-08-2013, 04:41 AM   #7
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Hi Adam

That sounds awsome and to get it all in at that price must have taken some serious patientce and keyboard surfing!

Can I ask how your exhaust works and where you got it? I would like to do mine and have the de-cat downpipes but am confused as to how to keep the secondary cats for the MOT but still change the exhaust. Does yours have full de-cat?
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      04-08-2013, 10:15 AM   #8
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interesting read...its incredible to me that a car like a 335i doesn't come standard with a lsd !
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      11-11-2013, 05:56 PM   #9
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2006 BMW 335i  [5.00]
wow!
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      11-13-2013, 06:26 PM   #10
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Great info Adam!

I am considering doing this... going to trackdays quite a lot more lately and instead of getting a quaife, this seems like a better alternative altogheter...

I've got one question...

I have a 335i DCT... so my only choice is the M3 DCT diff... but still... won't it be too short??.. i mean, going from 2.56 to 3.15... is quite a lot, isn't it?

If someone knowledgeable could elaborate on how this will affect my car performance and usability in long trips...

TIA
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      11-13-2013, 06:48 PM   #11
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I wish i could customise my gearing. I would longer gears for 1 & 2 and the shorter gearing from the M3 for 3rd, 4th & 5th Gears and use the longest 6th gear possible for motorway cruising.
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      11-14-2013, 04:14 PM   #12
N111CUK
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Going shorter isn't great because of the extra power you get from mods. I went longer from my old 3:46 to the DCT 3:15 and car is much better in 1st

Your car will have a very short 1st gear
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      11-03-2014, 08:42 AM   #13
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all the systems work ok?
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      11-03-2014, 10:03 AM   #14
N111CUK
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Quote:
Originally Posted by DimitrisM3 View Post
all the systems work ok?
So I've put 10k on this setup and its still going strong no issues. I wore out my standard front drop links so I'm either driving too hard "like I should be" or you may want some better front drop links.

I bought some on eBay from rndmotorsport231 I went with Vauxhall Astra spec which are approx 300mm in length

Has anyone else finished this type of conversion?
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