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      10-31-2011, 10:09 PM   #1
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M3 on 328i

I'm getting ready to install shocks, springs, and M3 rear control arms on my 328i. When I'm done, I'll have M3 spring rates, M3 shock valving, plus sway bars and lower control arms from the M3. My car is 10% lighter than the M3, so it won't be exactly the same. Plus, my spring rates are a little lower (3-5% lower).

It might look like I have some kind of fetish for the M3 -- and that may be true! -- but the thing is, the M3's suspension setup is a convenient target for a complete system of parts that were all designed to work together. I'm especially thinking of springs, sway bars, and shocks.

I have several goals, which are: A) Eliminate the unsettled behavior over large bumps, especially on the freeway. B) Eliminate oscillation after a bump. C) Achieve a neutral steer car. D) Improve steering feel. E) Make the car enjoyable to drive!

In order to do all this, I'm raising the car up a little, on the theory that part of the bounciness (A & B) is caused by compressing the bump stops too much. I'm increasing travel by 1) raising the car, 2) shortening bump stops, and 3) using shorter mounts.

I'm selecting spring rates that are more or less the same as the M3. Since the weight is off by 10%, and the springs are off by 5%, the damping coefficient is off by 7.5%. That's for damping body oscillations.

The other thing about the spring rates I wanted were to keep the "flat ride" characteristic, and make a "balanced" neutral steer car. My spring rates are an estimated 156 in front, and 525 in rear. My targets were the M3 rates, which are 160 and 550, respectively. (Those M3 numbers are for the coupe.)

To make the rear a little easier I decided to convert to the M3 camber link. This lets me use an original M3 shock, or an OEM replacement. I couldn't get a used M3 rear shock cheap, so I just got a Bilstein HD shock. To round out what I'm doing in the rear: Hyperco 525# racing spring plus a height adjuster made by AST.

I'll say more soon, but in the meantime, here's a photograph of the rear to hold your attention for a while.

Name:  Link Spring Shock 640.png
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2007 328i ZSP. M3 suspension: custom valved Bilstein shocks, Hyperco race springs, M3 lower control arms front and rear, M3 sway bars, and M3 subframe bushings. E46 front guide supports. Euro tail lights.

Last edited by luckyu; 10-31-2011 at 10:15 PM. Reason: corrected damping coefficient
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      10-31-2011, 10:48 PM   #2
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2008 E92 328  [2.50]
You should get one of those iPhone apps and run a skidpad/slalom somewhere, then compare after results.
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      10-31-2011, 11:16 PM   #3
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Totally agree..I am big fan of robbing the m3 parts for our cars. And also a fan that your opting for performance vs stance..
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      11-01-2011, 12:08 AM   #4
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Are you keeping your BMW PS springs in the front?
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      11-01-2011, 12:12 AM   #5
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Quote:
Originally Posted by tibra1 View Post
Totally agree..I am big fan of robbing the m3 parts for our cars. And also a fan that your opting for performance vs stance..
Thanks man! If I could have robbed the actual stock M3 shocks and springs I would have done that too!
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      11-01-2011, 12:23 AM   #6
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Quote:
Originally Posted by luckyu View Post
Thanks man! If I could have robbed the actual stock M3 shocks and springs I would have done that too!
At their pricepoint..it would prolly be worth risking a stretch in jail..
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      11-01-2011, 12:41 AM   #7
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Front corner weights

Quote:
Originally Posted by cvc 22349a View Post
Are you keeping your BMW PS springs in the front?
Originally, I was thinking of doing just that. But, I am using front springs from the 335d. The estimated spring rate of this spring is 156#, and that estimate is based on the known nominal 335i spring rate of 145# (to the best of my knowledge, Orb got this number from BMW). Vorshlag has measured a bunch of springs, and found the actual rate of the 335i sport spring to be a little lower, about 138#.

An alternative front spring to the one I chose is the performance spring for the 135i, which Jah29 measured at 160#. Exactly the right rate. The 135i is just a little heavier than the 328i, which means used on the 328i it would ride 0.3" higher. That means a ride height of about 14.3", not bad!

This may be a great choice of spring for someone looking to do a similar "M3 tune" on a 328i. There's a risk that the 1er coupe fender height is slightly different, though. I wanted to avoid that risk so I stuck with spring choices that came from sedans (e90), to match my car's body style. That way I could match equipment exactly and predict the ride height. (We'll see how well that turns out.)

Here are some front corner weights to give an idea of what's available. There are sport springs and performance springs for each car!

328i sedan manual. (3362 * .505 / 2) - 105 = 744 lbs
135i coupe manual. (3373 * 0.516 / 2) - 105 = 765
135i coupe auto. (3439 * 0.519 / 2) - 105 = 787
335i sedan manual. (3593 * 0.509 / 2) - 105 = 809
335i sedan auto. (3605 * 0.511 / 2) - 105 = 816
135i convertible auto. (3704 * 0.497 / 2) - 105 = 815
335d sedan auto. (3825 * .51 / 2) - 105 = 870
335i convertible. (4001 * .47 / 2) - 105 = 835

As you can see, the convertible is the heaviest car; but its rearward weight distribution makes its front corner lighter than the 335d's.

These car weights come from BMWUSA, straight off their web site. My understanding is that these are wet weights, and include some gas and a 165 pound driver. The estimate for unsprung weight comes originally from JAJ, I think. It came with the spreadsheet I've been using to model steady-state corner behavior.
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      11-01-2011, 01:41 AM   #8
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Quote:
Originally Posted by tibra1 View Post
At their pricepoint..it would prolly be worth risking a stretch in jail..
Yeah, I would only buy the M3 stuff used. I should mention that there may be a use for M3 front springs on the 335i. Jah29 says he has tried installing them on his 135i.

I think the M3 springs would jack up a 335i a little, but that can be controlled using SUFT015, the lowering perch sold by supremepower. It lowers the front by 0.4" by allowing the spring to perch higher up. So that's another way to get 160# in front, if you have a 335i.

Even the rear M3 springs might work on the 335i, but there are better alternatives for the rear spring.
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      11-01-2011, 01:43 AM   #9
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I might have went that route but really wanted the flexibility of coilovers..especially D/As to tweak all the settings.
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      11-01-2011, 11:39 AM   #10
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Quote:
Originally Posted by tibra1 View Post
I might have went that route but really wanted the flexibility of coilovers..especially D/As to tweak all the settings.
Absolutely, you're fixed up with ASTs. I was "putting info out there" for others who might be interested in a custom-valved setup similar to mine.
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      11-01-2011, 01:00 PM   #11
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Quote:
Originally Posted by luckyu View Post
Absolutely, you're fixed up with ASTs. I was "putting info out there" for others who might be interested in a custom-valved setup similar to mine.
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      11-07-2011, 07:20 PM   #12
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Bump Stops

One of my goals is to get more suspension travel, specifically more bump travel. I plan to get most of that by raising the car, but I also wanted to use a shorter bump stop both front and rear.

In the rear I decided to use one of the Z4 rear bump stops, because it's rumored that Dinan is using it in their M3 lowering kit. The part I chose was P/N 33 53 6 770 350, which includes the bump stop and protection tube. (The bump stop doesn't fit the E90 stock tube.)

It turns out this bump stop is 2.5" long, making it 0.375" shorter than the ZSP stock bump stop. Here's a picture of the two side by side:

Name:  Bump Stops.png
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As you can see it's not much shorter. In the future I might choose a shorter one, but a conservative change seems best for now. Also, Koni's bump stops don't seem to be used with the stock dust tubes, and I'd have to find a solution for that.
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Last edited by luckyu; 11-07-2011 at 09:50 PM.
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      11-07-2011, 10:24 PM   #13
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I should go over exactly what I'll be installing.

* Hyperco 10" 525# springs, w/ AST height adjuster & Swift bearings
* M3 rear lower control arm "camber link"
* Bilstein HD M3 rear shock
* 2.5" rear bump stop & dust tube from E85
* E46 front strut mount
* BMW 156# front spring from 335d
* Bilstein HD E90 front strut, valved to match M3, w/ shortened bump stop

If the front ride height is too high I'll install the SP lowering perch.
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      11-07-2011, 11:24 PM   #14
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AST Height Adjuster

Here's a photo of the AST height adjuster. AST recently changed their adjusters from fitting 2.5" ID to fitting 60mm ID, and this one is 60mm. Since I use 2.5" ID springs, I use an adapter, which I got from Vorshlag. There's also the Swift bearing there in the picture, underneath the adapter.

Min height 0.75"
Max height 2.6"
Height of tube, interference height, 2.875"
Weight 353 g

Name:  Adjuster Straight On 1024.png
Views: 2009
Size:  1.08 MB

In the following photo the 60mm-to-2.5-inch adapter is off, and you can see the Swift nylon bearing and race on top.

Name:  Height Adjuster 1024.png
Views: 2080
Size:  1.48 MB
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      11-10-2011, 05:22 PM   #15
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Lower control arm

Here are photos of the M3 camber link:

Name:  M3 Link Bottom.png
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Name:  M3 Link Top.png
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      11-10-2011, 11:11 PM   #16
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Dinan Rear Shock Mount

Here's a photo of the Dinan rear shock mount, together with the factory mount. The Dinan mount is on the right. The picture shows the bottom part of the mount, the "outside" half. The other half, not shown, goes inside the car.

Name:  Rear Shock Mounts.png
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You can see how much shorter the Dinan cushion is. The metal stems are the same length. On the Dinan mount the top washer is much thicker than the factory washer. The upshot is that the shock piston is offset by (Dinan says) 10 mm, so you gain bump travel and lose droop travel. This change has implications for coil bind, wheel rubbing, and of course droop travel.

Since I'm short on droop travel I won't be installing the Dinan mount, and I'll be sticking with the factory mount. Incidentally, whereas the Dinan mount is rubber the factory mount is made out of the same kind of MCU that the bump stops are made of.
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      11-10-2011, 11:17 PM   #17
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Awesome thread! kind of like the NA inline 6 e90 m3 that never was.
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      11-11-2011, 12:08 AM   #18
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Awesome thread! kind of like the NA inline 6 e90 m3 that never was.
Thanks man! I'm scheduled to install next week, so I can report how it feels.
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      11-11-2011, 12:39 AM   #19
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What day
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      11-11-2011, 01:39 AM   #20
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What day
Monday & Tuesday. Are you coming down this week or next week?
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      11-11-2011, 10:22 AM   #21
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Quote:
Originally Posted by luckyu View Post
I'm getting ready to install shocks, springs, and M3 rear control arms on my 328i.
Do you have rear subframe bushings?

For the love o'God man, M3 'em!
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      11-11-2011, 10:52 AM   #22
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What part of the bay area are you from?
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