Help me build a supension setup for my M3 swap!

[snuggz]

Hi to all, I've been a lurker here for a while now (awesome knowledge base guys) and haven't had the need to actually start a thread untill now...

My swap-pile currently consists of the whole drivetrain and some M3 brakes. I also snatched up an M3 front subframe and an M3 front Swaybar. What I still need is to take care of the suspension/diff and grab some wheels to fit these brakes under (omfg, M3 brakes are friggin' huge...)

So I've searched and read through TONS of info on this (both here and on Bf.c) and still feel quite clueless... I originally assumed I would go with an Mz3/M coupe setup, and after reading J!m's posts, this seems quite reasonable... I plan on finding a whole M coupe rear subframe, but it turns out those aren't in particularly high supply, so that'll have to wait...

I currently have access to a full (struts/springs) M roadster setup, AND there's a full M coupe setup for sale on another forum as well. Both are around $300 (quite attractive). My questions:

1. An M Roadster weighs about 3100lbs, slightly more than an M coupe... but from everything I've read, the M coupe suspension is quite a bit stiffer and a tad lower. How is this going to translate into my Ti?

2. Swaybars... Like I said, I've already got an M3 front sway, which I'm told will run with either the M coupe or the M roadster stuff (sway mounts on the strut housing rather than the LCA). What should I run for the rear? I can only assume the stock Ti sway is cheese... and I hate bodyroll like no other...

3. Am I better off just using, say, H&Rs and new springs rather than trying to run OEM parts? The M coupe stuff only has 19k on it, but I haven't heard particularly good things about durabillity...

Doner car is a 97' Active. I'd like to keep a decent ride feeling to it ( I had Koni Yellows w/ Eibachs on my Prelude, and while the handling was awesome, I would have traded some of it in for a better ride in the cabin) but obviously handling comes first.

Any input from the swap-gurus around here would be great.

Thanks in advance,

~nich

BTW-- I tried to post this in the Compact 6 section, but it said I didn't have sufficent clearence or some damn thing. Mods, where does this technically belong?

[J!m]

Well, I guess this would belong in engine swaps; although the question pertains directly to the suspension... Once you complete your swap, you will be able to post in Compact6 (check with Steve for "clearance").

If you read what I have posted for mods, it shows my exact suspension set up. I am quite happy with ride height (which may be a bit higher than some would like; however with the LTW splitter in front, if I go lower, I cannot drive on the road anymore), stiffness and lack of body roll.

To some extent, I got lucky; however I did do a lot of research (as you are doing) to see what factory parts would work best. Aftermarket spring manufacturers may be a better choice for your exact needs, but without experimentation, you never know...

[snuggz]

Jim-

Yeah, I figured it was something to do with memberships in Vc. No problem; just curious.

I'm quite familliar with your setup, and it's really why I was going in the OEM direction... your 1" trick is awesome and I plan on doing it as soon as I find the parts. What differences did you note between the Roadsters rear sway and the Ti's?

[J!m]

The M roadster sway is larger diameter than the ti sport sway.

The M Coupe sway (the one I'm using) is only slightly larger diameter (maybe 1/2mm- side by side they look identical) than the M roadster, but it does have a different part number than the M roadster...

I also used the M roadster end links for the rear sway; however I did not see any difference in them. Possibly firmer rubber? I do believe the P/N on the M roadster vs. ti sport end links is different. The through-hole is the same diameter in the rubber in both cases. I never had M coupe end links for the rear, so I do not know if these are radically different, I'd tend to think not since the bars are so close.

Even though the roadster is heavier, the weight is lower which may explain the 'softer' sway bar. I don't know about the differences between the roadster and coupe springs (for the rear). I have the roadster springs and I'm quite happy with them. Someday I may try a set of E30 M3 rear springs as well as a set of M coupe springs to see what I've been missing.

The Euro M3 front springs are "bangin' yo"; highly recommended for anyone with a swapped ti. Reasonable ride height for the street, ~20% stiffer than the US M3 springs, but they don't beat you up. Available at dealers across the US (they have to be ordered from Europe) very reasonably priced. If you wanted a lower ride height in the front (IE if you don't have a functional splitter) it would look better about 3/4 inch lower (with 17's). Drop hats are the way to go in my opinion. I just can't drop mine any lower!

[snuggz]

Jim,

Thanks for all the help -- I think I'm going to go with the M Coupe setup and assess the ride height/spring situation once the whole car is together. Any tips on sourcing an M Roadster/M Coupe rear subframe, or is it basically catch-as-catch-can?

[aceyx]

From an engineering standpoint, the M Coupe setup will be stiffer due to the body structure (mainly, the C pillar), not the bars.

Additionally, the M Roadster setup will have to resist more torsional flex, thus the addition of the x-brace on the 3er Convertible before it made it to the M3.

Springs in the Coupe will be heavier though.


So, again--strictly from an engineering and not personal experience standpoint--Roadster sway bars and Coupe springs/struts.

[J!m]

[quote=aceyx]From an engineering standpoint, the M Coupe setup will be stiffer due to the body structure (mainly, the C pillar), not the bars./quote]

The body is stiffer, but the question was directed to the bars. You may believe them to need to be the same (and they are quite similar), or opposite to what they are, I'm just reporting (from first hand experience and a dial caliper) the M Coupe sway is slightly larger in diameter and has a part number different than the one on the M roadster sway bar.

It is possible (although unlikely) the alloy of the bar was changed, and the stiffness of the bar is higher even though the bar is smaller in diameter, or is was a simple superseding of the part number to a new one used across the board (for both the roadster and coupe). I do not know the month/year of production on the two bars, so we can only speculate there.

[J!m]

Originally Posted by snuggz

Jim,

Thanks for all the help -- I think I'm going to go with the M Coupe setup and assess the ride height/spring situation once the whole car is together. Any tips on sourcing an M Roadster/M Coupe rear sub frame, or is it basically catch-as-catch-can?

Comb the 'bay, Roundel and Bimmer magazines in the back for BMW specific dismantlers. I was lucky, as my parts were only a couple years old when I got them. Now the roadsters and coupes are getting on in years, so more of them may be in the hands of younger, inexperienced drivers who are wrecking them...

Bimmers South (I think) was where I bought my engine; they're in Georgia if I remember correctly...

[snuggz]

Excellent info. I just sent payment on some M coupe stuff (with only 1,400 miles on it, supposedly); working on tracking down a Roadster rear end.

Thanks again, Jim.

[J!m]

No problem...