Project M325i Part 2 - Tuner Tech

Last month, we introduced yet another BMW project, this time a '93 325is. Our plan was straightforward: to tweak the E36 coupe to match the on-track performance of its factory-built hot-rod sibling, the M3 - yet we'd pull it off for much less than buying a used M3. More importantly, this wouldn't be a fuzzy, seat-of-the-pants comparison. Instead, we'd use stopwatches and chassis dynos to provide verifiable results.

In Part 1 last month, we detailed the E36 model history, showed off our black-on-black 325is and reviewed baseline testing: the 325is versus a stock '95 M3. The M3 lapped exactly two seconds quicker than the 128,000-mile 325is, which meant we had our work cut out for us or, more accurately, Bimmer Haus Performance did.

Tuner/driver Bob Tunnell of Bimmer Haus in Broomfield, CO, is guided by a single golden rule of car modification: suspension before power. Not that Tunnell isn't fond of neck-warping acceleration, but extra ponies without a chassis to corral them is, well, putting the perform-ance cart before the horse (enough equine metaphors).

For starters, Bimmer Haus recommended adjustable Koni gas shocks, H&R Sport springs, H&R's new sway bars and JT Designs' rear shock mounts. In addition, wheels and tires were upgraded from the stock 15" alloys to 17" AT Italia Type 5 Sport wheels and a set of grippy Yokohama AVS ES100 tires. By the way, all of the above (except the JT mounts) were secured through The Tire Rack's Upgrade Garage (www.tirerack.com).

M3 PartsWhile these components alone would've significantly improved the handling of our E36, Tunnell suggested we push the performance even more by converting the entire front suspension to M3 spec. BMW E36 owners are forever bolting on factory M3 body parts, yet the M3's real appeal lies in the subtle details of its suspension design and geometry.

At a glance, M3 front underpinnings look identical to those of a 325is. Not so. The M3 employs specific strut housings, strut bearing hats, lower control arms and control arm bushings, plus different springs, dampers and sway bars. For example, the sway bars connect upward via links to the M3 strut housings, rather than down to the control arm. More importantly, the M3 strut mounting hats offset the bearing - tilting the strut rearward for added caster, which increases directional stability and steering feel.

Underneath, the M3 lower control arm is a stronger casting and features a fixed outer ball joint, as compared to the stock 325i's floating ball joint. The result is a more direct feel. In addition, the lower control-arm rear bushing - known as the Q-bushing because of the shape of its mount - is solid rubber (rather than webbed) with an offset center. Again, increased caster. As an added tweak, Bimmer Haus swapped the strut-bearing hats, putting the one marked L on the right and vice versa. This increases the negative camber by half a degree for more front-end grip.

At this point, you're probably wondering what happened to our budget. Well, yes, it does affect it, but consider this: If your stock control-arm ball joints and bushings are worn out (and at over 100,000 miles, that's surely the case), opting for the M3 control arm assembly with new ball joints is only nominally more pricey than a stock unit. And since the Q-bushings are probably toast too, the same applies. As for the M3 strut housings and hats, they can be found inexpensively on eBay or from a fellow E36 owner who's switched to a coilover setup. Expect to pay about $150 for the pair. Spring and shock costs are not an issue, as aftermarket M3 components cost the same as 325i units.

Upgrading to the full M3 front suspension requires M3 lower control arms, control arm Q-bushings and spring hats. You'll also need M3 strut housings.	The M3 strut housing is different than the 325i. Note the sway-bar link bracket on the M3 housing, whereas 325i sway bars mount to the lower control arm.	The M3 lower control arm features a solid-mounted outside ball joint (right) compared to the stock 325i's floating ball joint.
Upper rear shock mounts are a weak point on the E36. We upgraded to billet mounts from JT Designs, which feature a replaceable rubber bushing.	M3 front control-arm bushings feature a solid-rubber design and an offset pivot point, which adds caster to the front-end geometry for improved stability and turn-in.	Koni shocks are a perfect match for the H&R springs. The adjustability on the dampers allows fine-tuning for a softer "street" ride and firmer "track" behavior.
Externally, there's no visual difference between BMW's open and limited-slip differentials, so they're a direct swap and an easy one at that.	H&R now offers sway bars for the E36. H&R's front bar is 28mm, compared to the stock 25.5mm; the rear bar is 21mm versus the stock 18mm. The bars are also adjustable. The kit comes complete with all mounting hardware and H&R's bushings.	H&R solved the age-old problem of squeaky urethane bushings by bonding a Teflon webbing to the bushing itself.