OK, this is a report, and a final sanity check. thanks in advance for any help received.
last year I bought B6 #203 as a potential track-day/weekend car.
this should work well, because the car has power, a decent chassis and the Alpina suspension, and a better brakes/tyres combination than the standard BMW. in fact, the brake disks are 298mm, which sounds very good for such a light car. the one potential question asked by many is whether the B6 suffers from understeer due to the heavier engine (M30). especially when compared to the agile M3.
after buying the car, I put on new Michelin Pilot Sports and had a Hartge strut brace cut and rewelded to fit the car. plus a bunch of normal stuff needed to get the car up to spec, including new front and rear brake disks and pads and a front brake caliper rebuild on both sides.
I just spent the Easter weekend at the Ring, and can report that the car is not -- in street form -- anything like a decent track car (yet). my B10 Biturbo has better balance, stronger brakes (relative to its size), and sharper turn-in. I know this because I spent 3 days with my B10 BT at the Ring last summer at one of the BMW schools, and also Dave W was at the Ring over Easter with his B10 BT and he very kindly let me drive a lap in his car. so my memories are fresh.
the B6 suspension seemed hard on the road, but there is far too much sway at the Ring. this is true even with the strut brace, and without the brace I'm sure it would be worse. [however, the car IS very well balanced in slides, and is a dream to steer with the throttle when the back end starts to break loose. power cures many faults
the brakes just didn't survive. I drove 12 laps in one day, but never more than 2 laps in succession -- followed by cool-down drives on the local roads. but after day 1 the brake disks were warped. SERIOUS judder through the steering wheel and the brake pedal on braking. plus dark blue patches on the front brake disks.
the engine is even better than I expected. it was built to pull the B9/B10 E28 Alpinas, and the performance in an E30 car gives the big grin.
plus it pulls the car through Hatzenbach and Adenauer Forst in 3d just like a Porsche. (OK, I know this because I caught rides in a race-prepped GT3 and a 993RS, and I was watching the shift points and tachometer VERY carefully as we drove).
the gearbox is more flexible than the Biturbo's. if you don't know it, the gearbox is a dog-leg Getrag built for a 5-series (I think). even with a poor heel-and-toe shifter like me, the car drops down one (or even two!) gears without complaint.
the engine does *NOT* make the car understeer. the understeer is there because the suspension is so soft that the car wallows in the turn. but if you get the balance right going in, the car will hold the line.
the car really wants to do better. tell me I'm crazy, but it was talking to me.
THE NEW NEWS
so I went to Ring Racing for some help on the juddering brakes. they bring out 4-piston Brembos and 323mm disks and track pads and braided lines. looks good, but the new stuff won't fit under the Alpina 16 inch wheels. so we need 17 inch wheels and different tires.
the brakes were fitted and they are awesome. kinda-like a Porsche in fact.
the 7.5x17 wheels take a bit off the acceleration - it's harder to spin them up to speed -- but with later braking I think the overall effect on the stopwatch will be positive. however, there is still a judder after 3 applications of the brakes. Ring Racing guesses that the aluminum adaptor (holds the disk to the hub) is changing shape when it heats, and will make steel adaptors for the front brakes. I will keep you all posted on whether this solves the problem.
but the soft suspension and the standard profile tires now allow the tires to rub. we rolled the inside of the rear arches a little, but it wasn't enough. even in Hatzenbach and Schwedenkreuz the tires were rubbing. I took Fuchsrore at 120 kph to avoid a grated cheese effect on the tires
but the turn-in was much better on the wider front tires. Karusell wasn't even on the menu, or Pflantzgarten, but the rubbing seems to be measured in mm not cm.
what to do now? well, I've left the car at Ring Racing. tomorrow I will probably ask them to install an adjustable Bilstein suspension front and back, plus low profile sport tires (R-compound). the combination should be right to avoid tire rubbing on the arches, and tighten the suspension a lot in the corners, but not to change the ride height so that the balance is upset.
then the car will be stealth defined: a basic-looking E30 which is fast, late to brake, quick to turn, grippy in the bends, quick out of the corners, and able to cruise the motorway with CD-player and aircon while traveling to the circuit.... what's not to like?
plus, every change can be reversed (except the braided hoses) if that's desirable in the future
all should be done in 2-3 weeks. if anyone knows of any reason why these changes should not take place, speak now or forever hold your peace....