I have a 1986 bmw 535is that I have been running in rallycross for the last year. I am debating getting more serious with it and attending the Southeast Divisional Championship and the National Challenge in Maryland.
The car will run in prepared rear. It is fairly close to stock except for shocks, sway bars, strut bars, a variety of polyurethane bushings, skid plate, front seats, and steering wheel. Other than a set of rally tires, the car is ready to go as is. Tinkering is fun and I have some budget to work with so I have a few questions.
What is the difference between a piggyback and replacement engine control? One of the performance upgrades on the car is a MAF conversion which is legal in class. However, it requires swapping out a chip in the ECU. I am guessing this counts as a replacement rather than a piggyback but I am not sure.
The rules say "Any brakes may be used". Can I replace the master cylinder? This isn't specifically for rallycross. I just want better brakes without jumping a class.
If I want to swap differential ratios, what are my options? The rules say "Differentials must be contained in a stock unmodified housing/third member with stock or optional ring and pinion ratios available for the specific model, body, and year of the vehicle only". Are the 528e, 535i, and M5 the same model? The M5 has a 3.91 gear ratio. I am not sure if it is allowed because it may be considered a different model and they were only available in the US in 1988.
Rules said:
9. Electronic engine controls may be modified or piggybacked, but not
replaced.
Chip would be fine.
Any brakes would include the master cylinder.
I would think only ratios for the 86 535is would be technically legal.
Like Evan said, chip is legal. You can't unplug the whole computer and plug in a standalone unit.
Chips is spot on.
Brakes literally mean anything in the brake system may be altered. Calipers, rotors, master, booster (or not), lines, ABS delete or install, hydraulic handbrake...
The DIFFERENTIAL may be changed. The ring and pinion may not. The differential must fit in the original housing. So, say, you can't get an XR4Ti and put a Chevy 7.5" Posi* carrier in there because it requires significant grinding to the case for clearance. But you can get a limited slip from whatever Sierra had it and bolt it into your XR4Ti's case with the XR4Ti's ring and pinion. Likewise, you couldn't install an R180 rearend in a Subaru that originally came with an R160.
- Yes, Posi. I will use the word Posi only if it pertains to Chevy limited slip differentials.
Thanks for the info. The differential is a bit disappointing. The BMW medium case differential was made for over a decade with about 10 different ratios to choose from. You just change the backplate to match the mounting location for your car.
I think those guys already covered your questions. I'm sure Nick will be sad that he no longer runs his e28 here in WDCR when he sees your car (he won MR here in 2014 and finished 2nd to me last year before a tractor-trailer smashed the car, and is now building an e36 M3)
bluej wrote:
cooooomeee to MR.... 
I'd tend to agree. Depending on the other competitors in your region, you might not be significantly less competitive in MR, and if it lets you make the car more fun and/or better suited to other things you want to use it for, why not?
I have been watching Nick's car for a while now on the e28 forums. I am pretty sad about his car as well.
The problem with MR is the car is currently ridiculously comfortable on road trips. Everything in Florida is 3 hours away so that is more important. The path to MR feels like it will turn the car into something I don't want to drive long distances.
The good thing is you can always bump to MR to run with them if you want. We seldom run PR because running with 9 guys in MR is more fun than running with 2 in PR.
ojannen wrote:
I have been watching Nick's car for a while now on the e28 forums. I am pretty sad about his car as well.
The problem with MR is the car is currently ridiculously comfortable on road trips. Everything in Florida is 3 hours away so that is more important. The path to MR feels like it will turn the car into something I don't want to drive long distances.
Running MR doesn't necessarily mean you have to go all that much further in building the car to be competitive. At the last event I was at, a newer MF Fiesta with some work done to it and on gravels with a very good driver lost to a bone stock Prius C on snows. And I've seen guys show up with a stock WRX on snows and put down better times than a lot of the guys running in MA/M4.
ojannen wrote:
The problem with MR is the car is currently ridiculously comfortable on road trips. Everything in Florida is 3 hours away so that is more important. The path to MR feels like it will turn the car into something I don't want to drive long distances.
So don't do those things. My car is long distance comfy and I (or at least the car) tend to podium/win nationally...
