Autocross nerd thread: The Ultimate E9X A-Stock SCCA Autocross Build?

[Richbot]

I'd have a hard time telling someone the E9x M3 is an Fstock car with a straight face at this point.

[Maypo]

Fabulous result, Rich! I know exactly how you feel about the car's performance. I was stunned at how good it was when I took it out last year. What do you suggest for FSB position?

BTW, I suspect your winning isn't all that ugly. ;-)

It's going to be a long week waiting for event 1 -- planning a trip to Vancouver, B.C. for their opener.

[Richbot]

I have mine on the stiffest setting and it seemed just right. A little too much for perfect balance in all situations (high speed push) but in 2nd gear it does the trick

For reference, Evolution school instructor Andy Hohl was at this event doing driving instruction. In a fairly well prepped SS C5 Z06, he managed a dirty 38.2 to my clean 39.6. So my car and driver combo still needed to drop about half a second to be competitive with the Andy Hohls of the world yesterday. But at least it's not multiple seconds. I think I know where to find half a second in my driving yesterday (sausage making at its finest).

"The waiting is the hardest part" should be the autocross theme song...

[Richbot]

Run #1, best raw time but dirty

Run #5, about a tenth off my best clean time

Not my best driving, but give me a break, it's been 12 months!

[m3kerry]

Rich i heard the end of 2nd gear but the course looked tight? How did you feel about your line?

Good driving.

[Richbot]

Neither of those runs has my best work in it, but if you use the 5th run as a reference, the entry to the last slalom where I didn't bring enough speed in and had to double-steer, the entry to the first slalom where I placed the car too far inside, and my entry to the 2nd slalom where I charged too hard and had to overbrake to make the next cone, all were either too slow or I had the car placed wrong. The steering on this car is a little numb with the bigass tires so it was easy to put in too much wheel and not enough gas or vice versa which threw me off, you can see it in those spots I mentioned.

Easy half a second left out there in driver stuff, as is clear from my very first run being .25 faster raw than my fastest clean run

I was on the limiter twice on all runs, once before 2nd slalom and once before finish. On the first run I was on the limiter for about a second before the finish lights! I actually got a decent amount of 3rd gear time one run, though I ended up punting on that idea. It's hard to tell from the video because it has a soft limiter. The course was tight in a couple spots but not tight enough to be "painful" and the car definitely shrank out there

[m3kerry]

Where does second gear end?

[Maypo]

That was a decent course. Slaloms leading into tight turns are demanding and a boon to small cars, but I like the generous cone spacing the designer offered and the fast slalom-finish. We have the latter around here from time to time and they are loads of fun.

I don't remember which exhaust you have, but the car sounds menacing.

[Richbot]

On the 25.6" 315 hoosier, 8300 rpm is 69 mph

I have the BMW Performance exhaust, love it. Video does not do it justice

[m3kerry]

Just for reference, the 1m goes 77 in 2nd with the 295/30/19 on it.

[dcstep]

Originally Posted by m3kerry

Where does second gear end?

With a 4.10 FD and the redline moved to 8600, my E92 M3 tops out at 72-mph in 2d.

Dave

[Be Stock]

According to my calculations with OEM diameter rear tires and 4.10 FD in a 6MT E9x you will need to rev to about 9050rpm in 2nd to hit 72mph.

If you are running 275/35/18s and a 4.10 FD you will need about 9400 rpm to reach 72mph in 2nd gear.

How did you obtain these numbers?

Originally Posted by dcstep

With a 4.10 FD and the redline moved to 8600, my E92 M3 tops out at 72-mph in 2d.

Dave

[dcstep]

Originally Posted by Be Stock

According to my calculations with OEM diameter rear tires and 4.10 FD in a 6MT E9x you will need to rev to about 9050rpm in 2nd to hit 72mph.

If you are running 275/35/18s and a 4.10 FD you will need about 9400 rpm to reach 72mph in 2nd gear.

How did you obtain these numbers?

I simply read the speedo. Given the likelyhood of speedo error, you might be right.

Dave

[m3kerry]

My bmw speedos are off 3 to 5 mph in all 8 i have owned.

[Richbot]

http://www.bgsoflex.com/auto.html

Much better than trusting the speedo

[Maypo]

Okay, our first event is in the can (as my wife likes to say). Somehow, somewhere, I have lost my GoPro camera, so no video to offer.

The course was 45-ish seconds and pretty good, although it had more steady-state turning than I care for. There was also one fairly snug slalom.

The site is a good size, made up of two identical unrestricted, rectangular asphalt sections, one 5 years old, one brand new one. The grip difference between the two was remarkable, and putting power down on the old surface was noticeably more difficult.

Weather was moderate: 55-60 degrees, but a chill breeze all day. Not bad for the 49th parallel.

The combination of fresh 295s and the big front swaybar was a good improvement over last season's bone-stock-on-tired-255 trial, but I think another jump in bar size is in order, although a damper upgrade may make that unnecessary. Also, Rich, I'm thinking the 315s in the rear may be mandatory (hence, your intuition was correct), since one steers with the throttle everywhere.

Here is a video from one of the fleet of Miatas that was there:

[Richbot]

Good job, looks you would have been one of the fastest raw times if not for the Mod cars! Don't give up on the RDSport bar before you try the bigger rear tires or try it in some grippier conditions.

What pressures were you running? I ended up at 37 front, 33 rear, which got me a little rollover in the rear but was really nice for forward traction. WHen I let it creep up higher than that in back I needed more opposite lock under power than I preferred. I'll probably run a little more front pressure next event and see what it does but I'm already at the high end of the sweet spot

[Maypo]

I started with the 37/33 you liked, and after checking temps, maintained 38/34. I tried 32 in the rear on my last (8th) run, but wasn't able to discern any difference on just one run. I'll be experimenting more with that.

I didn't have as much tire roll-over as you -- it stopped at the first mold line, but that may have been due to general lack of heat, thus grip.

I don't recall if you said how much toe you have in the rear, but I am at 0. I should probably try an eight next time, if I'm still on the 295s.

[Richbot]

I've got about 1/16" of toe-in in the rear, zero in front, About -1.5 camber in front and about -1.8 in the back.

You probably didn't plow as hard as I did in a couple corners either, I overdrove it a few places which is probably where the majority of the really outside wear came from. It wasn't "worn" nearly as far out as much as it was "scuffed". It was a very warm day for sure, we're going to have cooler weather and a sandy surface this weekend so we'll see how it acts

[CSBM5]

Originally Posted by Richbot

I've got about 1/16" of toe-in in the rear, zero in front, About -1.5 camber in front and about -1.8 in the back.

You probably didn't plow as hard as I did in a couple corners either, I overdrove it a few places which is probably where the majority of the really outside wear came from. It wasn't "worn" nearly as far out as much as it was "scuffed". It was a very warm day for sure, we're going to have cooler weather and a sandy surface this weekend so we'll see how it acts

How does this work on the street (zero front toe)? Tramlining? Pulling with pavement crown?

You guys have me interested in an E90 M3 now. I'm pondering one more so after reading this thread. I have to find one with options I want and without options I don't want (i.e. no sunroof, as can't fit in it with a helmet on with a sunroof not to mention the weight and the fact I never use a sunroof). I'm also extremely particular about a car's condition, so I'm not interested in most cars I see on the market...sigh.

[Richbot]

It doesn't tramline at all, really. Much better than say, my E46 328 with big summer tires on it. It's very relaxed at highway speeds, really, especially when you consider how quick the steering is, the big tires and how stiff the thing is. Must be an upshot of the new front suspension as the E46 had similar alignment with more rear toe-in.

I hear you about finding one in good shape. Looked at so many promising E46 M3's and E39 M5's that turned out to be disappointments before finally just biting the bullet and buying my car new off the lot. I can vouch that no-sunroof is the way to go, plenty of headroom with a helmet unlike our 335xi which rubs the top of the hat

[Richbot]

Sortof unrelated but not really, there are only a handful of us actively driving a BMW in SCCA A-stock

Matt Murray, former champ in HS in a 318ti I believe?, is driving his 1M at the DC prosolo against some serious competition in C5 vettes (Kozlaks and Savini). They made a 5-person class and he looks like he'd be in 4th place about 1.5 seconds behind Savini, Paul, and Lynn after morning runs if Paul hadn't DNF'd both runs on one of the courses. He's running the same tires Kerry ran at Dixie, not sure on the rest of the setup? Hope he can pick it up this afternoon!