E36 BMW: Autocross Build

[vdshenoy]

So I've been working on my new project car for a couple weeks now. I got it running 2 weeks back, took it to it's first autocross last weekend and it posted fastest time of day at it's first event!!! This was at a really fast course with about 150 other cars there on that day.

Why?....

Because I went from here....

to here...Oops...time to build another car...


Couple weeks back:
Picked up the shell


Threw out a LOT of junk and gunk




Sound deadening OUT



Cutting and dynaglassing fenders



Painting engine bay



All the glass comes out



LEXAN



Cut cut cut



Heat Heat Heat



Yay for nice parts



Prepping and painting lexan



CF Sunroof panel gets transferred over



Interior gets paint



Certifit bumpers arrive ... yay for CHEAP bumpers



Sitting pretty next to each other ready for the motor swap

[vdshenoy]

More painting


Initial preview in MS Paint!!!



Mock up spoiler for designing



Rear subframe of shell comes out



Engine bay gets emptied completely for the new engine



Went to Home Depot and "purchased" some downforce (autocross speeds....it would be serious drag at track speeds)



Right before she got crushed :weep:



Motor going in



Steering going in



Figuring out the wiring



Fuel pump getting changed



Got 'er running



Go Kart Stage




Bumpers and grill and stuff getting mocked up with a donated hood


Delivery from MA Shaw!!



Tail lights come in (bimmer forums member kubol87)



Cutting the bumpers for clearance



More cutting and chopping



Interior went in (got done 7 hours before her debut autocross!)


She makes the event


Sets FTD with full metal doors, trunk and hood

[tspool]

Damn!!! Sorry to hear that. How bad was the frame bent, that you had to start with new shell? But anyway best of luck and I'm subscribed.

[vdshenoy]

Got the doors on this morning and cut up some vinyl till I can afford paint before the next season.

[Steve J.]

All that weight savings and you put diamond plate floors in?

Have you done any testing with that trunk spoiler?

A huge drag wing would be much more effective, as I can't imagine much airflow actually getting to that wing at the speeds you are going.

How light are you allowed to go in your current class?

I'm diggin the all black though.

[vdshenoy]

Damn!!! Sorry to hear that. How bad was the frame bent, that you had to start with new shell? But anyway best of luck and I'm subscribed.

The unibody was totalled. If you look carefully, you can see a dent in the roof where it had bent in...the rockers were bent pretty bad and the entire floor of the car had folded up.....the metal in the corner of the engine bay right before the firewall was broken.

Car could have been stretched back with a frame puller, but it would NEVER have been straight again = useless to be a winning autocross car.

Decided to just junk it and get a new one.

Sold the hood, trunk and doors to a fellow bimmerforums member and started afresh....

CF hood and Trunk are due this upcoming week. I'll post pics as soon as they come in. I'm getting a custom shell only CF trunklid made here in Houston. It's estimated to weight 3.3 Lbs! My new fender flares will also be coming in this week but those wont be going on till later this year because I want to dynaglass them in before the paint job.

Ven

[vdshenoy]

All that weight savings and you put diamond plate floors in?

Have you done any testing with that trunk spoiler?

A huge drag wing would be much more effective, as I can't imagine much airflow actually getting to that wing at the speeds you are going.

How light are you allowed to go in your current class?

I'm diggin the all black though.

They're pretty light floor plates actually. More for the level floor surface than anything else...easier to left foot brake and stuff that way. Plus, the weight is all the way at the bottom, so it's not all bad.

A huge drag wing WOULD be more effective for sure, but it is illegal in my class. I am allowed a trunk spoiler like the one I've got, up to 10" off the trunk lid of the car. I've got mine right at around 8.5" off the trunk, set at around 70 degrees.

I tried it at the first event. I ran in the morning w/o the wing and in the afternoon with it, and there was definitely a difference to be felt in high speed cornering stability and quicker counter-steer correction at speed. It helped in braking too. This kind of spoiler has been tested by many autocrossers, and if you look at pictures of nationals this year, you'll see it on a LOT of cars. Just that mine is ghetto lol. It's temporary anyways.

With my 2.8L, I'm allowed 2100 lbs plus 100 lb weight penalty for running wheels larger than 16" tall. I'm on 18x10s right now. I had the gold car down to 2230 lbs, but that was with fully cut up metal doors. This new one I estimate will be event lighter with the CF doors and lighter and better build in total.

[Steve J.]

Yea, without a cage and those rules, 2200 should be very very easy. Even in the pictures above I see a lot of stuff that can be removed.

Any reason you did not go with the full 10" on the trunk spoiler? Are you allowed to use any other aero devices?

[vdshenoy]

Yea, without a cage and those rules, 2200 should be very very easy. Even in the pictures above I see a lot of stuff that can be removed.

Any reason you did not go with the full 10" on the trunk spoiler? Are you allowed to use any other aero devices?

What else do you see inside the car thats NOT structural? Is the package tray structural at all? I need to know these things before I cut away and then have to weld more metal in to support everything.

Reason why I didnt go with 10"?? Here's the truth...this entire spoiler I made from home depot is an experiment. If It works, I'll be getting one made more professionally. I bought a 24x48 sheet of lexan, cut the first spoiler to 13" wide so that it would be 3" of support behind the trunk and then the 10" spoiler. But as I was drilling it for the holes, I broke it...umm so I was left with 11"x48" and I was too lazy to go back to home depot to buy more lexan. Yeah...so 2.5" mounting and 8.5" of spoiler.

Now that it's done though, I think any taller would have been more harm than good because of the aggressive angle of attack. Never know till you test it though. If I do get another one made, it will be fully adjustable, angle and height.

I can use all the aero devices I want on the bumpers and stuff like splitters and canards, but I highly doubt they will be of any help at 0-70 mph. Anything else you'd suggest?

[Steve J.]

I don't think you'll be going fast enough to have "more harm then good" with that type of spoiler, as its not getting a tremendous amount of airflow. You are also not doing 70mph during turns, thats the speed you are hitting before you tap the brakes to settle the car before you toss it in between some orange pointy things. So lets assume your max speed on turns where you need the downforce (or where you can benefit from it anyways) is 50mph. You will need very aggressive wing setups to get anything usuable at that speed. Otherwise, spend the time and money developing your suspension geometry, it'll do 1000x more for you.

Are you allowed to modify susp geometry? With the frequency experienced during autox, damper tuning can play a huge roll as you are not in steady state for any extended time period.

Put a high drag high df wing on the front end, mount it to the chassis, it'll get you front grip at low speeds I.e. AM setups lol

Do you have to keep the Ebrake?

Stock steering column?

What suspension/brakes?

I've seen some funky brake rotor setups on some autox cars, not sure if you are up for that though, its a tad sketchy, but it works and saves a decent amount of rotational mass.

Pictures are a little dark, but there are a bunch of areas you can swiss cheese. back of the trunk box, some parts of the dash, some parts of the door sill area, etc.

[vdshenoy]

I don't think you'll be going fast enough to have "more harm then good" with that type of spoiler, as its not getting a tremendous amount of airflow. You are also not doing 70mph during turns, thats the speed you are hitting before you tap the brakes to settle the car before you toss it in between some orange pointy things. So lets assume your max speed on turns where you need the downforce (or where you can benefit from it anyways) is 50mph. You will need very aggressive wing setups to get anything usuable at that speed. Otherwise, spend the time and money developing your suspension geometry, it'll do 1000x more for you.

Are you allowed to modify susp geometry? With the frequency experienced during autox, damper tuning can play a huge roll as you are not in steady state for any extended time period.

Put a high drag high df wing on the front end, mount it to the chassis, it'll get you front grip at low speeds

Do you have to keep the Ebrake?

Stock steering column?

What suspension/brakes?

I've seen some funky brake rotor setups on some auto cars, not sure if you are up for that though, its a tad sketchy, but it works and saves a decent amount of rotational mass.

I'm losing the e-brake this week...just been too lazy to unbolt it and take it out. However, I do have the stock steering column and stock brakes. They are adequate, but I'm up for a change if it results in significant loss. Suspension is GC Advanced Designs.

[Steve J.]

Ok, so from that reply, it sounds like you have a lot left in it Just depends on how competitive your class in your region is, or even nationally.

How fast is your competition? If you are already faster than everyone you race, save the cash and just win, otherwise it might be time to move to another class if you want to be in a more competitive class.

You are also removing the actual Ebrake assemblies, cables, cable housings, etc, correct?

I think it was a couple of Honda's and Miata's that had the swiss cheeses brake rotors. Funky, ugly, and sketchy, but they worked

[vdshenoy]

Ok, so from that reply, it sounds like you have a lot left in it Just depends on how competitive your class in your region is, or even nationally.

How fast is your competition? If you are already faster than everyone you race, save the cash and just win, otherwise it might be time to move to another class if you want to be in a more competitive class.

You are also removing the actual Ebrake assemblies, cables, cable housings, etc, correct?

I think it was a couple of Honda's and Miata's that had the swiss cheeses brake rotors. Funky, ugly, and sketchy, but they worked

I'll be taking out the ENTIRE E-brake assembly. Yes.

Competition at divisionals, national tours and nationals are incredibly fast. The only car that I had as any real competition in Houston SCCA in FP was a killer fast E30 but it broke down at nats last year.

I've heard of swiss cheesing the front ends and covering w/ vinyl...but brake rotors? Couldn't that be extremely unsafe? Got any pictures?

[Steve J.]

Rotors: If done properly, it can be safe. You guys are braking for very short periods of time, with fairly cool conditions, and at low speeds, you can go pretty extreme. Check out Formula SAE brakes. Obviously they are smaller diameter, but scaled up a bit, they should work no problem.

In my opinion, if you are only using the car for autox for its entire lifespan, and considering those chassis are super cheap, not that you have to to get 2200#, but i would cut the crap out of everything, specifically everything above the CG.

Edit: Ok, real quick as I'm heading to sleep, but these were actually from an old BF thread we had. btw you can go even lighter than these with a shark tooth pattern 2 piece design

[Greg S]

What did you hit with the old car? Steve, I don't think you could do anything near as drastic with vented/veined rotors.

[Steve J.]

Who says they have to be vented/veined? Need to think outside the box.

Is the braking system "free," as in you can mount any rotor/combo?

Run a very small diameter disc and small 2 or 4 piston caliper.

[vdshenoy]

Who says they have to be vented/veined? Need to think outside the box.

Is the braking system "free," as in you can mount any rotor/combo?

Run a very small diameter disc and small 2 or 4 piston caliper.

They are free, but I don't want to mess with the factory brake bias. I like the way it feels and never locks even on super hard braking. I'm keeping ABS and power steering. They have spoilt me.

[PseudoRealityX]

I'll be taking out the ENTIRE E-brake assembly. Yes.

Woah, wait a second. I'd leave the E-brake in. Especially if you do, or are planning to do any ProSolos. Many of the starting lines are sloped enough that you'll roll if you don't have an E-brake. And obviously it'd be hard to do a real launch if you're trying to also modulate brake and gas with your right foot.

[GroovinPickle]

Nice build. I remember a year or so ago there was some discussion about the weight penalty for wheels larger than 16" being lifted, but I guess that didn't happen. Out of curiosity, why not run slicks?

My region has an FP driver that a couple of people have heard of...

[SHAHAB323IS]

you are my hero, that is one gorgeous car, both new and the old

[jmitro]

Ven, very nice job. car looks great. i've got your old doors stripped out and preliminarily mounted.

where did you get your CF sunroof panel? I've been looking for something like that.

[PseudoRealityX]

Nice build. I remember a year or so ago there was some discussion about the weight penalty for wheels larger than 16" being lifted, but I guess that didn't happen. Out of curiosity, why not run slicks?

My region has an FP driver that a couple of people have heard of...

Actually, unless he moved back, JT lives in Tampa, Florida. But yeah, John's definitely the benchmark. My favorite quote from a friend to JT as he pulled into the Impound shed after winning the FP National Championship...

"Good work John! Imagine how fast you would be if you did this more than once a year."

[jrtcbmw]

nice work, i followed your first build and this one is pretty good , good luck to you.

[DarkGift]

So lets assume your max speed on turns where you need the downforce (or where you can benefit from it anyways) is 50mph.

Autox is more than just traditional road course corners linked together. There are elements where you do use downforce at 60-70+ mph. e.g. Slaloms and offsets.

jmitro - here's the last thread where the CF sunroof was asked about and answered on this forum.

[Steve J.]

Autox is more than just traditional road course corners linked together. There are elements where you do use downforce at 60-70+ mph. e.g. Slaloms and offsets.

Yes, well aware of autox characteristics, did a couple years in a FSAE/AM car.

I'd be more worried about good dampers than aero for a 70+mph slalom. I would put quite a bit of money down that a car that has a better chassis setup in that class, same car, will be faster than a car with aero. For that class, mechanical grip wins.