BMW Compact Rally Car Build

[mjOlson]

Well, someone has to keep an eye on Dave wouldn't you say?

[cencalballer]

nice have you thought about maxattack at all? its a 2wd only series and several local places seem onboard with it. nice build cant wait to see how it turns out

[DaveKern]

nice have you thought about maxattack at all? its a 2wd only series and several local places seem onboard with it. nice build cant wait to see how it turns out

That's the tentative plan. Anxiously awaiting the 2010 schedule.

Not sure how competitive we'll be on a stockish motor vs. the turbo cars in the class (srt4 & mazdaspeeds), but it should be a whole lot of fun!

Dave

[cencalballer]

shouldnt be too bad. theres a couple golfs that are really fast but i do get your point cause that srt4 flys. gl with it hope the car and you can keep up with taht neon

[M3ANMUG]

Awesome! I can't wait to see more progress on this car and possibly see it out at CORE?


PS-Loved your EVO at PPIHC this past summer.

[harry328is]

Subscribed. Good luck with the build... can't wait to see this car finished!

[DaveKern]

Awesome! I can't wait to see more progress on this car and possibly see it out at CORE?

Yep, the plan is to have at least a few shakedown days at CORE. I'll try to keep this thread updated to let any people in the area know, as I'm always down to give ridealongs, nothing like jumping a car to make sure you've still got a pulse.

PS-Loved your EVO at PPIHC this past summer.

If you were only there to spectate on race day, the Evo was running about 1/3 of its normal power. We blew an IC pipe on the startline and had 4-6psi on the way up instead of 30psi. There's always next year though. I plan to do more track torture testing on the car at HPR or PMI, and hopefully I can drag along the BMW and will put Allison in the drivers seat to get her up to speed as well.

Dave

[DaveKern]

In the winter I work as an instructor at the Bridgestone Winter Driving School every weekend, so time to work on the cars is scarce. I just spent a week up in Steamboat Springs helping to get the tracks ready for customers, and as an early xmas present, I ended up with this weekend off. So, back to work on the car.

This time, the goal is to prepare the car for seam welding, which means getting all the seam sealer and tar off the car. Since I'm short on time, I brought an assistant.



Playing with liquid nitrogen is dangerous, so don't try this at home. We used a 3-man team to get this done in the most efficient way, and cycle out one person when their arms got tired, and to make sure nobody was freezing off any body parts. Below are Grant & Mitch at work.





Here's a shot of the car on the rotisserie. We didn't measure out beforehand, but ended up with about a mm of clearance on the rear of the car when rolling the car over.



Here's the rear wheel well just after we got started.



Here's a shot of the front wheel well as we are about done.



Here's a shot of the underside after the majority of the undercoating has been removed.



Here's what the floor looked like when we were done, what a mess!



I swept up all the material removed and put it in a box. There was probably another 4-8 lbs of sound deadening that I ended up vacuuming up from the interior, and we've still got a bunch of material still left in the car.



Thanks for following along!

Dave

[1slowcrx]

sooooo cool! Keep up the good work!

[TOOLEAN]

That is amazing. How much of that tank did you use? haha It's really cool to see how great the metal looks underneath, I guess I was expected residue or something to be left over.

[DaveKern]

That is amazing. How much of that tank did you use? haha It's really cool to see how great the metal looks underneath, I guess I was expected residue or something to be left over.

There's a little bit of residue still left, but with the low light in the shop, it doesn't show up on the pics too well.

We were told that once familiar with the process, a 180L tank would do a complete car. We started out with a leaky hose assembly and using a hammer. This ended up wasting a bunch of gas, but later we discovered an air hammer greatly speeded the process along. We ended up using two full tanks, but we're 90% sure that the second tank leaked 1/2 of the gas out from Friday night to Saturday evening, so if we were to do it again with proper equipment, I think one full tank would be about right.

Its not all without problems though. We found that if you cooled an area a bit too much, a blow with the hammer would shatter the metal underneath as well. We only had this happen in three spots, once in the middle of the back seat, once in the drivers rear wheel well, and once on the dash. Luckily, we just ended up with cracks, so when its time to seam weld, we'll fix those right up.

Dave

[lughed]

I love this video [ame]http://www.youtube.com/watch?v=XxRokrZqkSQ[/ame]

[citterly]

I love your rotisserie! What a great idea, those engine stands are $60 at harbor freight. I didn't realize the undercoating weighed that much.....

Nice work!

[nineball12]

here's some diff ration info for you. when i had my 4.44 diff in with the s50, my car topped out at about 110mph at 7200rpm's. with my 3.73's that i have now it does about 138, and they do make 4.27 gears if you didn't know about those, i've seen them in e30 convertibles.

[charbel]

awsome work. good looking car with no rust.. good luck with the build..

[mjOlson]

here's some diff ration info for you. when i had my 4.44 diff in with the s50, my car topped out at about 110mph at 7200rpm's. with my 3.73's that i have now it does about 138, and they do make 4.27 gears if you didn't know about those, i've seen them in e30 convertibles.

Be aware that the lower gearing (higher numerical number) the smaller the pinion which gets you into reliability issues. This is why Dave needs to be speaking with diffsonline like he was told. Please reference "someone needs to keep an eye on Dave" post above... Keep the blown diffs to the Evo Dave!

Dave, what dampers are you thinking of going with??

[DaveKern]

Be aware that the lower gearing (higher numerical number) the smaller the pinion which gets you into reliability issues. This is why Dave needs to be speaking with diffsonline like he was told. Please reference "someone needs to keep an eye on Dave" post above... Keep the blown diffs to the Evo Dave!

Most of the "expensive stuff" is still up in the air, cage, diff, suspension, seats, etc. I'm waiting to hear back from a couple potential sponsors to figure out what sort of budget we have to work with. If nothing comes through, the car may just end up being a track rat for 2010. There's no point in building another rally car if its just going to sit in the garage.

For the diff, I'm not even sold on using BMW stuff, there is a chance I may convert the rear to a 2nd-gen Toyota Supra diff, as its cheaper, and lots of high numerical options are available (thanks to the off-road guys). The fact that so many road racing builds add diff coolers makes me wonder if the BMW parts can deal with the extra heat that you'd see in rally conditions. I'd assume on slippery surfaces the diff is working even harder than on a road course. Of course if people here have thoughts on the matter, I'm all ears, I'm learning about all of this as I go.

Dave, what dampers are you thinking of going with??

Suspension is probably the biggest wild-card at the moment due to the huge variation in pricing options:

Low end (~$2,000) JVL, a guy in the PNW, builds very beefy non-adjustable coilovers based around a bilstein 48mm or 55mm insert.

On the high end, the CM3C cars use Proflex 3-way adjustable coilovers (~$7500). There are probably even more expensive options from Extreme Tech, Ohlins, and Reiger, but I think following the recipe from the CM3C cars would just fine.

In between those options there's AST, JRZ, Hotbits, and RS&SP. I've yet to price out or look at what options are available for these. I also need to determine what modifications are needed to the rear shock towers to run a proper coilover in the rear. I've heard that running the stock type setup with separate spring and damper leads to bent parts due to coil bind when jumping.

Dave

[mjOlson]

The spring position will also dictate your cage design. Do you have a link to the series rules?

[DaveKern]

The spring position will also dictate your cage design.

Ideally, I'd like to put the spring right on the shock, and have seen pictures of folks across the pond actually change out the rear end to Cossie bits. I don't want to go that far, as Cossie parts aren't common, but I'm guessing there's a way to convert to a strut assembly, away from the stock shock & spring setup. I'm told that the Proflex offering for the CM3C cars is a strut assembly.

Do you have a link to the series rules?

http://rally-america.com/rules.php
http://www.nasarallysport.com/main/rules

The car will compete in the Group 2 or Group 5 class, and from my read of the Rally America rules, you need to keep your orig. driveline configuration (front engine, RWD, engine & chassis from associated manufacturer), but other than that, there's alot of flexibility allowed. NASA is even more flexible about engine/chassis swapping, but since the MaxAttack! series may use both NASA and Rally America events in its championship, I have to be mindful of both rule sets.

Roll cage will likely be a kit from Custom Cages, and to keep its FIA certification, no modifications are allowed beyond what is spec'd from Custom Cages. I have confirmed that B-pillar gussets and door X gusset plates are allowed additions. Here's the diagram:



Dave

[boriksh]

Dave, great build, I am looking forward for the updates

[DaveKern]

We've pickeup up several sets of Compomotive TH Rally Wheels. They're 15x6.5" and the tires are 16x62x15s. This means they're 16cm wide, 62cm tall, and fit on a 15" rim. The newer version of these tires, now branded as BFGoodrich have switched back to the standard tire measurments, and will be what I hope to run during the season. I'm hopeful that there won't be any fitment issues with running a 195-70-15 or a 205-65-15.



These are Michelin rally tires and are fairly dated. They'll be good for practice days though.



The plan is to start chassis prep tomorrow.

Dave

[boriksh]

sweet wheels, how heavy are they?

[DaveKern]

sweet wheels, how heavy are they?

No idea really. Compomotive doesn't even make these anymore in a 15" size, so their website wasn't much help. Typically rally wheels are pretty heavy so that if you flat a tire on stage, you can continue on the rim for a while. Compared to the wheels on my Evo (Compomotive TH-3s 15x7" with 195-70-15), these feel light, but it could be that the smaller tire plays a role in being able to lift them easier. I don't have any wheels without tires mounted, so it'll be a while before I can get a wheel only weight.

Dave

[boriksh]

anyways, those are some nice looking rally wheels. Looking forward to more updates

[Dogsbody]

More bloody tires... All told, you've got to have close to 30 laying around?