BMW Compact Rally Car Build

[nineball12]

Is it a 188 medium case that'll work on a TI? LSD or open?

it's a small case lsd that came from an auto ti that i have recently acquired. i put a 3.25 in it when i did the 5-speed swap

[DaveKern]

it's a small case lsd that came from an auto ti that i have recently acquired. i put a 3.25 in it when i did the 5-speed swap

Gotcha. Everyone's telling me that for a 6-cyl engine, the small case won't hold up to the power output. My car was an automatic, so I've got a small case 4.44 too.

Dave

[nineball12]

i know of people running small cases with 6 cylinders and they seem to be doing fine, i'd just run it till it blew

[hamlerda]

Gotcha. Everyone's telling me that for a 6-cyl engine, the small case won't hold up to the power output. My car was an automatic, so I've got a small case 4.44 too.

Dave

The diff will hold the power just fine, now the axles are another story. I wouldn't worry unless you're building a drag car with slicks (this is how I broke my axle).

[DaveKern]

The diff will hold the power just fine, now the axles are another story. I wouldn't worry unless you're building a drag car with slicks (this is how I broke my axle).

We'll just be racing on dirt (for at least the first season), and rally tires are only available up to a 215 width, so there's not really alot of grip to be had.

Dave

[Bryson]

The diff out of an 88-91 325iS automatic is a medium case 4.10:1 LSD w/ 20% lock if that would fit the bill. Same diff as the e30 M3, will bolt into a 318ti as well of course

[DaveKern]

Got to work on the car a bit this afternoon. Not sure now when the car will go in for a cage, but there's still plenty of work to be done...and some playing.

We use stripper from the paint store to try and remove the tar residue from the interior. It worked reasonably well on small amounts of tar, but really didn't do much to remove chunks of the stuff. After having my arm get tired, we tried a different method.



Here's a shot of how it looked when I left for the day. Driver's side is now cleaned out, still need to work on the passenger's side.



Dave

[TOOLEAN]

Dave, is that fire?!?! haha, Liquid Nitrogen now this! You are having too much fun.

[DaveKern]

Dave, is that fire?!?! haha, Liquid Nitrogen now this! You are having too much fun.

Yep, giving it the ol' Fire & Ice treatment!

The leftover gasoline in the tank actually worked better than the cleaner...but when the flames got going, they really got moving, so I forgot to snap pics.

Dave

[DaveKern]

I got a chance to do a bit more work on the car this past weekend. Basically finished cleaning out the tar from the interior. Took much longer than I expected, especially after the liquid nitrogen treatment.



While I was cleaning the car I got to thinking about weight distribution, so decided to grab a wheel & tire to see what my options might be for mounting. Sure I could put it on the rear trunk floor, but if I could move it just in front of the rear axle, that's better from keeping weight from the far edges of the car...and a rally tire & rally wheel aren't exactly light.



The new rear shock turrets have been ordered as well, I hope to have them in the next couple of days.
Dave

[Dogsbody]

On the hood like an old Land Rover!

[boriksh]

On the hood like an old Land Rover!

ha ha, that would be cool, but serioiusly, i like the baja trucks style wheel access... in the trunk.

[PrezeS]

Hi Dave,
Just sold my gr2 GTi and got e36 coupe that I will prep this year for gr5, RWD is just so much more fun.
I did some reading about a diff options and 1990 e34 535i with auto tranny had a 4.27 r&p and some 80’s 5, 6 and 7 series six cylinder cars came with 4.45, all 188 mm that would fit e36 medium case, some of them were LSD. Now in order to fit in larger diff in 4 cylinder cars you have to swap over the sub frame, axel and driveshaft for 6 cylinder stuff. This is just what I’ve read on the forum, anybody can confirm this? I found a place that sells 4.27 r&p for $225 and 4.10 and smaller for $185 i’m going to ask them for 4.45 188 mm R&P.
Good read about different types of diffs in bimmers
http://www.metricmechanic.com/pdfs/metric-mechanic-differential-booklet.pdf

Chris

[Bryson]

the e36 coupe unfortunately shares no rear suspension geometry (diff included) with the hatchback.

The hatchback shares geometry with the Z3 and e30, with diffs useable from both along with select e28s

[DaveKern]

the e36 coupe unfortunately shares no rear suspension geometry (diff included) with the hatchback.

The hatchback shares geometry with the Z3 and e30, with diffs useable from both along with select e28s

Its probably a fortunate thing for him, as there are plenty more options for medium case diffs that will just bolt up (I think?).

I'm seriously considering having the rear end converted to a toyota supra diff as high R&P sets are a dime a dozen with the rock crawler guys. Ratios all the way up to 5.71 IIRC.

Sorry for the lack of updates on the Compact lately. I've been focusing on getting my hillclimb Evo ready for the season. We're looking to convert it to running a rear mounted radiator to help solve some overheating issues brought about by big boost and over 600whp.

Dave

[PrezeS]

the e36 coupe unfortunately shares no rear suspension geometry (diff included) with the hatchback.

The hatchback shares geometry with the Z3 and e30, with diffs useable from both along with select e28s

I guess I didn’t make myself clear. What I meant was that you can take an e34 gear set (or any other 188mm R&P), e36 m3 clutch pack (E30, E28 E34) and put it all in e30 medium case diff and bolt it up in the Ti. You would also need to use 6 cylinder axels and driveshaft from e30.
Now my situation is a little bit different but not that much, my coupe is 318is so I do have to change the axels and driveshaft to fit in the medium case diff. For now I will get the e34 4.27 R&P and e34 LSD, and put all in my spare assembly that came of e36 325 with 3.15 r&p, all for less than $500.

Dave
As for the supra diff, I understand where you coming from, JVL has been pushing the xr4ti guys for long time to switch over to Toyota assembly. Lots of gear sets for very little $$$$.

If I was running a 4 cylinder group F corolla or starlet I would definitely want something like 5.3:1 or 5.8:1, these cars also start with 4.x:1 ratio from factory so anything fewer than 5 turns is not really an upgrade. Since the straight six is producing amounts of torque that the corolla can only dream of, such of high gearing may not be necessary. Some of the top group F M3’s run only 4 speed gearboxes.
http://www.rengaskanava.fi/mikakiracing/uutiset.php

What is your plan for the suspension?


[ame]http://www.youtube.com/watch?v=kEFANvJhEsI[/ame]

[mjOlson]

Dave have you got Dan at Diffs Online opinion yet? Wait, is there an echo here? Oh no, just me REPEATING MYSELF. Can we put Allison in charge of the car build?

[DaveKern]

Dave have you got Dan at Diffs Online opinion yet? Wait, is there an echo here? Oh no, just me REPEATING MYSELF.

Nope, haven't reached out to anyone on the diff stuff yet, need to get the roll cage stuff figured out first. I can say the sites I looked at add a grand to get something above 4.27. I will need to do driveshaft, axles and a diff anyways, so the supra diff gets +s because I have one already and ratio changes and LSD units are worlds less expensive than the OEM BMW stuff. Downside is I'd need to pay for a little fab time to make it actually fit the BMW.

All that said, I'm almost tempted to put the car back together with the stock 4.44 small diff welded up to see what I think of the ratio before it gets blown apart. Like others have said, this motor has a different powerband than some other RWD cars that are attacking the stages, and it's certainly different than my Evo.

Can we put Allison in charge of the car build?

Sure, that'd free up a bunch of my time to get the Evo finished up...course she'd drop the coin on the Compact Cup body kit on the car before anything else gets done.

Dave

[mjOlson]

I think even a quick conversation with him would help you narrow down the good ideas from the bad.

Rally Mexico ready to go on the DVR tonight!!

Oh, and let me know if I (we) can help out with any safety gear again.

[Dogsbody]

I think even a quick conversation with him would help you narrow down the good ideas from the bad.

Rally Mexico ready to go on the DVR tonight!!

Oh, and let me know if I (we) can help out with any safety gear again.

Safety gear? At the rate Dave's going he might need some fire-proof Depends...

[DaveKern]

Safety gear? At the rate Dave's going he might need some fire-proof Depends...

When did you volunteer to co-drive?

Dave

Well, not major progress to report, but I moved the car off jack stands this weekend. Had 3 other guys give me a hand picking it up and walking it on the trailer. Surprisingly light, but very awkward.



Hopefully moving it to SCR in a couple weeks to get the cage work started.

Dave

[DaveKern]

Alright guys. After a couple weeks of no real updates, finally some progress to report. I brought the car up to SCR Performance/Built-by-Bones for the roll cage.

Here's a shot of the new rear turrets.



Since fancy remote reservoir shocks aren't in the budget, I'm looking at fitting longer shocks to gain some oil capacity. From my quick measurements, it looks like we could gain a max of 3-4" of shock length.



Built-by-Bones does alot of BMW roll hoops and roll cages, and this beautifully welded rear main hoop was sitting along the wall. This one is designed for a full-interior car, as you'll notice there's some space along the sides between the cage and the chassis. FIA rules allow for a 10 degree layback, so we tried to mock this up to see how far back I might be able to get my seat.



I'll be heading back up in a couple weeks to see how the progress is coming along.

Dave

[DaveKern]

Alright, finally things are going back together!

First shot is of the rear part of the main hoop from the driver's side.



Second shot is the same, but from the passenger side.



Last shot is from the rear hatch opening. You can see some wood we placed on the floor to try and get a feel for seat position.



I'll be heading back to the shop for more updates next weekend.

Dave

[DaveKern]

Cutting out the OEM shock mounts to make room for the new turrets. Plasma cutters ROCK!



After talking with our suspension supplier, we're going to fit shocks with 8" of travel, and we only needed to add 2" to the factory mounting location. Here's a shot of the turret fitted into position. Its been cut to fit, but we ran out of time to get the welding done that day.



Dave

[raoke]

Very nice...