BMW Compact Rally Car Build

[nineball12]

when i did my manual swap in my ti i had originally taken the key interlock cable out and my key was stuck.. i put the cable back in and looped it around in my dash and now the ignition works like normal.

[DaveKern]

before removing the ignition lock, follow the shifter interlock cable till it hits the ignition lock. i had one and all i had to do was unscrew the cable assembly from the ignition. it might be that easy on yours too.

Cable was removed over a year ago. Unfortunately I think it went into the scrap pile with the automatic shift lever.

when i did my manual swap in my ti i had originally taken the key interlock cable out and my key was stuck.. i put the cable back in and looped it around in my dash and now the ignition works like normal.

Interesting. We were thinking of attaching something flexible to the back side of the ignition column with a screw/bolt of the right length so its a simple matter of pressing in on the screw/bolt to release the key. I hate vibrating/rattling stuff in the car, so this idea may not fly.

Dave

[DaveKern]

Little more progress:





Dave

[Dogsbody]

What the heck? Now you're too good for a ratchet strap to hold the trunk closed?

[DaveKern]

What the heck? Now you're too good for a ratchet strap to hold the trunk closed?

I must be almost as old as you are, cause my memory is failing me. :P

I did have to use one at Rally Colorado when I was running as "0" car when the rear bumper broke off. I did take a sharpie to it so it at least blended in with the paint. LOL

Dave

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Got a PM from a member following the thread, and thought it'd be worth posting up my answer since I'm sure lots of you track'ers following along might have the same question:

I have been fighting with communication systems like chatterbox and others, but they just seem to 'hit or miss' and poor quality. Someone recommended that I talk to Rally folks about driver/navigator communication, that they might have something more robust.

Rally cars are a bit of a different animal since you're usually riding with the same person. The reason this makes a difference, is usually you'll buy a helmet that's plug'n'play with the intercom system.

Peltor, Stilo, and Terratrip all make intercoms that have a box that you plug both helmets into. The 9v battery powered systems seem to be best as they shield interference better...but make sure to use some foam between the intercom and rollcage to help reduce the chances of picking up any engine noises...and keep a spare battery in the glove box!

Stilo (what I use) and Peltor have everything integrated into the helmet, so you simply plug the intercom box into the helmet.

Terratrip (terrortrip?) is the more budget friendly system, but the one I had would buzz louder and louder the higher you revved the car. The advantage to this system is that many people retrofit a mic and speaker into the padding on the helmet. Peltor may also sell bolt-on mics and speakers, but I'm not 100% sure. I don't think Stilo offers any thing like that.

The downside with all the rally style comm systems is that they're somewhat permanently installed, so not sure if it'll work for you if you're jumping from one car to the next or have different passengers. Rally helmets are even worse in this regard as they have built-in ear cups which really drown out the noise....but they are oooh so sweet when you're plugged in.

Dave

[DaveKern]

Alright guys - need some help. I'm getting ready to install my harnesses (Schroth Profi HANS 6-points). This harness is setup to snap into those eyelet bolts.

Trans tunnel side mounting is a no-brainer. I'm going to use those kits with a eyelet bolt, locking washer, and huge backing washer. The outside edge I'm running into some issues. I would like to use an eyelet bolt that simply threads into the OEM seat belt anchor. Concerns about it not lining up properly when tightened aren't a big deal since at most I'd need to go full tight and back off half a turn and will then weld it into place.

I did some searching and someone mentioned the bolt is M10x1.5, but I can't seem to find any eyelets sold with that thread pitch. Anybody know where to source some? I only need two.

Thanks,

Dave

[TOOLEAN]

Alright guys - need some help. I did some searching and someone mentioned the bolt is M10x1.5, but I can't seem to find any eyelets sold with that thread pitch. Anybody know where to source some? I only need two.

Hey Dave, I checked the garage, they are M10 x 1.5, Studs in the front, tapped chassis holes in the back. I can't help you source the eyelets, sorry, but if you are planning on fully welding them anyway, does it matter? Get something close, drill out the holes and weld her up.

Good Luck with the search.

[DaveKern]

if you are planning on fully welding them anyway, does it matter? Get something close, drill out the holes and weld her up.

No real reson, only looking for the redundancy I guess. I'm sure they'll be plenty good if I just drill out the threads a litte bit and crossthread the hell out of that eyelet bolt as it goes in, AND then weld it into place.

Dave

[DaveKern]

Got another day off and spend some time on the BMW.

Rings for the lap belts are now bolted & welded into place. Hit them with a little bit of paint, so will be able to install the belts next time I work on the car.

Also decided to install some residual pressure valves in the brake lines, and have been tracking down the right fittings to get them to work. Thought I had everything needed, but the 1/8 NPT to AN-3 adapters weren't quite right, as something was up with the flare fitting on the AN-3 side. These valves are used to keep a couple PSI in the brake system to keep fluid from draining back to the masters (when floor mounted), and may also help to fight pad knockback that seems to plague cars that race on rough surfaces.

Nothing really worth taking pictures of....but more will be coming soon as the rest of the car gets put back together.

Dave

[DaveKern]

Made some progress tonight. Got the Wilwood residual valves installed in the brake lines down at the master cyl.



The adapter rings for fitting the Toyota Supra diff just arrived. This will let me use E30 6-cyl axles.



Dave

[e30-323ti]

Those axle adaptors look very famiiar

Except mine are onto larger E28 axles/CV's

I thought I read earlier you decided not to go with the supra diff?
What ratio(s) did you settle on?
I imagine a 3.73 out of a 5sp turbo would go well in a rally car with your ZF box & 1:1 5th gear.

On the residual pressure valve's, do you need those because you are using the single pot sliding calipers (more knock back etc... than say a fixed 4pot)?

Some pics of mine FYI
(E30 with E28 subframe & Supra Diff)

[DaveKern]

I thought I read earlier you decided not to go with the supra diff?
What ratio(s) did you settle on?
I imagine a 3.73 out of a 5sp turbo would go well in a rally car with your ZF box & 1:1 5th gear.

On the residual pressure valve's, do you need those because you are using the single pot sliding calipers (more knock back etc... than say a fixed 4pot)?

The 'skipping the supra diff' comments from earlier were simply so I could get the car on the road faster. I've got access to a terrific ice driving facility in Steamboat Springs called the Bridgestone Winter Driving School where I wanted to start getting some drive time. The school is only open until the first week in March, so in the rush to get things done, I figured running a small case would be ok, but knew it wasn't going to be a long term solution as I'm running a 6-cyl motor.

I had hoped I could just fit together two BMW driveshafts to make the M3 trans and small diff connect, but no such luck. That meant a custom driveshaft was in order, and give my current budget (or lack thereof), it didn't make sense to pay to have a driveshaft made just for a day or two of driving. So, now I'm just trying to get that supra one ready to drop in instead.

What ratio(s) did you settle on?
I imagine a 3.73 out of a 5sp turbo would go well in a rally car with your ZF box & 1:1 5th gear.

4.56 is what we decided to go with. I was leaning towards the 4.88, but that was when I thought a safe rev limit was 7500rpm. I don't need/want to run the motor too hard, and from my experience, high revs can kill motors. Rally is so much more of an endurance thing, so figured the 4.56 would still give me ~120mph given my tire sizes. That's probably 20mph more than I really need, but we'll see how it does out on the stages and probably have another diff built with different ratios. That's the beauty of the Supra conversion, 2-3 diffs for the price of one BMW.

On the residual pressure valve's, do you need those because you are using the single pot sliding calipers (more knock back etc... than say a fixed 4pot)?

The reading I'd done suggested if the master cyl was below the calipers that you might get some fluid drain back, but also that they could help with pad knock back. For ~$30 each (with fittings), I figured it was worth seeing how they'll help. As I rush to get the car finished for some ice time, I'm leaving the brakes as-is. I do plan to at least upgrade the fronts to wilwood 4-pots by the time our first race rolls around.

Dave

[nineball12]

I had hoped I could just fit together two BMW driveshafts to make the M3 trans and small diff connect, but no such luck. That meant a custom driveshaft was in order, and give my current budget (or lack thereof), it didn't make sense to pay to have a driveshaft made just for a day or two of driving. So, now I'm just trying to get that supra one ready to drop in instead.

An m3 driveshaft will bolt to a small or medium case diff... they have the same flanges...

4.56 is what we decided to go with. I was leaning towards the 4.88, but that was when I thought a safe rev limit was 7500rpm. I don't need/want to run the motor too hard, and from my experience, high revs can kill motors. Rally is so much more of an endurance thing, so figured the 4.56 would still give me ~120mph given my tire sizes. That's probably 20mph more than I really need, but we'll see how it does out on the stages and probably have another diff built with different ratios. That's the beauty of the Supra conversion, 2-3 diffs for the price of one BMW.

And where are you getting your diffs from? mine are about $60-$70 from the pull yards...

[DaveKern]

An m3 driveshaft will bolt to a small or medium case diff... they have the same flanges...

That wasn't my experience. The 95 M3 used a different trans than the other years, and it only came with a "CV" style end, which is a 6-bolt, which wouldn't fit onto my small case TI diff.

There were other non-CV style M3 driveshafts, but the transmission length was different on those...so no luck with plug'n'play.

And where are you getting your diffs from? mine are about $60-$70 from the pull yards...

I got one from the guy who built my suspension, but for my next one, I'll try to find one locally at the junkyard. When I was talking costs on BMW stuff, I was factoring in a full rebuild from some of the better known shops. Factory locking isn't good enough for rally duty, but the bigger decision maker really was the lack of inexpensive R&Ps above 4.1 for BMWs.

Dave

[DaveKern]

Spent another day at the shop.

Driver's seat & harnesses all adjusted, passenger one not installed yet because I need to figure out battery mounting first.



Spent quite a bit of time figuring out how to mount the diff. Ended the day with the front mounts tacked into place, and have a good idea or two for the rear mounts. Hopefully I'll be able to have the driveshaft guy come down and take measurements for the custom driveshaft.



Dave

[TOOLEAN]

Hey Dave, looks great! Just an FYI - there are mixed opinions Residual Pressure Valves, have you run them before? Personally, I didn't like them. Keep up the good work!

[DaveKern]

Hey Dave, looks great! Just an FYI - there are mixed opinions Residual Pressure Valves, have you run them before? Personally, I didn't like them. Keep up the good work!

Would you mind sharing your experience with them and what you did/didn't like about them?

Dave

[nineball12]

That wasn't my experience. The 95 M3 used a different trans than the other years, and it only came with a "CV" style end, which is a 6-bolt, which wouldn't fit onto my small case TI diff.

There were other non-CV style M3 driveshafts, but the transmission length was different on those...so no luck with plug'n'play.

Dave

i have a '95 engine and trans too. The driveshafts are completely interchangeable, they have splines and you can change the length of them. Even one from a manual 328 works... just has to be 4 bolt. Anyway, I can't wait to see vids of this thing in action.

[DaveKern]

i have a '95 engine and trans too. The driveshafts are completely interchangeable, they have splines and you can change the length of them. Even one from a manual 328 works... just has to be 4 bolt. Anyway, I can't wait to see vids of this thing in action.

Is it possible you had a different transmission from one of the late 95 build cars? Its my understanding that the ZF transmission from the 95 M3 was a different length than the other years based off looking at DSSR lengths. I had no luck locating a 4-bolt 95 driveshaft, every single one I found had the 6-bolt CV style end. Either way, no big deal, hopefully I'll have the Supra one in there sometime soon.

Dave

[DaveKern]

Finally got a chance to get back to the car tonight. Got the diff lifted into position and measured for the custom driveshaft. Also installed helpersprings so I'll be able to lower the car to somewhere around 1" over stock ride height and not have the springs rattle around.



Dave

[fsmtnbiker]

Is it possible you had a different transmission from one of the late 95 build cars? Its my understanding that the ZF transmission from the 95 M3 was a different length than the other years based off looking at DSSR lengths. I had no luck locating a 4-bolt 95 driveshaft, every single one I found had the 6-bolt CV style end. Either way, no big deal, hopefully I'll have the Supra one in there sometime soon.

Dave

The ZF transmissions are all the same. The difference is in the shift-selector joint that goes on the transmission, and they are interchangeable. Any manual M3 driveshaft should be the same length, with the difference being either the 4-bolt or 6-bolt flange.

If you are in a pinch, we have a 4-bolt M3 driveshaft up at SCR.

[bmwplanet]

I think Im a little late on this but we just have HDPE riveted to the bottom of our saab rally car and that is holding up remarkably well in the dirt rallies. Im building a 95 M3 to use on tarmac rallies but Ill leave the offroading to you!

nice work!

[DaveKern]

Hey guys - another question that I'm having trouble finding through the search function. All the threads that get listed have 5-20 pages to weed through.

I'm looking at mounting the battery in the spot behind the passenger seat along the floor. This will let me build a battery bracket that's only two sided (top & front), and really ensure that in a roll-over situation I won't have a flying battery to contend with.

The standard 34/35 size Optima batteries are just about 1/2" too wide for my liking (sit too close to the seat), so I'm looking at downsizing a little bit. Don't want to go mini-battery because you never know when an alternator might crap out on stage, and want to make sure I've got something that'll get the car started without drama.

So, wondering if any of you guys have downsized batteries for racing purposes and what you're using. Basically, how small is too small?

Thanks,

Dave

[HoJo]

Look into a battery sized for an Acura TSX. They are small, I would estimate 5"x10", and pretty light. The factory ones are 500cca.

[DaveKern]

Look into a battery sized for an Acura TSX. They are small, I would estimate 5"x10", and pretty light. The factory ones are 500cca.

That's what I picked up, its a "D51" size. To me looked like a good option, but the ratings on it were a little on the low side. Comparing Optima to Odyssey seems a bit tricky as they use different cranking intervals to rate their batteries.

I used to use a PC680 in my 323GTX and it would start the car with no problems....unless the ECU mapping didn't cooperate and the car wouldn't fire by the 5th or 6th try.

I plan to stick with off the shelf chip tunes for the BMW, so I'm thinking that hard starts shouldn't be much of an issue, right?

Dave