1991 BMW 318is rally cross build

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formyhealth

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irish44j


I've run the same set of Bilstein HDs for almost five seasons of rallycross + WM Winter Rally and still fully functional. They're pretty inexpensive and worthwhile. I have Konis on a couple of my cars and they're excellent, but tend to be firmer than Billies. I think of the dozen+ e30s that run locally, most or all of them are on HDs, none are on Konis.

15" wheels is a plus - more tire options for sure. Look on demontweeks (UK) - lower prices even with shipping than most US distributors on various rally tires ("tyres" lol)

I figured as much, most everyone on r3v would agree as well. I'm sure I'll end up with the Bilsteins for now, the price difference for the two aren't terribly far off any how.

Thank you for the link, browsing now.

FWIW I've been very happy with the four sets of DMack DMG3's I've owned. Less happy with the Yokos and Hankooks. I hear the Dmacks in 15" size are a BITCH to mount though (14" DMacks are pretty easy though)

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irish44j


FWIW I've been very happy with the four sets of DMack DMG3's I've owned. Less happy with the Yokos and Hankooks. I hear the Dmacks in 15" size are a BITCH to mount though (14" DMacks are pretty easy though)

Do you have one of those harbor freight jobbies for debeading/mounting tires? Or do you just use a few bars?

Those DMACKs are a pretty good price, are you running softs or hards? I was interested in the maxsport rb3s as they are ~$88 a piece so I could get 8 of them for about $150 more than a set of 4 of the DMACKs.

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formyhealth

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irish44j


FWIW I've been very happy with the four sets of DMack DMG3's I've owned. Less happy with the Yokos and Hankooks. I hear the Dmacks in 15" size are a BITCH to mount though (14" DMacks are pretty easy though)

Do you have one of those harbor freight jobbies for debeading/mounting tires? Or do you just use a few bars?

Those DMACKs are a pretty good price, are you running softs or hards? I was interested in the maxsport rb3s as they are ~$88 a piece so I could get 8 of them for about $150 more than a set of 4 of the DMACKs.

I have a friend who I rallycross with who has proper tire machines in his basement and does all my tires. I would think it woudl be nearly impossible to mount gravels just using bars.

I run medium compounds on the DMacks usually but have a couple softs as well. Depends on the temperatures/surfaces of your local venue. In Oregon you guys are probably on cooler dirt/mud so softs may be preferable.

Also Maxsports are retreads. Some guys local use them for rallycross and they're fine (though apparently a lot softer sidewalls than most other gravel tires), but I woudln't use them for stage rally.

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irish44j


I have a friend who I rallycross with who has proper tire machines in his basement and does all my tires. I would think it woudl be nearly impossible to mount gravels just using bars.

I run medium compounds on the DMacks usually but have a couple softs as well. Depends on the temperatures/surfaces of your local venue. In Oregon you guys are probably on cooler dirt/mud so softs may be preferable.

Also Maxsports are retreads. Some guys local use them for rallycross and they're fine (though apparently a lot softer sidewalls than most other gravel tires), but I woudln't use them for stage rally.

Dang, lucky dude it'd be nice to have a friend like that. Thanks again for the advice, retreads would probably be cool with me for practice and such, trying to keep the price down for now because I'm new to the sport and am trying not to dive in head first like I do with all my other hobbies (which are now on the back burner)

I think rallycross a 2.93 might be better. Mostly first gear with smidge of 2nd. I know in a Suby the 4.44 sucks in RX, 3.90 seem to do more better.

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Grant Hughes

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NoCoast
I think rallycross a 2.93 might be better. Mostly first gear with smidge of 2nd. I know in a Suby the 4.44 sucks in RX, 3.90 seem to do more better.

I feel like I can stay in 2nd for most of it because of how short the 318is gearing is. I'll have to go out and give it a go before I decide what will be best.

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NoCoast
The other good source for 4.1 medium case ring and pinions is from the 90-92 or so E34 5 series cars.
Also, helical diffs are shit, stock are better so if you wanted the 5.x from Motamec you just need the ring and pinion, not the helical shit diff.

Kern's coupe has always run the 4.44 168 mm diff with a M52 2.8L with S52 cams and a bunch of other shit. It actually seems fine in rally use so a small case 4.44 LSD is probably the best option for a M42 powered car.

I recently traded a 4.26 medium case diff for my Compact. Working on building the 4.10 for the road race car.

In that case (no pun intended) I may keep the small case 4:44 diff. I'm running that exact engine set up and was planning on keeping it as a spare, but if it held up in his car it should hold up in mine.

Was Kern's differential modded at all or left alone?

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Nate.Vincent

In that case (no pun intended) I may keep the small case 4:44 diff. I'm running that exact engine set up and was planning on keeping it as a spare, but if it held up in his car it should hold up in mine.

Was Kern's differential modded at all or left alone?

Or, or, or, you could sell it to me!

So my uncle called me today, he is having problems with his 1998 528i wagon and just wants to get it out of his garage, so it looks like I'll have 2 wagons now.

I'll have lots of parts off the wagon for sale in a few weeks when I get it towed back to my house.

decided I'll keep it, it's a nice color!
Exciting!



Edited 1 time(s). Last edit at 05/29/2016 02:11AM by formyhealth.

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NoCoast
I think rallycross a 2.93 might be better. Mostly first gear with smidge of 2nd. I know in a Suby the 4.44 sucks in RX, 3.90 seem to do more better.

You guys must have some slow/tight courses. A 2.93 with a G240/M42 at our events would result in constant 1-2 shifts throughout the course and being below the torque curve in 2nd, it seems to me. Then again, my car routinely hits 60ish a couple times per run on our courses. Our course designers are stage guys, so they like to keep it pretty open

Hmm....I have an open 2.xx out in the shed. Maybe if I'm bored I'll throw that into the car and see for sure at a test&tune or something....



Edited 1 time(s). Last edit at 05/27/2016 08:14PM by irish44j.

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irish44j

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formyhealth

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NoCoast
The other good source for 4.1 medium case ring and pinions is from the 90-92 or so E34 5 series cars.
Also, helical diffs are shit, stock are better so if you wanted the 5.x from Motamec you just need the ring and pinion, not the helical shit diff.

Kern's coupe has always run the 4.44 168 mm diff with a M52 2.8L with S52 cams and a bunch of other shit. It actually seems fine in rally use so a small case 4.44 LSD is probably the best option for a M42 powered car.

I recently traded a 4.26 medium case diff for my Compact. Working on building the 4.10 for the road race car.

I did want to stick with a small case diff, if for nothing else other than simplicity. That's a a good idea about the 5.x ring and pinion, I'll remember that when I've got some more float cash.

For rallycross I'd definitely stick with it. The medium case is heavier. The only reason to really go medium case is for the additional lockup. I think I mentioned earlier that the stock small-case LSD is 25% lockup, while the stock medium case is 40%, with the option to add a third clutch pack to bring that up to 60%. I've switched between the two on subsequent events and with both diffs being freshly rebuilt to stock spec, the additional lockup on the medium case is apparent. Kind of your call on whether you prefer more lockup or not - also dependent on how slippery the surface you run on is.

That said, just find any LSD 3.73-4.10 with functonal LSD or rallycross, unless your plan is to make this a high-budget build. On a limited budget there are a lot of things that will make you MUCH more competitive than changes in diff ratios. First thing is tires, #1. Second is a quicker steering rack. Third is a decent suspension (at very least some Bilstein HDs and some IX/IS springs if you want to keep the budget down). Also go find a chip. They're cheap for M42 and fatten up the midrange as well as adding 500-1000 to the redline, which is useful for rallycross in particular.

For stage later on , that's when your diff ratios can have a larger effect as you'll be using more gears and have a much wider range of speeds.

Also, the M42 can launch in 2nd even with the 3.91. But it's not the fast option unless you are on some really slick stuff.

For Rallyx it all depends on the course. until he knows how fast he can go on course he has no idea what ratio is best.

For stage lower is better. Especially with our retarded 3rd gears. Given money, time, and guarantee that I would trailer my car to every event, I would buy that ring gear for 5.44 in an instant.

AFAIK both medium and small case Diffs are 25% locking from the factory. nothing to loose/gain there. The Med case is certainly not 40% stock. Says so on my fancy Germany delivery sheet. Both are build-able for more.

4.10's are readily available in both small and medium form near me. not sure if you live in black out zone. As I said before for Rallyx you will have no idea what gearing you need until you try the course and find out how fast your car(and you) can push it on the straits. But any where from 3.73 to 4.10 should be easy to find.

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paperpaper

For Rallyx it all depends on the course. until he knows how fast he can go on course he has no idea what ratio is best.

For stage lower is better. Especially with our retarded 3rd gears. Given money, time, and guarantee that I would trailer my car to every event, I would buy that ring gear for 5.44 in an instant.

AFAIK both medium and small case Diffs are 25% locking from the factory. nothing to loose/gain there. The Med case is certainly not 40% stock. Says so on my fancy Germany delivery sheet. Both are build-able for more.

4.10's are readily available in both small and medium form near me. not sure if you live in black out zone. As I said before for Rallyx you will have no idea what gearing you need until you try the course and find out how fast your car(and you) can push it on the straits. But any where from 3.73 to 4.10 should be easy to find.

You're not wrong! I am having a difficult time locating an lsd variant of the small case differential here in Oregon. I've tried a used part search website with no luck, I have found some on Ebay but who knows really?

I'm still looking though, I figure a 4.10 would be fine for me as of now, and then can and will change the ratio when changing venues.

Its rallycross, run whatever ratio comes with the diff.
Ironically I was reading an article today about Xtrac devising and building a test rig for mevhanical differentials, which until then were essentially untestable aside from on track/road.
A 20% diff from an M3 could be a 40% diff in a M42 engined car....

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Grant Hughes

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paperpaper

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irish44j

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formyhealth

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NoCoast
The other good source for 4.1 medium case ring and pinions is from the 90-92 or so E34 5 series cars.
Also, helical diffs are shit, stock are better so if you wanted the 5.x from Motamec you just need the ring and pinion, not the helical shit diff.

Kern's coupe has always run the 4.44 168 mm diff with a M52 2.8L with S52 cams and a bunch of other shit. It actually seems fine in rally use so a small case 4.44 LSD is probably the best option for a M42 powered car.

I recently traded a 4.26 medium case diff for my Compact. Working on building the 4.10 for the road race car.

I did want to stick with a small case diff, if for nothing else other than simplicity. That's a a good idea about the 5.x ring and pinion, I'll remember that when I've got some more float cash.

For rallycross I'd definitely stick with it. The medium case is heavier. The only reason to really go medium case is for the additional lockup. I think I mentioned earlier that the stock small-case LSD is 25% lockup, while the stock medium case is 40%, with the option to add a third clutch pack to bring that up to 60%. I've switched between the two on subsequent events and with both diffs being freshly rebuilt to stock spec, the additional lockup on the medium case is apparent. Kind of your call on whether you prefer more lockup or not - also dependent on how slippery the surface you run on is.

That said, just find any LSD 3.73-4.10 with functonal LSD or rallycross, unless your plan is to make this a high-budget build. On a limited budget there are a lot of things that will make you MUCH more competitive than changes in diff ratios. First thing is tires, #1. Second is a quicker steering rack. Third is a decent suspension (at very least some Bilstein HDs and some IX/IS springs if you want to keep the budget down). Also go find a chip. They're cheap for M42 and fatten up the midrange as well as adding 500-1000 to the redline, which is useful for rallycross in particular.

For stage later on , that's when your diff ratios can have a larger effect as you'll be using more gears and have a much wider range of speeds.

Also, the M42 can launch in 2nd even with the 3.91. But it's not the fast option unless you are on some really slick stuff.

For Rallyx it all depends on the course. until he knows how fast he can go on course he has no idea what ratio is best.

For stage lower is better. Especially with our retarded 3rd gears. Given money, time, and guarantee that I would trailer my car to every event, I would buy that ring gear for 5.44 in an instant.

AFAIK both medium and small case Diffs are 25% locking from the factory. nothing to loose/gain there. The Med case is certainly not 40% stock. Says so on my fancy Germany delivery sheet. Both are build-able for more.

4.10's are readily available in both small and medium form near me. not sure if you live in black out zone. As I said before for Rallyx you will have no idea what gearing you need until you try the course and find out how fast your car(and you) can push it on the straits. But any where from 3.73 to 4.10 should be easy to find.

FYI also depends on which G240 he has. The early G240 actually has longer gearing 1-3 than the G260 in your 325. The late 318is G240 has a longer 1-2, but a much shorter 3rd (1.61 vs. 1.40).

As to the diffs, I certainly could be mistaken, but I've been told that by Jon Thayer (who basically rebuilds BMW diffs nonstop) and also (IIRC) by someone from Metric Mechanic. I have two totally rebuilt diffs here (3.91 small case and 3.73 medium), both rebuilt to stock spec with OEM parts. The ratios are not very different in reality, but in terms of on-course feel the 3.73 most certainly *feels* like it has substantially more lockup. Could be butt-dyno, but I know this car pretty damn well. One would think with larger clutches in the medium case, it would have more lockup - that seems logical. But I don't know if the ramp angles are the same, so.....

As to small vs. medium, there are things to "lose and gain." The small case is substantially lighter (I have swapped them back and forth many times, I know it well). The medium case has a spacer in it allowing for a third clutch pack to be installed for additional lockup with no modifications to the case. The small case does not, so you're stuck with two clutch packs no matter what. You can increase lock a bit using the Porsche clutch packs and different preload, but that's fairly mnimal.



Edited 1 time(s). Last edit at 05/31/2016 04:20PM by irish44j.

All i know is BMW claimed 25% from factory with Med case so take that gray space as you will. Certainly a third plate will yeald more ( especially when you mess something up and the diff binds to full welded lol). All I have is form info so all grain of salt.

Really for Rallyx run what ya got as long as it is LSD. hell weld a open one. smooth is fast and the rest is just bullshit talk anyways. as long as you got both wheels pushing forward you have got it made. Join your local e30 FB pages and scrounge the junkers. you will find something. I know that pacific northwest has huge e30 following. respect your elders is filmed out there. along with the e30 picnic.

just as long as you beat the xraty's.