1991 BMW 318is rally cross build

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Robert Culbertson


That's exactly where I'm talking about

Couple'a buddies of mine used to play around in their subies when it snowed, always got more snow there then in Independence.

Just googled Falls City. Damn, makes me feel deprived of good roads here in New England.

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Thomas Kimsey
Just googled Falls City. Damn, makes me feel deprived of good roads here in New England.

I think there is only one paved road in Falls City (kidding of course) but the amount of gravel roads in falls city and off towards Valley of the Giants is crazy.



Edited 1 time(s). Last edit at 05/26/2016 03:57PM by formyhealth.

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.

---

Grant Hughes

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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.

So is the idea with the 4.1 or 4.44 diff is to run 1st-4th?

2nd (2.02:1) seems a bit too tall to launch in, even with a 4.88 or 5.whatever. Maybe the mighty m42 has enough power. I know the Volvo doesn't have enough oomph to launch a 1.93:1 with a 4.88 unless it's on snow.

The spread from 2-5th does look nice for a 4.88+ though. Really nice.

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Robert Culbertson
So is the idea with the 4.1 or 4.44 diff is to run 1st-4th?

2nd (2.02:1) seems a bit too tall to launch in, even with a 4.88 or 5.whatever. Maybe the mighty m42 has enough power. I know the Volvo doesn't have enough oomph to launch a 1.93:1 with a 4.88 unless it's on snow.

The spread from 2-5th does look nice for a 4.88+ though. Really nice.

So with a ~6500 stock redline and 4.44s, 2nd gear shows me ~54 mph and a theoretical top speed of ~134 (which I'll never hit in rally-x).

I don't think that a 2nd gear launch is totally out of the question. 5.44s would be FUN anyway.


What kind of HP does to Volvo put down?

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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.

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formyhealth

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Robert Culbertson
So is the idea with the 4.1 or 4.44 diff is to run 1st-4th?

2nd (2.02:1) seems a bit too tall to launch in, even with a 4.88 or 5.whatever. Maybe the mighty m42 has enough power. I know the Volvo doesn't have enough oomph to launch a 1.93:1 with a 4.88 unless it's on snow.

The spread from 2-5th does look nice for a 4.88+ though. Really nice.

So with a ~6500 stock redline and 4.44s, 2nd gear shows me ~54 mph and a theoretical top speed of ~134 (which I'll never hit in rally-x).

I don't think that a 2nd gear launch is totally out of the question. 5.44s would be FUN anyway.


What kind of HP does to Volvo put down?

If you're planning to drive to events on the highway, 5.44s would be so not fun.....Not sure how close you are to your venues though. We truck 2 hours into the mountains for ours and are moving around 80mph. M42 with 5.44s would be screaming the whole way, lol.

Also keep in mind your tire diameters. We have a half dozen e30s running locally. Some are running 175/65/14 gravels, others are using much larger BFG all-terrains, and the rest are in between. Tire height can have just as much effect on gearing as your diff ratios.....so figure out what tires you're going to run first: snow tires? all-terrains? rally/gravel tires? 14" sizes have limited selection if you're going to run stock bottlecaps/weaves so you may not be able to get THE size you want in THE tire you want in many cases.

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irish44j

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formyhealth

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Robert Culbertson
So is the idea with the 4.1 or 4.44 diff is to run 1st-4th?

2nd (2.02:1) seems a bit too tall to launch in, even with a 4.88 or 5.whatever. Maybe the mighty m42 has enough power. I know the Volvo doesn't have enough oomph to launch a 1.93:1 with a 4.88 unless it's on snow.

The spread from 2-5th does look nice for a 4.88+ though. Really nice.

So with a ~6500 stock redline and 4.44s, 2nd gear shows me ~54 mph and a theoretical top speed of ~134 (which I'll never hit in rally-x).

I don't think that a 2nd gear launch is totally out of the question. 5.44s would be FUN anyway.


What kind of HP does to Volvo put down?

If you're planning to drive to events on the highway, 5.44s would be so not fun.....Not sure how close you are to your venues though. We truck 2 hours into the mountains for ours and are moving around 80mph. M42 with 5.44s would be screaming the whole way, lol.

Also keep in mind your tire diameters. We have a half dozen e30s running locally. Some are running 175/65/14 gravels, others are using much larger BFG all-terrains, and the rest are in between. Tire height can have just as much effect on gearing as your diff ratios.....so figure out what tires you're going to run first: snow tires? all-terrains? rally/gravel tires? 14" sizes have limited selection if you're going to run stock bottlecaps/weaves so you may not be able to get THE size you want in THE tire you want in many cases.

Lol! I could imagine it now, sitting at 4800 rpms at 80 in 5th.

The wheels are 15s, and the tire size is a 195/65 so that's where my previous calcs came from.

I'm excited to try out the z3 rack I've recently acquired. Have you heard anything good about the koni str.ts? (Orange). I can get a full set for ~$200 but if they are garbage I'll just pick up some bilsteins for the time being. (Until I decide to drop a few g''s on some JVABS)

Also, I saw some Maxxis gravels in medium compound for about $150 a piece which isn't horrible.

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formyhealth

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Robert Culbertson
So is the idea with the 4.1 or 4.44 diff is to run 1st-4th?

2nd (2.02:1) seems a bit too tall to launch in, even with a 4.88 or 5.whatever. Maybe the mighty m42 has enough power. I know the Volvo doesn't have enough oomph to launch a 1.93:1 with a 4.88 unless it's on snow.

The spread from 2-5th does look nice for a 4.88+ though. Really nice.

So with a ~6500 stock redline and 4.44s, 2nd gear shows me ~54 mph and a theoretical top speed of ~134 (which I'll never hit in rally-x).

I don't think that a 2nd gear launch is totally out of the question. 5.44s would be FUN anyway.


What kind of HP does to Volvo put down?

The Volvo puts down 95hp at the wheels... maybe. It revs to 8k with a junkyard bottom end with ~ 200k miles on it.

I keep on forgetting that you're doing grass-o-cross instead of stage. 14in tires snows and go have some fun. I fully agree that there are many places to gain speed before you drop money on lower gearing.

Also, rock whatever blown out struts you have on the car currently. You'll be amazed at the speed you can carry when you never lift.
Or upgrade to some Bilstein HDs. Inverted struts are way stiffer and stronger than non-inverted struts.

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Robert Culbertson
Also, rock whatever blown out struts you have on the car currently. You'll be amazed at the speed you can carry when you never lift.
Or upgrade to some Bilstein HDs. Inverted struts are way stiffer and stronger than non-inverted struts.

Hahahaha! Sounds like a plan, I figure I'll try out as soon as I finish with the poly bushings and steering rack, sitting in garage right now.

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formyhealth

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irish44j

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formyhealth

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Robert Culbertson
So is the idea with the 4.1 or 4.44 diff is to run 1st-4th?

2nd (2.02:1) seems a bit too tall to launch in, even with a 4.88 or 5.whatever. Maybe the mighty m42 has enough power. I know the Volvo doesn't have enough oomph to launch a 1.93:1 with a 4.88 unless it's on snow.

The spread from 2-5th does look nice for a 4.88+ though. Really nice.

So with a ~6500 stock redline and 4.44s, 2nd gear shows me ~54 mph and a theoretical top speed of ~134 (which I'll never hit in rally-x).

I don't think that a 2nd gear launch is totally out of the question. 5.44s would be FUN anyway.


What kind of HP does to Volvo put down?

If you're planning to drive to events on the highway, 5.44s would be so not fun.....Not sure how close you are to your venues though. We truck 2 hours into the mountains for ours and are moving around 80mph. M42 with 5.44s would be screaming the whole way, lol.

Also keep in mind your tire diameters. We have a half dozen e30s running locally. Some are running 175/65/14 gravels, others are using much larger BFG all-terrains, and the rest are in between. Tire height can have just as much effect on gearing as your diff ratios.....so figure out what tires you're going to run first: snow tires? all-terrains? rally/gravel tires? 14" sizes have limited selection if you're going to run stock bottlecaps/weaves so you may not be able to get THE size you want in THE tire you want in many cases.

Lol! I could imagine it now, sitting at 4800 rpms at 80 in 5th.

The wheels are 15s, and the tire size is a 195/65 so that's where my previous calcs came from.

I'm excited to try out the z3 rack I've recently acquired. Have you heard anything good about the koni str.ts? (Orange). I can get a full set for ~$200 but if they are garbage I'll just pick up some bilsteins for the time being. (Until I decide to drop a few g''s on some JVABS)

Also, I saw some Maxxis gravels in medium compound for about $150 a piece which isn't horrible.

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)

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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.