E30 M3 S62 Build - Loads of queries about 4x4 drivtrains

[Jonsku]

A centimeter or two is a large amount to be moving the rack around... It's a ridiculous amount to be moving the rack around with no analysis or measured data relating to the car's existing bump steer situation.

Well, I've dropped the front subframe in my cabrio by 20mm, and on top of that lowered the car by ~80mm. I can notice the difference in the bump-steer, but it's nothing disturbing or anything, just a small change in the behaviour of the car. Not optimal for the track, but what the hell, either is the car.

In real world, such small things do not require any further analysis / measured data. Real track cars / competition vehicles are totally different thing. "Hobby-E30" is very far from those kind of vehicles...


Instead of being scared of moving the rack around by couple of centimeters, lets just concentrate on the real problems such as "how to fit the engine" :)

[nando]

well, instead of endless debating - how would one measure the bump steer curve?

[The Dark Side of Will]

No, one shouldn't "throw away" performance, but what one should do is realize that there are much bigger problems in the swap than offsetting steering by a centimeter or two..

A centimeter or two is a large amount to be moving the rack around... It's a ridiculous amount to be moving the rack around with no analysis or measured data relating to the car's existing bump steer situation.

maybe the bump steer will get *much* worse with the E46 rack - maybe it won't. I don't know. I don't think anyone can really say without trying it..

This is my point. Not only do you have no idea what you have now for bump steer, but people are proposing mods without any ability to analyze what effect those mods would have on bump steer.

Until someone *measures* the bump steer, we won't know what the car has stock or lowered. Without a plot of the shape of the stock curve, none of us have any idea what moving the rack around will do to the bump steer.

It's the blind leading the blind saying "Yeah, that ditch can't really be very deep"



Less suspension movement means less effect from bumpsteer, but not everyone wants to ride around on 700# springs

[nando]

that was basically my point. of course it affects bump steer. so does lowering my car almost 2" - but I haven't noticed any *real* change in bump steer, and the car still drives very well.

I've got an E46 XI rack sitting at home. still don't know if I want to use it or not. the stock ix rack does work fine, but with the slow stock E30 steering ratio, you have to adjust your driving style to suit.

maybe the bump steer will get *much* worse with the E46 rack - maybe it won't. I don't know. I don't think anyone can really say without trying it..

[Jonsku]

It's not going to be as nimble as a 4 cylinder E30, that's for sure

However, that doesn't mean it's ok to throw away performance elsewhere in the build...

To me it comes across as though your expecting this car to become a show queen or cruise night hero and no longer be the ultimate driving machine.

No, one shouldn't "throw away" performance, but what one should do is realize that there are much bigger problems in the swap than offsetting steering by a centimeter or two..

I've to be a bit skeptic on "ultimate driving machine", but for sure it will be very interesting to see what comes out of this project! :)

[The Dark Side of Will]

It's not going to be as nimble as a 4 cylinder E30, that's for sure

However, that doesn't mean it's ok to throw away performance elsewhere in the build...

To me it comes across as though your expecting this car to become a show queen or cruise night hero and no longer be the ultimate driving machine.

It seems to me that anyone with the funds and the good sense to buy an E30 M3 in the first place is going to want to do the build right.

Although I'm not using an M3 body (well... yet) that's certainly how I'm going to do mine...

[Jonsku]

I'm not over-reacting. I'm apparently the only one who understands that single millimeter adjustments matter.
If it's not that important, why does every purpose-built racecar have bump steer adjustment to account for production variations in chassis dimensions, which are on the order of 1 mm?

The small optimizations are what really make the difference between a well-sorted car and an assemblage of hot-rodded parts.

The swap has enough problems to solve without making more along the way.

Of course 1mm makes difference in car behaviour. But, the question here is that "does it really matter?"

"Self-made AWD" E30 with S62 is very far from a race-car, no matter how or where you look at it. There's no way you can make it handle even remotely "like a race-car", due to the physical constraints the swap imposes. That is a fact you have to acknowledge when starting this kind of swap. The handling will not be as good as when it was before the swap..

If you want a well behaving E30, stick with M42 / S14 or go with M54 / something similar (light, doesn't require "any" body modifications).

[The Dark Side of Will]

Increased bump-steer will not affect the cars drivability too much compared to e.g. E30's that have been lowered by 60mm in the front. i.e. your E30 driving charasteristics will be roughly the same, depending on the total change in the angle, of course.

Yes, you need to be aware that bump-steer will increase, but on the other hand you've much bigger problems to solve. Don't give a shit about the small change in bump-steer, Will is way too overreactive on that..

I'm not over-reacting. I'm apparently the only one who understands that single millimeter adjustments matter.
If it's not that important, why does every purpose-built racecar have bump steer adjustment to account for production variations in chassis dimensions, which are on the order of 1 mm?

The small optimizations are what really make the difference between a well-sorted car and an assemblage of hot-rodded parts.

The swap has enough problems to solve without making more along the way.

[Jonsku]

Been going over this with the guys on E30 tech for MONTHS.

If you move the inner tie rod ends from their stock locations, you *WILL* create bump steer.

yes, I understand that. the question is, how much and will it matter?

but if an E30/E36 rack is the same width, it might make more sense to use that if you could make mounts.

Increased bump-steer will not affect the cars drivability too much compared to e.g. E30's that have been lowered by 60mm in the front. i.e. your E30 driving charasteristics will be roughly the same, depending on the total change in the angle, of course.

Yes, you need to be aware that bump-steer will increase, but on the other hand you've much bigger problems to solve. Don't give a shit about the small change in bump-steer, Will is way too overreactive on that..

[The Dark Side of Will]

The problem the driveshafts have now is that the splined shaft moves around in the splined sprocket, and if not lubricated correctly, this motion will cause both parts to destroy themselves. While there *are* plenty of applications which use slip yokes, those yokes are *FAR* more robust than BMW's splines. I think the fixed yoke conversion is the way to go because it completely eliminates the failure mode, rather than merely mitigating it.

Also, those splines weren't designed to handle high horsepower/torque. A fixed yoke with the longest possible spline engagement will help make the drive more robust at high power levels.

[Turk]

Why not have a spline immediately attached to one of the ujs? will still keep its single piece rigidity that way, and can allow for around 10mm movement max, One of the reasons other then the heat is the twist element the outer parts have experience due to mounting points etc. I think its defo a sensible and fairly simple addition.

[The Dark Side of Will]

I made the mistake of planting the idea in my Dad's mind of building my mom's car into the "first of kind" automatic S52B32 powered E30 iX, so I may yet build the fixed yoke myself, in which case I will thoroughly document it.

I can sketch a couple things up too.

I really don't think you want a manual rack in a V8 AWD E30... Not fun even with the M20 from what I hear.

Unless there ends up being serious interference with the driver's footwell, I'm expecting to use a one piece driveshaft with u-joints at both ends... although I'll have to build some plunge into it somehow. I may either use a CV at one end or find a plunging fitting to incorporate in the middle.

There "shouldn't" be any movement between the T-case and the diff, *BUT* the engine and transmission case are made of aluminum and climb by about 150 degrees F from cold start to operating temp... Being bolted to a rigid steel driveshaft that doesn't change temp as much and doesn't grow as much with the temp it does change will be a recipe for some eventual problems.

[Turk]

Those custom racks look interesting indeed :D Though I was having another play today and am beginning to think that the m3 rack may be a fit.

Could you do me a favour and measure from the centre of the rack 'body' to the upright of the knuckle/upright housing? Don't know if I've quite explained that properly but my brain has turned to mush and I can't remember the proper word :p

Part of me still thinks a manual rack might be the way to go. No banjos and a much skinnier set up. maybe something off of a 316 or such?

Are you going to create a 'centre bearing' for the front shaft? Maybe mount it to the sump, then a long spline to give some movement coupled through the bearing maybe?

Have you drawn up any diagrams of your fixed yoke theory? though i think I know what youre saying I'm struggling to picture it.

[The Dark Side of Will]

This won't affect my build, but might be useful to you if you're using the E34 T-case.

I just had a *duh* moment regarding my proposed "Fixed yoke conversion" for the front output of the E30 and E34 T-cases.

I had been thinking that the yoke itself would have to be made from scratch, which would be an effort that is not inconsequential.

However, I realized that the yoke could be made using only the front end of the ruined driveshaft. Since the driveshaft would be scrap anyway and is probably already in the car, it's available essentially for free.

The fitting would be made by parting off the shaft 4-5 inches (whatever depth is required to bottom out the yoke in the front output sprocket) from the front differential flange. The 4-5 inch section would be splined to take advantage of the full length of spline engagement in the front output sprocket, drilled axially and tapped.

The T-case would be disassembled and a hole drilled in the back of the front output sprocket, along with a corresponding hole in the rear case half. The T-case would be reassembled. The yoke would be installed and secured into the sprocket with a bolt that would be installed through the hole in the rear case half.

I haven't figured out *exactly* how the hole in the case half could be sealed yet, but there are enough, bungs, fittings, plugs and caps on the market that something relatively simple could be bought and installed. It would probably be necessary to weld the bung to the rear case half, but that's not a big deal.

[The Dark Side of Will]

The only way in which the clearance to the sump and rack should be a problem is if the engine is as low as it can be over the rack and the bellhousing is still too high. I'm pretty confident in all the other clearances in terms of engine size and position.

If you get the engine as low as it can be over the rack, then the lower oil pan WILL hang below the crossmember.

The interference between The spool valve on the stock iX rack and the E53 diff is the only thing that's keeping me from having a fully assembled mockup right now.
As I said, I have a strong idea about how to fix that.

The E46 rack pushed the spool valve too far to the left. It would still interfere with the diff unless rotated forward, would interfere with the mount tower if rotated forward, required a chunk to be cut out of the crossmember immediately below the spool valve and required a mount adapter that would have raised the rack and affected bump steer.

Gordon Murray said that the automotive problem is fundamentally one of packaging. BMW's products are highly engineered and very specific considerations have been paid to getting everything to work right within the packaging constraints of the design. This not only applies when reworking the iX design, but when adapting other production components to the iX system.

For example, because of the way the crossmember is designed, in order to move the rack forward, it would have to move forward 3 to 4 inches in order for the tie rods to pass the crossmember. Lengthening the steering arms at the hubs this much would slow the steering down dramatically, as well as perhaps not fitting inside 17" wheels. Moving the rack without lengthening them will change the ackerman angle of the suspension significantly... not a huge deal, but definitely a nuisance.

Fundamentally, if I am dissatisfied with the iX steering rack, I will commission an aftermarket company to produce a replacement identical in fit but with a faster ratio and different weighting.
For example:

http://www.mavalgear.com/unisteer.html

http://www.woodwardsteering.com/

http://www.titan.uk.net/steering.php

http://www.flamingriver.com/index.php/products/c0014/s0005

There might even be something workable in the Quaife catalog, although I seriously doubt they'd be willing to build just one...