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

[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]

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.

[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]

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]

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]

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]

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! :)

[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..

[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]

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

[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" :)

[The Dark Side of Will]

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

http://www.lmgtfy.com/?q=how+to+measure+bump+steer

[The Dark Side of Will]

Well, I've dropped the front subframe in my cabrio by 20mm, and on top of that lowered the car by ~80mm.

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" :)

As I've said before, all that does is change the point on the stock bump steer curve at which the suspension operates.

If the rack is moved relative to the ball joints, the shape of the curve will change... and without knowing what the curve looks like beforehand, there's no way to know what it will look like afterward.

BMW chose the stock rack position because it was the best position they could find to minimize bump steer over the full range of suspension motion. Anything you do with the rack is going to make bump steer worse.

You're looking only as the best case scenario and saying that the whole pie isn't so bad.

[Turk]

I unfortunately don't have a car to measure required on. If someone can measure the lengths of the rods and draw a diagram in paint or such, I can then post the results of the bolting up.

[Jonsku]

As I've said before, all that does is change the point on the stock bump steer curve at which the suspension operates.

If the rack is moved relative to the ball joints, the shape of the curve will change... and without knowing what the curve looks like beforehand, there's no way to know what it will look like afterward.

Ahh, you should've said that in the first place! ;) Or then I just didn't get it.


Anyway, isn't it so that also in this case the rack position will be changed "together with the subframe". Meaning, that the bump-steer curve will not change, after all..