24V AWD Swap Knowledge Base

[The Dark Side of Will]

the only real problem is the tie rods.

No, it isn't.

The *LENGTH* of the rack--distance between inner tie rod pivot centers--is important to bump steer. It's not as important as the vertical position of the rack, but it's important.

[The Dark Side of Will]

Well this turned ot to be interesting :) I can measure what you want!

Basically... how far forward does the engine have to move in order to be out of the firewall? How far forward of where it sits now would you want it to be in a finished swap?

That's pretty much the only thing I need to know in order to figure out how far to move the rack.

Meanwile i took this apart a little more:

Cool!

Btw, what do you think about just lowering the subframe like 5mm? Would that change any geometry too much?

Wouldn't hurt... the M60 swap guys frequently do it... but wouldn't help anything either. Like Nando said, the pan would still hit the rack.

[LJ851]

Will, how far does your analytical approach say you could move the rack forward or backward before the arc of the tie rod differs from the control arm enough to cause bump steer?

Another consideration is the multiplication of side loading the rack will see with increased angle on the tie rod.

[nando]

No, it isn't.

The *LENGTH* of the rack--distance between inner tie rod pivot centers--is important to bump steer. It's not as important as the vertical position of the rack, but it's important.

it's not that much different. the stock ix tie rods would almost work but you'd have no adjustment left for dialing in toe, etc.

[The Dark Side of Will]

Will, how far does your analytical approach say you could move the rack forward or backward before the arc of the tie rod differs from the control arm enough to cause bump steer?

Another consideration is the multiplication of side loading the rack will see with increased angle on the tie rod.

To visualize what I'm talking about, go find a graph showing the two arcs. This will invariably be a projection in front or rear view. You can see that moving the rack into or out of the page would have no effect on bump steer. My only tweak to that assessment is that the view projection isn't necessarily a straight front of back view... it should be perpendicular to the plane of the control arms, which can be something other than level if the suspension has anti-squat or anti dive geometry.

The real world is less cut and dry. For example, if the lateral separation between the inner ball joints is different than the lateral separation between the lolipop bushings, then the control arm pivot axes are not parallel (I don't know if they are or not... I haven't measured yet). This means that moving the rack fore/aft would also result in some change in bump steer, but still not as much as moving it up or down.

As we discuss this, I'm talking myself into making the rack mounts shimmable.

it's not that much different. the stock ix tie rods would almost work but you'd have no adjustment left for dialing in toe, etc.

ANY difference will lead to bump steer. You should be able to shim the height of the rack to minimize bump steer around your ride height, but it will increase as you get away from your static ride height.

Anti-dive: I'm not sure if a RWD E30 has anti-dive or not, but much anti-dive on the front end of an iX can result in front end wheel hop on hard launches.

[nando]

Ok. So does lowering your car or moving the rack around (potentially). The question is how much? Because the e46 rack would work without moving it forward.

[The Dark Side of Will]

Because the e46 rack would work without moving it forward.

That doesn't pass the smell test for me... based on Nisse's photos.

[nando]

I mocked it up a few moths ago. Its wider so the diff doesn't hit it.

here's the E30 rack:


diff is all sorts of into contact with the rack. the engine is way back in this pic too.

E46:


engine is still about 1/4-1/2" back than the M20 at this point, but that's probably doable without messing with the firewall:


also if I cut those "nubs" for the spash guard off I could move it forward a little bit more.



what I'd really like is a bellhousing face to subframe measurement for the M20 ix to see how this relates to the stock engine placement.

here's all my mockup pics:
http://www.325ix.com/photos/index.ph...Engine_Mockup/

[LJ851]

Will, I think you are forgetting I think that the steering arm is not moving during the rack movement. The further you move the rack forward or back changes the front to back angle of the tie rods and which changes the shape of the arc the tie rod ends will travel in. If you move the rack forward 6 inches you will have bump steer out the ass.

The end answer is still the same in my book though, measure the bump steer before you commit to a rack location.

[Nisse Järnet]

Basically... how far forward does the engine have to move in order to be out of the firewall? How far forward of where it sits now would you want it to be in a finished swap?

That's pretty much the only thing I need to know in order to figure out how far to move the rack.




Cool!



Wouldn't hurt... the M60 swap guys frequently do it... but wouldn't help anything either. Like Nando said, the pan would still hit the rack.

I can mesure this tomorrow!

[Nisse Järnet]

I mocked it up a few moths ago. Its wider so the diff doesn't hit it.

here's the E30 rack:

http://www.325ix.com/photos/index.php?action=resize&file=2013/S54ix/Engine_Mockup/12-06-2013/CAM01150.jpg

diff is all sorts of into contact with the rack. the engine is way back in this pic too.

E46:

http://www.325ix.com/photos/index.php?action=resize&file=2013/S54ix/Engine_Mockup/12-06-2013/CAM01151.jpg

engine is still about 1/4-1/2" back than the M20 at this point, but that's probably doable without messing with the firewall:

http://www.325ix.com/photos/index.php?action=resize&file=2013/S54ix/Engine_Mockup/12-06-2013/CAM01152.jpg

also if I cut those "nubs" for the spash guard off I could move it forward a little bit more.

http://www.325ix.com/photos/index.php?action=resize&file=2013/S54ix/Engine_Mockup/12-06-2013/CAM01155.jpg

what I'd really like is a bellhousing face to subframe measurement for the M20 ix to see how this relates to the stock engine placement.

here's all my mockup pics:
http://www.325ix.com/photos/index.ph...Engine_Mockup/

If you put the E46 rack centerline in the same spot as the E30 rack, would you still gain some room between the rack and oil pan? If so, du you have any idea of how much? Rear and up?

I might be able to get the measurment you want :)

[nando]

yes, that's what I did. the engine is still a little back from what I believe to be the original M20 position, but it's within 1/2" instead of 1 1/2"+.

you have to bend one of the pipes that goes into the rack to make it sit in the right spot, and actually you'd have to make a pocket just under the steering knuckle in the subframe to make it sit flush but you can still get it close enough to figure out if it will work or not. I believe it will.

if moving the E46 ix rack 1/2" is on the table (assuming bump steer isn't terrible), you should definitely be able to make the engine go far enough forward to miss the firewall. but moving it forward on the stock subframe is problematic because of how it passes through where the subframe mounts to the body, which is why I just put it in the original location.

[Nisse Järnet]

yes, that's what I did. the engine is still a little back from what I believe to be the original M20 position, but it's within 1/2" instead of 1 1/2"+.

you have to bend one of the pipes that goes into the rack to make it sit in the right spot, and actually you'd have to make a pocket just under the steering knuckle in the subframe to make it sit flush but you can still get it close enough to figure out if it will work or not. I believe it will.

if moving the E46 ix rack 1/2" is on the table (assuming bump steer isn't terrible), you should definitely be able to make the engine go far enough forward to miss the firewall. but moving it forward on the stock subframe is problematic because of how it passes through where the subframe mounts to the body, which is why I just put it in the original location.

Ok sounds good! The only problem with this is that the CVs will probably hit the subframe At least on the passanger side.

[The Dark Side of Will]

The further you move the rack forward or back changes the front to back angle of the tie rods and which changes the shape of the arc the tie rod ends will travel in.

Not in the front view projection.

Case in point:



You can move Point B into and out of the page all you want (within reason) without affecting bump steer.

I'm going to have to weld something up to get it into the car to measure bump steer... so the production process pretty much looks the same either way to me.

Also, this article talks about how to calculate ackerman: http://www.autospeed.com/cms/article...le-Part&A=3039

[The Dark Side of Will]

what I'd really like is a bellhousing face to subframe measurement for the M20 ix to see how this relates to the stock engine placement.

here's all my mockup pics:
http://www.325ix.com/photos/index.ph...Engine_Mockup/

I should be able to get that measurement this weekend.

Don't forget that the ANGLE at which the engine sits has a lot to do with fitment. If Nisses didn't need a transmission, he'd have been able to install the engine without cutting the firewall ;)