BMW 3.5 Z finally begins in earnest

[alternativez]

Well, last night I slid the engine and 5 spd trans (from my 85 635) into the Z. It almosts fits without alterations. The hood lies on the distributor and the intake plenum, so I need to figure out how to get the front down a couple of inches as it sits or move it all back 2 or 3 inches so it will drop down an inch or so. I see options right now of trying to lower the Z steering rack, exploring cutting into the oil pan to remove a few inches across the lower front, or cutting into the firewall. There may be other solutions such as changing the hood, but those are the most obvious. Lowering the rack poses a small problem with the steering shaft universal joint and the cross member, and who knows what else would be compromised in the steering, so I'm not liking that one. Cutting into the oil pan would only be possible if the crank allows it, and even then it is not sounding like a great idea, so it looks like cutting into the firewall or doing some creative massaging with a body hammer may be the best and least invasive solution. I like that the engine would sit even slightly deeper into the body for better weight distribution. I like the placement of the shifter, I think; although I haven't reattached the linkage, it looks like it will come out exactly where it used to or a little farther back where I would prefer. I want it to fit as high as possible, so I can use a short shift kit and cut down the stick to move more like a toggle than a lever.

There is plenty of extra space between the front of the engine and the front framing where the radiator would be mounted. There is still the question of fitting power steering, but I think I will leave that as a later contingency . The Z rack and pinion was very responsive and wasn't very heavy at slow speeds, as I recall, but I have gotten spoiled by power. I wouldn't mind not having that entire system however; it is just more weight, more clutter, more work, and more things to leak, and I am not sure what power rack would fit. AC should be no problem, I may have to move the compressor upwards very slightly, but that shouldn't be too difficult. Again, one of the later stages of the project. I could live without AC if necessary, the Z has a great ventilation system, but I want the comforts of a really nice car. Since there is so much room in front of the engine, I'll probably dispense with the stock viscous clutch cooling fan and use an electric pulling fan on the engine side of the radiator.

Looks like plenty of room for working on everything, and plenty of room for a supercharger...

I'm anxious to get the entire car with engine up off the ground, so I can get under and see how everything else will fit, design mounts, etc. Pretty exciting. I think it will work. I can feel it accelerating out of a corner already. Later, Jim

[AChev]

Wow, creative idea jim. I love hearing about new things people are doing with the Z cars, inovative minds at work. I'm sure the 635 engine will be nice, producing plenty of torque. Good luck with your build, continue to update, im anxious to hear about it, as I am a Z and a BMW guy like you.

P.S. I am sure a few people will telly ou this so I'll just get it done in the first post. Over at hybridZ they will be more interested then some here will be, because they focus purely on swaps and other modifications. I would like to continue hearing about your journey though

[jmortensen]

Lowering the rack poses a small problem with the steering shaft universal joint and the cross member, and who knows what else would be compromised in the steering, so I'm not liking that one. Cutting into the oil pan would only be possible if the crank allows it, and even then it is not sounding like a great idea, so it looks like cutting into the firewall or doing some creative massaging with a body hammer may be the best and least invasive solution.

Lowering the rack also changes bumpsteer. Could be used to fix bumpsteer in a Z if lowered the right amount since the rack is too high relative to the control arm pivots in the stock location, but could also really screw it up, and you'd really need to measure to get it right.

I agree with you that moving the engine back is the way to go if you can. I wouldn't be too worried about cutting into the oilpan if that ends up being the easiest solution. Look at how shallow it is at it's most shallow point. You can go that depth all the way across if you have a dry sump. The only reason for the sump is that it is a sump and it stores the extra oil. If you had to really modify it and lost a whole lot of capacity you could add "wings" to it like a Nissan Comp oil pan to get back the capacity.

[alternativez]

Hey thanks for the thoughts, guys. Yeah, I posted at HybridZ also. I've been around there for some time, too, mostly just cruising. These and Roadfly E24 and 2002 are favorite forums. I appreciate the mention of bumpsteer, as I am planning to lower the Z a bit, and wondered of the combined effects of lowering chassis and then lowering the steering rack. Still, it does seem a last resort to screw with steering. I've sat on this Z for over 15 years through many other past and current projects, and it's just now things may be falling together to do it, but time and $$$ are scarce commodities.

[bemmerguy714]

good job man. i got alot of respect for u now. Great idea!!! keep me updated! i definatilly wanna hear all about this!!!!!!! BMWs guts in a z!!! genius!!!!! :cheeky: :cheeky: :cheeky: :cheeky: :cheeky:

[alternativez]

Thanks, It's working out pretty well so far. Actually by removing the steering rack I was able to shoehorn the engine et al into a proper position without surgery. I as amazed. I will massage the front top of the tunnel for s slightly better angle and more clearance, but that is no big deal. Shifter is in the original hole. Now just have to deal with the rack. I'm a patient person, and the answers will come, often so simple and convenient, if you go at it from a Zen perspective. I think I can cut the engine mounting points off the 6er crossmember weld them directly to the Z crossmember and also devise a way to bolt them to the frame rails and the stock 6er mount bushings will work. This would add strength to the structure as they would work as a gusset or brace without adding much weight. I hope to hear more from jmortenson about the bumpsteer and moving the rack, btw, that was a great FYI article! You out there? If I lower the car about an inch, will moving the rack about an inch downward have a positive or negative effect on the steering geometry? I could possibly alter the front of the oil pan, but again, it's a wait and see situation, before I do anything drastic. Gotta set the diff in and get things lined up first. Bought a small welder at a garage sale this morning, just to be able to tack things up for a real welder. Thanks again guys. This is so cool. Jim

[Arne]

If I'm visualizing this correctly, lowering the rack will make the bumpsteer worse, not better. When you lower the car, you are already lowering the rack (as well as the rest of the car) in relation to the wheels. Lowering the rack will make that worse.

[e_racer1999]

^^that's what i was thinking.... i think that the dry-sump idea would be the best idea, provided it will allow more clearance in the area that you need it.

[jmortensen]

If I'm visualizing this correctly, lowering the rack will make the bumpsteer worse, not better. When you lower the car, you are already lowering the rack (as well as the rest of the car) in relation to the wheels. Lowering the rack will make that worse.

I don't think so. Bumpsteer isn't about the rack getting lower or higher in relation to the ground as the suspension moves through the travel. It's about getting the angle of the control arm equal to the angle of the tie rod. Lowering the rack the right amount will make the bumpsteer better. Think about it this way: if you raise the control arm pivot you can make the bumpsteer better. So that means that the control arm pivot is too low in comparison to the inner tie rod. So options are to lower the rack or raise the pivot. This graphic from Rob might make it clearer. I know it helped me when I managed to confuse myself... http://forums.hybridz.org/attachment.php?attachmentid=155

The downside to lowering the rack is that you can't later raise the control arm pivot. A closely related issue to bumpsteer (on a Z anyway) is roll center. The roll center is such that when you lower the car more than a couple inches it gets too low and actually goes below ground. A roll center below ground increases body roll. You can mitigate that issue with "bumpsteer spacers" which are really "roll center raisers". One issue with bumpsteer spacers is clearance for the wheel. You can't just keep adding bigger spacers because of tie rod to wheel clearance issues, which is why you can buy different heights of bumpsteer spacers for 14 and 15 inch wheels.

So everything will be fine in your BMWZ if you leave it near stock ride height. You can choose to lower the rack and actually improve the bumpsteer in doing so if you lower it the correct amount. You'd need to measure the bumpsteer while you lowered the rack to get it exactly right. Or you could conceivably use the JTR method and just lower it 3/4" and it should be in the ballpark. If you decide you want to lower the car a lot you may run into issues with the roll center, which means stiffer springs to control the body roll and the $$$ struts to handle the spring rates if you're feeling racey. If you haven't already looked, it's not going to be real easy to move the rack.

If your plan is to lower the car 1" and drive it on the street, I'd say don't mess with the bumpsteer at all, and cut the oil pan to gain clearance at the crossmember, especially if you're not going to race the car.

[alternativez]

Hmm, very good stuff. Thanks guys. These thoughts have been running around loose in my head, so to read this discussion helps to clear things up. I did appreciate Rob's graphic, and lying under the car last night put some more of this into perspective. Of course I really don't want to mess with the steering, and true, the rack relocation isn't the easiest thing to do, but I was just wondering from the perspective of combining the ride height and relocating to acheive a positive effect.

The sump of the pan isn't a problem actually;it fits pretty well right behind the crossmember; it's just the area directly in front of the sump, below piston #1. The pan isn't at its least depth there, but I can't remember what exactly is in that area of the pan, and I'm thinking lopping off a bit of the pan could be problematic because the pump may be right there, but it's been a while since I've had the pan off one of these. Gotta get out the books. Now you've gotten me thinking again, less pan depth, lower engine, more room for play, hmm...it's nice to have intelligent people to ponder ideas with. Thanks, Jim

[bemmerguy714]

how about an update on the project! keep us posted. some pics wouldnt hurt either.

[nixcars]

Jim,

Try this out, how about placing a spacer between the x-member & the chassis rails where it bolts up to... then to rectify bumpsteer, buy the spacers that go between the strut & steering link... this will do the trick.

Nick.