Help choosing BMW project

So, I really enjoy having a car to tinker with, its always a great way to waste a weekend when you have nothing better to do. It gives you something to read about when your bored online or in a book store. And of course its always a great way to learn something new about a different sort of system/setup. I'm nearly finished with my 16v volkswagen setup, I really don't want to take the mazdaspeed apart, save maybe a few minor tweaks, and my sister will be needing a car to put around in, and throw down at the autocross events here and there. I have as one option a 90-93 Miata, but I've already a pretty good idea of what we'd like to do. Now, here I'll pitch my ideas so that you guys can educate me and point me in the right directions, etc. What I'm looking for is a later 89+ e30, or an early (first two years) e36, BMW 3 series. I would like the lightest chassis possible while retaining the best, or near best handling we can. I was thinking a 318, except am turned off by the e36's trailing arm vice multilink setup. Of course, the e30 has the multilink anyway. If it were a 318, e30 or e36, would it be possible to transplant an I-6 relatively easily, would you need motor mounts and brackets made, cut driveshafts, etc? Is it possible to transplant different drivetrain options to a 318, e30 or e36, such as the IS limited slip rear end, or possibly, somehow, the 325xi awd setup? From what I understand, the 325 and 318 are the same foward of the doors, for both chassis codes, so it could be possible, was my thinkin on this. Also, I understand there is an interesting I6 setup for the E30 using the 540TD crankshaft and a few other rotating assembly parts from different I6's to make a stroked 2.7 I6. That's all I really have thought about thus far.
Another thought is, obviously I have mentioned really 4 different chassis setups, the 318 and 325 of either the e30 or e36 codes. Most likely the e36 setups would handle best, with the 325xi most likely the best, and the 318ti not as good as a 325. At least, thats what I've gathered, but its a subjective thing, so without driving one I couldn't be sure. I was wondering what sort of upgrades are availiable to a e30's suspension, and will it handle as good as, say, a Miata without adjustable coilovers on about 350 275 spring rates and a set of bilsteins on a set of 215's and 16in rims? I would say that this would be a nice target, not crazy agressive, but above average handling.
I really hope I didn't make a fool of myself with this, thanks for the help. If anyone has a good place for me to do research, I'd appreciate it. Also, the idea would be to do a mildly comprehensive tear down of said vehicle, with a budget of 3-5,000 after car's purchase for upgrades. New bushhings and wear parts, new front end rebuild, etc, would be included, so it won't go that far I assume.

If you want a 6 cylinder car, it wouldn't make any sense to start with a 318...just get a 325 to start with and save yourself a lot of trouble.

The idea would be the 318 is smaller/lighter, hopefully being a benefit you otherwise wouldn't get in a 325.

'92 325 = M50 non-vanos.

There, wasn't that easy?

The base E30 car without the engine is going to be the same weight no matter what. I think they all came with sunroofs, and it's easy enough to swap manual windows into them.

The E36 guys make a big deal about the 'superior' suspension over the E30 but sometimes simplicity can work really well. Nothing wrong with the E30 rear design.

05rdstrturbo wrote: The idea would be the 318 is smaller/lighter, hopefully being a benefit you otherwise wouldn't get in a 325.

Welcome to real life. Just start out with a 325. What you're wanting to do is basically make your own 325, except yours will be much more likely to have weird little problems due to the motor swap. I recall reading that the best bang for the buck swap in a BMW involves an LS1....

Ok, so consider we start with a Bmw 325 E30, or E36. Should I be looking for an I, IS, or XI? I am leaning to the XI, but I understand the IS rear-end swaps into a base I easily, how would the handling be, and what sort of differential and transfercase is availiable with the XI model? Also, what kind of things can you do to get a bit better handling out of these (tires, wheels aside.) Anything uncommon, or pretty much straight forward matched springs/struts, bushings, etc. Any places on the chassis it would be a good idea to weld up to increase rigidity? I'm looking for ideas to start a small build sheet, so I can at least have a bit of direction.

Sounds like you want an E30. I wouldn't worry about I vs IS. The differences just aren't significant. Find the nicest one in your price range. I don't know enough about the XI. They are a bit tough to find. I guess that all depends on whether or not you want AWD. If you do, get an XI. If you don't, or don't care, go for an I/IS.

BMW has a habit of not making the rear subframes as stout as they could be. If you decide to start pumping out a bunch of power from an E30, the rear subframe will eventually tear. I've also heard things about the transmission mounts in the E36 getting sloppy later in life, and causing the car to pop out of gear.

You can swap big engines into the front of an E30. I went to a track day where the hands-down fastest guy was running an E30 with an S52 swapped into it. (And the driver was scary good, and had done a bunch of other tuning to the car).

Swapping diffs between BMWs is super easy. Actually, a lot of parts swap really well.

If you go with the E30, you can get a lot of great upgrades by sourcing parts from Z3s. The diff is the same as that fancy IS one, only with extra cooling fins. Also, there are a number of front suspension and steering bits that make great upgrades for an E30.

Edit: And for the love of god man! Paragraph breaks! Have you not heard of them?!?

The iX (the e30 model was called an iX, later on for the e46 cars they swapped it around to Xi) came with 3.91 gears with a manual transmission, 4.10 with an automatic. That's for US cars; I believe euro iX's had 3.64 gears. The iX had a viscous coupling in the transfer case that would automatically transfer power from the front to rear wheels as required. The rear differential also had a viscous coupling. You can read more about them at http://home.earthlink.net/~wardellhix/iX/general/iXfaq.html. Unless you're going rallying, I'd stick with the two wheel drive cars since the iX's are kind of hard to find, and there's not much in the way of aftermarket upgrades for them.

05rdstrturbo wrote: The idea would be the 318 is smaller/lighter, hopefully being a benefit you otherwise wouldn't get in a 325.

They're the same, EXCEPT for the E36 318ti, which is a kind of stubby sawed-off E36, with an E30 rear suspension under it (I think).

Someone has done a six-cylinder M3 engine swap into one, then supercharged it, and run it in One Lap. Forget the name, or how well it did. But IMO an E30 would probably be easier to find.

Great writeup on the Ix, thanks. I think it may be what we are looking for, but its hard to say. I haven't asked my sister if she would like to autocross or rally or what she really wants to do with the car, we just want to get a good performer to fix up, and a 3 series was the best choice we think. We would still be for an early OBD1 E36 in the right price range, but haven't heard much of what people can do to these things. I have seen that near everyone with an E30 on bimmerworld does the bilstein and H&R setup. I dunno, but for a miata, that would be a weak setup, really. Are there any setups that would net better handling than this? I would not like coilovers, since the car didn't come with them, it would mess with the design of the suspension, whcih I don't want to do. Thanks for the input so far, really good ideas