It’s probably the most expensive option for 200+hp, short of an S14, if you’re paying a professional. If you’re able to do the fabrication work yourself, you can do a good job with wiring, you understand enough about how an engine runs to tune it yourself, and your engine is still in good condition, you could probably do it for ~$5k.
I promised myself at the beginning of my 2002 project that I’d never total up what I spent on the car, so I can’t give you a precise number, but I went the route of paying a professional, and it was probably closer to $20k. I had him convert to fuel injection first and add the turbo later, and I bought a lot of the parts myself, so the total was spread over two years. A stronger clutch is probably something to budget in, but I did that with the 5 speed during an uncommon bout of foresight.
The main challenge for either approach is finding a good exhaust manifold. There’s a guy on another forum that makes one, an eBay China special, or custom. I chose to go with the latter as my mechanic was in the process of building a jig to aid fabrication for some other customer turbo cars anyhow. Not sure that would’ve been a viable option for me otherwise.
Then you need to be willing to do some cutting of the nose. My radiator was moved a few inches to the driver’s side, and a hole was punched through the core support for the air filter. The valence was cut so an intercooler could be installed behind a turbo style air dam as well. My car is far from pristine, so this didn’t bother me, but I’d struggle with doing the same thing to a nice car.
A stock engine will make 180hp/200tq at the rear wheels with just 10psi, or 160/160 at 7psi.That’s almost enough for such a light car. Note how broad the torque curve is.
I’m confident this would be reliable power for many years on a low mileage stock M10, but my motor was tired, and the turbo made that more obvious (blow by pressure in the block is pushing oil out all the seals), so now I’m waiting on parts for an engine rebuild. I’m going for a stout build that’ll allow for more boost if I want it, but will be specced pretty close to a mild street build. I-beam rods, 8.75 or 9:1 compression forged pistons, some port work, a turbo cam grind (higher lift, but lower duration than a 272), and an o-ring head gasket. I’m hoping the cam, and port work will gain a bit more 5k-7khp with the same boost levels, but I’m content with current torque, and from what I’ve read, 200lbft is about the limit for what the 245 trans, guibo, and e21 lsd can reliably handle. I don’t really want to test this, and take on the added expense and weight of moving up to the 26x trans and medium case differential.
As is, boost is immediate above 3.5k, and comes on just above 2k. Very streetable, usable power and the car will easily keep up with traffic on the freeway. On a track, it still feels underpowered vs most of the modern cars that run at local DE events, but still a massive improvement from N/A and pretty fun.