Duke's advice is good. I have a 3.5 with mild mods in my car now -- 10:1 pistons, Schrick 282 with Schrick springs, chipped Motronic. It's only a little stronger than a stock Euro engine. I have the receipts from the PO for that build, it was upwards of $4k The engine started life as a 3.3, so the machine work was a larger part of the bill than normal.
There is a lower threshhold for any kind of engine work; just the basics of bearings, rings, gaskets, valve seals, water pump etc. will get you to $500 or so. The cost ramp for building serious NA power is steep from there. Look at the prices from Metric Mechanic and Korman.
I'm doing what Duke suggested for my first turbo. I found a wrecked 745i cheap, sold off everything I could and was left with the M106 and all the turbo goodies for approximately free. As of now the budget is looking like about another $2k to have it in the car and running. Some of that is things like a nice Spec clutch, and of course the aforementioned $500 of basic rebuild parts. Some of it is things that would cost less with a TDC manifold -- like a modified stock BMW wastegate, because mine is too far gone to save. If I could use a stock TiAL or the like, I'd only have to spend $250 instead of $500.
If I had a stock 3.5 instead of the 10:1 engine, I would just drop on the Turbo head and save the cost of the bottom end rebuild. It's too bad, because my NA engine only has about 20k on it. Oh well, guess I'll have to stick it in my e9..
Regardless, I'm getting a bargain. I plan to run conservative at around 12psi, and will hopefully see almost 300whp. I'm realistic about the capability of the BMW turbo gear. I know Duke is not losing any sleep, but for the first project, it will be a nice kick in the backside and a good way to learn.
Besides, I'm waiting for Sweeney to perfect the twin turbo setup...
