Don't turbo that engine, get an S54 in there.
Also, 136bhp to 400bhp with a turbo? That's going to drive like poop on track, surely?
No I don't want to swap the engine, the M20 has to stay. And its 170HP. These engines love boost. It won't be used on track aside from strip racing and I'll have high and low boost settings. Daily mode of about 300bhp I expect.