I have a 91 gmc sierra extended cab, short box, with a 350. I'm looking to get a big power boost. Would a turbo help or not. I am open for any suggestions also.

A new computer would help a lot. A westers tune would boost your rear wheel hp by about 30-35. It would also help your gas milage. Also if you do get a turbo or super charger later then you can have your tune re-tuned to get the most out of it.

boring the cylinders gives a little power but all 8 add up to a lot of power.

IF you add a turbo to your 350 it could possibly blow your engine. If you really want power rebuild your engine and make it a 383 stroker.