You would probably gain around 20 hp, 30 or 35 ft/lbs of torque. You would not gain 45 hp, that's like gaining an hp per added cubic inch. That kind of gain would not be seen on an otherwise stock motor. You need all the complimentary parts to let that motor breath. Bigger heads, cam, intake, free-flowing exhaust... Simply upping the displacement won't give you very big gains.
Yeah what 67stang390 said. You wont see huge gains but I think you'll see more torgue than anything. If your on a budget like most of us. Start out with a 347 and get the stock stuff ported. That way when you do get heads, cam, and intake. You'll notice better gains with each additional mod.
I don't even know if 20rwhp will be seen, unless the stock shortblock is in really bad shape with lots of blow-by. Your peak numbers will more than likely drop in rpm a good bit as well. Like was said, if you have to replace it anyway, its not a bad idea, but don't expect much at all.
You would probably gain around 20 hp, 30 or 35 ft/lbs of torque. You would not gain 45 hp, that's like gaining an hp per added cubic inch. That kind of gain would not be seen on an otherwise stock motor. You need all the complimentary parts to let that motor breath. Bigger heads, cam, intake, free-flowing exhaust... Simply upping the displacement won't give you very big gains.
In 2005 Im going to go w/ a 331 Stroker Short block from DSS Racing. Only reason b/c I plan on putting alot of power to the rear wheelsw/ a power adder and I dont want any issues w/ my current block that is creaping up on 120,000 Miles. A 331 Short block is about $2,500, TW Heads $995, TFS Stage 2 cam $150ish, and I already have the Intake done, plus ods and ends like water pump, harmonic ballancer, and timming chain. So over all you will save money building a Short block VS a Long block. If I were you I would mod your current motor, Heads, Cam, Intake and then upgrade to a 347 or 331 if you feel like you need to.