Ok guys my chevelle is slow. I got a 350 in there. I want to get a big block. Either a 427 or a 454. My dad says go with 427, he says this because he likes to rev up his engines and he said 454's dont rev as well. What would make more power? How about mileage? Also, he said a nice tight automatic would make the car faster then a 5 or a 6 speed manual. Whats everyone think?

Lots of questions there! Welcome to TC.

427 and 454 will make the same amount of power, the 427 will need another 500-800 rpm to match the 454 though, eg, the 454 may make peak power at 6200, while the 427 needs 6800, given the same camshaft. 427 should get better gas milage, all else being equal. 427 will want deeper gears to allow it to rev, while the 454 uses its torque to pull shallower gears better.

6 of one 1/2 doz of the other, just different flavors is all, and require a slightly different driveline setup.

BTW, 454s can rev too, just don't build revs as fast as the short stroke.

In today's modern world, tell your dad , if he has the scratch, get a 4.5" bore block and use a 3.76" stroke 427 crank for a really revvy BIG big block. Also the trend has been towards bigger and bigger big blocks, which mans they don't have to rpm well to make huge amounts of power, I'm talking 540 c.i. and up.

Lastly, the best I've run is around a 12.2x or so, with a soft 60' time ( deliberate) using a manual transmission. IMHO, I could put a T350 auto in( I prefer them to T400s at this power level), 3500 stall, and run real easy 11.90s. So, yes, more often an automatic is a bit quikcer at the track, while a stick car will top end better and give better ( 1-3 mpg we've seen) highway milage.

Although using an overdrive auto with a lockup converter evens the playing fiels between a stick car and an auto in regards to gas mileage.