Um 351's font have trouble spinning. but the fact is stock block for stock block the 302 block has a much lower power potential due to the fact that around 500hp they like to split down the middle. Now if you like to be limited to that kind of power you would have been better off keeping your 302, Getting some decent heads/ intake then supercharging/ spraying/ or turbo it. Bigger engines have bigger heavier rotating masses thats a given. But that doesn't really matter when you make it up in cubes. The 347 is at the 302's limit. He could later pull the 351 out and throw a 408 rotating assembly in it. Hell a 2.0 liter Honda has a lighter assembly but its about the potential. Get over the 351 hurdle now and you'll never regret it. Besides 351 will keep you fuel injected and you get to cross over into big block territory when stroked. Nothing like a 408ci 500+ hp motor on pump gas all motor. Get forced induction and you'll be making power on pump gas that a 347 only wishes.
We don't buy mustangs because they're the fastest sports car. We buy them for the potential.
Stock 351 has 408 potential "reliably" Dart blocks you can stroke it even further by another 50ci or so.
LOL so when he drops in his stock 351w shortblock and goes slower than the same parts on a 347....the potential of his 351w will make him feel better huh? I didnt say a 351w cant spin, it just eats up more power because its heavier. At such a close of displacement this matters when u have a stock 351w! Upgrade the rods/crank on the 351w and fine, its a new ball game.
Im not trying to convince you or anyone else of what to do, just simply pointing out things about every option. Not every person wants or has the funds to make a small block act like a big block. More cubes = better heads = more fuel = more $$$$$$$$$$. Im not saying a 351 doesnt have more potential, it obviously does. Im just pointing out some facts...thats it. Nothing more nothing less.
-A STOCK 351w shortblock will make an engine/car SLOWER than a 347 because of the rotating weight. The 351w could "feel" better, but the 347 car will run a faster time.
-Weights of stock and aftermarket rotating assemblies vary. You can get aftermarket parts for the 351w to lighten it up a bit, which then takes away my first point. 4 cubic inches will not make up the difference with a stock 351w. Just making sure no one over looks this fact.
-To go along with the previous post, not everyone wants a fire breathing turbocharged 408 cubic inch motor stuffed under their hood. Define your goals, decide which is the best path to get there. If his goal is a 400cubic inch motor, or even a 427, why are we even discussing 347s?
-302's have dart blocks also. Again...define your goals. Some guys are HAPPY with 347s. Some guys are happy with 427s. Some guys regret going as extreme in both cases. GOALS GOALS GOALS....define them carefully.
-People have said the roller ready 351w blocks are not as strong as the older ones. I believe if you search under Rick91gt's name he has said a 94-97 roller 351w block is only as strong, if not a little stronger, than a 302. Why do you think most aim for late 60's early early 70's blocks?
The right answer is different for every one of us. Some guys like the idea of having room to grow like you are describing, other guys want a high revving 306, other guys want the best of both worlds and opt for a 302 based dart block. I have had a 351w in my car. I have had a turbo on my 302. I cant imagine stuffing a 351 into my car WITH all the turbo crap. Is it possible? Yep. But space was a headache with a 302, so for me if i wanted to stay with a turbo, i'd probably either get a dart based 302 block or just say forget it, and get used 302 engines and keep blowing those up LOL