The 351 blocks are a little stronger than the 302 blocks, but not much.
Eh. 302 blocks, particularly the late roller blocks, are a gamble above 400 HP, and on borrowed time above 500. On the other hand, 500 HP with a main-studded 351 is considered mild, with a lot of guys doing 600+ without a second thought. Like any factory block, there are always large variations, but the 351 seems to be an honest-to-goodness 2-300 HP more stout than the 302.
The big advantage is that there is enough metal in the bottom to drill it for 4 bolt caps. 4 bolt caps walk a lot less which prevents the fatigue issues that lead to cracks in Windsor style blocks. With stock 2 bolt caps they really aren't much better than the 302 blocks.
The early W had enough meat for the conversion, but the later ones do not. Main studs with the proper lube and torque seem to limit cap walk enough for the late Ws to survive though. 351s have more meat, blind holes, bigger fasteners and bigger, thicker caps than the 302. The 302 with its smaller thru holes and paper thin mains just lack the reinforcement to reliably last under elevated power levels.
Don't get tied up in all the supposed hard hp figures each block can handle. What causes a block to crack has a lot more to do with how it makes power than how much it makes. 700hp out of 351 block is not atypical, but then again there are guys making 900 to the wheels with stock 302 blocks with big turbos and less rpm. RPM is the real killer. The higher and more frequently you rev it, the faster it will crack.
I agree, HOW you make the power has a lot to do with block survival, and RPM is hard on parts in general. You need to show me an example of these 900 HP stock 302 blocks though- that's a bold claim even for a Mexican or a B50!
I also wouldn't judge Ford for how they built each block. A 351 Windsor engine is not a performance engine like most people believe. It's a big heavy block that's got a lot more metal in it because it was designed to be a truck engine. It's designed to be a higher load more frequently. The 302 was also used in cars, and needed to be lighter for performance. The way they should have built a performance engine was to deep skirt it like their European counterparts were doing at the time. All modern performance V8s have deep skirts, where as the block rigidity in a Windsor style engine ends at the crank centerline. The larger performance engine of the time from Ford were the FE style blocks.
Kurt
Really, what probably should have happened, is they should have continued offering a 4-bolt version in the Windsor family like the early Boss 302 blocks. I could never quite wrap my brain around why they had the 4-bolt 351C, and then the 351/400M had (unused) provisions cast into the block for 4 bolt mains, and they even had engineering history with a 4-bolt 302, but they failed to ever offer a production 4-bolt 302 (or 351W) beyond the Boss cars.
People argue that cost was a factor, but the modular motors have probably twice the fasteners in them as the SBF.
Eh, now I'm just rambling.
