The weight difference... I don't want to say for sure, but its somewhere around 40lbs between the block and crank.... in the world of things, its not THAT much... but.... if you start with a 425 that weighs less then a 500 and add an Edelbrock intake manifold (22lbs instead of 45lbs) then you are now running a big block Cad for nearly the same weight as an SBC..... if your pockets are bottomless and you get aluninum heads, you have a massive enigne with very little weight.
Which pre-war production engines for cars are bigger then the 500? One of the largest that come to mind is the Cadillac V16 from the 30's.... but even then, that beast was 7.3L.... produced a smooth 165hp @ 3,000RPM and 320ft-lbs torque @ 1,200RPM IIRC.
Also, keep in mind the 425, while choked back with emmissions... isn't AS bad as the 472 and 500.... reason being... no AIR pump at all.... loose the origanal cat tho, thats a must (I drained the beads from mine)..... shes got EGR, but that is actually a good thing (and I ended up dumping EGR with the modified '68 472 intake manifold) and the carb is slightly lean (that was corrected with the performance rebuild) so that left the lack luster 8.2:1 compression as the only thing left, besides the smogger cam.... but because of that, I could run 87 and she'd never blink..... 87 will actually give it a little more power for the fact that it'll burn more easily.
The worst case 500 was making 180hp, the 425 makes 180hp...both these numbers do not reflect real world numbers, in general, the 500 was making more power, especially early versions of the 500 and the hi-po 472. But again, keep in mind, for what the 425 is, its making ecent power, and has some awesome potential too.... the 425 just dosn't get much credit because.... well... why get a 425 when you can have a 500, ya know? but she is a gem of an engine.... 1,400 miles in 36 hours without even flinching..... she would cruise at 75 all day and the only way I knew it was still running was the slight exhaust leak form the left manifold, the indication on the tach... and the fact that the car maintained its speed and the AC did its job.... and in the world of things, the 17mpg wasn't horrible either, cause if I was driving a gasoline pickup, thats what I'd be getting too.
a 500 is making around 300hp and 450ft-lbs torque.... even the smogger ones. I know I haven't updated it in ages, but take a look at the database thread (stickey at the stop) there are 2 articals of a BB Cad build up in there, and in the one, they throw a stock 500 on a dyno and they coudln't believe the numbers.
today, 6.0L is a big engine.... but the 368, wasn't making THAT much power not to say its a bad thing, but honestly, trying to make a 368 into a 1/4 mile beast woudln't be very sensable, it was at a bad era, cause the HT4100 was coming out which had what people wanted at the time..... The thing i like most about the 368, is the fact that the V8-6-4 stuff was slapped onto that thing.... I want a V8-6-4 368, and boost the power slightly... then wire up the solenoids manually (easy to do) to only have V8/V4 mode.... I think low-mid 20's would be possible for fuel mileage, and that'd be pretty sweet. if I had a 368, I would run it as is, if I had plans for hi-po, I'd step up to atleast the 425..... but thats not to say the 368 is left out.... AFAIK, she still has the claim of the smallest big block made .
