Just a discussion we have been having on a setup
for my buddys new project boat

If you had a 454 with a 5psi roots blower making lets say
600hp and changed the shortblock to a 502 shortblock but used
same cam,heads,blower,everything from the 454 what would the gain of the
50 extra cubic inches actually be.
My guess is around 65hp and 75lbs tq due to the cubes and the unshrouding of
the valves due to the bigger bore
my buddy says because of the loss of boost on the bigger shortblock
it would actually be a smaller difference to the tune of 50hp and 50lbs tq
to where it would not be worth doing ..

Any real life experience with this swap anyone?

anyone?

he is correct but if you speed the blower up to maintain the 5 lbs boost,the 502 will make more hp and torque,i am guessing app 60 to 70 more.

..

X2

Also, if you use the same cam, the peak torque and HP will move down a couple hundred rpms.

thanks

and compression ratio will be higher with same heads, unless compensated with pistons...

huh??????????

Yep.

The 502 will show less boost with the same blower pulley. If the blower is large enough to stay in its efficient rpm range with a bigger pulley, then it should be pullied up to the same boost level. If the blower is small, then you may already be spinning it at the top of its efficiency range. Spinning it harder will make more heat (and show more boost) and not more power. A 250 blower is minimum for a 502, and a 420 is even better.

Unshrouding valves from the larger bore is good for 10hp on a 400 hp big block. You should maintain that 10+ hp benefit on the blown motor as well.

The larger displacement is good for 50+ hp (if the boost is the same as before).

So, you'll see about 60 hp more with the 502 running the same boost as the 454 - and like has been said, your torque peak will drop 150 rpm.

If you cam to retain your same torque peak ALSO (add 5 degrees of duration both sides), then you will see another 15 hp. But if you recam.

If you are running flattop pistons at zero deck on the 454, and you are running flattop pistons at zero deck on the 502, then your compression ratio will go up. If it's currently 9:1 as a 454 and the deck is the same on the 502, then your new CR will be 9.8:1.

If the 454 is running more than .046" squish right now, then making certain that the 502 is running no MORE than .046" will help keep detonation away and the motor will run better (assuming you keep the static CR reasonably low).

So, keeping same cam, heads, ignition, blower, blower pulley, etc - you will see 5.5 lbs of boost instead of 6, and you will see a big increase in torque, and a small increase in hp.

Keeping the squish tight and bumping up the boost will release those hidden horses.

If the $$ are in the budget, I will choose a 502 over a 454 or 496 any day for a build.

MC