I have a 1965 425 with A stamped heads in a 1980 olds cutlass with 3:73 gears. And i have a 455 out of a 68 toro. with big valve c heads. I have already had the heads rebuilt. Im trying to figure out if i should put the c heads on the 425 or just build the 455 wanting a good street engine. And is it true all 425 had a steel crank?

 

Use the 455 block with the 425 crank...if it is strictly a street car, I wouldn't really be to concerned about the 425 crank over the 455 crank. You could sell the 425 to fund the 455!

 

why is it better to use the 455 block with 425 crank?

 

i understood if you did that you must also use 425 pistons and rods, so you end up with a 425 anyway but its in a newer block. the 425's had better steel in the block

 

The 425 crank is forged, which is stronger than the stock 455 crank.

 

Why give away 30 cubic inches? I'd go 455 but thats just me. You could still drive the car the way it is for a while too.

 

the 425 heads are original and need rebuilt and i have the 455 c heads allready rebuilt thats why was wondering if i should just put them on the 425 or just build the 455

 

In general, the 425 will be better for high rpm, the 455 will give you better torque. The C heads will flow better than the A heads, particularly if they are ported properly, but you may run into pushrod geometry problems. However, the pushrod holes can be enlarged to compensate.

The 425 does have the steel crank, so that's a plus. But if you use the 425 crank, you will end up with 425 cid.

So, it really comes down to what you want :-)