Supercar Reunion #8

[retengw31]

Well this may be more info than you need, I wrote this in response to an email from Rob before I saw this post. Anyhow, here's the breakdown on 425 vs 455 with the 400 derivatives of each added in.

Anyhow, the 425 is basically the same as the 455 except for the larger stroke on the 455 (4.25) vs 4.0 on the 425. Bores are same at 4.125. The 425 was used in the big cars from 65-67 and the 455 replaced it in 1968 and ran until 1976.

The shorter stroke on the 425's made them higher revving (with more peak horsepower up high), but less torque all through the power band. They both had excellent metallurgy in the blocks (at least the early 455's did), and used very similar heads (67 425 and and 68 455 heads were both C castings and identical). 425's also used a forged crank vs a nodular iron cast crank on the 455's. Later 455's used crap cast iron cranks (73-76). 425's also used long 7 inch rods.

425's had some wierd valve and cam arrangements. Each year they tried something new until they realized, they just didn't last in the high rev areas (over 6k). They tried to keep as much oil down low on the cranks as much as possible (huge main and rod bearing diameters) and valve train durability suffered as they addressed the oil problems. 455 didn't experience that as it wouldn't run much above 6k.

65 425's (A blocks), had a 45 degree lifter bank angle with the standard .842 dia lifters, and crappy valve hold downs and pivots. In 66 they went to the B block with a .921 dia. lifter, 39 degree bank angle, and much cleaner and better valves and rocker arrangements. That carried through 67 into the 455's in 1968, but they went back to the standard .842 lifters in 68 also. All 455's are 39 degree bank angles with .842 lifters.

Both the 425 and 455's had big intake valves (2.07) and small intake valve (2.00). Toronados got the 2.07's. Both had 1.62 dia exhaust valves.

The 400's in the 442's were derivatives of these engines but with smaller bores. The 65-67 (E blocks)were almost perfectly square at 3.99 x 4.00, but the 68 and 69 (G blocks) had to go way down to a 3.875 bore with the 4.25 stroke to stay at 400 (GM edict back then). The 65-67 400 used the same sand core for the water jackets as the 425, so could easily be bored out to 4.125 (or even 4.250) whereas the 68/69 400's had a unique sand core and was a thin wall casting. Couldn't go much bigger than 60 over without danger. They weren't that great of a performance engine, but great for cruisers and Vista Cruisers.

So to answer your question, I'd go with the 455. Much more plentiful, more bang for the buck. Can keep compression down, and use moderate gearing. You'll have to go way up in compression and gearing to make the 350 come alive. I run a 4.56 and Casey runs a 4.33. Both are very high compression engines.

If you're into Pure Stock or FAST racing, the only combination for a 68 with the 455 would be a Hurst (silver/black) and the 350 would have to be a Ramrod W31.

I'm doing a 68 W30 with a 67 short stroke 400 right now. Won't be able to run either PS or FAST, but may be OK in the new Factory Appearing Class at NSCA. Engine ran 11.60's all day in Chris Hemminger's 71 Cutlass Supreme. Has a Hurst type treastment in red and black.