ncboat

I have scoured this and other sites to try and find exactly the difference in the two engines. I have not convinced myself that I have digested all the information correctly.
Here is what I believe I know as facts about the 1957 and 1958 371's. Beginning with the block the deck height is the same and all blocks are the same. The rods are the same and compression height of the pistons is the same yr to yr. The 14 heads of 57 have a slightly larger combustion chamber than the 16 heads by a few cc's. The head gaskets, per a Victor catalog, were the same in 57 and 58 with the exception of special "thinner" gaskets for the J2. I can't figure out where the 1/2 point compression increase in 1958 was derived.
Can someone straighten me out please. This is important as I plan my build so I don't "stack" compression increases.
thanks for the experience shared.

Charlie Jones

There's your answer right there.
Those " few cc's " make the 1/2 point compression difference.

OLDSter Ralph

Ok, let me try to simplify this a little. The block, rods, pistons, bore/stroke and deck height are all the same. The differences are in the #14 and #16 heads combustion chamber CC's and head gaskets. It can be confusing until you sit down and look at the NHRA Tech specs, side by side.
ALL engines except 1957 4 barrel were 10.0 C.R. Only the 1957 4 barrel engine was 9.5 C.R.
I have the downloaded NHRA Tech sheets for both 1957 and 1958. I will gladly share what I have, if you PM me your email address.

OLDSter Ralph

This should make the head (1957 #14, 1958 #16) combustion chamber CC's, head gasket thickness and compression ratio clearer.

ncboat

You guys are awesome. The NHRA charts are Gold. From what I am gathering the 58 engine had a thinner head gasket at .040 vs the 57 of .050 and larger combustion chambers. Subtle but effective. Is that a correct observation?
Does this also indicate a valve Lift of 455 on a factory 57 cam?

Charlie Jones

Almost, the '58 chamber was smaller than the '57.

OLDSter Ralph

I have studied the NHRA specs between 1957 and 1958.
1. The 277 HP base engine in 1957 had a .050" thick head gasket that dropped the compression ratio to 9.5.
2. All 1958 engines used .040" thick head gaskets.
3. The 300 HP and 312 HP engines in 1957 used a .025: thick head gasket.

4. The 1957 had smaller combustion chambers at 72 CC's.
5. The 1958 had larger combustion chambers at 75 CC's.

I am suspecting the column labeled "cam lift" is actually "valve lift".
6. 1957 engines had two cam lifts. .419/.435" for the 277 HP and 300 HP. .451/.455" for the 312 HP engine.
7. All 1958 engines had only one cam lift .435/.437".

8. If you scan the columns marked "lifter" you will see that "H" (hydraulic lifter) were used in all 1957 and 1958 engines EXCEPT the 1957 312 HP. The "M" means mechanical (solid) lifters.

9. Deck height is nearly the same at .001" for 1957 and .002" for 1958.

10. Valve sizes are the same for all 1957 and 1958 engines.

11. Valve springs for 1957 are an "Outer" and a damper.
12. Valve springs for 1957 are "Outer Only" which points out that the new "Bee hive" springs were used, as Charlie has stated.