Upgrades and Boring Limits Valves
If you are replacing the valves on a 1954 264 or 322 always use the larger 1955 or 1956 exhaust valves. The 53 322 valves are shorter, no oversize available. If you have 1955 or 1956 heads with bad exhaust seats then the larger 1957-1958 364 valves can be used, same valve spring installed height of 1.5. If you are replacing valves in the 57-58 364 heads then we would use the larger ones for a 59-66 364-401-425. They are cheaper and better. They use a valve spring installed height of 1.6 instead of the 1.5 so use new valve springs or shim them. The later valves are a must for high lift performance cams so you don’t get coil bind. We also have oversize 401-425 valves. All nailhead valves except the 1953 322 are the same overall length but lock grooves are .100 lower on the 1954-58 valves. Boring limits. All nailhead blocks will go .060 overbore EXCEPT the 425, anytime you bore them more than .040 you should sonic test the block. I have only had two 425 blocks that safely bored .060. FYI 705 blocks are NOT 425 blocks.. In the old days many 401 blocks were bored 1/8″ to install 425 pistons, the blocks were rust free so some got away with it. I would never sacrifice cubic inches for good ring seal. Honing deck plates would be needed with these big overbore blocks and of course, sonic tested. Other Recommended Upgrades Rubber crank seals and roller timing sets for the 1957-66 engines. Brass freeze plugs (all nailheads) Stiffer valve springs (slightly) some companies are valve springs that are too stiff! Stronger tube style push rods or adjustable ones Valve seals on intake guides only unless you are using T/A roller rockers then all guides need seals. Our guides are machined for seals. Always Balance your engines when rebuilding, no exceptions! NEVER use hardened valve seats Bronze guides can only be used with roller Rockers!