L78 Dyno

[VintageMusclecar]

L78Kiwi:

The skirts on that piston have been knurled to take up excessive piston to wall clearance. Standard practice back in the day, but <span style="font-weight: bold"><span style="text-decoration: underline">not</span></span> the way to fly today.

Am I seeing a 2 piece top ring there? Either way there's an awful lot of carbon between the top and 2nd ring, not a sign of good ring seal.

Measure the bores, I'm betting they're pretty worn and need to be machined. Be sure to have the block honed with a torque plate using the same gasket &amp; head fasteners the engine will use in service.

You can get away with 11-1 compression on 91+ octane pump gas, but it's a bit of a tightrope walk. Temps need to be kept at 160°, and timing needs to be kept at 36° or below, which probably leaves some power on the table.

With today's piston technology, you can special order pretty much anything you want in a piston. I would advise dropping the compression back down to 10.5 or less and move to a modern metric ring package to free up some power.

If you need any help with parts, let me know, I'll be glad to help.