MiguelsC2

No flow testing..Just "Joe" testing.I will try a higher initial timing before I go to filing on my brazed rotor head (or is it stator?).

65tripleblack

I'm happy that you took my advice on the cam, the 1.6:1 rocker arms, steel shim head gasket, port matching, pocket porting, and guide plates. You should have a sweet running engine in your Corvette, which you'll enjoy driving!

You didn't advance the cam the additional 2 degrees for a total of 4, as I suggested, which would have given you more cylinder pressure and therefore more torque at low and midrange. 2 degrees is OK as well, but your slight compression deficit would have fully utilized the additional cam advance. Since you have a lot of "margin" left before detonation sets in, you can very likely set your initial timing at 20 BTDC with 18 degrees centrifugal, all in by 2200. Run the stock vacuum can and limit the vacuum advance to 14 degrees for a total cruise timing of 52 degrees. The engine should not detonate with these settings with ordinary 93 PON fuel.

If you had your heads flow tested after they were ported, then publishing the results would be appreciated.

65tripleblack

You probably wouldn't have to elongate the autocam limit slot, since stock centrifugal advance is about 17 or so crankshaft degrees (8.5 distributor degrees). Most likely, you'll have to shorten the slot.

The optimal WOT timing for a vintage SBC whose burn characteristics have not been changed due to swapping heads with modern fast burn chambers is about 37-39 degrees BTDC. That is where you should ALWAYS BEGIN when "mapping" your spark advance. Give the motor as much initial advance as it will tolerate, up to about 20 degrees, and then adjust the centrifugal advance limit slot/bushing to make up the difference between the initial and the total WOT amount. If your engine tolerates the full bore 20 degrees of initial, then that means the limit slot/bushing must provide an additional 17-19 degrees, for a total of 37-39. Adjust the spring rate to have the centrifugal come all-in as soon as possible without detonation. The quickest that you'd want to see should be "all-in" by about 2200 RPM.

Finally, spark timing at "cruise" should be much more advanced than at WOT because cruise mixtures are leaner than WOT mixtures. Lean mixtures burn slower than rich mixtures, and you always want max cylinder pressure to be reached at the same time: 15 degrees ATDC. 52 degrees total spark advance at cruise is about optimal for a vintage SBC, which means that the vacuum advance should be about 14 degrees (38 + 14 = 52). The vacuum can should be chosen based on the point that it fully deploys. The vacuum of full deployment should be 2 degrees lower than your idle vacuum (14 in-hg in your case), or 12 degrees.

MikeM

I'm glad that cam worked out for you. I like 'em!

MiguelsC2

Thanks, now I get to have some fun with it. Heading out to the shop now. Time to get it dialed in.