Put the car on the dyno today.
Air/fuel mixture was good in the mid 12's. Car sounded great. Until about 4600 rpm, then it went rich (11's) and both torque and horsepower took a BIG nose dive. And the car sounded awful at that point, just like before.
We installed new plugs, and got pretty much the same thing.
The shop recommended I ditch the 40-yr.-old Holley because they have no way to jet the top end due to the secondary bowl just having a metering block instead of jets. A 750cfm QuickFuel was recommended. Summit part number QFT-Q-750. 600 bucks for that carb. Dang.
Hmmm..... valve springs are probably cheaper to try first.... I completely forgot about this old posting, and failed to discuss the springs with them.
Un-filtered dyno data:
"Filtered" dyno data:
Here's my setup now, vs. 2 years ago:
460 from a '73 Mercury.
stock, unmodified D3VE heads.
750cfm Holley vacuum secondary carb.
Accel Street Billet distributor and Accel Super Coil.
"Aftermarket" cam, but specifics remain unknown.
275/60 R15 rear tires.
stock C6 trans.
3.50 rear gears.