I'm hoping to get feedback from people who know firsthand (or can point me to others' results) about the RPM limits of the LD340 intake manifold with the plenum divider removed per Direct Connections' instructions and an exact deep-port gasket match.
The racing class rules I'm bound by restrict my intake manifold to either a factory cast-iron or LD340, and I know the intake will limit performance compared to a quality single plane. I'm trying to get an idea of the RPM range the engine can practically use with the LD340 to help me in considering cam profiles. The engine is a 360 gas race engine (no street use), 12.5:1 static compression, headers and unrestricted exhaust, four speed, and low rear gearing. I'm restricted to a Holley 4150 750 cfm.
The ported heads flow the following:
Lift Intake CFM Exhaust CFM
.400 256 171
.500 277 189
.600 285 195
.700 281 197
Can anyone give input on their experience of what RPM the power flattens out or starts dropping off with the LD340 on a race engine?