the RPM is definitely different , very large volume and runner lenth. that one is closer to the LD340 in volume. the LD4b is a large port intake too....

the edelbrock performer is a great manifold to build power from idle to 5500. it has different plenum volume. also narrower runners than the ld4b to increase velocity.

i have not had a chance to try a ld4b . the performer, rpm, and streetmaster single i have tried on my 318.