Its hard to find a good dual plane manifold for the cleveland. Edelbrock has yet to make a Performer RPM that would greatly help the street driven 351c. The x-celerator gives awesome low end for being an open plane and tremendous top end. I had my x-celerator intake runners extend to build more bottom end power.(its a simple mod) The funnelweb is another top of the line manifold that can't be beat. However the cost is way high compared to a x-celerator. I've seen x-celerators sell on e-bay for 100$ while the funnelweb costs about 425$ new.
Anyway I hope this helps.
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