My experience with the fenderwell headers is they peak pretty early. They improve the numbers below peak TQ, and can show a slight gain in the peak TQ value.
But they didn’t carry the TQ all that well past peak, and as a result...... the HP number suffers.
On the dyno here, with those headers........ I’d be expecting solidly over 600TQ, and maybe 625-635HP...... if the curve hangs on well enough.
Edit- after looking at an old test with a 493 and FW headers, the 625-635hp might be a bit generous.
