in a low-compression 318,
installing a 340 cam; 268/276/114+4, ( perhaps 208/
[email protected])
with NO OTHER changes,
your cylinder pressure will drop about 15%, from about 134 to 115; due to the late-closing intake valve.
This will drop your low-rpm performance about 25% from a P/V of 110 to 84.
read about P/V here
V/P Index Calculation
You will certainly be disappointed if you keep the current stall and gears.
The factory 340 cam has only about 44* of overlap, so the rpm has to be set very slow, and timing very retarded, to hear any rumpiddy-rump. IMO, it is NOT the best choice unless you already own it.
The comp Xe268 is 268/280/110+4 and is 224/
[email protected] almost three sizes bigger and the overlap is 54* ; But the intake closes 4* sooner so not quite as doggy down low. I had a cam of about this size; 270/276/110/53* overlap and 223/
[email protected]; but in my 367 the lope was just barely noticeable at 700rpm with 14* idle timing. My Scr was 11/1 with alloy heads, and I had a 4-speed so stall was not an issue.
With either of these cams, your Scr should be brought up for best results. 115psi is not very much pressure.