Something does not seem right there. My iron headed 318 Magnum (stock cracked heads) with a Comp 20-746-9 HR cam (.506" lift), Magnum Swap valve springs, HD MP lifters and stock rockers will pull well past 7K under 20 psi of boost on E85 (and 18°of timing). I have an MSD Programmable box and a HVIC coil going thru an MP distributor, 8MM wires to NGK -7 plugs gapped at .045". I finally experienced blowing out the spark at 26 psi. My engine NA will not rev over 6K. I think it may be lifter pump up.
