Not an exact HP loss number but..... I went from headers and 3", dump at the rear exhaust to 340 HP manifolds, TTI 2.5" x-pipe system. My best time with headers and slicks was a 11.78 @ 118. My best time with manifolds and E70-14 (Firestone Wide Oval, Redlines) was a 13.2 @ 105. The 13.2 pass was on a Ram clutch with at least one broken pin.
Some other changes between the two were.
SS springs to Mopar HD springs
Electric fan and water pump drive to stock set up
Battery in trunk to battery under the hood
original 340 and X heads, Ported and balanced
Crower solid street roller cam
Victor 340 with Holley 800 DP
