Here is a dyno test I did on a mild, low compression (less than 8.0:1) 455 with stock heads, with headers.
First test had 2.5" pipes from the headers to a set of 3" FlowMasters, then to 2.25" tailpipes.
Second test is full 3" pipe, 3" 14" case Borlas ProXS mufflers, to mandrel bent 3" tailpipes. There is a 2.5" H-pipe ahead of the mufflers. First pull this combo made more power across the tested range, but the AFR leaned out big time. The test shown is after going several steps smaller on the primary metering rods (Qjet).
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'73 T/A (sold). Low budget stock headed 8.3:1 455, 222/242 116lsa .443/.435 cam. FAST Sportsman EFI, 317rwhp/385rwtq on 87 octane. 13.12 @103.2, 1.91 60'.
'67 Firebird [sold], ; 11.27 @ 119.61, 7.167 @ 96.07, with UD 280/280 (108LSA/ 109 ICL)solid cam. [1.537, 7.233 @93.61, 11.46 @ 115.4 w/ old UD 288/296 108 hydraulic cam] Feb '05 HPP, home-ported "16" D-ports, dished pistons (pump gas only), 3.42 gears, 275/60 DR's, 750DP, T2, full exhaust
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