I believe the same concept of marking a crayon on your exhaust when your installing an H or X-pipe. Whereever the crayon part stops melting is where the H or X-pipe needs to go.

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347 Stroker/XE284H(284/296 dur, 240/246 dur @ .050), BG 650 VS Speed Demon, Ported Victor Jr intake, Jack Roush World Product (ported from 180cc to 195cc) Jr Heads(upgraded to 2.02/1.60 valves) 260cfm/190cfm @ .550 lift, 11:1 comp... 450-475HP