This summer I took off my slightly massaged 2.25" RA manifolds with a 2.5" headpipes / X pipe and replaced them with RARE oversized manifolds and their 3" headpipes. Ran new 3" X pipe back to the 2.5" mufflers. Gained only .75 mph in the 1/8th mile. That was fumbling with a 4 speed and street tires but i did run my best mph ever but not by much.
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72 lemans,455 e-head, UD 255/263 solid flat,3.73 gears,,,10" 4400 converter,, 6.68 at 101.8 mph,,1.44 60 ft.2007
(cam 271/278 roller)9"CC.4.11gear 6.41 at 106.32 mph 1.42 60 ft.(2009) SOLD,SOLD
1970 GTO 455 4 speed #matching,, 3.31 posi.Stock manifolds. # 64 heads.A factory mint tuquoise ,69' judge stripe car. 8.64 @ 87.3 mph on slippery street tires.Bad 2.25 60ft.Owned since 86'
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