I believe what he did was use the very beginning of a 2.5” pipe with flare, maybe 2” and then welded that onto a 3” mandrel bent head pipe. So the very beginning is necked down but the rest is all 3” . Not ideal I guess compared to 3” the whole way. I believe it’s the same flange as a standard 2.5”. Like I said they call these oversized but comparing the ID of these compared to my other standard aftermarket manifolds there wasn’t much of a upsize but there is some.
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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. 8.45 @ 88.1 mph on slippery street tires.Bad 2.19 60ft.Owned since 86'
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