S&S have 1 5/8" primaries... same as SLP and TOGs. Pacesetters and TOG Xtremes are the only headers for Grand Prixs with 1 3/4" primaries. That's why some people complain about a loss in torque with Pacesetters... primaries are too big for most everyday applications.
1 5/8" primaries will suffice for probably 80-90% of 3800 motors.
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'97 SE with alot of mods