Headers and exhaust. Another 928 "engine expert" (who has never built a 928 engine, been near a flow bench, or has never built a set of headers) insisted that they would not work for this engine, as the primary pipe diameter was way too big for this engine and that I'd built these as a mistake and should have known better.... Another troll. Nothing further from reality possible. They work fantastic! Gobs of torque and great top end power.....exactly as I designed them. Shocking!