the biggest advantage as far as flow goes on 18 degree is un shrouding valves. Its also easier to achieve more compression without a dome. that being said un shrouding a chevy head if you could to the max will not let it flow sbm numbers. that is taking in consideration port angle, cross section, chamber shape,plug location pinch etc... what does this have to do with the exhaust anyway your the one not listening when the primary subject is about how well sbm exhaust works
