[Excaliber]

The machine shop may be right! Consider this: What really makes AFR heads 'special' is their consistent flow throughout the rpm range. While other heads may flow better at peak CFM they tend to loose out on flow compared to AFR heads at lower to medium rpm. The advantage this offers is better 'streetability', more torque at a lower rpm range, crisper throttle response. It's not just valve size but the way AFR runners and ports are set up. Smaller ports, runners,valve size generally provide better throttle response at lower rpms in general. Thus the machinist take on the smaller valve GT40 heads may perform well. Better than AFR? Well thats a tough one. In my opinion AFR may well be the BEST head out there for overall performance because of their well thought out design. Worth the extra money over a nice ported set of GT40 heads? Tough call. You looking for PEAK horse power at max rpm? You could do better than the GT40's or the AFR's in that case!