It only flows 230ish cfm through each runner unless you deburr the welds inside the runners and open up the throttle body flange. The heads only flow 180ish cfm. Sorry, it is not lightning fast, only marginally faster than any 5.8 of the era. I had a 92 with 5.8 I bought new and drove for 14 years, so I have BTDT with ported heads, ported intake, ported plenum, and the GT-40 upper plenum is a bottleneck, period. I still have one. A healthy 302 runs out of steam with the GT-40 around 5200rpm, so to say the 351 runs great, is not honest, IMO. I built one of the first 351 EFI conversions back in 1987/88 in my 86GT, and even ported the GT-40 throttle body flange to 75mm, etc. It was great but still went flat in upper rpms because of lack of airflow. A ported Cobra plenum that has been cut apart and welded back together can flow 300 cfm, and a ported Explorer plenum cut and ported can flow 300-305cfm. I have done more of that than probably anyone in the USA, and had several in magazines back in the Super Ford days. Joe-JDC