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I get lots if inquiries about the "valve size" in the Ported Thumper Heads...I have to answer that, this way:The Flow numbers is the amount of air the ports will flow, at a certain cam or valve lift. The larger the flow numbers, the more RPM is needed to get the power from the Heads, and that upper RPM will hurt the lower torque numbers and throttle response! Two thing make a good head! Flow volume AND velocity!! The Velocity of the air is what fills the chambers, which allows the engine to build power. The faster the air speed, the quicker the power is made! There are a number of ways to build flow. The first is to port the work as you know. The second is to install larger valves (i.e. 1.94s and 1.60) Which is good, but, if it's TOO big, in the ports and valve size the air will become "lazy", slow moving. The way to speed the air up is to install a steeper rear gear (4.11s-4.57s) to allow the engine to turn higher RPM, to build up the flow speed( velocity). Try this.. A 302 with a 850 carb! Runs killer on the top end..7000 rpm and up.. but a dog on the lower RPM. Same idea on head flow... too big of a camshaft.. same problem.. lazy air movement at the lower RPMs..But screams thru the top end! Most of my heads are on cars that are in the mid to low 12 sec range! The heads will allow low 12s and 11s with more engine work..but mostly dual purpose cars! So I dont build for the 7500 + RPM engines.. ( I can and will..but not for this purpose ) I want crisp, fast, throttle responce, snap off the line on a mildly modified engine ( bolt ons and cam) I want a Head, that will pull hard and strong to 6500 ! (more with proper Camshaft) So...I want VELOCITY and Flow Numbers!! I do this by keeping the stock valve size and doing a 5 angle valve job! The 5 angle acts as a boost to the air flow as the valve just leaves the seat, and also when the valve is just about closed! This Increased Low Lift flow allows the air to Fill the chamber faster!! The faster the chamber is filled the more power the engine will make! With the good flow numbers the Head will keep making power till you lift off the gas!! ( Do you know that the GT40Ps have a smaller exhaust valve than the GT40s?? And the Ps pull MORE power, according to tests) Remember " it ISN'T what you have, Its How you use it!!" No need to notch the pistons for the larger valve....Extremly responsive and quick throttle responce.... and HP capable to run low 12s N/A and in the 11s and 10s with a power adder! ( Like NOS)
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