It all depends on the amount of boost. At 10psi with GN1's, you may be flowing as much air as you would at 17psi on stock heads. Impossible to say without a ton of data. Say you're running a stock GN, and you throw on GN1's, and then crank the boost back up to stock levels (cause it will drop), and maybe you'll gain 50hp. On a modified street motor, maybe 100. Whats the CFM rating at 28" with GN1's....anyone know?
Heres an example coming from my mustang background. Take a 99 GT. 260hp. the heads flow about 185cfm on the intake. Take a 99 Cobra (which I had). 320hp. Heads flow about 225 on the intake. Thats the main difference between the 2 motors. Forget about the extra cams on the cobra, cause they do nothing to create more power. So you have a 60hp gain, stock for stock, from a 40cfm gain on the heads. Now throw a centrifugal blower at 12psi on the cobra and on the GT. Only mods on the 2 cars are a good exhaust system. The GT will make about 375hp at the wheels. The cobra will make almost 480 (mine made 500rwhp). Thats a 105hp difference in blown form, from a 40CFM difference between heads.
Basically, next to displacement, heads are everything. They dictate the potential of the motor, and anyone who says different is full of it. If you want alot of potential out of the TR, throw some ported GN1's on it. Ported by someone who knows what they're doing. Not some guy who thinks hogging the ports out and matching the "holes" to the gasket is the way to go. You can have 2 different sets of heads, that flow the same CFM, but one set can make ALOT more hp. Reher-morrison (Pro-Stock engine builders) had 2 different sets of heads that flowed the same cfms at all lifts, and 1 set of heads made 125hp more than the other ones. Thats cuz there is so much more to heads than flow numbers.
