kingarthur said:
With a turbo kit, porting the heads doesn't make much sense. I guarantee that the boost will fill your cylinders to any extent you might wish.
Simply put, and meaning no offense, but that is simply wrong. Ported heads help a boosted engine take in the pressurized air better.
Ported heads help most when the boost is provided by a pressure generating mechanism like a turbo or a centrifugal supercharger (Procharger or Vortech) and somewhat less (about 40% less) when it is from a flow generating unit like a roots or modified roots (screw type) blower like an Eaton or Wieand. Its gets pretty technical as to why. Here is a link to a thread on another forum where it is explained a bit: if you go down to the second message in the thread you will come to a long posting from me on this.
http://www.corvetteforums.com/Procharger_the_best_fi_option_out_there?/m_3783/tm.htm
You get gains in a lot of things you care about when you port the heads: lower heating, less likelihood of detonation at any particular HP output, gains coming in at lower RPM, and ultimately, more HP. Now, a couple of points: if you have an engine that is running a certain size SC with a certain pulley size producing a certain boost, and you take the heads off and port them, the boost pressure you see will drop, because the resistance to flow is now less with the ported head. But more air is actually flowing, and thus more power. BUT THEN, you can use a smaller pulley (or just depend on the turbos to spool faster) and you can generate EVEN MORE air flow at the same pressure as before.
But turbos respond even better, which is why you really want to port the heads with them: you don't even have to change out a pulley size, they do it automaticallyt.. All that i discussed above with the SC happens when you port the heads, but in addition, the exhaust is now greater, so they spin up faster.
A data point: on my present Procharged 427 vette, with standard Pat II aftermarket heads it produced 570 RWHP at 8 lbs of boost with an SC outlet let temp of around 280 and a temp after the intercoolers of around 170. (It would go to much more boost and power but why we weren't at the time is a long long story). Anyway, without changing Sc or pulley, we put on a set of special ported, big valve (2.08 versus 2.02 inch) intake valve PATIII heads that flowed 340+ vs the PatII's 307. HP jumped to 590 at only 6 lbs of boost and an outlet temp went to 250/160. We then changed out to a smaller pulley and went back to 8 lbs boost. RWHP was 640 at 285/170 degrees.
You can view the engine at:
http://www.corvetteforums.com/albumphoto.asp?albumid=4&asortType=2&apage=1