Hi,
The major differences in these cylinder heads are shorter exhaust ports,larger chambers(which require a different piston) and upgraded valvetrain,with individual rocker arms and all the related parts.These heads were used to facilitate installation of a Buick v6 in place of a small block chevy,and in the process,a few horsepower were gained. Not a bunch, certainly not 40 or more! Detonation resistance may be higher due to the chamber design, which accounts for the extra boost(16.5 psi)these cars carry.In addition to the GNX intercooler(not bigger, more fins per inch),this results in an honest 300 net horsepower,and subsequent 13 second quarter miles.These cars will also do 150 plus mph.Not bad, for a six.I would say 90% of the TTA's performance is the extra 2 or so psi the chip gives it, aided by the chassis, heads and intercooler. I have only experienced detonation with my car once, at 25 psi boost on pump gas. Compared to my Regal, which pinged constantly, that's pretty good.Hopefully, the rebuild I have just done on the Regal will help that issue.