While it's true that cylinder heads abound for the LS motor, we are always excited about testing the very latest offerings. Case in point, the new Pro Action heads from Racing Head Service (RHS). Having been in the game long before the introduction of the Gen-III and Gen-IV small-blocks, RHS made a name for itself by performance-porting the original small-block Chevy heads. Factory fresh, the 23-degree iron heads were obviously not high on performance, but having a set of RHS-ported Chevy heads stepped up performance considerably.
Its success with the original small-block has carried over to the modern Mouse. Research and development from RHS is in full swing, as its engineers continue to increase the number of offerings from an ever-growing line of performance cylinder heads (and blocks). Though we anxiously await the new CNC LS1 heads, to say nothing of their LS7 offerings, we took a long look at their current crop of as-cast LS1 heads from their Pro Action line.
According to RHS, the Pro Action line of cylinder heads was designed to combine the performance of CNC porting with the affordability of as-cast heads. This was achieved through a combination of race-proven head design and what RHS has labeled ôClean Cast Technology.ö Power output is (partly) a function of head flow, which in turn is a function of port design. The Clean Cast Technology is said to provide just such an optimum as-cast port design that maximizes flow without the need for additional porting. The Pro Action RHS heads were available in a couple of different configurations, including as-cast P-ports with no valve job and a pair of assembled heads featuring either 205cc or 225cc intake ports. For our stroker application, we chose the larger 225cc intake ports, but in all reality, the smaller 205cc heads would easily support the modest power output of our mild street motor. We selected the larger 225 heads more for what the future may hold than the current combination.
The 225 designation for the RHS LS1 Pro Action heads was derived from the volume measurement of the intake port. While this may seem a tad on the large side for enthusiasts who grew up on the original SBC, rest assured that acceptable port size has increased through the years. Where we might be tempted to run a set of 195cc heads on a typical 23-degree street small-block, we wouldn't hesitate to install a set of 205cc heads on a diminutive 5.3L (roughly equivalent to a 327 Chevy). Testing has shown that these port volumes are not detrimental to low-speed power production.
One need only look at the (relatively) massive port volume of the current LS3 offerings (260cc) to illustrate this point. In addition to the more-than-adequate port volume, flow from the 225cc RHS heads was optimized through a 2.05/1.60 stainless steel valve combination and highly efficient combustion chamber design. All this was achieved using stock valve angles and centers, stock port locations with all the necessary accessory holes drilled and tapped. Basically, the RHS Pro Action LS1 offerings were ready-to-run, high-performance bolt-on cylinder heads.
Call us skeptics, but what sounds fantastic on that dimly lit press release is oftentimes somewhat less so in the light of day. What we wanted to know was just how good were the new RHS Pro Action heads, and (as always) we conjured up a way to find out exactly that. What better way to test the merits of the new heads than to compare them directly to their production counterparts?
1 The test motor started out life as a simple 5.3L truck piece. The iron block was treate
2 The bottom end included a forged-steel crank (4.0-inch) and matching 4340 (6.20-inch) r
3 Up top, we see the forged pistons from Probe Racing combined with ARP head studs and ne