The CNC porting that was performed on these heads increases the flow without significantly increasing the port size. There is an optional porting program that will open the heads up to the Max Wedge size, but we wanted to stay with the standard size on these heads since our focus was more on street performance than drag racing. The Max Wedge size ports will increase the airflow and the power output, but then you must use an intake manifold and intake gaskets with the larger Max Wedge sized ports. Since nobody has produced a factory bathtub type intake gasket with the larger Max Wedge port size, there is no good way to seal off the valley area when using Max Wedge ports on stock replacement heads. Maybe the aftermarket will finally step up and produce a stock bathtub type intake gasket with the larger port size so that people can start to bolt large runner, single carb intake manifolds onto stock type Max Wedge heads.
We know from experience that standard port sized heads on a 505-inch short-block will produce a torque peak around 4,000 rpm. Given that information, as well as the compression ratio and exhaust header diameter, we were able to call up Comp Cams and tell them what they needed to know to grind us a cam that would work well with our motor.
Camshaft And Valvetrain
We knew that the size of the cylinder head ports would limit the power peak to less than 6,500 rpm, so there wasn't any reason to install expensive valvetrain parts designed for speeds higher than that. The street roller camshafts from Comp Cams are designed to provide high power output from a cost effective and durable valvetrain. These street roller profiles are easy on the valvesprings, but you do still need to use a valvespring that is designed to handle the higher loads that a solid roller camshaft generates.
Comp Cams has a wide selection of street roller cams in their catalog, but when we contacted them about a cam for this engine, they told us that with 505 inches and 12.5:1 compression ratio, we would be better off with a cam that is a little larger than any of their current catalog offerings. Fortunately, Comp has a wide library of Xtreme Energy roller profiles on hand, so they were able to quickly come up with a profile that matched our needs. The cam that the Comp engineer recommended for us was just one size larger than the XR292R in their current catalog. Our cam, which most likely would be called an XR298R if it was in the catalog, uses a 4877 intake lobe and a 4878 exhaust lobe. We had the camshaft ground on a 108-degree lobe separation angle with the intent of installing it two degrees advanced. The cam lobe specifications are 260/266 degrees of duration at .050-inch lift with gross valve lifts of .627 and .637 inch with 1.60 ratio rocker arms.
The Mancini heads are designed to operate with flat tappet camshafts and a maximum of .600-inch lift as delivered, so we needed to replace the valvesprings with a set that would be compatible with our roller cam. The valvesprings that Comp recommended we use with their roller cam was PN 26094-16. These 26094-16 valvesprings are good for up to .650-inch lift, which was just perfect since the combination of 1.60 ratio rocker arms and the tight .016-inch valve lash on the cam gave us a net valve lift of .620 inch. We had decided to run 1.60-inch-ratio rocker arms rather than the stock ratio of 1.50, in order to make a little more power. In addition to the extra lift, the 1.60-inch rocker arm shifted the pushrods away from a clearance problem that we saw when we mocked up the engine with 1.50 ratio rocker arms.
Paul Roberts from Gray's Automotive...
Paul Roberts from Gray's Automotive sets the valve lash before we fire up Project 505 on the dyno. The lash on the RAS rocker arms was rock solid after a dozen dyno pulls. The spray bars in the Indy valve covers provided a little extra oiling for the valvetrain during the long day of dyno pulls.
We used the cam-lift checking...
We used the cam-lift checking tool from Mancini Racing to verify the lift of our Comp Cams street roller. With the RAS 1.60 ratio rocker arms, we were right at .627-inch gross lift on the intake valves. Notice that the special retainers from Comp Cams provide extra clearance for the rocker arm.
We also tried a carb spacer...
We also tried a carb spacer from Wilson. The Wilson carb spacer is a merge type of spacer where the four individual holes are smoothly merged into one large opening. The notes on top of the Holley Dominator are there to keep track of which jets we're running in the various circuits.
We used a full lineup of parts...
We used a full lineup of parts from Comp Cams for this motor. The camshaft is from the Xtreme Energy street roller family. We also used PN 829-16 Comp roller lifters, PN 26094-16 valvesprings, and the new PN 1732-16 retainers.
Camshaft thrust is easily...
Camshaft thrust is easily adjusted by changing shims behind the bearing retainer. We set up this motor with 0.007 inch of camshaft endplay.
We used a T-fitting at the...
We used a T-fitting at the oil port in the back of the block to feed the spray bar oilers that are located in each valve cover. Using the spray bar oiling system drops the oil pressure by just 5 psi.