Bowers did experiment a bit with the pistons, making mill-cut grooves in the piston crowns in the vicinity of the spark plugs: “I looked at the chamber shape and design and tried to gain some turbulence in the spark plug area of the chamber. It was just an experiment. I don’t know if it helped it or not, but it seemed to help reduce the tendency to detonate. I made horizontal and vertical cuts with a ball mill that line up with the spark plug.” Wrapping the pistons are Total Seal conventional rings in a 1.5mm/1.5mm/3mm ring package, featuring moly top rings with Napier second rings to improve oil control.

Top End, Cam, and Valvetrain

With the wide proliferation of cylinder heads available for LS-series engines, there are seemingly endless choices on how to top the engine. Bowers selected the factory LS7 cylinder heads, based upon flow bench testing. “We took all the cylinder heads that we could use, and filled them to a volume that we thought would be effective in this rpm range, and the LS7 head proved to have the best flow.” The cylinder head was modified to optimize midrange flow and torque production over a wide operating range, with the final intake port volume reduced to 256 cc, from the factory 278 cc. The intake ports feature a vane in the transition from the runner to the bowl, which Bowers designed to improve the wet flow characteristics: “We were trying to direct the air and fuel off of the spark plug. The vane pushes the air to the side and keeps the big drops of fuel that come at low speed off the plug. It also helps to even out the flow and picks up the overall intake port flow.” To fit the LS7 head to the smaller bore of the 6.0L block, the exhaust valve diameter was reduced to 1.560 inches.

Complementing the cylinder heads is an intake manifold from Mast Motorsports. This manifold was purchased fully CNC ported, however, as with the heads, the volume of the manifold was reduced to improve flow velocity and enhance the engine’s torque production in the lower end of the powerband. Completing the induction is a TPIS 114mm single butterfly throttle body, with FAST 36 lb/hr injectors and FAST fuel rails. A FAST XFI ECU operates the injection system. Bowers was impressed with the FAST electronics: “It was absolutely the best stuff we’ve ever used. It is super easy to tune and control, and it is very forgiving, and they have great support for it too.” FAST also supplied the XIM box to control the MSD coil-pack ignition.

To work the valves, Bowers selected a Bullet single-pattern hydraulic-roller grind with 237 degrees duration at .050. Bowers explained his selection: “We looked at all sorts of grinds, but I thought with the merged header collector and the other things we had going, I didn’t need any extra exhaust duration. I was trying to make a bunch of midrange power, and when I figured everything in, I thought that up to 6,500 rpm the single-pattern cam was great. If I would have added 4-5 degrees of exhaust duration or more it would have hurt the low end.” The lobe separation angle was ground at 104 degrees. Bowers elaborated: “The tight lobe separation seems to make a lot more midrange torque, which was our focus on this engine. If I default to a tight lobe separation cam, that will always pick up midrange torque.”

To allow the Bullet cam to work to its potential, the rest of the valvetrain needs to be up to the task. The heads were filled with Manley LS7 replacement valves, with the aforementioned reduced exhaust valve diameter. The rockers are 1.8:1 Harland Sharp bolt-on aluminum rollers, which feature an adjustable pushrod cup. The rockers work with the Bullet cam to deliver .648-inch lift at the valve. COMP heavy-wall 3/8-inch pushrods transfer the motion from a set of COMP limited-travel hydraulic roller lifters, while PAC beehive springs control the valves. With a peak engine speed target of 6,500 rpm, this valvetrain combination performed beautifully.