The Harland Sharp rocker arms...
The Harland Sharp rocker arms are a bolt-in installation on the OEM heads, and provide adjustability in the valvetrain where the OEM engine has none. The 1.8:1 ratio rockers deliver .648-inch lift via a 237-degree duration at .050 Bullet single-pattern cam.
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.
In keeping with a goal of...
In keeping with a goal of maximizing torque over a broad rpm range, the intake ports were reduced in volume from 278 cc to 256 cc, using epoxy where required. An interesting vane design was formed in the bowl area of the intake runner, with the intention of improving wet flow into the chamber.
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.
To make the most of the cylinder...
To make the most of the cylinder head castings, they need to be filled with top-quality components. The Manley valves are controlled by PAC beehive springs, with Manley beadlock hardware keeping it all together. The Harland Sharp rockers feature a 1.8:1 ratio, while stout 3/8-inch COMP pushrods reduce the potential for valvetrain deflection. Motion from the Bullet hydraulic roller cam is transferred by a set of COMP limited-travel hydraulic lifters.
A single-plane intake manifold...
A single-plane intake manifold from Mast Motorsports serves as an appropriate complement to the modified LS7 heads. The fuel rails and injectors are both FAST items.
The manifold was CNC ported...
The manifold was CNC ported as delivered, and was mildly reworked by Racing Engine Design. The intake manifold unbolts lengthwise to separate at the centerline, providing unrivaled access for further porting or modifications of the runners and plenum. Epoxy filler was added, primarily at the bottoms of the runners to reduce the manifold volume and match the configuration of the intake ports in the heads.
A huge 114mm single butterfly...
A huge 114mm single butterfly throttle body from TPIS funnels the air into the manifold, directing it straight downward and into the ports. Bowers tells us the large throttle body works well with the tall plenum of the Mast intake.
A modified set of Schoenfeld...
A modified set of Schoenfeld headers handle the exhaust. The headers feature a 1.75-inch primary tube diameter, with merge collectors. Experimentation determined that the primary tube length tuned the rpm range, while the merge collectors helped midrange with a small sacrifice at the top of the powerband.
A FAST XFI system handles...
A FAST XFI system handles the engine management electronics. Bowers is very impressed with the capabilities and ease of tuning with the FAST system.