416ci LS3 Engine Build - Part 2 - Top End

Building up the top end of The Beast

Jeremy D. Clough Jan 1, 2014 0 Comment(s)
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LS3 Top End Assembly LS7 Pro Elite Heads 2/27

1. For the top end, we selected LS7 Pro Elite heads from RHS. These 355-T6 aluminum units come fully assembled with lightweight Manley valves.

LS3 Top End Assembly Valve Stem Lock 3/27

4. Note the rounded mounting surface for the valve stem lock. While I haven’t seen it specified, it makes sense that the radius avoids creating a stress riser better than a square-edged cut would.

LS3 Top End Assembly CNC Ports 4/27

2. The RHS heads are also CNC-ported. There’s still a lot to be said for the line-of-sight approach to flow, and there’s clearly plenty of that here.

LS3 Top End Assembly Valve Stem Install 5/27

7. Since removing the valves damages the seals, new ones were installed when the valves were put back in. The numbers denote the spring heights with the valves installed.

LS3 Top End Assembly Valve Mating Surface 6/27

5. Here’s the mating surface of the valve after lapping. The frosted grey area is the area that’s been lapped.

LS3 Top End Assembly Valve Lapping 7/27

3. The first step in our head work was to disassemble the heads and “lap” the valves into their seats in the combustion chamber. The heads were then surfaced, to ensure a true surface where they mate to the block.

LS3 Top End Assembly Valve Stem Compressing 8/27

8. A pneumatic tool is used to compress the valve stems and slip the retainers into place.

LS3 Top End Assembly Bolt Anchor Point 9/27

11. Unlike factory LS heads, the RHS units feature a six-bolt configuration. Mated to an RHS (or LSX) block with the anchor points for those extra bolts, this arrangement offers significantly increased clamping force, a plus on boosted engines.

LS3 Top End Assembly Dual Spring 10/27

6. Good springs are crucial, especially at high rpm. The dual-spring feature is added insurance: If one of the two breaks, there’s still another to keep the valve from dropping.

LS3 Top End Assembly Comp Hydraulic Roller Lifters 11/27

14. With the cam in place, we dropped in the Comp hydraulic roller lifters and installed a factory lifter tray to keep them in place. The lifters had previously been soaked in solvent to prepare them for installation.

LS3 Top End Assembly Comp Cam Cam Shaft 12/27

12. Comp Cams provided the cam, which features 0.605-/0.615-inch lift, 238-/248-degrees duration, and a 112-degree LSA. After being lubed, it was slipped carefully into its bearings in the block.

LS3 Top End Assembly Combustion Chamber Size Check 13/27

9. After machining, the heads were cc’d to check the size of the combustion chamber. In our case, we wanted to stick with the factory 10.7:1 ratio.

LS3 Top End Assembly Comp Shaft Rockers 14/27

16. In addition to providing more stability than traditional stud-mounted units, the aluminum Comp shaft rockers come drilled with oiling holes to keep everything lubricated.

LS3 Top End Assembly Roller Rocker Base 15/27

15. The next order of business was to install the base for our Comp 1.8-ratio shaft-mounted roller rockers. Part of the installation process was measuring for the optimum mounting height, then shimming the base.

LS3 Top End Assembly Cam Degreeing 16/27

13. After the Comp Cams timing set was installed, it was adjusted to degree in the cam. The cam gear on the Comp set uses a screw on an eccentric to give some adjustment without having to disassemble everything.

LS3 Top End Assembly FAST LSXR Big Mouth Throttle Body 17/27

19. We paired the LSXR with one of FAST’s beautifully machined 102mm Big Mouth throttle bodies. It’s every bit as big as it looks it the picture.

LS3 Top End Assembly Combustion Multilayer Steel Head Gasket 18/27

10. After putting a multilayer steel head gasket in place, the heads slipped onto their ARP studs. The fasteners were then torqued down, followed by the top cover.

LS3 Top End Assembly Pushrod And Rocker Shaft Install 19/27

17. Once the bases were shimmed and torqued in place, we could install the pushrods and bolt down the rocker shafts.

LS3 Top End Assembly FAST Fuel Rail Install 20/27

23. To install the assembled rails, we aligned the tops of the injectors with their respective holes in the underside of each rail, then pushed the rails down, essentially “plugging in” the injectors. After that, we indexed the fuel-rail mounting brackets with their holes in the intake, screwed them down, and put the crossover in place.

LS3 Top End Assembly Pedal Assembly 21/27

20. While the factory Corvette throttle body uses drive-by-wire actuation, the FAST unit is cable-operated. That means you’ll need to add a cable to your pedal assembly and, more than likely, change out your engine computer.

LS3 Top End Assembly FAST Injectors 22/27

21. With their O-rings lubricated, the eight FAST injectors slipped easily into place in the intake. Thanks to a healthy flow rating of 65-lb/hr, they should provide plenty of fuel to feed our big-inch stroker.

LS3 Top End Assembly FAST LSXR Intake 23/27

18. FAST’s LSXR intake is made of lightweight polymer. The LS7 version we used features raised ports, removable runners, and a 102mm throttle-body opening.

LS3 Top End Assembly Valve Cover 24/27

24. The height of our valvetrain kept us from using stock valve covers, so we used this set of cast-aluminum covers instead. They came in a black-crinkle finish, with oil-control baffles already installed.

LS3 Top End Assembly FAST Fuel Rails 25/27

22. Along with the injectors, FAST supplied a set of red-anodized fuel rails and an -8 AN fuel crossover. We used an aluminum AN wrench to ensure we didn’t scratch up the anodized fittings.

LS3 Top End Assembly Valve Cover Install 26/27

25. Here’s a shot of one of the covers as installed. As you can see, they come with mounting studs that retain the factory centerbolt mounting arrangement.

LS3 Top End Assembly 27/27

26. Done. Our LS3 stroker is now officially together, and ready to hit the dyno.


Comp Cams
Memphis, TN 38118
Racing Head Service
Memphis, TN 38118
Fuel Air Spark Technology
Memphis, TN 38118
Grimes Automotive Machine


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