It's taken a while-OK, a year to be exact-to get our 2008 Pontiac G8 GT back in action. Frequent GM High-Tech readers may have remembered us taking this seemingly stock G8 (except for the ProCharger P-1SC kit and tune) and adding a set of SLP 1.85:1-ratio rockers, stock LS7 lifters, and American Racing Headers 1 7/8-inch long-tubes, which pumped out a whopping 482 hp and 429 lb-ft of torque at the wheels, all with a mere 8 psi of boost. The G8's owner gained every last bit of enjoyment out of the newly found power before swapping blower pulleys, jumping boost to 12 psi, and trying to take the G8 past the 500hp mark. It was at that point where we'd taken the stock 6.0L to its limits-ultimately ending up with a busted ring land.
Having to now deviate from our original plan of beefing up the fuel system and adding a little methanol injection, we now had to take a few steps back and build up the bottom end of the L76 to withstand the additional thrashing it will endure. After removal of the 6-liter powerplant at Tune Time Performance, the L76 was taken to B&B Automotive Machine Shop in Lynbrook, New York. It was at B&B where the block was cleaned up, honed, and readied for assembly, along with polishing the crankshaft and balancing the rotating assembly, but once again we took it a step further. The L92 cylinder heads were untouched, so while apart we decided to have the valves unshrouded a bit and the exhaust ports massaged some for a quicker exit.
After placing a few phone calls, we obtained a set of Mahle forged low-compression pistons, Eagle H-beam forged rods and ARP hardware to keep the engine together with confidence. In order to handle the anticipated gain in power, the owner called upon Pat Barrett at Level 10 Transmissions to beef up the 6L80E transmission. And once again G8 mastermind Matt Hauffe and the crew at Tune Time Performance in Toms River, New Jersey, would be orchestrating all of the planned modifications including installation and dyno tuning.
Beyond adding strength to the bottom half of the 6-liter, some additional go-fast goodies were ordered, such as a FAST 102mm LSXR intake manifold and a Comp Cams centrifugal blower-friendly LSR cam. Between the ported heads, new cam, intake, and a larger D-1SC blower as well as a rotating assembly built for punishment, we are expecting some big numbers out of this grocery-getter-while still utilizing (near) stock cubic-inches. And best of all, we will have plenty of headroom for further mods should we be in need of more horsepower.
| LIFT |
BEFORE |
AFTER |
| 0.100 |
52.44 |
53.27 |
| 0.200 |
115.97 |
115.12 |
| 0.300 |
152.64 |
154.36 |
| 0.400 |
176.80 |
182.62 |
| 0.500 |
188.89 |
198.75 |
| 0.550 |
192.07 |
208.06 |
Beyond cleaning and honing...
Beyond cleaning and honing the L76 engine block, the first order of business was to install the Calico coated camshaft bearings from GM Performance Parts. Calico coatings reduce friction and wear versus a conventional style bearing. Next, a Comp 0.614/0.624-inch lift, 222/238-duration cam was installed, being careful not to nick any of the cam bearings. A liberal amount of break-in lube should be applied.
It was now time to install...
It was now time to install the main bearings, stock crankshaft, and main caps. In order to keep the bottom end together we obtained main studs from ARP. Studs are always preferred over bolts to reduce stress on the threads, create proper alignment and torque specifications, and to ensure clamping force is even across the board. The stock crank is still in premier shape, just needing a slight polish and chamfering of the oil galleys.
Once the crankshaft is installed,...
Once the crankshaft is installed, all mains are slid into place and properly torqued via a torque wrench. This is important, as it is imperative that all main caps be evenly tightened to ensure proper bearing wear and even tolerances.
In order to handle the substantial...
In order to handle the substantial increase in horsepower we ordered these 4340 steel H-beam rods from Eagle (PN CRS6125O3D2000). While these are not the lightest rods on the market (620g), they are one of the strongest, and in order to handle the pressure induced from a power-adder, we'll take strength over weight any day. Eagle indicated that these rods will handle upwards of 1,100 hp. For additional strength we called Summit Racing for a set of ARP L-19 rod bolts, which are much stronger than the standard ARP2000 units. All L-19s are rated to between 220,000 - 270,000 psi strength.