When we last visited our Classic American Muscle CAM-S autocross project we were preparing for our first shakedown runs with the new suspension, exhaust, brakes, and interior components installed on our twin turbo 2003 Corvette Z06. While on the dyno, however, we experienced a few hiccups that were a sign of bigger problems to come. So, follow along as our journey takes a dark turn. But don’t worry, because there’s light at the end of this tunnel.
With much excitement, we headed out to a Cal Club Region SCCA autocross practice day anticipating huge gains in handling over our baseline testing. Heading out for the first run, engine detonation was noticeable as soon as the car began to build boost – any attempt to go past half throttle (or even maintain throttle as the turbos did their job) yielded unpleasant sounds under the hood. It was decided that partial throttle runs were not going to provide the suspension tuning data we needed, so we cut the test day short and went home disappointed.
With our CAM-S Corvette back in the shop, a leak-down test revealed that the more than decade-old Lingenfelter Performance Engineering (LPE) engine was not as fit as a fiddle. While we still don’t know the complete history of this particular Corvette, we do know that LPE built it for the 2004 Car and Driver magazine Super Car Challenge, and that at one time it took part in the One Lap of America – so we know it the car has been exercised.
The combination of the leak-down numbers and a few other issues that were bothering us prompted us to plan for a mild motor rebuild. Our hope was that a simple refresh might return this car to its former glory. But that’s not to say we felt like the car had a long way to go; a fairly recent run on the Dynojet at Extreme Performance yielded 716hp to the wheels on pump fuel, and we experienced clutch slippage at 720lb-ft of torque on a Dynapak at Church Automotive Testing. Considering those data points, we felt that while the motor may not be at full song, it’s probably not missing much power.
However, as the engine disassembly got underway, we ran into a number of issues that showed we were, perhaps, in for a bigger project than we anticipated. The primary issue we found was a damaged cylinder sleeve, very likely the cause of the out of spec leak-down results. Fortunately, a bad sleeve can be replaced in a GM LS engine with relative ease – it just requires a little machine work and a new liner. But, as often happens with projects, one thing led to another.
With our GM C5R block out for machine work, it was time to start looking at some of the other components. While inspecting the cylinder heads, there was evidence of a previous repair where a crack had been welded and smoothed. While that repair had been adequate, we wondered about its longevity considering the fact that we wanted to push the engine harder. The decision was made to shift from a motor refresh to a serious upgrade. After all, everyone needs more power.
The GM Performance Parts (GMPP) catalog was the cure for our cylinder head woes, thanks to its CNC-ported LS9 head assembly. Originally fitted to the supercharged ZR1 Corvette, these heads were engineered to work under pressure, and the CNC porting offers additional airflow – a more than competent replacement for our LPE modified LS6 heads.
Even though the GMPP cylinder heads come ready to run, we couldn’t pass up the opportunity to upgrade them with help from Comp Cams. A Comp Cams Beehive Valve Spring Kit would replace the original LS9 hardware; including a set of upgraded Beehive Springs, titanium retainers, as well as new locks, seals, and spring seats, this kit contains everything needed to handle ridiculous amounts of horsepower. The unique Beehive Spring design increases high-rev valve control, reduces weight, and increases spring life, all of which is vital in boosted or race applications.
We had not planned to change the camshaft since we knew the LPE-spec unit could exceed 700hp to the wheels and was still in good shape, but then Comp Cams educated us on how technology has evolved over the years, and with the new cylinder head package we could likely find additional power gains here, too. While this sounded good to us, the technical expertise needed to build the cams was beyond us, so we stepped aside and let the engine builder work directly with Comp Cams. In no time at all, the Comp Cams team had transformed one of its Custom Ground Camshaft Cores into a new unit for our engine and the cam was on its way to the shop.
Mating up with the camshaft would be a set of Comp Cams Short Travel Hydraulic Roller Lifters, which are designed for high-revving applications. The patent-pending design limits the lifter’s internal piston as it is pumped up, reducing power loss at higher rpm.
The next piece of the puzzle is the Comp Cams Max-Lift BSR Shaft Rocker System. This bushed shaft rocker system increases system stiffness, improves valvetrain dynamics, and reduces deflection. Thanks to its superior control characteristics, very aggressive camshaft profiles can be used.
The final piece of the valvetrain overhaul was the Comp Cams Keyway Adjustable Billet Timing set. This timing set offers eight degrees of cam timing adjustment, and features a heat-treated, double-roller timing chain.
With the block back in order, we sourced a new set of pistons from JE Pistons, which is optimized to work with the new LS9 cylinder heads. The pistons would marry to the crankshaft via the LPE-spec connecting rods, which were still in good shape.
With the motor out, we began to evaluate the ancillary systems in the hunt for more problems, and we believe we may have found the source of some of the detonation problems – one of the turbocharger wastegates had a seized actuator, preventing it from bleeding off pressure.
Not knowing for certain the last time the pressure side of things had been serviced, we sent the turbochargers to Turbos Direct for a rebuild and took the opportunity to have a thermal coating applied to the housings. New actuators and wastegate springs would also be installed at this time, resolving the original problem.
As is all too often the case, the mechanical portion of the engine rebuild has taken longer than expected, but we anticipate having everything ready to go back in the car by the time this issue reaches your mailbox. Once that’s done, we’ll jump into our next portion of the project: a new intake system. Oh, and we’ll also be hunting for a clutch that can harness the power of this beast.