February 2011 Chevy High Performance Q&A

Under Pressure

Kevin McClelland Jan 11, 2011 0 Comment(s)
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My son, Daniel, and I were trying to beat the clock by purchasing a totaled ’06 GTO to steal its LS2 for his ’94 Mazda RX-7 engine swap. We got all the cool hardware from the GTO that we wanted to make the swap a dream. Well, this past weekend was time to break down the engine for the camshaft and heads upgrade we had planned.

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With the rear suspension/differential rebuild and the front suspension completely gone through, it’s time for the powertrain. The GTO didn’t look to be that well taken care of. At 42,000 miles, it was already on its second set of (baked) tires. As we split the engine and the trans, the first thing we noticed was the nice blue color of the pressure plate of the clutch! I’ve changed my fair share of clutches, and the hue of blue of this clutch was impressive.

With the engine now up on the stand we were ready to break it down to the short-block. The plan was to install a custom-ground camshaft that I had selected. Our goal is to make this car completely California emissions-legal and go through the referee process. Once approved, you get a decal in the doorjamb and you can have the car inspected at any smog station in California. So I had chosen to stick with GM-designed camshaft lobes but mix them up a little bit since I had access to both LS6 and LS7 camshaft profiles. I had a stick ground with the LS7 intake lobe and the LS6 exhaust lobe. This specs the camshaft out at 210/218 degrees duration at 0.050-inch tappet lift, 0.562/0.547-inch max lift, with 1.7 rockers. This is all ground on an emissions-friendly 116 separation angle. As for cylinder heads, we’re going to try out the Cadillac LSA Gen IVs, very similar to the rectangle-port Gen IV L92 engine’s except for a swirl vane in the inlet port to promote high swirl, and a unique kidney-shaped combustion chamber to promote tumble. With this mixture motion, they are much less susceptible to detonation than their L92 counterparts. The only thing we’re not real keen on is that they are down about 30 cfm at max lift, but they beat the L92 heads all the way to 0.400 inch of lift. I know they’ll make killer torque and horsepower until our mild camshaft runs out of headroom.

Back to the condition of the engine, as Daniel was taking it apart he called me over to check out the monster oil spill in the floor of the manifold plenum. The breather system on the LS engines can be less than effective. If you have any leakage of cylinder pressure it can force oil vapor right through the valley and into the intake manifold. This also answered why the rear main seal was leaking slightly. This guy had fun with his Goatbut didn’t service it too often. We’re down to the short and the engine looks fine except for some residual oil on the heads of the pistons. Well, those fresh new pieces are going to have to stay in their boxes a little longer. We’re breaking down the short for a quick ring and bearing swap. I will be much happier now knowing we’ve touched everything before dropping it in his car. Don’t get under pressure to finish your projects. What’s a little more work anyway? Until next month, have fun with your projects.




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