There comes a time in every project's life where it's all about refining the combination. When all of the parts are working together and the car drives the way you like, but you just need to make a couple more tweaks to the powertrain to really dial it in. Such is the case with our 2003 C5 Z06, which has been together for a couple of years sporting a docile 227/230 duration camshaft, a pair of "ported and polished" LS6 cylinder heads, a set of LG long-tube headers, an underdrive pulley, and a Vararam cold-air intake. This combination was perfect for driving every day and could get down on the street with the best of them.
At 417 rwhp, the LS6 was making good power without suffering from too-big-of-a-cam syndrome, and it was perfectly happy to fire up cold and drive to the Keys if we so desired. That said, it could have used just a little more power across the board and it really would have been nice if the throttle response was just a little crisper. We're not talking about major 100-rwhp jumps here that require new injectors or parts, just 20 to 30 lb-ft of torque and a nice climb through the powerband to get our lightweight and nimble Z06 running in tip-top shape. As it were, adding that kind of power on an already optimized setup wasn't a simple task, as the current combo was working together well. All of the low hanging fruit, such as a cold-air intake, long-tube headers, or pulley upgrade had already been completed and there was no way we were going to build a new motor or add an expensive forced induction system to make the new power.
With ported LS6 heads, even a cylinder head swap was risky, as the LS6s are known performers when setup correctly. But, what the factory does really well, the aftermarket can do even better, and after researching our options, we decided that a cylinder head and intake manifold swap were the perfect parts to refine our engine combination and bring in additional power without destroying the calm demeanor of the Z. But as we said, we were going up against a quality set of heads already (ported 243-casting LS6 heads), which meant we were going to have to call in the big guns at Air Flow Research (AFR) if we wanted to make the swap worth while.
Enter Tony Mamo and the airflow specialists at AFR. They've been in the LS game for a very long time and all of their heads have been proven performers on a variety of combinations. After consulting with Tony, and explaining our goals, we settled on testing a set of AFR Mongoose 215cc LS cylinder heads paired with a FAST 92mm intake manifold and a 90mm drive-by-wire LS2 throttle body. With 61cc chambers, and a Cometic .040-inch compressed gasket, Tony spec'd our 215cc heads to give us a small increase in compression—without exceeding the limits of pump gas—and to squeeze maximum performance out of our relatively small camshaft. Billed as a "medium port, high velocity" cylinder head, the 215s work perfectly on a 4-inch bore package, but work very well on a 346 that has been optimized for the well flowing (312 cfm) heads. These 100-percent CNC'd beauties come standard with a 5-angle valve job and can be milled to your desired chamber volume by AFR at the time of your order.
Additionally, Tony suggested we tweak our air intake system, ditching the stock LS6 intake manifold and 78mm throttle body for an upgraded unit from FAST. As luck would have it, FAST recently re-released the wonderful 92mm LSX intake manifold, which had been on the back burner since the release of the 102mm LSX-R manifold. The 92 works incredibly well for small cubic-inch motors and retains excellent street manners and throttle response when paired with the right parts. Unfortunately, finding a 90mm drive-by-wire throttle body is always a bit of an issue (hey aftermarket, you listening?!), but the crew at Scoggin Dickey Parts Center have been hoarding take-off LS2 units for years, and have them in stock for anyone looking to do this swap. We ordered the throttle body, Cometic head gaskets, and a set of ARP head bolts from Scoggin Dickey, and they showed up almost immediately, as they usually do from the pros at Scoggin. Lastly, we teamed up with Howard Tanner and Jay Healy at Redline Motorsports to complete our upgrades, leaning on them heavily for their expertise in OEM quality installations and calibrating. After all, no matter how much (or how little) power you make, the tune can make or break the project, and with Howard on the dyno, you know you're going to get a ride that drives better than stock, with maximum performance and safety.