MD: And the change was not clean. In '05, we used 24X, in '06 when OBD-III came in, we used a mixture of both 24X and 58X, and in '07 and after, we used 58X, so you've really got to get specific. On the LS2 engine, we used both, and the cam sensor changed with 58X, from 2X to 4X.
DG: So, you have to be careful. You can't use a 58X controller on a 24X engine or vice-versa, without a lot of headaches. In the hot rodding world, the set-point controller is what I would use, using the current oxygen sensors as a rough guide to see where you are. Or, you can use wide-range aftermarket controllers to tell you exactly where you are. With a little trial and error, you can spark it until it knocks and then back it off, fuel in until about 12.5 to 1, and you'll be pretty close. You might not get that last two horsepower, but you won't burn holes in your pistons. You'll be pretty close to what we can do with a whole lot more finesse because of what we're required to do for the government.
SC: So, our hot-tip combination is the LQ4 iron-block truck engine or the aluminum 6.0 combined with the '07 and later big-port aluminum heads on it, for a reliable, lightweight 400hp engine. Where do we go from here? Camshaft?
MD: In '01, the base LS1 Corvette cam and the truck cam were the same profile and the same part number. In '05, we went to 6.0 liters on the Corvette, 400 hp, and used the '01 LS6 cam, which was 13.3 millimeters in lift. It's not the same part number, because we moved the cam sensor from the rear of the block to the front of the block, but it's the same lobe profile and timing are the same. So, what I would recommend is the Gen III '01 LS6 camshaft, with 13.3 mils lift versus the 12.2 mils in the truck engine, so you gain a millimeter or 40 thousandths of lift without any internal clearance problems. All of the rocker arms are 1.7:1 ratio, and they're all the same, investment-cast steel, very nice parts, but if you use the '07 cylinder head with the big ports, those heads use an offset intake rocker arm to compensate for the larger ports, and you'll have to use those on that head. Gen III and Gen IV pushrods are all the same, too.
SC: So, what would be the best available valvetrain combination?
MD: The '02 and later LS6 engine had the 14-millimeter lift camshaft, long with lightweight valves and stiffer valve springs, if you're looking to run the engine at higher rpm levels. You should run the entire combination, or you will be hitting valves to pistons. The 13.3 lift cam would work well with everything. We also did an ASA cam for the ASA spec-engine program. It's an SPO part with more duration and more overlap in it, and it sounds great at idle. All of our cams are made from very, very good steel, and we test it to the limit.
SC: Do you have any cautionary words about today's fuels?
MD: We can run 11:1 compression ratio with today's premium fuels, but you'd better have a very good cooling system and a low-temperature thermostat in your engine. The problem is that you can't hear knock at high engine speeds, so you're running blind. Better to keep the engine cool.
DG: You'd probably be okay at 11.5:1 with 98-octane premium fuel. Your readers don't have to do 28 consecutive passes, or run in Death Valley like we do, so it would probably be okay.
MD: The Gen IV engines have the knock sensors on the outside of the block and they are flat-response sensors that measure vibration. You can use those to run compression ratio up, because they can hear what you can't hear. If you put the big head on a 6.2-liter engine with the flat-top piston in it, you get 10.5:1. On a 6.0, the number comes in at 10.0:1 with a 68cc chamber.
SC: What can you do on the exhaust side with production parts?
MD: We recommend the Corvette cast exhaust manifolds. The sheetmetal ones are nice pieces, but they are now 10 years old, so the cast pieces might be a better choice. The Corvette manifolds have the center take-down versus the rear take-down. The LS7 long-runner manifolds are fabricated, but they are going to be hard to find. Any older Corvette manifolds are tubular and if they're not cracked, they'd be very good.