GM Engineers Tell Super Chevy How To Build The Best Budget LS Combos With Factory Parts
After a recent discussion with the Editor about the best combination of performance in and dollars out, we decided to go to the source to find out what the GM powertrain engineers would do if they were in our shoes: big power and torque ambitions and a very skinny wallet.
We sat down with Dean Guard, chief engineer for all of GM’s powertrain small-block engine programs, and his right-hand man, Mark Damico, to talk about what’s currently available in the way of LS small-blocks in America’s wrecking yards and want ads, which parts go best with other parts, and how to build lots of power, torque and reliability with stock GM parts.
SC: If you were building an LS small-block for street performance use, where would you start?
MD: The ’01 and later LQ4 truck engine with aluminum heads gives you 360 hp and six-liters of displacement, with an iron cylinder block. The cylinder heads and the ports are the same as those on the LS6 engine, but the LQ4 has bigger combustion chambers, about 71cc. Stock compression was 9.4:1. If you pick up the LQ9 piston, which is a flat-top piston, you can get back to 10:1 compression. Or, you can just look for an LQ9 engine, which is rare because it was built for the Cadillac Escalade, but we built hundreds of thousands of LQ4 engines for the trucks, so they’re easier to find. If you use the piston and rod assembly from the LQ9, which has floating pins, you get the compression, and the 400 hp.
SC: Is there a thinner production head gasket that you could use to get even higher compression without compromise?
MD: We’ve avoided it because you can get into pushrod problems. We went to a multi-layer steel gasket in 2001. When we set up the engine, we designed it for the graphoil gasket, which was 1.33 millimeters compressed. Multi-later steel gaskets can go down to 0.7 millimeters.
SC: So, you’d recommend the iron-block truck engine for long-term durability?
MD: Unless you really need the lighter weight of the aluminum version to take weight off the nose of the car. The 6.0-liter LS2 and L76 aluminum engine (SSR, Trailblazer, CTS, and Corvette) or the 7-liter aluminum engine is about 100 pounds lighter, but it will be a lot more expensive and harder to find. If you’re going to build an engine from the 6.0 or 6.2 truck engine, you should look into the ’07-and-later cylinder heads. They have bigger ports, larger valves, and more airflow, and they bolt right on.
SC: Every one of the LS engines since 1999 has come with electronic fuel injection, catalysts, oxygen sensors, black boxes, and so on. Would you recommend buying all of the electronic components along with an engine package, or going to the aftermarket?
DG: You’d have to have the oxygen sensors, for sure, or run an open loop, where the engine will run rich all the time. For most applications, all you really want is the right fuel and the right spark and everything else is not important to what you’re doing. There are a lot of decent set-point controllers out there, but the problem is, you have to buy it, and you have to do the work. You have to have the resources to where you can sweep the spark and sweep the fuel and determine how rich you want to be, with how much spark. One of the things you have to watch out for is that we changed from 24X to 58X when we changed from Gen III to Gen IV, which means the crankshaft position sensors used to read 24 times per engine revolution on the earlier engines but Gen IV engines read 58 times per revolution, once every six degrees.
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.
SC: It’s pretty apparent that if you use the right combinations of production parts, you can make a lot of reliable power and torque.
MD: If you take a 6.2 engine with the big heads and you’re not running catalytic converters [in an older car], with a long-duration cam and low backpressure, you’re getting tons of extra horsepower. The engines won’t respond with the backpressures that we have to have, but when you drop the backpressure on these engines, they respond. The LS3 engine, the Corvette engine with the big heads on it, is rated at 436 horsepower with the flapper valve in the exhaust system. You should be able to make 475 hp with unrestricted exhausts.
DG: Our ability to put all this stuff together analytically these days will usually get us within three percent of what we ultimately get on the dyno. Our new engine lab allows us to replicate the duty cycle of any racetrack in the world, and we can even replicate what an engine’s oiling system feels in cornering with a couple of our dynos. We used to have to rent a racetrack for a whole week with a bunch of different oil pan designs, hire drivers, hire ambulances, and then download data from the car and wait for three hours while it was analyzed. We don’t have to do that anymore. We can do all that right here in the lab.
SC: For those who do amateur road racing, club days and track days, do you have recommendation for those high-g cornering situations?
MD: The ’05 Corvette oil pan is better than the earlier gullwing or batwing pan, because it actually controls oil better in terms to keeping the oil close to the pickup. It’s functionally is superior in terms of max g’s. You can run longer at the same g level without running into oil starvation. If you’re going for sheer power and minimal windage, you want to use the larger truck pan, which has less windage and plenty of volume to handle the fore-aft acceleration, but if you’re going around corners, the ’05 Corvette pan is the one to use. The Z06, the ZR1 and the 2010 LS3 engine in the Grand Sport all have dry-sump systems that can be adapted to most of the earlier engines for road racing. But you have to use an LS9 crankshaft in order to drive the pumps. Because today’s high-performance tires can give you three to four tenths of a g more cornering force, we had to change over to dry-sump for the high-performance engines. But remember, the starter ring gear on the flywheel is now going to be the lowest thing on the engine, so, while you can lower the engine in the chassis, you still have to have room under the car for that.
SC: You’re now at 638 hp in the LS9 engine. Is there room for more?
DG: I’m not sure, but I think it would be nice to get to 650! There are still a lot of people around here with a great deal of passion about the small-block.