GEN III Power
Alex Zorin, via Car Craft e-mail: In reference to the story "480 HP for $3,775" in the Apr. '07 issue: Is 425 hp from a stock LQ4 typical? The advertised horsepower figures I have seen for LS1 engines are in the 350hp range, and isn't the latest LS2 Corvette engine rated at 400 hp? Is the power difference because you went carbureted (over EFI), or does the factory rate with rear-wheel horsepower? Compared to the supercharged Gen I ("445 HP for $3,995," June '06), this Gen III made more power and only cost a shade more. That really got my attention and set me thinking.
Jeff Smith: We believe that there is an increasing number of car crafters who have begun to notice that the Gen IIIs are amazing and capable of exceptional power. It's getting more fun by the minute! The only thing we did to this iron-block 6.0L engine was add a set of headers and carbureted intake manifold. The stock GM horsepower rating for an LQ4 6.0L (364 ci) varies by vehicle. Most appear in trucks or the larger vans. The most conservative horsepower rating is 300 hp at 4,400 rpm and 360 lb-ft of torque at 4,000 rpm, and the most for the LQ4 is 325 hp. From what we've researched, there were noise issues with some trucks, which prevented GM from making more horsepower. This means they probably went conservative on the rating by restricting the inlet tract in order to meet noise regulations. Keep in mind that the new SAE horsepower-rating system (SAE J2723) is very conservative and requires the engine to be fitted with all the accessories and the complete exhaust system. The factory numbers are flywheel numbers. Despite the fact that we've seen information on more than one Web site claiming that these are rear-wheel horsepower numbers, it's not true. We tested our engine with none of the SAE restrictions. We also installed a carburetor and headers with a very free-flowing exhaust system. All of that could easily be worth 100 hp when you consider how restrictive the stock engine is in OE truck applications.
Even so, we were surprised that a carbureted 364ci engine with 9.4:1 compression and a stock cam could crank out 425 hp. And you can see what happened when we screwed in the very mild Hot cam-it made 483 hp! There are several reasons that these engines make such good power, but the main consideration is a set of excellent stock cylinder heads. Even the stock 6.0L aluminum heads offer a 15-degree valve angle and great flow characteristics right out of the box. Add a camshaft to an engine with a set of good intake- and exhaust-flow numbers and you'll make power.
Yes, the new LS2 is a great all-aluminum engine at a 4.00-inch bore and 3.62-inch stroke, and it's got some power potential rated at 400 hp with 10.9:1 compression. But I think there's a better car-crafter engine out there. Let's talk about the new-for-'07 L92, a 6.2L engine designed for the Cadillac Escalade with 403 hp at 5,700 rpm! It's got a 4.065-inch bore and 3.62-inch stroke that specs out at 376 ci. It's all-aluminum with 10.5:1 compression and, of course, those 320-cfm intake port heads with equally massive 2.165-inch intake valves. Let's talk about power, boys! Stick a camshaft in and uncork it with a big carburetor and a set of headers and watch what this baby will do. If it's rated at 403 hp in the Escalade, that means if we put headers, a cam, and an intake on it, it might make 480 hp right out of the box! This is a more sophisticated engine with GM's Displacement on Demand system, but that's easily overcome. This engine will be hard to find for a year or two, but if we could build any engine out of the GM fleet (except the LS7 because it's so expensive), I'd put my money into an L92.
You mentioned superchargers, which brings up yet another interesting idea. Imagine building a Gen III engine with those large-by-huge L92 heads, a relatively stout cam with a wide lobe-separation angle, then stuffing a Magnuson-style blower on it! And let's go one step further: Eaton is about to release a new four-lobe rotor supercharger called the Twin Vortices Series (TVS), which moves more air with better efficiency than the previous design, which was pretty damn strong. This means more airflow at the same boost at a lower discharge temperature, equating to even more power. This entire engine package would be somewhat pricey, and Magnuson doesn't have an L92 blower manifold designed-yet. But be assured that once Magnuson has a manifold and one of those TVS blowers, we'll be all over it. If more than 700 hp sounds like too much, you're reading the wrong magazine.
If you start with a boneyard engine like we did, it would be easy to duplicate our 550hp package with a 4.00-inch-bore LQ4 6.0L 346ci motor. Stuff in a 4.00-inch-stroke crank, and 600 hp from a 402ci motor using the same L92 heads is certainly achievable.