Sometimes the simplest combinations are the best. And sometimes it’s a matter of over-achieving a bit too. You may have read editor Henry De Los Santos’ editorial in the June, 2014 issue where he outlined the plan for a supercharged 502 big-block Chevy. If not, there’s this Chevrolet Performance ZZ502/502 crate engine that’s been hanging around the CHP shop. Henry also had a Vortech V7 YSi blower that was well suited for this project. One day it was like that Reese’s Peanut Butter Cup commercial where the chocolate and peanut butter collide. The idea of combining this basic 502ci Rat with the Vortech supercharger - “Hey, you put boost to my Rat motor!”
It turned out to be a really good idea.
Before we dive into the results that you already know because you’ve jumped ahead to the dyno curve, let’s take a look at what’s inside our ZZ502 base engine. The ZZ502 long block is based on GM’s Gen VI iron big-bore block. The bore and stroke are an excellent 4.470x4.000 and the big advantage is the near 4.500 inch bore diameter. It’s no secret that big-blocks really like larger bore diameters not just for the displacement, but because this allows those big valves to do their work more efficiently. The four-bolt main block houses a forged steel crank and spins shot-peened forged steel rods with a set of forged 9.6:1-compression pistons. So right away, this motor offers all the right components for a great street engine.
The Gen VI block has revised water passages in the deck surface (compared to the Gen V) so that it will readily accept even older MK IV heads. Also of major importance is this block incorporates a hydraulic roller camshaft with the Gen VI snout, which means the factory limiter plate eliminates the hassle of setting cam endplay with a bushing. This also means that with factory roller lifters, we can change cams and not have to buy new lifters. This also eliminates the worry of breaking in a flat tappet cam.
The factory cam is pretty tame with specs of 0.527/0.544 lift and 224/234 duration at 0.050-inch. But once we get into the testing, it’ll become apparent that the weak link in the valvetrain is the valvesprings. As you’ll see, this is the ZZ’s Achilles heel. The heads on the ZZ502 are aluminum oval port Bow Tie castings with good 2.250/1.88-inch valve sizes and the big oval ports are fairly efficient. Since the long block did not come with an intake, we bolted on an Edelbrock Victor Jr. oval port intake complete with a set of ARP intake bolts.
Since the engine was already assembled, all we had to do was bolt the supercharger to the front of the engine. That went really quickly and after we added a load of COMP Cams Muscle Car high-zinc 10w30 oil, we pressure lubed the engine, buttoned it up, and headed for Westech.
After bolting up our blown ZZ502 to Westech’s SuperFlow dyno, the first order of business was to run the engine naturally aspirated (NA) with the Demon 750 carburetor to baseline its out-of-the-crate power. Chevrolet Performance says this monster will make 502 hp. Once we adjusted the carb a little leaner and set the timing at 36 degrees, we quickly had 500 hp at 5,500 rpm. For torque, we only made 529 lb-ft at 4,200 which is substantially less than the 567 lb-ft that Chevy advertises. This is easily explained because we were using a big, single-plane intake compared to the dual-plane used by Chevrolet that could easily account for most of that difference. We had bigger plans, remember?
A big thing worth mentioning is that while this engine uses a mild cam, the horsepower curve tips over pretty low, at 5,800 rpm. We attribute this to the soft valvesprings. Rat motors generally need more spring pressure to support the rpm. This would become even more apparent with the blower test.
We didn’t spend much time with the NA power numbers because we couldn’t wait to hear the siren song of the supercharger. All we had to do was return the jetting back to the Demon’s blow-through settings, bolt down the Airaid carbon-fiber bonnet, and cinch up the 8mm cog belt. Now we were ready. The initial tests were with reduced timing until we could get the air/fuel ratio to where we wanted, which required a couple of fatter jet swaps. We finalized the timing at 25 degrees total advance with Rockett Brand 100-octane race gas and the engine really responded. With that accomplished, Westech’s Steve Brule spun the 502 out to peak power and we watched the numbers climb.
We’ll get to the horsepower numbers in a minute, but what’s impressive is the huge torque gain that comes from even small boost numbers. One criticism of centrifugal blowers is they don’t make instant boost, but even with only 3.6 psi, the Vortech blower still managed to add 195 lb-ft, boosting the torque from 534 to 729 lb-ft, which is a solid 36 percent gain. Despite the fact that we limited the boost to a max 10 psi, the average torque gain was 264 lb-ft over the naturally aspirated numbers. And that’s just the torque. Moving over to the horsepower side, again with just 10 psi, the Vortech pushed the peak power up to 822 hp for a gain of 322 horsepower, which is nothing less than a 64 percent improvement in horsepower.
As is usually the case with tests like these, there’s enormous room for improvement. If you look at the power graph, you can see that the blower test stopped at only 5,800 rpm and that the curve was still climbing. We stopped here because at 5,900 rpm the valvesprings gave up and the engine went into serious valve float. That means if we had been using stronger springs along with better pushrods, lighter retainers, and more precise roller rockers, our 502 probably could have made upwards of 840 to 850 hp with this stock cam. While that’s great news, we think this package has even more potential. So our plan is to return in a month or so with a slightly longer duration hydraulic roller cam with more valve lift, better springs, roller rockers, and stronger pushrods and evaluate that combination. And this is still with the original Chevrolet Performance oval port heads. We think this 502 will make more power at a little higher engine speed without sacrificing reliability. So look for even bigger numbers from this simple combination of displacement and a little bit of boost.
01. The basic ZZ502 comes with a balancer and covers. All you have to do is add an intake manifold, distributor, carburetor, and a few other details and it’s ready to run. With a hydraulic roller cam, you don’t even have to sweat the break-in, which makes living the Rat life much easier.
02. The Vortech V7 YSi supercharger is the overachiever in our story. This is really a smaller version race blower that’s capable of up to 1,200 hp at maximum boost of 30 psi. We didn’t utilize half of this blower’s potential, but it’s nice to know it’s there.
03. We bolted the blower in place with Vortech’s install kit. When you consider the extensive fabrication work required to plumb a pair of turbochargers, mounting this centrifugal is child’s play. The original install took a leisurely 3 hours. Now we could do it in about an hour.
04. We added a Moroso Gen V/VI pan both to improve windage control and increase capacity. This also included a new Moroso oil pump, pickup, and a hardened oil pump drive.
05. The only oil pan modification was to add a hole in the pan for the Vortech oil return fitting. The blower is fed pressurized engine oil from a braided steel hose connected to an adapter fitting at the back of the block.
06. The original pulley drive created a rather aggressive 8.1:1 overall step-up ratio. What we really needed was a smaller crank pulley that will be ready for Part II. Vortech also advises not to back-bend that reinforced 8mm cog belt. That’s why the tensioner pulley pushes against the cogged portion of the belt. These cogged belts do not need excessive tension like serpentine belts.
07. The intake system consists of an Edelbrock Victor Jr oval port single-plane intake and a Demon 750-cfm blow-through carburetor.
08. The key to a successful blow-through carburetor are these annular boosters. These boosters are much more sensitive to airflow and will pull more fuel than a typical drop-leg booster.
09. We also tried Airaid’s new carbon-fiber hat and it certainly contributed to our excellent power numbers.