The 1,000-horsepower mark has always been a definitive high-water mark for a street car. As technology has improved, the refinement and control of power-adders has progressed to a point where a 1,000-horsepower street car is a relatively attainable goal. However, reaching 1,000 horsepower naturally-aspirated is still a herculean task, let alone doing it in an engine for the street. Enter Hardcore Horsepower and Mike Petralia.
“This engine is still a work in progress,” says Petralia of the 632 cubic-inch big-block Chevy. “It is going to be a street engine for a local customer for his ‘88 Camaro in a semi-Pro-Street build. The goal is a 1,000 horsepower pump-gas street motor, and this will be the test mule for a crate engine package.”
Building a Foundation
Starting with a Dart Big M Mark IV engine block with billet main caps, Petralia blueprinted the block, as his blocks come completely machined and clearanced direct from Dart. The block is then outfitted with King Racing bearings, with the clearances set on the loose side, since the engine will utilize a Melling “Shark Tooth” extra-high-volume oil pump.
From there, a Lunati forged 4340 steel crankshaft with a 4.75-inch stroke is utilized. “The increase in popularity of 632s over the past couple of years is due in large part to affordable 4.75-inch stroke cranks coming to market,” Petralia says. “Before that, it was at least a two-thousand dollar proposition to get into a 632 crank.”
Attached to the Lunati crank are forged steel Lunati I-beam rods to handle the occasional jaunt to 7,000 rpm. 4.600-inch 2618-forged aluminum flat-top pistons from JE sit in the bores, with the bores honed with slightly more piston-to-wall clearance in preparation for some nitrous use in the future. With that in mind, the Total Seal AP Steel piston rings were file-fit with a slightly-larger gap as well.
The oil pan is a straightforward Moroso steel unit with built-in windage screen, crank scraper on the right side, and trap door baffling around the sump pick-up area. The pan has pressed in reliefs for rod clearance to accommodate the large 4.75-inch stroke. To maintain timing under all loads, Petralia used a billet roller timing set from SA Gear and PBM.
The Upper Crust
Topping off the stout shortblock is a pair of aluminum heads that Petralia prefers to keep under wraps. While the brand and runner sizes are kept close to the vest, he will, however, disclose that he has completely worked over the intake and exhaust ports to flow over 425 cfm on the intake and 355 cfm on the exhaust.
Petralia is similarly tight-lipped about the camshaft specs, but did reveal that it was a Comp Cams custom unit, that has over 0.800-inch of lift at the valve, and more than 280 degrees of duration at .050-inch. Comp Cams triple valve springs are used to control the valve motion, and measure 330 pounds-per-inch at the seat, and over 900 lb/in when open. The camshaft profile selected is aimed more at naturally-aspirated performance than nitrous use, since 99-percent of the engine’s life will be spent without the aid of nitrous oxide.
Comp Cams 7/16-inch steel pushrods sit atop Erson bushed solid-roller lifters. The combo actuates Crower stainless steel shaft rockers with a 1.8:1 rocker arm ratio, which if you do some backwards math, gives you an idea of the camshaft specs.
“All of the engines I build at this power level run shaft rockers,” Petralia says. “I prefer stainless to aluminum in this application, since I’ve seen aluminum pieces fail when subjected to long-haul street duty when running triple valve springs.”
Fueling The Fire
Topping the combination off is a visually-impressive intake manifold which is CNC port-matched to the intake ports from the manufacturer. From there, Petralia does a complete porting job on the intake by hand. Sitting atop a custom carb spacer is a Quick Fuel Technology QFX-4700 series carburetor, which flows 1,150 cfm. The thirsty carburetor is fed by a fuel system made up of Holley and Aeromotive components.
Keeping the candles lit is an MSD billet distributor, and Lemon’s double-stepped headers help boost power by scavenging every last wisp of exhaust gas out of the cylinders. Starting with a 2-1/4-inch tube at the exhaust port, the runners expand to a 2-3/8-inch tube diameter, before merging into a 4.0-inch collector.
Running The Number
When Petralia hooked the engine up to Hardcore Horsepower’s in-house engine dyno, he only got partway through his power run before an oil leak put an end to the day’s testing, with the final recorded numbers at 927 horsepower and 829 pound-feet of torque.
“I was a little disappointed we didn’t make 1,000 horsepower with it,” Petralia says. “If you notice on the dyno sheet, we stopped the pull at 6,500 rpm, because we had an oil seal blow out on the front of the intake manifold.”
Not content to just fix the oil seal and put the engine back on the dyno, Petralia decided to try a different camshaft while the engine was down. “I tore it back apart to change cams, to chase that 1,000 horsepower number. The power curve shows that the engine wasn’t done making power at 6,500. Now that I’ve changed the cam, we’ll get even more out of it on a full pull.”
While 75 horsepower may not sound like a lot, in a naturally-aspirated combination, it’s a hefty jump. “The engine should make power past 7,000 rpm, so I’m counting on that to help get it past the 1,000-horepower mark as well,” says Petralia.
Now 7,000 rpm out of an engine designed for the street might seem excessive, but everything about this engine is excessive. “It’s a very radical street motor,” says Petralia. “I don’t worry about peak horsepower RPM, based on whether it is a street motor or race motor. I’m giving the customer the power he wants with the fuel he wants. He wants 1,000 horsepower, naturally-aspirated, on pump gas. In order to do that we have to turn some RPM.”
However, Petralia points out, that it won’t need to be spun to 7,000 rpm on the street to make decent power, as it still has significant grunt under the curve. “This engine is so big, he doesn’t have to shift at 7,000 rpm to get solid power. With the automatic transmission, without his foot to the floor, the engine will probably be shifting mostly at 4,500 rpm,” Petralia says. “You can see the dyno, even starting the pull early at 3,500, the engine is over 750 foot-pounds of torque.”
So while the initial dyno pulls fell short thanks to an abbreviated dyno session, Petralia is bound and determined to meet the 1,000 horsepower mark, and once that’s achieved, push past it. “The engine’s sole purpose is to be a very powerful pump-gas big-block Chevy for the street. It does that, and idles at about 1,000 rpm” says Petralia. “Once we get it back on the dyno, we’re going to add some race gas and spray it with probably a 200 shot. I didn’t build it as a nitrous motor, but it’ll handle that.”
With plans to have everything back on the dyno in a few months, we’re eager to see results with the revised cam profiles, and then what kind numbers the engine posts with giggle gas. Make sure to stay tuned, as Petralia has promised us first crack at the results from the next Hardcore Horsepower test session.