The Big Torque: Hardcore Horsepower Builds a Big Block Chevy That Makes 700 Ft.-Lbs. of Torque

You need cubic inches to make torque. Hardcore Horsepower had Dart overbore one if its four-bolt “Big M Sportsman” blocks to 4.600 inches, then bolted in a 4.250 inch stroke Scat forged crankshaft. Combined with the 6.385-inch Scat rods, you get 565 cubic inches of big block Chevy. Those two gauges are measuring rod bolt stretch to make sure the bolts are within spec. If the bolts have stretched too much, they are in danger of snapping under load.

The engine will run on pump gas, so the compression had to be kept reasonable. The Dart block was surfaced to put the pistons .017-inch below the deck at TDC. Combined with the AFR cylinder heads’ 121cc combustion chambers and .040 x 4.620 inch MLS head gaskets, final compression ratio came out to 10.25:1.

Hardcore Horsepower had Comp Cams custom-grind a hydraulic roller camshaft. The .617-inch lift cam was degreed in straight up at a 116-degree lobe separation angle. The cylinder heads are AFR Magnums. The aluminum heads feature 305cc intake runners, CNC machined 121cc combustion chambers, and 2.250 inch intake/1.880 inch exhaust valves. AFR says the Magnums are ideal for big cubic inch torque monsters like our 565.

Even though the 565 won’t see the high side of 6,000 rpm, controlling crank windage is still important with long-stroke engine. Hardcore Horsepower installed a Canton Pro Power Plus louvered windage tray to keep oil off the crank and air out of the oil. Canton Racing also supplied the oil pan and pickup; the pump is a Melling high volume unit.

Dart blocks don't include an oil filter adapter, so they installed this nice Summit Racing billet piece.

The Holley multi-port HP EFI system runs 55-lbs./hr. injectors from Trick Flow Racing. The Holley single plane cast aluminum intake with a 4150-"Cloverleaf" flange is included in Holley's kit, along with everything else needed to install and run EFI.

After warming up the engine on the dyno, the rocker arms were re-lashed to spec. You can also see the beat-up old two inch diameter Hooker headers Hardcore Horsepower has had around the shop forever. Mike Petralia feels it’s important to test with something similar to what’s actually being used out on the street.

Since this engine is big, Petralia wanted to try bigger headers. He installed a set of Hooker Competition headers with 2.250-inch primary tubes and four inch collectors, plus adjustable primary and collector tube extensions. The big race pipes cost some power down low in this relatively low-compression engine.

The longer lines on the graph are a full pull with the two inch dyno headers. The pull started around 1,500 rpm and finished just shy of 6,000 rpm. The bold lines are a shorter pull with the Hooker Competition headers. You can see that torque (blue lines) was down in the lower rpms, but then climbed to a best peak of 702 ft.-lbs. at 4,400 rpm. Horsepower peaked with 653 at 5,400 rpm with the big headers too. Note the thin blue torque line starts at 500 ft.-lbs. at 1,800 rpm!

This chart shows the dyno results with the two inch headers. This street monster had no trouble pulling 509 ft.-lbs. at 2,000 rpm, 599 ft.-lbs. at 3,000 rpm, 666 ft.-lbs. at 4,000 rpm and 689 ft.-lbs. at 4,500 rpm. That’s turbo-diesel torque without the noise, smell, and black smoke!