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BBC 565 EFI 648-653hp-689-702tq #14-31 GRAPH OVERLAY
Hardcore

A set of Mahle PowerPak forged pistons swing on Scat 6.385-inch long forged H-beam rods. The pistons have a healthy +13cc dome and Mahle’s GRAFAL® coating to reduce drag, piston noise, scuffing, friction, and cylinder bore wear. The rings are file-fit.

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!

Any time you can put an engine together that makes enough torque to strip the concrete off the Hoover Dam, yet still gives away very little hint of what’s really lurking under your hood, you’ve built yourself a winner.

Mike Petralia of Hardcore Horsepower did just that with a 565 cubic inch big block Chevy engine destined for a tricked-out ’70 C10 Chevy truck. The engine cranks out 650 peak horsepower at 5,400 rpm and 700 ft.-lbs. of tire shredding torque at 4,500 rpm, yet idles at 850 rpm and pulls enough vacuum to run power brakes. That’s one awesome street motor.

The peak power numbers don’t tell the whole story. Over the course of a three-day test and tune session Hardcore’s Land & Sea engine dynamometer, the 565 laid down more than 500 ft.-lbs. of torque at 1,800 rpm and 600 ft.-lbs. at 3,000 rpm.

Petralia knew he needed cubic inches to make that kind of torque, so he had Dart punch out the bores of a Big M Sportsman GEN VI block to 4.600 inches. To reach the final displacement of 565 cubic inches, he dropped in a 4.250-inch stroke Scat 4340 forged crank. Petralia and his crew hung Mahle Motorsports dome pistons on Scat’s forged steel H-beam connecting rods and balanced the rotating assembly was balanced using a Trick Flow harmonic damper up front and an SFI-approved external balance flexplate out back. Since the Chevy GEN VI block uses a one piece rear main seal, most aftermarket forged cranks require this kind of offset balancing.

Comp Cams ground the custom hydraulic roller cam with .617 inches of lift on both intake and exhaust sides. Petralia degreed the cam with a Trick Flow double-roller timing set.

The Air Flow Research Magnum rectangular-port cylinder heads came straight out of the box except for the valve springs, which Petralia had AFR swap to 410 lbs.-inch springs suitable for hydraulic roller cams. Other valvetrain components include custom-length Comp Cams 3/8-inch pushrods and a set of Summit Racing 1.7 ratio roller aluminum rockers.

The 565 was topped with a Holley HP EFI system upgraded with 55 lbs.-hr. Trick Flow fuel injectors. This is a multi-port system that can self-tune as you drive, yet allows you to fine-tune the system on the dyno. The results speak for themselves.

If this sounds like an engine combo you’d like under the hood of your street hero, check out the Hardcore Horsepower Big Torque 565 Engine Combos at SummitRacing.com. They list virtually everything you need to build an engine to Hardcore Horsepower’s specifications. And you know what kind of power that makes.

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Author: Alan Rebescher

Editor, author, PR man—Alan Rebescher has done it all in a 25 year career in the high performance industry. He has written and photographed many feature stories and tech articles for Summit Racing and various magazines including Hot Rod, Car Craft, and Popular Hot Rodding, and edited Summit Racing’s Street & Strip magazine in the 1990s. His garage is currently occupied by a 1965 Ford Mustang.