Dyno Testing a 565ci Big-Block

By Jeff Huneycutt – Images by the Author

The old adage about making power goes: “There’s no replacement for displacement.”

Every dyed-in-the-wool car guy knows it. We’ve all heard it. And we all know the rejoinder is: “Unless you have boost.”

002 Merlin big block Chevy engine bare block machine shop assembly high performance build — The baseline for both builds includes a World Products Merlin IV cast-iron block that can handle huge power without an issue. The 10.2 deck height is also critical in order to squeeze in the 4.750 inches of sweep needed to get to 632 ci.

Yes, boost is the answer when it comes to helping little engines make big power. Whether it’s a supercharger or turbo, boost makes magic happen. So, what happens when you have both? What happens when you already have boost and add displacement? That, friends, is the question of the day.

003 Crankshaft machining precision engine balancing high performance rotating assembly — Engine builder Keith Dorton cuts a second keyway into the snout of the forged Molnar stroker crank because the resistance that comes from spinning a blower too much for a single keyway and woodruff key to handle.

We recently came across a golden opportunity to put this to the test and couldn’t pass up the chance to do a little dyno testing. This became possible when our friends at Automotive Specialists in Concord, North Carolina, were sent a new engine build that the original engine builder was having trouble tuning on the dyno. The engine was a 565ci big-block with a giant 14-71 blower from The Blower Shop (TBS).

004 Molnar connecting rod forged piston high performance Chevrolet big block internals — The pistons are flat tops from JE. As you can see, the compression height for the rings has been minimized to fit in the longest connecting rod possible, so an insert is used in the wristpin bores to help support the oil ring. The forged H-beam connecting rods are from Molnar Technologies and measure out at 6.700 inches long.

EFI and cylinder head specialist Jeff Dorton had the engine with a Holley Dominator ECU up and running in no time. With a little tuning, the engine was able to make peaks of 1,111.4 hp at 6,500 rpm and 940.4 lb-ft of torque at 5,500. That is plenty for most of us, but the engine’s owner was unhappy. He was led to believe the engine would make over 1,200 hp and was surprised to find that the displacement was just 565 ci and not 632 like he wanted.

005 Custom ground camshaft billet core high performance Chevy big block valvetrain upgrade — Both cams were quite similar, but Dorton switched to a small base circle cam from Jones Cam Designs for the 632 to make a little more clearance for the connecting rods to swing by. This one is ground with 278/285 degrees of duration at 0.050 tappet lift, 0.425-inch lobe lift, and a 110-degree intake centerline.

So, the owner asked Automotive Specialists to keep the engine and fix the issues. To help keep costs contained, together they made the decision to build a brand-new, 632ci short-block and use the cylinder head, blower, and other components. Then the old short-block, which was still perfectly good, could be sold or used on another project.

006 Merlin big block Chevy short block assembly Jesel timing setup ATI Super Damper — A highly efficient Jesel belt drive controls the cam timing. You can also see the ARP studs in place to help keep the cylinder heads clamped to the deck when the boost rises.

That’s great news for us because rarely does an engine go across the dyno twice with a single significant change that we can test. It’s just too costly in terms of both time and money. Since both versions will be on the same dyno, it’s an excellent opportunity to see just how those additional cubic inches will affect the power curve—especially considering we’re adding boost to the equation.

007 Stef’s custom aluminum oil pan baffled high performance Chevy big block lubrication system — A fully fabricated Stef’s aluminum oil pan provides enough room for the long-stroke crankshaft. It also has a deep sump to be able to maintain a good supply of oil for the engine even when the revs are up for long periods of time.

Yes, both horsepower and torque should go up. But how much? And will the upper rpm range or the lower be more affected? Typically, the horsepower-per-cubic-inch ratio decreases as the cubic inches go up (that’s why it’s usually unfair to compare horsepower per cubic inch between a tiny four-cylinder and a big-inch V-8), so since this is one of the biggest gasoline street engines you can build, will the horsepower improvements be disappointing?

008 Engine assembly technician installing Stef’s oil pan on high performance big block Chevrolet — Windage can be a big issue with stroker engines because the crankshaft has a deeper swing into the oil pan. To help minimize its effects, the Stef’s pan kicks out the side of the pan to give room for the oil to sling off the crank and not bounce right back onto it. In order to secure the pan to the block, it is necessary to run the bolts through the pan. The holes are either sleeved to seal out oil or threaded so that plugs can be installed after the bolts are tight.

Only one way to find out.

The 565ci Chevrolet big-block usually is derived with a 4.600-inch bore and 4.250-inch stroke. Even for an aftermarket block, 4.625 inches is usually the absolute limit for the bore size, so for a 632ci engine with an additional 67 ci, the 4.600-inch bore is kept while the stroke is lengthened a full 1/2 inch to 4.750. That, of course, basically requires a 10.200-inch tall-deck block to fit all the stroke without crashing piston skirts into the crankshaft’s counterweights at BDC.

009 CNC ported cylinder head polished combustion chambers high flow big block Chevy heads — The cylinder heads are a set of 24-degree Head Hunters from Brodix. The chambers are large at 123 cc, making the final compression ratio for the 632 engine 9.64:1. The valves are sized at 2.400 for the intakes and 1.850 for the exhausts. You can see the two extra studs on each head that thread into the block to provide additional clamping load.

In addition to the cubic inches, the additional stroke also makes for a couple of other differences. The big one is compression ratio—both the original configuration and Automotive Specialists’ updated 632 used flat-top pistons. The same Brodix cylinder heads with 123cc combustion chambers were also kept. So, thanks to the extra stroke, compression ratio jumped from 8.8:1 for the 565 build to 9.64:1 for the 632.

010 Close up CNC ported intake ports high performance airflow Chevy big block cylinder head — The Head Hunter line of cylinder heads are fully CNC-ported with a 24-degree valve angle to help flow. At our max intake lift of 0.703 inches this head can flow an impressive 455 cfm.

You might think that this negates the test to see how cubic inches affect power, but we’d disagree. Increased compression is a natural by-product of adding cubic inches. You’d actually have to make additional changes to lower compression again, so in our book more inches and higher compression go hand-in-hand.

011 Big block Chevrolet Brodix aluminum heads dual valve springs high performance valvetrain assembly — The psi valvesprings with Xceldyne retainers are installed at 2.050 inches. That provides 220 pounds of seat pressure and 750 over the nose. This shot helps illustrate the big-block’s canted valve angles that help improve flow into the combustion chambers and make this engine such a great performer.

Another change that’s a by-product of the additional stroke is the rod/stroke ratio. A lot of people place a lot more importance into rod/stroke ratio than we do, so we’ll touch on it. The 565 combo in a 10.2-inch deck height block is a 4.250-inch stroke with 6.800-long connecting rods. That makes the rod/stroke ratio 1.6:1. The 632 with the same block uses a 4.750-inch stroke with slightly shorter 6.700 rods. As a result, the ratio dips to 1.4:1. Whether that is a little or a lot depends on your perspective (for comparison, a stock stroke 350 Chevy small-block with 5.7-inch connecting rods is also 1.6:1), but the change in ratio really won’t affect power production. If anything, it is more of a long-term concern because the shortened ratio will increase lateral loading between the pistons and the cylinder wall, and bore wear eventually becomes something to keep an eye on.

012 Big block Chevy Brodix heads roller rockers pushrod guide plates high performance top end build — The rocker arms are a set of Jesel’s Sportsman Series aluminum-bodied rockers that mount to a very rigid steel rocker stand. They are the stock 1.7:1 ratio, so gross valve lift will be 0.723 inches.

Finally, there’s one last change that’s worth noting even though it didn’t affect horsepower. Because of the additional 1/2 inch of stroke, engine builder Keith Dorton switched to a camshaft ground on a reduced-base circle. The basic specs were the same, just on a smaller lobe diameter to ensure that there will be no contact between the camshaft and the big ends of the connecting rods as they swing by.

013 Big block Chevy fully assembled billet front drive Jesel belt system high performance accessories — Although it likely won’t be seeing tons of road miles, this is still a street engine. So, it’s equipped with an alternator, power steering pump, and even an A/C compressor that’s all driven by a serpentine belt setup from CVF Racing.

So how did it do? Glad you asked.

On the engine dyno with the 565ci setup we saw peaks of 1,111.4 hp and 940.4 lb-ft of torque. Because it limits the rpm ramp speed, an engine dyno can damage the pistons in a high-torque engine if you begin the pull too low in the rpm range. That’s why the pull is from 5,000 to 6,500 rpm. But the averages in that range were a very healthy 1,013.3 hp and 962.2 lb-ft of torque.

014 Supercharged big block Chevy custom headers billet pulley system race engine assembly — The giant 14-71 blower from The Blower Shop is a beast, so Jeff (left) and Keith Dorton use a shop crane to safely lower it in place without scratching up the mating surfaces or tearing the large gasket that seals the blower to the manifold.

Then the engine was pulled down, inspected, and cleaned, and then rebuilt with the new short-block. When Keith and Jeff Dorton got it back on the dyno in its 632ci form, it produced peaks of 1,253 hp and 1,106 lb-ft of torque. That’s improvements of 141.6 hp and 165.6 lb-ft of torque. The averages improved by 157.3 and 109.4 respectively to 1,170.6 hp and 1,071.6 lb-ft of torque.

015 Supercharged big block Chevy MSD ignition system fuel lines high performance tuning setup — The extreme size of the 14-71 blower means it extends over the distributor boss in the intake manifold. Not only must you use a “spider”-style cap like this, the distributor must be installed before dropping the blower in place. That big blue AN fitting cap you see also had to come off before we could fit up the plug wires.

So, the improvements are solid but not outrageous. On the dyno chart, the shape of the horsepower and torque curves were basically consistent across the pull without any real drop-off as the rpm increased. An average gain of 157.3 hp by adding 67 ci comes out to 2.35 hp/ci, which sounds about right with approximately 12 pounds of boost. We never even changed the blower pulley. If anything, there might be a little more power to be squeezed out of the 632 because the 160-lb/hr injectors were at 80 percent duty cycle. But the customer is happy with the new power numbers and can’t wait to put the big-block into his Chevelle. We’re happy with a great day on the dyno and need to get things cleaned up so we can bring you another engine test next time!