When some guys consider the AMSOIL Engine Masters Challenge, they often envision wild, custom, one-off engines. Some will imagine engines built strictly for the event and dyno results. Granted, there are some exceptions; however, for the most part we get real street or race powerplants, just as capable in a car as they are on the pump. The fact is, the vast majority of the competition engines are built with a street or race application in mind after the event. Such is the case with this 566-cube big-block Chevy. As builder Eric Roycroft relates, “This isn’t a wild, one-off Engine Masters Challenge engine. It is the type of Chevy that can readily be duplicated.” No, it’s not your dad’s 427 or 454, but it is indicative of what can be bolted together with today’s mainstream aftermarket parts. The power potential here is what makes the big Chevy today’s go-to high-horsepower source.
Eric Roycroft is a man familiar with the annual AMSOIL Engine Masters Challenge competition, having a history of coming to the competition with straightforward, but formidable engine combinations. Looking at the multiclass event for 2015, there was a broad choice on just what type of engine to build, and a decision to make on just where he might best fit in. This time the decision was helped by the fact that he pretty much had the required weapon locked, loaded, and nearly ready for action right in his garage. As Eric tells it, “I had about 80 percent of the parts on hand to make a competitive big-block Chevy, so it seemed like a practical choice. Most of the short-block was there to build a 566-cube combination, using a 4.600-inch bore and 4.250-inch stroke. I had the Dart block, the Scat crank and rods, and even a good set of heads to go with it.”
“I knew it would be good for its size, but in reality it was too big for the competition. If I was starting from scratch, and building specifically for the competition, I would have gone 100 cubes smaller. I did know that this is a very good combination that makes good power. It is a very common combination, and I didn’t have a lot of time. I had a good chance to win unless someone came in with a smaller engine that was really good. If I tried to make it smaller, the heads would be too big and I’d have to change everything and just about start over. I just had Diamond make some changes to their stocking pistons to meet my compression ratio needs, and I did piston-guide the rods because I think that is worth some hp, but the short-block is really run-of-the-mill.”
This bore and stroke formula is popular due to the readily available Dart big-bore block. The 4.600-inch bores dwarf what can be done with a production Chevy block, and it has the beef to handle all the power and rpm you can throw at it. The short-block was assembled with off-the-shelf aftermarket parts, including a Scat 4.250-inch crank, Scat 6.350-inch rods, King engine bearings on both the rods and mains, Total Seal Gapless Top rings, and a replacement-style Melling oil pump. Roycroft wasn’t jiving us when he said the bottom end was simple.
Heads, Induction, and Cam
To top the big-inch bottom end, Roycroft once again kept it simple and took advantage of parts he had on hand. As Eric details, “I have had these Pro Topline heads for years. In fact, I think they quit making them. Since I had them I figured I might as well use them, and they seemed like a good match to the engine. I bought them from a buddy, and it is a shame they don’t make them anymore because they are really good heads.” The large 360cc intake port heads definitely have the capacity to handle the cubes. Roycroft filled the bare head castings with 2.300/1.900-inch Manley valves. Other than a valve job, and a minor blend of the machine work into the bowls, the heads were otherwise unmodified—neither ported nor flow-tested.
To complement the cylinder heads, an Edelbrock Super Victor intake was selected and once again used with very few modifications, other than minor blending of the plenum entrance. This intake comes with the size and capacity to handle a big-inch Chevy right out of the box. Carb expert Dale Cubic reworked the 1250 Holley Dominator carburetor. As Eric explained, “I sent him a 1250 carb and he put on his metering blocks, performed his magic, and sent it in to me with his calibration sheet. I didn’t have to do anything to it. I put it on the engine and made some minor jetting adjustments and it was right on. We did tune it in competition because of the difference in the air in Ohio compared to Georgia where I live, but that’s it. I use Dale because he is good at what he does and you can expect it to be right on. It wasn’t too trick, just a basic job.”
Once the long-block was assembled it was left alone, but the camshaft was an area where Eric experimented. As he tells us, “I tried three cams in it all with very close lift and duration specs, with the difference being the lobe. Initially, I got two cams. I felt the intake runners on the heads were a little big, which leads to lower air speed, so that steered the cam specs. We took a little bit of a guess on it based on previous experience, and started with a pair of cams from Competition Cams. The first cam we tried was a less intense and slower lobe, but it turned out to be the better of the two. I wanted to try again, so I sent the other cam to be re-ground with yet another lobe profile, but once again it wasn’t as good as the first. We changed the lobe we used and what I thought would be better wasn’t. One had a quicker opening but it was worse on power. Why that was the case, I never determined. I ended up just using the one that worked. What I learned was what you think will work may not work.” The cam specs ended up at 260/260-degrees duration at 0.050, with 0.792-inch lift delivered via Trend pushrods operating 1.8:1 WW Engineering shaft rockers. The cam was ground on a 104-degree lobe separation angle and is driven by a Jesel beltdrive system.
The engine had a chance to show its capabilities in competition at the 2015 Engine Masters Challenge, hosted by the University of Northwestern Ohio. Here it was pitted against stiff competition, coincidentally including another 566-cube Chevy with the same basic bottom-end configuration. It is against the dyno where the huge power potential of these big Chevys really shows. The big displacement translated to big torque, with 664 lb-ft showing right at the bottom of the curve at 3,000 rpm, rising to a peak of 777 lb-ft by 4,900 rpm. That is torque that will get you moving in a hurry. On the power side of the equation, the engine certainly wasn’t short, pounding out a stout 851 hp at 6,500 rpm. Keep in mind, those power numbers came about without expensive custom porting or one-off race parts. This 566 is just a great example of the kind of power a well-executed, serious, but basic big-block Chevy is capable of. That just goes to show why the big-block Chevy has become the go-to engine in just about any application where serious power is needed.
1. This 566-cube Chevy big-block is built on a stout foundation, featuring a Dart Siamese-bore block allowing a bore size of 4.600-inch to be easily accommodated. Note the hefty four-bolt main structure. A Scat 4.250-inch crank and Scat rods complete the bottom end. Bearings are by King.
2. Filling the bores are Diamond pistons, where they were ordered as shelf parts from Diamond with a modified dome to provide a compression ratio of 11.4:1. The 6.350-inch H-beam Scat rods come with ARP bolts.
3. A profile view shows the very short skirt of the 1.325-inch compression height Diamond pistons. Note that the piston pin protrudes into the oil ring groove, requiring an oil ring support rail. Rings are Total Seal Gapless Tops, in a 0.043/0.043/3mm package.
4. The pistons feature vertical gas ports to aid ring seal under compression. The pistons achieve a zero deck height, which provides a 0.040-inch quench clearance with a Fel-Pro composition head gasket.
5. A Moroso deep-sump pan contains the AMSOIL 5w20 motor oil. Note the integral louvered windage tray. The oil pump is a stock replacement Melling unit.
6. Heads are a used set of Pro Topline 360cc cylinder heads, which are no longer manufactured. Note the support bar for a set of WW Engineering shaft-mounted rocker arms.
7. The heads came to Eric as bare castings, which he filled with Manley 2.300/1.900-inch valves. The chambers measure 119 cc to give a compression ratio of 11.4:1. Other than a minor blending of the valve job machine work, the heads remained as-cast, with no further porting or flow bench work.
8. Lunati solid roller lifters are worked by a custom Comp cam. Eric tried three cam profiles, surprisingly finding the least aggressive made the most power. Note the screens epoxied into the drain-back areas to catch any debris from a failed part.
9. Here we see the mechanics of the valvetrian. Eric gives high praise to the Lunati solid roller lifters as a great value. The WW Engineering rockers deliver a ratio of 1.8:1, and mount to sturdy shaft supports. Trend formed pushrods set the standard in the industry.
10. Here we see the assembled valvetrain. The shaft-mounted arrangement is much less prone to deflection and false motion than the stock stud-mounted setup, improving rpm capability while allowing much higher spring loads.
11. Taking the load off the valvetrain at high rpm are Manley titanium retainers and locks, holding stout PAC #1247 springs installed at 2.050-inch.
12. A Dale Cubic-modified Holley 1250 Dominator carb works with an Edelbrock Super Victor intake to mix the air and fuel and send it to the generously sized intake ports.
13. The three-circuit carb was reworked internally by Dale Cubic and features their proprietary metering blocks. Also visible are the flanged boosters.
14. The Edelbrock Super Victor (PN 2927) intake has the capacity to feed a large-displacement Chevy big-block. The manifold was mostly as-delivered, with minor plenum blending being the only modification.
15. Fitted beneath the carb was a Wilson open manifold spacer. Spacers add plenum volume, changing the characteristics of the intake manifold and the power curve itself. This provides an easy tuning point for the induction system.
16. Up front you see an armada of MSD ignition components, including the HVC II coil, front-mounted billet distributor, and crank trigger. Note the Meziere electric water pump and Innovators West damper.
17. The ignition timing is fixed without a curve, handled by the rock-steady MSD crank trigger arrangement. This gives error and scatter-free ignition timing, and is adjusted by moving the pick-up unit on the graduated bracket.
18. The distributor itself, working with a crank trigger, is free of all timing duties. It simply routes the spark to the appropriate cylinder, and the only consideration is proper phasing. It is driven by a cogged belt from the crank.
19. Headers are from Dynatech, and feature stepped primary tubes with a merge collector comprising the secondary. Note the unusually long collector required to mate with the exhaust system in the dyno cell.
20. Contributing to the good looks of Eric’s Chevy big-block are these faux carbon-fiber valve covers. We have to say Roycroft’s Chevy was one well detailed piece.
21. On the dyno, the big Chevy produced a huge torque curve topping out at 777 lb-ft at just 4,900 rpm, while recording 851 hp at 6,500. Those are stout numbers for a single four-barrel Chevy big-block capable of running on pump gas.
22. The team of Eric Roycroft, Gerry Stone, and Dale Cubic had much to be proud of at the 2015 Engine Masters Challenge, earning a runner-up finish with a very basic combination.
Roycroft 566ci Chevy Big-Block
Builder: Eric Roycroft
Bore: 4.600 inch
Stroke: 4.250 inch
CID: 566 ci
Deck height: 9.8 inches
Compression ratio: 11.4:1
Engine fasteners: Dart and ARP
Camshaft: Comp solid roller
Cam journal: OEM
Timing chain: Jesel belt
Lifter diameter: 0.842 inch
Valvesprings: PAC 1247
Installed height: 2.050 inch
Retainers/locks: Manley titanium
Intake duration: 260 degrees @ 0.050
Intake lift: 0.792 inch
Exhaust duration: 260 degrees @ 0.050
Exhaust lift: 0.792 inch
Rocker arms: WW Engineering 1.8:1
Lobe separation: 104 degrees
Installed centerline: 104 degrees
Top ring: Total Seal 0.043
Second ring: Total Seal 0.043
Oil ring: Total Seal 3mm
Gas ports: Vertical
Main fasteners: Dart
Main bearings: King
Rod length: 6.350 inch
Rod bearings: King
Main bearing clearance: 0.0032 inch
Rod bearing clearance: 0.0027 inch
Cylinder heads: Pro Topline
Combustion chamber volume: 119 cc
Intake valve diameter: 2.300 inch
Exhaust valve diameter: 1.900 inch
Cylinder head gaskets: Fel-Pro composition
Piston quench clearance: 0.040 inch
Intake manifold: Edelbrock Super Victor
Carburetor: Dale Cubic 1250
Carb spacer: Wilson
Distributor: MSD front-mount
Spark plug wires: MSD
Damper: Innovators West
Water pump: Meziere
Oil pan: Morsoso
Oil pump: Melling
Fuel: VP 101 Unleaded
Engine oil: AMSOIL 5w20
|566 Chevy Big-Block: Built by Eric Roycroft|
|Tested At UNOH: SuperFlow DTS Powermark Dyno|