Chevy 566ci Big-Block Build and Test
Go-To Power: Building a 566-cube 850hp Chevy for the street
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.
Regular Street
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.
Dyno Time
