The big-block Chevy has been in a constant state of evolution since the General rolled out the first W series in 1958, and the Mark IV engines that debuted in 1965. For the past 50-plus years many aftermarket manufacturers have designed more efficient and better ways to move the air and fuel in and out of the cylinders. We've seen plenty of cast iron and aluminum cylinder heads and each time the main goal has been more horsepower and torque. One company that has been around through the entire lifespan of the big-block Chevy--and then some--is Edelbrock. With no signs of the big Chevy's popularity slowing down, the Edelbrock engineering team, led by Dr. Rick Roberts, is constantly working on new products for it. The engine might be over half a century old, but the techniques employed to design new parts are cutting-edge.
The latest chunk of aluminum from Edelbrock has been dubbed E-CNC and it replaces the RPM XT cylinder head. One quick look at the specs shows the E-CNC (rectangular port, PN 79559) has a left head intake runner volume of 344 cc and the right head intake runner carries a volume of 352 cc. The exhaust port volume is listed as 142 cc. Moving from there, the intake valve angle is 24.5 degrees x 4.4 degrees and the exhaust side shows it being 15.5 degrees x 4.2 degrees. The heads come with a good set of valvesprings that can handle up to a 0.700-inch-lift cam. The E-CNC is very popular in engine packages that fall between 496ci to 565ci, but that is not to say the heads can't be used on a smaller engine or one slightly larger. If the E-CNC finds its way onto a 600ci-plus engine don't expect huge hp numbers, but rather more of a stump-pulling torque engine.
Edelbrock stuffs the E-CNC with 2.300-inch intake valves and 1.880-inch exhaust valves to achieve 377 cfm (intake) and 271 cfm (exhaust) flow numbers. Both results were achieved at 0.700 inch lift on a flow bench using a 4.500-inch bore and 28 inches of water. Roberts offered some insight into designing a cylinder head and it starts with sizing the valves. The process begins with CAD/CAM engineering software that allows a virtual reality 3D image to be created.
"My design philosophy for heads starts with selection of the intake valve size," Roberts told us. The engineer said that the most important part of the equation is getting the correct targeted flow at 100 percent volumetric efficiency--air consumption at peak power rpm. "Using this volume flow rate, I calculate the cross-sectional area that will produce an average air velocity of 300 ft/sec during the 180 degrees from TDC to BDC during the intake stroke.
"From the cross-sectional area I calculate the diameter of a circle and that's my intake valve diameter. I will design the port with a throat of about 88 percent to 90 percent of the valve diameter, and if possible try to keep a constant cross-section area throughout the port. All of that will pretty much dictate the volume of the port for a given engine platform."
The exhaust valve target measurement is around 80 percent of the intake valve diameter--provided there is enough bore size to fit it. The E-CNC carries 1.880-inch exhaust valves, which are properly sized given the 80 percent requirement. Roberts offered an example of a 555ci engine, like the Pat Musi crate engine we checked out for this article. It moves roughly 1,000 cfm at 6,250 rpm. That would require a flow area of around 4 square inches, which works out to be an intake valve with a 2.30-inch diameter.
The Edelbrock staff likes the 2.300-inch intake valve due to its ease of availability and versatility. The valve size is suitable for engines slightly larger than 555 ci and/or have a higher rpm range than 6,250 rpm.
"Like many products, this one was an evolution," comments Roberts. He went on to tell us that when he worked in a head porting shop many years ago, a normal routine would be to angle-mill the cylinder heads after extensive porting and chamber work was completed. The milling would create more issues as the bolt holes need to be modified thanks to the angle mill. Roberts simply included that step in the design process for some of the Edelbrock big-block cylinder heads that preceded the E-CNC. Some of those heads have a 1-degree rolled deck as part of the design so the porting shops could skip that modification. The only downside was that it affected the exhaust port location and header selection. This time around as Roberts and his engineering team designed the E-CNC heads, they made sure the exhaust port was back in the stock location. The E-CNC heads feature a 1.5-degree rolled deck, which effectively moves the exhaust port location (which was higher than stock in previous versions of this head) much closer to stock. Now most off-the-shelf headers have no issues bolting on to it.
The new location of the exhaust port instantly made another Edelbrock offering more attainable to the masses--the Edelbrock 555ci crate engine. This engine was originally offered with the Edelbrock/Musi Victor 24-degree cylinder heads but the E-CNC is a better fit for the engine combination.
"These heads work great and make really similar power to the bigger Victor 24-degree heads and a guy doesn't need to get a new set of custom headers to run this engine," says Pat Musi, owner of Pat Musi Performance and whose name adorns the valve covers of the Edelbrock crate engine. Musi told us that even though the E-CNC has smaller ports (when compared to the Victor 24-degree heads), the engine makes peak power below 6,000 rpm. If it had been more cubic inches and higher rpm, then the Victor 24-degree heads would work better, but in this application the E-CNC is sized perfectly.
He went on to say that for people who want to build a budget stroker engine using a stock block, he'd recommend a 496ci engine with a moderate compression ratio and a hydraulic roller camshaft to go along with the E-CNC heads. As he puts it, the engine would be an excellent on the street and not break the bank.
The Pat Musi 555ci is a popular crate engine and it is in stock, ready to ship in either carburetor or EFI styles. "If a guy calls us in the morning and is in the area, we could have it on the dyno and ready for him to pick up by the end of the day--if the dyno room isn't being used," Musi says with a smile on his face.
The triple nickel, as he refers to it, is a proven package that delivers nearly 700 hp in its EFI trim and approximately 675 hp with the carburetor on top. The difference in power between the induction setup is attributed to the better-flowing EFI throttle body when compared to the 800-cfm carburetor. Each 555ci engine is run on the dyno before being shipped to the customer.
Over 50 years of big-block power and the aftermarket is still booming with excitement and new products. The big-block simply gets better with age thanks to help from modern technology.