Matt Bieneman of MBE Cylinder...
Matt Bieneman of MBE Cylinder Heads and Manifolds stands with his Dodge cylinder head that's being fine-tuned on the flow bench.
You might think that after all these years the pushrod V-8 has been in existence, cylinder head design would have been perfected. Think again. When it comes to cutting ports and combustion chambers for stock car racing, cylinder head specialists are still refining the art of power.
The reason cylinder head designs are still advancing is there are so many variables that must be optimized, and engine builders are still learning exactly how they all work together. Elements such as port volumes and shapes, combustion chamber shape, seat depth, and valve angle, just to name a few, involve the cylinder head. Add in the rest of the engine and you get thousands of decisions that must be made-and nearly every one affects the next decision down the line.
Next to the hand grinder, the greatest tool allowing advancements in cylinder head designs has easily been the computer-specifically CAD programs. Hooked to CNC milling machinery, computer technology has helped cylinder head specialists dramatically increase repeatability from one head to the next, which in turn has allowed them to consistently inch progress forward a bit at a time. Computer power also allows flow bench precision down to tenths of cfm in terms of airflow. There may be few big gains left in racing, but the small gains are still plentiful, thanks to these tools. One of the biggest is including the intake manifold when designing the intake port.
Matt Bieneman is a former cylinder head specialist with Joe Gibbs Racing as well as a few drag racing teams. Recently, he went on his own to form MBE Cylinder Heads and Manifolds and was willing to share a few of his philosophies for making power in CNC cylinder heads. Since starting MBE, Bieneman has outfitted intakes or manifolds for Joe Nemechek's Busch Series team (including his pole at Daytona in 2003), Travis Kvapil's Tri-Star championship in 2003, and Ray Evernham's Nextel Cup teams.
Interestingly, Bieneman says he pays more attention to port shape and volume than flow numbers when working with a new head. "We just use the flow bench to fine-tune our work," he says. "We don't even turn the flow bench on until we feel we've gotten all our areas right."
CNC head ports often work...
CNC head ports often work with specific head manufacturers (MBE, for example, is a Dart distributor) to receive raw castings. This gives them a head with plenty of material that needs to be cut away, but it also allows them plenty of material to work with.
The areas he's talking about are the port dimensions, which are broken up into several areas from the port entrance all the way to the bottom of the combustion chamber. "When we start looking at a new cylinder head, the first thing we look at is where the seat depths need to be," he says. "You need to get the right seat depth in relation to the spark plug location. You want the plug about as deep as you can get it, but in stock car racing you can rarely move the plug location, so you have to work with the seat depth. Seat depth and location also have a bearing on where the port is and the angle of the port. What it does to the chamber volume isn't too important yet because we haven't decked the head. Once you feel you have all those relationships right, you can move on from there.
"Then we'll start grinding out a combustion chamber by hand. Once you sketch where the cylinder walls meet the deck of the head, you can decide where the exhaust needs to be. The exhaust is always close to the edge of the chamber because it isn't required to flow as well. The intake is farther from the cylinder wall because you have to minimize shrouding of the airflow as it moves into the chamber. Moving air will follow a surface, so you need to use the combustion chamber to guide the incoming air/fuel mixture into the chamber."
Bieneman also says he has moved away from heart-shaped combustion chambers (chambers with material between the intake and exhaust valves opposite the spark plug). He has found that, at least with his designs, they harm the efficiency of the combustion. Instead, a straight cut between the intake and exhaust valves opposite the spark plug usually results in knocking 111/42 degrees advance out of the assembled engine. The result is a more efficient engine with better power production.