Matt Bieneman, owner of MBE Cylinder Heads and Manifolds, prepares to test a new SB2 head
"We treat every project as an R&D opportunity."
That's what Matt Bieneman, owner of MBE Cylinder Heads and Manifolds, says about remaining competitive while working with so many different types of engines. "It doesn't matter what we are working on," he explains, "we are always looking to see how we can make our next set of heads better than the last set. And whenever we find anything, we always try to find ways to see if what we found with a particular set of heads will work with other styles."
Unlike many racing enterprises that feel the need to specialize in just one thing or one type of racing in order to get an edge, MBE works with cylinder heads and manifolds for everything from Nextel Cup engines, to DIRT Big-Block Modifieds, to Sprint Cars, to 500-inch drag motors. And the company has experienced success: MBE works closely with Richard Childress Racing, which had two cars in the Nextel Cup 10-race championship series, as well as Danny Johnson, winner of Super DIRT Week XXXV at the New York State Fairgrounds. We spent some time at MBE trying to find out what it takes to make a competitive cylinder head and intake manifold system for a big-block Modified. The most surprising thing we learned during our time in MBE's shops is just how much of what we talked about applies no matter what type of engine you are racing.
This shows how much Bieneman has to move two of the intake ports on an 18-degree big-block
For most big-block Modified racing applications, Bieneman says he uses an aluminum 18-degree Dart casting along with a matching intake. This head works well for racing because he says he can easily get the chambers-even after porting-down to between 80 and 84 cc's. In a big-block engine, that's small enough to get by with flat-top pistons, which increases cylinder efficiency. As a result, engines with these heads typically run around 34 degrees of timing instead of 40 or so for an engine with a larger chamber and domed pistons.
The biggest trouble with the Dart head, according to Bieneman, is matching the intake ports. Unlike the typical Chevy small-block, the valves on this head are in the same locations on all cylinders (I-E, I-E, I-E, I-E), but the intake ports are angled so that the 1 and 2 and the 3 and 4 runners are beside each other at the port entrance. As a result, the No. 1 and No. 3 intake ports are significantly shorter than the 2 and 4 ports and typically flow 30-50 cfm better. To pick up the flow in the weaker ports, Bieneman says he has to relocate the intake runner 19 degrees, which moves the port opening (where it meets the manifold) 0.230 inch. This shortens the ports and brings the flow numbers much closer to the 1 and 3 ports.
This photo shows you just how much the entrance to the port must be moved to achieve a 19-
Of course, it isn't as easy as welding one side of the port and grinding out the other. Such radical movements interfere with the pushrod holes and the mounts for the rocker arm stand. Bieneman bushes all the pushrod holes and recuts them in the correct locations. All pushrod holes are large enough to accept 7/16-inch pushrods (instead of the smaller 3/8-inch ones, which are more likely to flex). He also recommends using a 0.165 wall pushrod for even more strength.
These cylinder heads, like most small-block heads in upper-division racing classes, utilize shaft-mount rocker arms to minimize deflection. Since the ports have been moved so much, many of the existing bolt holes extend into the ports. It doesn't make sense to disrupt the flow by sticking a bolt into an intake runner that has been so painstakingly ported, so the mounting locations for the stands must obviously be moved. This can become prohibitively expensive for a one-off set of cylinder heads, but MBE has done so many that Jesel can provide you with a set of rockers for an MBE 18-degree head.
On a big-block intake, it is easy to see the difference between the two interior runners.
It is also important to equalize the length between the two inside and two outside runners
Bieneman points out that getting big numbers on the flow bench is nice, but unless they tr
Here's a comparison between a Chevy SB2 head (bottom) and a cylinder head for a 500ci drag
A little work is required to make the flow patterns in the intake manifold even. Just like on a small-block, the offset cylinder banks indicate slight variations between the two interior runners on each side. It's more pronounced on a big-block because of the greater distance between bore centers. On the stock manifold design, the intent is to make the angle almost identical on all runners at the transition where the manifold meets the cylinder head. However, this means one of the runners must make a very sharp turn before the entrance into the cylinder head intake port. Bieneman says it is better for the engine if that runner is shortened to match its mate. This is done by grinding the wall on the inside of the turn to straighten the path a little.
The details may be slightly different, but these are the same tricks that small-block porters have been taking advantage of for years. Although it is often impossible to achieve for many different reasons, the more you can equalize the volume and quality of the air/fuel mixture entering all eight combustion chambers, the more power you can make. This allows you to achieve the best possible tune for every cylinder. If, for example, you have a runner that is restricting flow or causing the fuel to fall out of suspension, the air/fuel mixture entering one combustion chamber will be of a different quality from the air/fuel mixture entering the other seven. Since there is no way to have the carburetor pump more fuel to this one cylinder or set the timing differently for that cylinder, it won't produce as much power as the other seven.
Relocating the ports also entails moving the pushrod holes. Bieneman handles this by bushi
Believe it or not, Bieneman says one of the tricks he has found to make more power with these heads is to shrink the exhaust port and use a smaller valve. He says that when he has finished porting a set of heads, the exhaust port will actually be about 5 cc's smaller, and the usual 1.900-inch exhaust valve will be replaced by one that's only 1.800 inches in diameter.
This achieves two significant results. First, Bieneman says the smaller port produces more velocity, which improves that port's volumetric efficiency. We often hear that better velocity numbers in the intake ports is important because it means better cylinder filling at high rpm levels, but it is also important in the exhaust. At high rpms, higher exhaust port velocity translates into better evacuation of combustion remnants from the combustion chamber and also helps with scavenging.
Veteran cylinder head porter Dennis Warner puts the finishing touches on a new combustion
Second, the smaller port and valve have an interesting advantage that many of us wouldn't think of. Bieneman actually uses the port and valve design to limit the effects of valve overlap. Overlap is helpful to use the exhaust's scavenging effect to begin filling the cylinder with fresh air and fuel before the piston has begun its downward stroke. However, large valves can sometimes block the air and fuel from actually getting into the cylinder. Instead, the tops of the intake and exhaust valves form a floor and guide the incoming air/fuel charge out of the exhaust port until the exhaust valve closes. In order to get enough duration, cam designers are forced to put in excessive amounts of overlap.
Bieneman says his exhaust port design actually reduces flow at lower levels of valve lift. For example, the exhaust flow at 0.100 and 0.200 inch of valve lift is actually worse than the traditional port. But at 0.300 and up the flow is much greater. As a result, the incoming air/fuel charge that enters the chamber during the overlap period is less likely to flow out of the exhaust port and be wasted. On the dyno, the effect is more low-end torque and greater fuel efficiency.
An example of the raw port Warner begins with and his finished work.
Bieneman points to a similar phenomenon that many small-block cylinder head porters-himself included-discovered when they began putting radical 55-degree valve seats into high-lift heads. The steep seat angles are very harmful to flow levels at lower valve lifts, but in race engines these seats somehow resulted in better low-end torque. Bieneman says it confused many engine builders until they realized that with the shallower seats and current cam lobe designs, they were sending too much of the incoming air/fuel charge right out the exhaust ports. The assumption was that you wanted to maximize flow at every point of valve lift to get as much fuel and air into the cylinder as possible. But too much of that air and fuel was being lost. Killing off a portion of low-lift flow actually helped performance because more air and fuel was being burned inside the combustion chamber. The lesson to be learned here? Bieneman stresses that good numbers on the flow bench are nice, but unless those numbers relate directly to success on the racetrack, they don't mean a thing.