Matt Bieneman, owner of MBE...
Matt Bieneman, owner of MBE Cylinder Heads and Manifolds, prepares to test a new SB2 head design on the flow bench. Bieneman says that many performance tricks learned with heads for big-block Dirt Modifieds or even drag racing can be translated into performance gains for small-block stock car heads.
"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...
This shows how much Bieneman has to move two of the intake ports on an 18-degree big-block cylinder head just to raise the flow numbers to the level of the other two ports. The red line is the original port angle while the blue line is the new port angle after work has been completed.
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...
This photo shows you just how much the entrance to the port must be moved to achieve a 19-degree change in port angle. The walls (A) of this raw port will eventually wind up at scribe marks "B."
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...  On a big-block intake, it is easy to see the difference between the two interior runners. On a small-block engine the difference is less noticeable, but it can also cause a difference in air/fuel flow. Bieneman tries to equalize the runners by cutting into the wall on the inside of the turn for the runner on the right. This straightens and shortens the flow path. |  It is also important to equalize...  It is also important to equalize the length between the two inside and two outside runners on each bank of cylinders. The air and fuel only see the inside wall of the runner, so you can shorten the length on the outside runners by grinding away the divider wall in the plenum. |  Bieneman points out that getting...  Bieneman points out that getting big numbers on the flow bench is nice, but unless they translate to results on the dyno or at the track, they aren't worth much. It may be unusual to see a big 500-inch drag motor in Circle Track, but Bieneman says he's learned tricks from these motors that he has utilized in small-blocks built for stock car racing. |