By Bruce Simurda, Dune Buggies and Hot VW's
Bug Patch's New Tuned-Porting CNC-Machined Heads feature a unique approach to high performance
| BY BRUCE SIMURDA | |
| Suppose you could purchase a set of ported VW
high-performance cylinder heads that were so precisely machined, if one were damaged, you
could simply buy another "off-the-shelf," and it would match the original
exactly in flow and performance. It sounded like a very intriguing idea to us, so when we
discovered that Bug Patch, in Santee, California, was doing it by porting big valve VW
dual port heads on CNC equipment, we had to investigate ourselves. Don Bolton, of Bug Patch, is somewhat of a computer/ machinist nut, and has been selling specialty-built computer-controlled milling machines for years. He's also been actively involved with his VW business, selling parts, doing machine work, and building engines in his small, but well equipped shop. So when the idea of porting heads on a computer-controlled milling machine came up, he jumped in with both feet. Of course, special tooling had to be fabricated, and many, many hours were spent developing the programs that would be able to properly shape the intake and exhaust ports, as well as the combustion chambers. To facilitate the design, a head was cut in half, the desired size of the new ports determined, and test plugs built the exact size of the new enlarged ports. Then, using the test plugs, Don determined exactly where material needed to be removed from the ports. His idea was to only remove the necessary amount of material - to improve flow and create a port is as close to the same diameter throughout as possible, thereby maintaining maximum velocity. As you can imagine, it took quite a bit of time developing the tooling and programs necessary to do exactly what he wanted. |
The process is actually accomplished on three
different machines. One mill is dedicated to profiling the chambers, while another
contours the intake ports from the chamber side. Finally, a third machine, with a full six
heads mounted to its fixture, carefully machines both ends of the exhaust ports, and the
intake ports from the manifold side (the heads must be rotated three times for these
procedures). And while we do have to say that the CNC-machined head is not as
"finished" as a hand-ported and contoured head, with a small lip at the
seat-to-port area, the finished product is impressively good. Getting a hand-ported finish would only take a few minutes with a "flapper" wheel! Intake manifolds can also be match-ported on the CNC. Currently, Bug Patch offers completed 043 (3/4-inch reach spark plugs) dual port heads with stainless steel 40mm intake and 35.5mm exhaust valves, and heavy-duty single valve springs for just under $600.00 a set. Tests have shown these heads to flow over 155cfm on the intake side, and just under 120cfm on the exhaust (all measured at .500-inch lift), which are very impressive. But, best of all, the heads have shown to be nearly identical in flow, thanks to the CNC porting. Future plans call for programs to be written for other heads, including 044s and the large Type 4. Bug Patch's CNC-machined "Tune-Ported" heads are definitely an interesting concept, one that offers great performance with the ability of immediate replacement ... if disaster should strike. And when your sedan or buggy is down awaiting repairs, time is definitely of the essence! |
| TOP OF PAGE, finished heads that were ported by Bug Patch on their CNC machine - look pretty good! RIGHT, in designing the ports, a head was cut in half to determine where material needed to be removed. you can see the test plug on ported side left. |  |