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Words And Photos: Richard Holdener
If you are a Chevy guy and heading out to the performance super market for parts to build your 900-hp big-block, what stuff might we find in your cart? Oh sure, there will be the usual suspects, like high-compression pistons, roller cam, and a single-plane intake. But, what if we told you they were having a sale on oval-port cylinder heads?
Most big blockers would walk right by said sale items and head over to the isle with rectangular port heads, right? Conventional wisdom suggests big power requires big cylinder heads, but don’t count out a set of AFR oval port heads, especially after they have been given the once over by Merlin the (flow) magician at Mamo Motorsports. If this 565 BBC is any indication, there are a great many big blocks sporting the wrong shape intake ports.
Truth be told, even the magician himself, Tony Mamo from Mamo Motorsports, was hesitant about using oval-port heads on a build-up looking for 900 hp. At the insistence of Dan Ledbetter, Merlin stepped up to the challenge to create a 900-hp big-block using oval-port heads, and like any good magician, he had a trick (or two) up his sleeve.
It would take impressive oval-port heads to support the desired power level, so the easiest way to make great heads is to start with good ones, meaning something from Air Flow Research. Starting the project with the 300cc Magnum oval port heads, Mamo Motorsports was able apply some magic to coax even more flow and power from the impressive castings. According to the magician, head flow topped the 400cfm mark after all the wand waving. Of course, the heads were only part of the program, and the rest of the motor needed to be up to the task as well.
Once the head flow was taken care of, the rest of the big-block required attention. Starting with a Dart Big M block, the first three weapons in the arsenal of power were cubes, cam, and compression. It is always easier to reach a given power goal with a bigger motor, so Dan and Tony stepped the build-up to a full 565c.i. Next on the performance to-do list was cam timing. The big-block received a solid roller profile that offered a .779/.750 lift split, a 280/282-degree duration split, and 112-degree lsa. Rounding out the three Cs was a static compression ratio of 14.0:1, thanks to domed Ross (4.60-inch bore) pistons (with Total Seal Rings) and small (111cc) combustion chambers.
The power level and rpm dictated forged internals, so the 565 also received a Callies 4.25-inch Magnum series stroker crank and Ultra rods. Also included in the short block were a Moroso oil pan and windage tray, Mellings oil pump and vacuum pump from Jones Racing Products. Rounding out the build were an ATI damper and Edelbrock mechanical water pump.
With the bottom end taken care of, it was time for some power producers. With the stout short block at the ready, they guys applied the Mamo Motorsports’ oval-port heads. In addition to receiving the custom porting and chamber work, the heads featured a 2.30/1.88-inch valve package, PAC 1224 springs designed for the solid roller application, and T&D shaft rockers. Feeding the magic oval-port heads was a Dart single-plane intake ported by Roger Helgeson. The intake was flanged to accept a 4500-series Holley carb.
The 565 was fed by an 1150 Holley but not just an out-of-the-box version; this 2-circuit Dominator was given the once over by Sean Murphy Inductions. Ignition chores for the high-compression big-block were handled by an MSD billet distributor. After a break-in, some fresh Lucas oil and dialing in the jetting and timing, Tony the magician waved his magic wand and Presto Change O, the oval-port headed 565 produced peak numbers of 900.7hp at 6,900 rpm and 759.2 lb-ft of torque at 5,500 rpm.
It makes us wonder how many other rec-port big blocks out there might benefit from a little oval-port magic.
When you see a graph like this, you immediately think a big motor with big cylinder heads. What makes this 565 BBC so impressive was not just that it produced 900 hp without the use of nitrous or forced induction, but that it did so using oval-port heads.
You need big flow numbers to reach 900 hp, and that is exactly what these oval ports from Mamo Motorsports delivered.
Sources
ATI
atiracing.com
Edelbrock
edelbrock.com
Holley/Hooker
holley.com
Jones Racing Products
jonesracingproducts.com
Lucas Oil
lucasoil.com
Mamo Motorsports
mamomotorsports.com
Moroso
moroso.com
MSD
msdignition.com
Total Seal Rings
totalseal.com
