Competing in the NMRA’s Open Comp class gives a racer the opportunity to build a vehicle to their heart’s content – there are very few rules relating to the vehicle other than safety, and as a result the class is comprised of Ford-powered vehicles like Kenny Thomas, Jr.’s 1970 fastback Mustang.
The car previously had a wedge-head big-block Ford engine installed between the framerails, but Thomas always aspired to build the engine you see here – a Hemi-headed big-block Ford. The project took three years from start to finish; sourcing parts and pieces to build the perfect engine didn’t happen overnight.
“I blew up one 460 up that had a C9 block. When we got to looking at it we realized that this was no way to race. The block’s thin.. we just decided to spend the extra money and build it right,” says Thomas.
The 638 cubic inch engine is based around one of Eliminator Performance Products‘ 10.300-inch deck height Premier siamese-bore blocks that uses 8620 billet-steel main caps, A1 fasteners, and has been optimized in all stress areas for big horsepower potential. Terry Walters Precision Engines performed the machine work and assisted Thomas in procuring a number of the parts used in the build. A 4.75-inch stroke Scat billet crankshaft came from C&C MotorSports, and a set of GRP‘s 6.700-inch aluminum connecting rods drive the Walters-spec forged-and-coated CP pistons making 14.0:1 compression up and down in the 4.630-inch cylinder bores.
“I always wanted the Boss 429 engine, and when Jon Kaase Racing Engines came out with these heads, I decided I had to have a set to build my engine around,” says Thomas.
This isn’t the first engine he’s built; he estimates approximately 75 engines have been through his hands over the years, using skills he picked up from his father, Ken Sr., a former NASCAR racer from the 60s.
“My dad’s a gearhead, and I got it from him. He helps me out, and we work on it together. He’s about 80 years old but he still gets it like it’s nothing,” Thomas says.
An unexpected challenge came during the engine build as Walters discovered that the camshaft needed to be balanced in order to run straight and true without wrecking valvetrain parts.
“That was an adventure for us. Terry made a counterweight to go onto the back of the camshaft to balance it properly,” says Thomas.
Camshaft specs are what one might expect for a monster engine such as this; huge-by-large with a whopping 289 degrees of intake duration and 288 degrees of exhaust duration at .050-inch lift.
As with any engine build, checking the specifications prior to performing any machining processes is a wise idea – and in this particular case, a very good one.
“Terry discovered that the number three main bore wasn’t correct when he checked the line hone, and saved me a fortune in the process,” Thomas explains.
The Kaase heads are the star of the show here, and ride on a set of Cometic multi-layer steel head gaskets. The heads were purchased in assembled form, with no porting, and that’s exactly how they were installed. Thomas spent time inside the Kaase intake manifold with a grinder, mostly smoothing out the sharp corners, and spent dozens of hours measuring, fitting, and assembling the engine into form. An Aeromotive A-1000 feeds the Pro Systems 1200 cfm carburetor VP‘s Q16 oxygenated fuel.
Thomas also fabricated the headers to allow the engine to fit into his Mustang, using 2.250-inch primary tubes and 4.000-inch collectors. A Jesel belt drive, ATI Super Damper, and Stef’s oil pan housing a dry-sump oiling system finish off the external pieces.
The engine was assembled in Thomas’ home shop and subsequently run on the dyno at Walters Precision, where it cranked out a whopping 1,100 horsepower and 930.4 lb-ft torque.
“I had Terry set the bearing clearances .0028-inch on the rods and .003-inch on the mains. They spent a lot of time at making sure everything was perfect, like every engine they do. I can’t say enough good things about Terry Walters and his crew,” says Thomas.
Click the video and check out the sights and sounds of one nasty Hemi-headed big-block Ford crushing the dyno!