Ingenuity popped its head up as Mark came up with his own front-mount, beltdriven distribu
Trick Flow's new Twisted Wedge cylinder heads were chosen for their improved design. The new castings relocate the inlet valve and runner to the "correct" side of the cam where the air and fuel don't have to make a 90-plus degree turn to enter the combustion chamber. The heads are designed for a 1.84-inch valve but replacement of the intake seats allowed Mark to install custom Manley 1.900-inch valves for better flow. COMP Cams supplied the custom hydraulic roller cams that would work with the heads. While most cam grinders list their cams' dimensions at the cam lobe itself, MME points out that due to rocker ratio and lobe design it is critical to actually measure and degree the cam specs at the valve to determine what the engine actually sees. Mark says this is especially important for overhead cam engines that aren't ground to typical pushrod engine shapes. "Cams for that thing are sort of weird anyhow. Cam durations for it being an overhead-valve motor are pretty much out the window compared to a pushrod motor." Regarding the unusual choice of running more intake than exhaust duration, he says: "I thought it was going to be pretty much intake-starved. There's just not a lot of manifold available for that thing either. I had pretty much one shot at it, and I think it could probably handle more camshaft." Noting how different the cam requirements were for OHC versus OHV engines, Mark says: "One thing I learned doing 2300s for dirt track cars years ago was that the guys around here who were building circle track 2300s were building cam specs identical to what they would if they were building a small-block Chevy or a 351 Windsor. None of these guys ever actually degreed cams on four-cylinder engines." Noting that cam card dimensions are typically measured at the cam and not the valve, a pushrod engine measures cam duration at the cam lobe and lift at the valve, whereas an OHC engine measures both duration and lift at the valve. Comparing cam cards for the two engines is like comparing apples and octopi. COMP ground as aggressive a cam as they thought they could, and even so, the factory lifters and followers were used. Racers who have messed with old OHC 2300 Ford engines know how critical it is to get valvetrain geometry right on OHC/rocker arm engines, or it will spit the rockers clean out. Mark says that using a hydraulic lifter to set up the geometry was tricky since it wanted to depress, but in the end, it worked without incident.
Modern tuning with the laptop can be much quicker and simpler than changing jets, spilling
Choosing an intake manifold for such a test might seem daunting when dealing with a small-block Chevy due to the overwhelming number of options, but for the 4.6-liter the choices are few. The Edelbrock Victor Jr. intake will accommodate both a square-bore carb, and has cast-in bungs for injectors. This made the choice obvious. Only minor porting was done to the intake to make sure there were no obstructions and the runner dimensions matched the heads.
For the carb setup, MME used a Pro-Systems modified Holley 950 HP. During testing, they wanted to check all the variables so they made sure to record inlet temp as well as fuel consumption, oil pressure, and water temp. Using these measurements, they could get a better view of the efficiency of the combination.