Picking up where we left off on our Project Boring 4-Valve, we have completed the short-block assembly. Now it’s time to move on to the cylinder heads. The key takeaways from our short-block were the custom pistons, which were lightweight and included valve reliefs. We also chose a factory cast crank to lighten the rotating assembly by 12 pounds, and Gen-3 Coyote rods. The cylinder heads are pretty straightforward, with mostly shelf parts from Ferrea, COMP Cams, and Melling. But there are a few tricks we will share.
Starting With The Cams
Todd Warren, one of the owners of Apocalypse Performance in Dayton, Ohio, is heading our project with help from the guys at Exigent Solutions in Cincinnati. Warren says that cam selection starts with the pistons, which have those valve reliefs. “The pistons allow you to run a lower intake lobe center. You can add more duration without killing the mid-range power, which for road racing cars is critical. You can get a big peak number without them, but you have to retard the timing significantly.”
The stock cams have 190 degrees of duration on the intake and 197 degrees on the exhaust, with .397 inch lift. But with the new pistons, Warren can add a lot more duration. “Had the pistons been flat tops, without reliefs, the cams would have to go in at like a 114 lobe center. I look at the intake valve closing point and see where I want it and where that’ll put the peak power. Then, I can add duration to it. The amount of duration I can add depends on whether or not there are valve reliefs. So that’s how I came up with the integration that I did,” explains Warren.
Warren’s cam specs move the lobe center to 110 degrees on the intake. Warren transforms the whole camshaft profile to produce that mid-range power. “Without reliefs, you’d probably lose about 25 pound-feet of torque over this,” says Warren.
You can significantly improve the power band by moving the lobes just a little; only a couple of degrees is all that’s needed to increase the power and extend the RPM range for more midrange power. “These cams aren’t extreme or anything; it’s just that you can put the power where you want it by moving the intake and exhaust lobe centers a little,” Warren says.
Warren notes that shelf cams didn’t offer the durations he wanted at that intake centerline, nor do they offer the lift he’d like to see — he spec’d .512 inch of lift at the valve. Warren chose .500-inch lift valve springs from Comp Cams (P/N 26123-32) to control the valves. They are a beehive spring designed to increase valvetrain stability. The spring pressure is lower for better valvetrain life, but with the reduced weight of both the spring and retainer, it offers more control than a heavier spring. The design enables the valvetrain to handle more lift, more RPM, and more aggressive cam profiles.
Managing The Valvetrain
Warren used standard off-the-shelf performance valvetrain parts for the retainers and locks. “We went with the off-the-shelf COMP Cams offerings with the springs and the standard retainer. We didn’t want to go crazy with exotic or custom parts, because this is more of a budget build,” he explains.
For the valves, Warren chose to go with Ferrea factory-sized 37mm intake valves and 30mm exhaust valves because the .5mm oversize was not available. Ferrea recommended its Competition Plus-series valves (P/N: F1450P intake, P/N: F1451P exhaust), which are made from a proprietary aerospace alloy. Both the intake and exhaust valves come with a 7mm stem and factory-style three-groove retainer grooves.
According to the guys at Exigent Solutions, they didn’t do anything fancy with the valve job. Dan and Glenn from Exigent did the work and told us that it was just a standard three-angle valve job, but they did install new bronze valve guides and milled the heads to a mirror finish for the MAHLE MLS head gasket set.
32 Lashes With Melling
Melling offers the OEM-style lash adjusters and cam followers, which means we could use new parts. The lash adjusters we used are actually those used on the exhaust side of GT500 engines. “The intake adjusters are a different size and cannot be used in the standard 4.6 four-valve heads,” says Warren. “They’re shorter to allow for a raised intake port because the lash adjuster sits directly above the intake port. So the shorter adjuster for the GT 500 allows for a straighter shot into the valve. That’s why the exhaust adjusters from the GT 500 will work in all two-valve and four-valve heads. They’re interchangeable.”
The GT500 cam followers, along with being both lighter and stiffer, feature a smaller oiling hole. While that might seem counterintuitive, Warren says the selection is based on a theory. “The thought is, that the cam journals and lash adjusters are fed from the same oil supply. Some people believe the cam journals get more oil with the restricted lash adjusters because less oil passes through it, diverting more oil to the cam journals. That is the theory. I don’t know if anyone has ever tested it on a dyno, though.”
Optimizing Cooling Of The Head
Another modification that Warren made was with how the coolant flows through the heads. Warren utilized a slick Cobra Engineering head cooling modification that helps cool the back two cylinders more uniformly on the driver’s side.
“The driver’s side head does not allow the coolant to flow from front to back, like the passenger side does,” Warren explains. “The passenger side has an outlet on the back of the head that feeds the heater core.”
When you install the cooling mod, Warren says you’re trying to mimic the passenger side. “The passenger side head allows coolant to exit out the rear to feed the heater core and this tends to keep this head cooler. Adding the Cobra Engineering Cooling mod allows the coolant from the driver-side head to exit out the rear of the head in an attempt to replicate the passenger-side coolant flow. Coolant from both heads is then directed to the back of the water pump.”
Ostensibly, the goal of the cooling modification is to equalize cylinder temps and help prevent detonation. — Todd Warren
Warren also used mostly stock fasteners throughout, including the head bolts — which are torque-to-yield bolts — so they had to be replaced at the outset. For that, we went with a set from MAHLE Aftermarket. Warren says they didn’t use head studs because it was a mild naturally aspirated build, and were being budget-conscious. With the goal of 400 rear-wheel horsepower, it won’t stress the head bolts that much.
Our Boring 4-Valve project is coming along nicely and will be ready to hit the racetrack soon. Stay tuned for Part 3, as we cover timing component selection and modifications. We promise it will be more exciting than an Elon Musk tweet!
- Cams: Todd Warren-spec custom COMP Cams
- Valve springs: COMP Cams 324 lb/in beehive springs, P/N: 26123-32
- Retainers – COMP Cams 7-degree steel, P/N: 799-32
- Lash Adjusters: Melling: 11-14 GT500 (used exhaust on both intake and exhaust side)
- Valves: Ferrea Competition Plus, 37mm Intake P/N: F1450P, 30mm exhaust P/N: F1451P
- Head bolts: MAHLE Aftermarket, P/N: GS33269
- Head Cooling Modification: Cobra Engineering