Last month, we put together our 402's short-block with forged internals from Lunati and Wiseco, and went over how to set up bearing clearances, ring gaps, and other essentials for assembling an engine that will hold up under the rigors of a heavy right foot. This month, we'll put together our top end, and go over a process that has become hotly debated in recent years: breaking in a flat tappet cam.
More than a few readers are probably wondering why we went with a flat tappet cam in the first place. Why not a "modern" roller valvetrain that will make gobs of power? Well, first, roller cams aren't exactly modern. Most people don't realize that roller cams in engines go back to the early part of the 20th century, and are just as old as flat tappet cams. The first aftermarket roller tappets came out in the ‘50s, designed by Bruce Crower. By the ‘60s, most of the performance valvetrain companies had roller cams and lifters in their product lines for use in racing and hardcore street applications. But these were expensive, and flat tappets still ruled the world.
It wasn't until the late-'80s when roller cams became standard from the factory that their affordability in the aftermarket started to increase, and almost 30 years later roller cams are as common as flat tappets, but they still haven't been able to depose them as top dog, sales-wise. The reason still comes down to cost. When going to a roller cam, you're typically looking at an increase in cost of build between $1,500 to $2,000. That includes the cam, lifters, pushrods, valvesprings, retainers and locks, and cam button spacer. For the engine builder on a budget, that is a hefty price increase.
Flat tappet cams still offer great power, but on a more budget friendly level. And for racers who compete in classes where rules specify them, flat tappets are the only option. So, in sticking with our theme of a real world, budget-friendly big-block build, we chose a flat tappet cam. Specifically, we went with a mechanical/solid lifter cam, for that old school feel.
The main issue with flat tappet cams today is their break-in procedure. Twenty years ago this wasn't a problem. But the EPA tightened standards on motor oil and forced companies to remove most of the heavy metals that were in the oil, so breaking in flat tappet cams became problematic. Zinc and other ingredients in oil were having a negative effect on certain factory emissions control equipment. These metals were critical for initial flat tappet break-in. Without them, the break-in procedure wouldn't go properly, and you'd end up with a cam lobe (or several) wiped out.
Thanks to the performance lubricant companies, this is no longer a problem. Special "heavy metal" oils are now readily available from Comp Cams, AMSOIL, and others that help ensure cam break-in goes smoothly …as long as the break-in procedures are followed.
1. First up is dropping our Lunati mechanical lifters (part no. 70984) in place. Moly paste (included with the cam kit) is used on the lifters to protect them during initial start up before oil pressure comes up. The moly paste also helps to protect the lifter face while it burnishes to the cam lobe. Even though they're called flat tappet, the face of the lifter actually has a slight crown to it. The lifter spins on this crown, on the cam lobe.
2. Part of our Cometic gasket kit is Cometic's MLS (Multi Layer Steel) head gaskets. MLS gaskets are comprised of multiple layers of stainless steel, giving them increased strength and creating the ability to rebound and resist corrosion. The outer layers are embossed and coated on both sides with Viton (a flouroelastomer rubber based material heat resistant to 250 C/ 482 F). Viton is designed to meet the demands of a variety of harsh sealing environments, load conditions, and surface finishes. The center, or shim layer, is uncoated stainless steel, which can be varied to accommodate multiple thickness requirements, such as controlling compression ratio.
Our heads were fully cleaned, then the seats enlarged to accept the bigger factory 2.190 intake and 1.880 exhaust valves, over the stock 2.065-inch intake and 1.725-inch exhaust valves. The factory cast iron valve guides were tight and showed no signs of needing replacement, so they were just cleaned up, checked for burrs, and prepped for our new valves.
4. Our valves had a three-angle valve job done on them. A three-angle valve job increases flow performance of a head by giving the valve three different faces to seal against the valve seat. This process also helps smooth out flow around the face of the valve, keeping the air/fuel charge from slowing down while going around the valve face. If the charge slows down, that's power lost by not having as much of a charge in the cylinder as possible. The faster the flow, the more of a charge you can get in the combustion chamber while the valve is open, increasing horsepower.
5. Jason does some light bowl work to the heads to make sure the valves aren't shrouded, thereby restricting flow.
6. Jason also did some port matching work to the intake ports on our heads, so they would match up better with our Cometic intake gaskets and give us some extra flow.
7. Time to assemble our heads. First, Jason installs our new pushrod guideplates, and screw in rocker arm studs. On the rocker studs that go into the intake ports, Jason uses non-hardening thread sealer to make sure there are no vacuum leaks, and to keep any oil from seeping into the intake ports.
8. Next, Jason uses a valvespring micrometer along with a valvespring cup, retainer and lock to check what height the valvesprings will install at. The springs themselves are spec'd out at 142 pounds on the seat (when the valve is closed) at a height of 1.940 inches. The cam calls for between 120-130 pounds on the seat. After measuring with the retainer, our height came out to 1.949 inches. This means the springs will set up a little taller than spec, giving us a light enough seat pressure to work with our cam. If the measurement had been too short, we would've needed a set of valve locks that would move the retainer up, decreasing seat pressure. If the measurement had been too tall, we would have needed special valvespring shims (easily available from any cam company) and shimmed the spring up to get the required seat pressure.
9. With our measurements set, Jason uses a valvespring compressor to compress the spring so the locks can be installed. Our valvesprings have a max lift of .794 inches, well below the .550-/.570-inch lift of our cam. This means we won't be anywhere near coil bind. Running a spring constantly near coil bind can overstress the spring and cause it to fail prematurely.
10. With the heads fully assembled, they're set down on the block. With our combustion chamber size, pistons, and head gasket thickness, our net compression should be right around 10:1, safe for pump gas but still capable of great power.
11. With the heads in place, our ARP head bolts are installed, after using thread sealer on the bolts that go into the block's water jackets. If you don't use sealer on these bolts, you could end up with water seeping into the oil and combustion chamber. On the bolts that don't hit water, ARP's thread lube was used, along with using it under the heads of all the washers.