THE BIG-BLOCK FROM HELL cont’d
Our rotating assembly places the pistons 0.002-inch below the 10.190-inch-tall deck. Note that although the
dish takes up most of the piston face, sizable reliefs still needed to be cut into the face for the valves. The
photo on the right was taken during the mock-up phase of the build, so you’ll notice that the top of the
piston doesn’t have the thermal barrier coating applied yet.
At the time of this build, ARP didn’t have the right length head studs in stock, so we were forced to
order +0.250-inch longer parts and then turn them down in a lathe.
Cometic multi-layer steel head gaskets were employed and measure 0.040 in thickness with a 4.600 bore.
We chose Manley titanium valves and retainers to make the valvetrain as light and reliable as possible. The
intake valves measure 2.450 inches in diameter and have 5/16-inch stems, and the exhaust valves are 1.80 inches
in diameter with 11/32-inch stems.
The valvesprings are LSM’s 700A 1.670-inch od units, minus the inner spring. The cam profile is designed
around this particular rate, and by removing the inner spring, it all works out. Pressure at the seat is 310 pounds,
and the open pressure is 835 pounds.
Because we have more than 300 pounds of seat pressure, we chose the 0.250-inch-wide beam J2K Mohawk rocker
arms, which are the strongest rockers Jesel offers (4a). The J2K’s design is further strengthened with tool
steel lash adjusters and extra-wide 0.250-inch needle-nose rollers. Our rocker arm ratio is 1.7:1. Our block
wasn’t machined for lifter bushings, so we opted for Jesel’s tie bar-style lifters. The oil circuit
in these lifters sends pressurized oil to the roller, bearings, pushrods, and upper valvetrain. Another benefit
of these lifters is that they are available with offset pushrod cups to aid in moving the pushrods away from the
intake runners in heads like ours.
Mocking up the rocker arms and supplied stands revealed that we’d have to machine the bottom of the
stands to get the geometry perfect, so that the roller swept across the tip of the valve porperly (4b).
We used Pro Filer’s 12-degree Hitman cylinder heads because DNE has built several engines with them and had the experience to make prepping these heads for our motor fairly painless. Dave sent the bare heads to MBE Performance Parts to have the changers blended, a 5 angle valve job performed, and the runners cleaned up. The exhaust ports are huge to begin with, so those were left untouched. For an as-cast part, out of the box, these heads are pretty nice, and the work that MBE did really took these heads to competition level quality. The 12-degree valve angle promotes high-speed airflow into the chambers, and the port designs work really well in a naturally aspirated configuration. After the port work was finished, Dave chucked the heads into his mill to clearance the intake ports for the pushrods. We also spent a considerable amount of time cc’ing every single port and chamber as part of the design phase of this engine. Here’s how the heads spec’d out after the port work:
(flowed on a Super Flow 1020 bench at 28 inches of water)
INTAKE RUNNER: 507 cfm
EXHAUST RUNNER: 319 cfm
INTAKE PORT VOLUME: 475 cc
EXHAUST PORT VOLUME: 187 cc
CHAMBER VOLUME: 55.5 cc
According to Dave, with this chamber volume the compression ratio is around 12:1 and, based upon previous
engines he’s built that are still running, is completely safe as long as you pay attention to the details
and maintenance required of an engine like this one.
Once the mockup phase was complete, we ordered pushrods from Manton. Our pushrods
for the intake taper from 7 /16-inch to 3 / 8-inch with a 0.168-inch
wall thickness. Our exhaust pushrods taper from 1 / 2-inch to 7 / 6-inch with a 0.1888-inch wall thickness. Perhaps the coolest
aspect of Manton’s pushrods is the quick turnaround time. We ordered our custom
pushrods, and they were delivered two days later.
Pro Filer’s Hitman single-plane intake manifold was designed in conunction with the pros at
Reher Morrison Racing Engines. Features include a 1-inch-tall spacer cast into the manifold,
a one-piece design, and spread ports that align beautifully with Pro Filer’s
12-degree heads.
We also had MBE port-match the intake, massage the transition from the plenum to the runners,
and equalize the runners as close as possible without going to the expense
of filling and epoxy work.
After installing the intake manifold, we turned our attention to the oil pump drive unit.
Dave coated the shaft seals and bronze gear with assembly lube, and after determining that the cam gear was meshing
nicely with the drive gear, he applied silicone sealant to the slip collar of the drive unit
to prevent any future oil leakage.
Topping off the manifold is a Quick Fuel Technology P-4512 1,250-cfm three-circuit
carburetor (9a). Like any good custom carb, Quick Fuel built this one specifically for this
engine, but it also features items that are standard on most of the company’s carbs, such as lightweight aluminum fuel bowls, notched
floats, and jet extensions on the secondary side. The extensions prevent the jets from
becoming uncovered during hard launches, ensuring that fuel is always on tap during holeshots.
The metering blocks are precisely machined from billet aluminum to prevent warping and leaking
down the road (9b). This carb also features annular boosters, polished venturi surfaces,
Teflon-coated throttle shafts, and stainless steel
throttle plates and hardware. Before the carb was bolted
to the manifold, we slid-in a combination phenotic spacer to isolate the base of the carb from the
hot manifold (9c).
To connect the camshaft to the crankshaft and ensure accurate timing between both, Dave
installed a Jesel beltdrive system. This system not only damps harmful valvetrain harmonics but is
also stronger than a chain setup, and the belt is the only maintenance item on it that will need
replacing later on. in the meantime, we’ll enjoy easy cam timing adjustments and
cam swaps without having to remove the cover.
—courtesy Sport Truck magazine; Photography: Mike Finnegan
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