427 Chevy Big Block - Radical Rat

Bottom-ends are for reliability, while the combination of upper components creates the power-producing character. We couldn't wait for a look inside the Brodix intake and Brodix raised oval-port heads.	Note that the intake manifold ports were not extensively hogged-out with porting. Shaver relates that port sizes need to be no larger for an engine of this displacement. Subtle modifications could be found under close examination.	With the intake removed, a look inside the valley shows an oil splash baffle, which helps reduce hot oil splash on the underside of the intake. Note the standpipes, while the oil drainback is isolated to the front.
Intake port size needs to be proportional to the displacement. These ports measure about 300cc, which is by no means big for a Chevy big-block, but plenty for a 434. The 375 to 380 cfm of max airflow is unreal for a port of this size.	On the exhaust side the flow is not as critical, but good flow here helps extend the powerband. These generous ports won't hold the power back.	With the big Crane roller cam, an extra stout valvetrain is mandatory. This set-up from Crane is more than up to the job, including the bridge-like girdle.
Stud-mounted Crane roller rockers and 0.080-inch wall thickness, 7/16-inch diameter swaged-end pushrods completed the bulletproof valvetrain.	Driving the cam is a Jesel belt drive. Shaver made a point to emphasize that dialing in the cam timing is worth power. With the Jesel, the cam can be bumped in minutes, with no disassembly required. The ATI Super Damper has earned a reputation as an industry leader, and it's a nice finishing touch to Shaver's healthy big-block.

What's A "Rollover" Head?
It's one of the most effective modifications common in the old days when modifying small-block Chevrolet engines was giving those old iron heads a heavy dose of angle milling. Back then, choices in aftermarket heads were limited, and this approach had definite performance value, particularly in building race engines. Angle milling is done by tilting the head in the mill to take more material off the plug side of the head. With the Chevy's steep 23-degree factory valve angle, the chamber is deeper than most, and angle milling reduces the chamber volume much more effectively, while taking less material off the decks than flat milling. Much smaller final chamber volumes are possible. Angle milling also had the effect of rolling the axis of the heads, which helped straighten the valve angle, improving flow. The down side was extensive correction to the manifold flange, which would then need corrective milling to align with the manifold. The head bolts would usually need to be spot faced on the mill to correct the contact surface with the head fasteners, and sometimes the bolt holes themselves would need reworking to prevent binding.These days, aftermarket manufactures are already wise to these tricks, and rollover heads refer to cylinder heads that are configured much like the old-school custom-angle mill pieces, with a shallower valve angle and smaller chambers. The difference is that these "rollover" heads are machined with the "rollover" valve-to-deck angle as part of the design, so the heads bolt-on without any special machining.

Got Quench?
A piston dome configuration is critical to making power. One of the keys is matching the dome to the chamber layout. Considerations here are the final dome volume, dome shape, and quench clearance. The dome volume is a major component in the final compression ratio. Normally with a custom piston, the builder will specify the total dome volume to achieve the desired compression ratio, considering the other relevant components in the engine combination. The "quench" clearance is simply a measurement of the piston-to-head clearance in the flat "quench" areas of the cylinder head, adjacent to the chamber.

Running the piston tight to the quench area results in quantifiable benefits. As the piston moves up to TDC on the compression stroke, the gases in the quench area are quickly displaced by the rapidly decreasing volume, which adds turbulence to the chamber. This turbulence helps with flame propagation for a quicker, more efficient burn. The remaining end-gasses in the quench area are the last to light, and often it is here that detonation develops. A tight quench clearance results in just a very thin layer of gasses in the quench area. These compressed gasses are actually at a higher temperature than the surrounding metal walls of the pistons and cylinder head. As a result, these gasses are actually cooled, which reduces the tendency to initiate detonation. Actually, it's from this cooling effect on the remaining gasses that the term "quench" is derived.

Another often overlooked benefit of a tight quench occurs 360 degrees later, during the overlap period. Here, end gasses consist of residual exhaust and spent mixture. A tight quench helps isolate the working chamber for more effective scavenging, and less residual exhaust making its way to the next combustion cycle. Shaver set his engine for a quench clearance of 0.042 inch.