IHRA Chevy Big Block - From Street To Strip

Consider this: For three seasons of knock-down, drag-out competition in IHRA's fiercely contested Stock ranks, the big-block in Monty Bogan, Jr.'s bright-yellow '69 Camaro routinely screamed to almost 7,000 rpm between gears and generated enough torque to yank the front tires off the ground on almost every pass.

In those three seasons, however, Bogan never had to crack open the engine. No valve adjustments. No bent valves. No spun bearings. Nothing.

Oh yeah, and each of those wheels-up, 7,000-rpm passes was made with less than 2.5 quarts of oil in the motor. You read right. Bogan ran the engine for three seasons with the dipstick barely getting wet. In fact, most passes would see the oil light start to flicker just as the car crossed the traps. To anyone other than a dyed-in-the-wool Stock competitor, this sounds like a nutty way to treat a high-dollar race engine. But, such is the nature of this competitive class of drag racing, where finding the slightest performance edge within the rules-in this case, reducing crankcase windage-has become equal parts science and art.

In addition to standard Stock class competition, Bogan is also a key competitor in the growing Top Stock field. Top Stock pits mostly classic musclecars against one another on a Pro Tree. Although a weight break is given to small-block-powered cars, most Top Stockers run a big-block to push the heavier, less aerodynamic '60s iron through the air in about 10 seconds on 10.5-inch tires.

The rules of Top Stock allow many types of cars to compete, but the engines in them must be based on readily available crate engine packages from the original manufacturer-an engine designated by the manufacturer and approved by IHRA. For GM Top Stockers, the ZZ 502/502 crate engine is the accepted big-block.

With the competition in Top Stock really heating up, Bogan felt it was time to give his never-been-touched engine a much-deserved rest and drop in a fresh, more competitive combination. With some advice and guidance from GM Performance Parts-where the crate motor was coming from in the first place-Bogan enlisted the service of McLaren Engines (a division of McLaren Performance Technologies in Livonia, Michigan) to build the rules-complying crate motor. We followed along as McLaren's Curtis Halvorson completed the assembly, then tuned the engine on one of the company's dynamometers.

Halvorson has years of experience building racing engines-everything from bracket cars to supercharged monster truck motors. His insights during the Top Stock engine build-up revealed two things: First, it doesn't take exotic, unobtainable parts to build a reliable, consistent, and powerful race engine. Second, what works on the track isn't necessarily what you want for a street engine.

To stay within the rules there are things that can't change, such as crankshaft stroke. But, within those guidelines, there are ways to build the engine for the track that will increase horsepower. The best way is to build to the rules, not over them. In the case of Bogan's engine it works; compare the factory-rated 502's output, at 502 hp and 567 lb-ft of torque, to that of the Top Stock version outlined here, which made 657 hp and 598 lb-ft.

IHRA rules mandate a manufacturer's...        read full caption IHRA rules mandate a manufacturer's crate engine. In the case of the Chevy 502, it's available in kit form, which means a bare block to begin the assembly. Although many components of the street-intended kit are replaced for this racing application, a surprising number of them are retained. McLaren overbored the engine .060 inch, even though IHRA allows a .070-inch overbore. The .060 job leaves room for a future rebuild.	Before any of the reciprocating...        read full caption Before any of the reciprocating assembly was installed, the engine was treated to a thorough cleaning and deburring of casting flash and other sharp edges. Here, the oil galley at the rear main bearing cap was smoothed and radiused. This minor step in block preparation smoothes the transition of oil out of the galley, which reduces cavitation and oil pressure fluctuation. And since the engine will likely be run consistently with less than 3 quarts of oil, ensuring constant oil pressure is an obvious concern.	There are four oil-return...        read full caption There are four oil-return ducts in the big-block's lifter valley. For the Top Stock engine, the front three are blocked off, while the rearmost duct is screened off, and a small trough below directs returning oil to the back of the engine. This is done to prevent the oil from dripping onto the crankshaft, thereby causing windage. The blocking plates and trough were handmade from .040-inch aluminum, while the plates and screen were affixed with Devcon epoxy.
As the stock crank in the...        read full caption As the stock crank in the 502 crate engine package is a balanced, forged piece, it's retained for the race engine. But, it was rebalanced after the engine's new pistons and rods were fitted to it. The existing external balance holes were simply drilled farther-McLaren took 105 grams from the front of the crank and 115 grams from the rear. Once rebalanced, the crank was micro-polished before being dropped in the block. Installed, crank endplay measured .005 inch, which is close to a street engine's specs. If the engine were to be used in a manual-transmission car, more clearance, from .007-.010-inch, would be acceptable, as the rear of the crank would typically endure more heat expansion.	The stock main bearing caps...        read full caption The stock main bearing caps are used, and ARP studs are used for added strength and less wear from constant removal. The caps can be torqued down a bit more accurately with the studs, too. In this case, the caps are torqued to 100 ft-lb in a two-step process.	Because the engine will be...        read full caption Because the engine will be used strictly in a high-rpm racing environment, McLaren swapped the 502's stock, but nonetheless stout, rods and pistons for stronger, race-specific parts (stock rod and piston are in the background). A piston with a full floating wrist pin was desired (stock is forged with a pressed pin) because there's less friction load at higher rpm and the piston is less likely to be damaged if the engine is disassembled. The new pistons are from Ross and are the only IHRA-approved slugs for Top Stock. Per the rules, the wrist pin location is stock, but the location of the "ring pack" is a variable. As for the rods, they're lightweight, forged H-beams from Carillo, with mandatory stock (6.135-inch) lengths. Interestingly, there's no specific compression ratio limit in the rules, but with cylinder head restrictions, the new pistons will provide compression in the 9.8:1 area.