The brain controlling Mike Stine’s big-block is the XFI fuel injection computer by FAST. A
Some things are just a flash in the pan. A trend here today and gone tomorrow. The things that last and become embedded forever in our culture are those things that get it right from the start and just keep getting better. Such is the case with the almost 50-year-old big-block Chevy. Yeah, we know the small-block had a decade head start, but the fact that the big-block has been basically the same for almost five decades—that’s two generations of hot rodders—must mean that the General did something right, especially since that powerplant is still the main choice among the high-power bracket racers across the country today. That’s not the only thing that’s been on the job for decades. Veteran engine builder Mike Stine has almost as many years massaging those engines as they’ve been around; it’s the primary reason he chose one as his entry into the 2011 AMSOIL Engine Masters Challenge (EMC).
Mike has been building engines with his two brothers (and a lot of support from his wife!) since the early ’70s, and the Stine family has amassed a throng of circle track records and championships with their expertise in small-block Chevy and Ford powerplants. Mike is a Chevy man through and through, so when it came time to pick the engine for this build, he decided on the old porcupine engine: a big-block Chevy. The Mark IV engine that was the basis of this build has a past rooted as deeply in racing as the Stines themselves. In 1962, General Motors covertly began the design of a completely new revolutionary engine to replace the W block motors. Those old 348 and 409 Mark I engines were neat to look at and made decent torque, but just didn’t have the right stuff to make the top end power needed for racing. As the 1963 NASCAR season got fired up in Daytona, a slew of Chevys blasted around the track with an engine that was kept totally secret up to that point. It was the Mark II big-block Chevy “Mystery Motor,” and it shared almost nothing with its predecessor.
Even for a big-block, with fuel injectors sitting downstream there is only the need for a
The new big-block was designed as a big-bore, short-stroke engine with beefy mains down below and high-flowing heads up top. As the Mark II was progressing on the racetracks in ’63 and ’64, there was a short-lived development program for a larger bore-center version dubbed the Mark III, but it was a no-go from the bean counters due to the high cost of retooling. By then, the fewer-than-50 Mark II engines produced were about used up as GM pulled the plug on their racing programs. Thankfully, the growing pains of the Mark II were worked out and an updated version was ready for placement in production vehicles for 1965. The Mark IV big-block’s reign began.
Since this particular engine was to be quite a bit different than the high-revving roundy-round motors they are used to producing, the brothers Stine, with Mike in the lead, aimed their rpm range a bit lower and wider than usual, as is required by the EMC rules. That meant this would be a serious torque monster. As Mike would tell you, there are two ways to build torque, otherwise seen as brake mean effective pressure (BMEP). The first option is to go for a small bore with a big stroke. First, let’s assume that the engine produces “x” amount of cylinder pressure. Let’s call it 200 pounds per square inch. With the 4.25-inch bore, that means there are 14.2 square inches of surface area on the piston crown for that pressure to push down on. A little math yields us 2,837 pounds of force shoving that piston down. That’s a ton of weight! Well, more than a ton, but moving on. That force is then transmitted through the arm of the crankshaft at an angle with the result becoming torque to twist that crank. The second design option is to use a big bore with a small stroke. Assume a 4.50-inch bore with that same 200 psi of pressure. That would result in 3,180 pounds of force. That cylinder pressure gives the same force as setting a Fox-body Mustang GT on top of your piston! You’d think that naturally this would produce more torque to the crankshaft, however, since the stroke is shorter, there is less of a lever arm to multiply that force, and it may in fact be less average torque per revolution than the first option. Choices, choices.
With their background in circle track racing, the build team went with a header design by
Mike went the route of a square combination, meaning the same bore and stroke. This played to his advantage as he was rules-restricted in lift and rpm, and history showed that a pretty long stroke was favored for average torque and a pretty good sized bore is needed to unshroud the valves enough to get air in there for high horsepower. Then there was the next decision. Rod length. Please, can we talk about rod length? I mean, you never see anything about it on the Internet, right? Ugh. OK, there is some science to it though.
The angular relationship between the rod and crank is ever changing and so as that force we were talking about before is pushing down on the piston, the rod is cocked over and making a compound angle with the crank arm. If you know the cylinder pressure at every point as the piston is going down, and you know the angles among the cylinder, rod, and crank arm, and you’re really good at calculus, you can actually determine the average force transmitted to the crank throughout a revolution. But—and there’s always a but—this is a four-stroke engine, so the crank has to make another revolution before the cycle is complete. Now you have to figure out what the importance of rod length is as it relates to the exhaust and intake flow, and the dwell at TDC and BDC, and so on. The long and short of it is that, in general, a long rod tends to benefit a bad cylinder head and a short rod tends to favor a good cylinder head. And Mike’s head is a good one, so he opted for a stock-length BBC rod.
An MSD flying magnet trigger wheel sends a pulsing signal to trigger the ECU, then finally
Mike likes to size the intake plenum to the engine size and operating range of the engine.
Brodix offers an intake manifold that matches the runner design in the heads, but only for