Pro Stocker!
PRO STOCKER!
ROUNDUP
NHRA drag racing is a balance of power
KEVIN CAMERON
DRAG RACING IS HUGE IN THE U.S., and Pro Stock Motorcycle has number-four billing at NHRA nationals. The three Ages of Pro Stock are: 1) Age of Suzuki, when big-inch Fours based on the 66mm-stroke GS1100 and 1150 dominated; 2) Age of the Vance & Hines big Twin-to boost partisanship, rules were written to match 160-cubic-inch Twins with two valves and pushrods against two-valve, 101-inch Fours; V&H built such a “Harley V-Rod” from scratch, zero H-D parts, and made a winner of it; 3) Age of the S&S Twin. S&S not only built a winner from scratch, it also broadened its R&D base by selling engines to others-order today at $50,440.44!
NHRA Pro Stock is a “managed parity” class, in which wise persons keep things right by periodic adjustments to displacement, weight or other variables. Trouble is, the big-inch Twins have dominated. A year ago, the Schumacher Electric team, together with Suzuki and McLaren, produced a faux “Suzuki” to challenge the equally faux “Harleys.” Some “political R&D” at the end of 2006 allowed billet, fuel-injected, fourvalve Fours to step up from 92 to the full 101 inches. The engine has been delayed by development snags, suggesting limited funding.
Current Suzukis, like Steve Johnson’s shown here, are 89 x 66mm, using aftermarket head and cylinder block atop a 19808vintage crankcase originally designed for the 100 horsepower of the GS1100. Most run Lectron carburetors. Valves in the Vortex II cylinder head are 46 and 38mm and lift to about 40 percent of diameter. The cranks are the old-tech roller type-a race version with V&H or
Falicon rods sets the user back $4K and goes, as Johnson puts it, “15 miles” (that is, good for 60 runs).
Talking with users, you get the idea that there’s a little animal inside each crank. If the animal is happy, you get a good run. If it’s sick, you go .020 second slower. I asked Byron Hines about this.
“The crank in these engines is not well-supported at this power level,” he said. “Any little deviation and you can get some angle into a crankpin and the big-end (bearing) starts augering-the rod running to one side, against the sidewasher. That friction is enough. It’s kind of an art to break ’em in on the dyno.”
At V&H, they run a crank in an engine of known output-their “Bureau of Standards.” If the power is a little short, they know it’s not a good crank.
How much power? The official chat is 350 hp at 14,000 rpm. Well, maybe 340 is a flash reading, and peak is more like 12,700 or 13,200. The adventuresome lads and lasses at the throttle rev them to a 14K upshift point. There’s maybe 300 hp at the rear wheel to heave these heavy bikes to 190 mph in fewer than 7 seconds.
Originally, the idea was Pro Stock-a class to showcase the latest big,
hot stockers. Then the need for power required tall cam lobes that would have overhung the edges of the tappets. They enlarged the tappet bores for bigger tappets. And how ’bout a new head casting to keep even bigger tappets from busting out? Throw in big, adultstrength ports. For even more lift, radius tappets keyed against rotation arrived-at $350 apiece. Pro Stock is not for the faint-of-pocketbook.
Every part has a story. Originally, the valves were bigger, but then were made smaller and swung apart. Isn’t bigger better? Make ’em too big, lift ’em far enough and intakes hit exhausts like cymbals. Bad! So, mentally agile machinists (that is, software writers) reposition everything, then adjust diameters. Presto: big valve lift, no valve clash and more airflow. Power up, up.
Are these “Rice-Burners?” Hmm, with U.S.-made cams, valves, head, cylinder, crank and pistons, they are almost as American as a Chevy small-block.
Oh, wait, those PSI valve springs are made of the finest available spring wirefrom Kobe Steel in Japan. Good chance there’s J-wire in everyone else’s springs, too. Globalization strikes again.
The big Twins aren’t just fast. Their extra displacement makes up for the Fours’ greater ability to rev, but many claim that displacement also lets them get a decent run out of a less-than-perfect clutch setup. Suzukis, even with equal power, fall off their narrower peak.
I asked Hines about this. He replied, “A lot of teams retard ignition during the launch, which detunes the engine so it doesn’t send the tire up in smoke, but that makes it hard to recover if it bogs.” If the statistics are one-sided, won't NHRA handicappers fix it? The answer could be that Pro Stock is not just racing. It’s also drama: Good Guys versus Rice Burners. Spectators stay home if there’s no drama. Do the Bad Guys win half the time in the movies? No! They win just often enough to feed the suspense. I’m not saying this is Pro Stock; it’s just an idea. Now let’s hear your theory.
