The tree goes green and power is unleashed. Clutches bite and engine torque turns 10-inch-wide slicks. The bikes hunker as tire sidewalls are twisted into wrinkles. Roughly 2,000 pounds of force at the tire footprint launches each bike. This is a beautiful moment of balanced forces—front wheels lift and wheelie bars may touch lightly, but so perfectly does this all happen that nothing upsets the force being generated between rubber and pavement. The bikes cover the all-important first 60 feet in barely over one second. You can’t fall 60 feet that fast on this planet.
Drag Racing Outgrows Production Parts
NHRA’s Pro Stock Motorcycle (PSM) drag racing class began in the 1970s, based on modified production motorcycles. That made it attractive to both spectators and to beginning builders. Those were the heady days of horsepower revolution—two-stroke 750 Kawasaki H2s and four-stroke 903 Z1s raced against the new GS Suzuki fours and “built” Harleys.
In the light of day at NHRA nationals, spectator attention was carefully focused on Pro Stock Motorcycle by maintaining basic visual connection to production models we might own and ride—but radically modified according to the traditional American belief that too much is just enough.
In the final days of World War II, aviation was the number one US industry in dollar volume, running three shifts of skilled machinists, welders, fabricators. In August 1945 it all stopped, and in two years it fell to 17th. A flood of surplus technology poured onto the market at pennies on the dollar. Want a Lockheed P-38 Lightning? Yours for $1,200. One fast-mover bid on thousands of surplus platinum-gapped aircraft spark plugs and put high-school kids to work with diagonal cutting pliers, nipping off the bits of precious metal.
Pro Stock Motorcycle Outgrew Its Roots
Performance in NHRA Pro Stock Motorcycle rose so high that it has outgrown the 1970s production hardware from which it grew. Usable GS Suzuki crankcases are now rare. Like the Top Fuel cars whose engines are “Chrysler-inspired” but 100 percent Mopar-free, so the engines of today’s PSM retain only conceptual similarity to the original production powerplants.
This is what happens when many inventive minds and hard-driving personalities devote themselves to going quicker and faster over decades. At the recent Charlotte, North Carolina, NHRA national I spoke with Eddie Krawiec, an active PSM rider, and with Andrew Hines, a driving force in Vance & Hines’ latest PSM creation. Hines said stock crankcases for the 1970s–80s Suzuki GS-series are gone, so teams running Suzukis turned to 1100 and 1150 cases. But crankshafts spinning at 14,000 rpm want out so badly that 40-year-old cases may be good for only five runs!
Why? Because this year’s Gen III Vance & Hines “Hayabusa” PSM is making 400 hp at 13,800 rpm—five times the power of the original engines. That requires strong support to prevent longitudinal whip. Vintage castings can’t give it.
The Origin of Billet Engines in PSM
At the beginning of this century NHRA had a brainstorm: Do something for the large numbers of Harley-Davidson riders and admirers who were finding less and less encouragement at the drag races. Just as has happened to stock Suzuki parts at the 400 hp level, Harleys built from a mix of stock, modified, and aftermarket parts weren’t up to the job of competing with more modern designs, similarly modified.
Why not build a completely new engine sharing identifiable features of Harley-Davidson V-twins, but designed for drag racing with enough displacement to make them win races? Build it, call it a Harley, and see if people believe it! Harley-Davidson and Vance & Hines made it happen in 2002: a 60-degree V-twin with two giant valves per cylinder, operated by pushrods and rockers. They gave it 160ci, and to reliably contain the power, its entire structure was CNC-milled from solid billet. Old-time hot-rodders operated lathes and milling machines by hand, but this was Byron Hines learning the mysteries of CNC via Solidworks and CATIA—the way aerospace does things.
It worked. It has worked for years, so well that when aftermarket manufacturer S&S wanted in on the act, its mighty V-twin was assigned the name “Buell.” Harley fans now had solid winners for which to cheer themselves hoarse. Their sworn enemies, “rice-burners” and “crotch rockets,” were cut down to size.
Suzuki builders responded with higher-lift cams—until the taller lobes threatened to overhang the edges of their tappets. They bored tappet guides bigger, for bigger tappets. When that ran out of metal, they switched to “radius tappets” (humped-up in the middle to increase lift, and keyed to prevent rotation). And then V&H and others began to CNC-machine entirely new Suzuki heads from billet—a new tool in the cam-lift race.
At Last—A Billet “Suzuki” to Equal the Billet Harleys
From time to time over the years NHRA have seen fit to adjust PSM rules, over time nudging Suzuki displacement to the present 107 and 113 (with differing weights). The most recent change has been to approve a complete “billet Suzuki” with four valves per cylinder (as in all present-day production Suzukis). Although the billet engine shares a number of features with the original GS engines of 1976-onward (their central cam drive and roller crankshaft) its official name has to be “Gen III Hayabusa” because that is Suzuki’s current new model delivering highest straight-line performance.
Why the V-twins Get 160 Inches
People want to know why the V-twins get 160 cubes when the fours get only 107 or 113. The answer is simple. The fours, whose strokes are short, can reach revs roughly 40 percent higher than can the monster twins. If we multiply 113 cubes times 1.4, we get 158.2. This tells us that NHRA-approved PSM twins and fours can pump the same volume of fuel-air mixture per minute (cylinder displacement multiplied times rpm), giving them equal potential for making power. The rest is up to the builders, tuners, and riders—with NHRA tweaking the rules as needed to keep the ticket demographics sweet.
The basic rest of the PSM rules is that wheelbase is 70 inches maximum, rear tire width is 10 inches, and the fuel is an approved gasoline.
What Brings Suzuki and Vance & Hines Together?
After a long partnership with V&H in PSM and American Flat Track, Harley-Davidson recently ended that relationship. Suzuki saw Pro Stock Motorcycle as the ideal venue in which to present its new Gen III Hayabusa production motorcycle. Hayabusa lives in its own special category because it embodies ultimate street acceleration. It drives one of the largest aftermarkets in motorcycling because its buyers further customize and intensify it for their own purposes. It is very much in Suzuki’s interest to preserve and cultivate that “special relationship.”
The Little Guy Versus the Big Outfits
Americans have always rooted for the underdog, but drag racing at its highest levels can no longer be based on DIY hot-rodded production motorcycles in the old way. If you or I decide to give PSM a try, we’ll find ourselves competing against the very people who supply the parts we need to be competitive—outfits like Vance & Hines.
In reading for background info, I discovered a wonderful sentence written by someone calling himself “McGuire”:
“The history of Top Fuel and Funny Car seems to be that anyone that strays from the herd with a new idea goes bankrupt before they get the idea developed or find the right combination…or they do get it right and the rule book is changed to outlaw their innovation.
Does this mean the little guy will always lag behind the outfits like V&H who produce the parts everyone needs to be competitive, and which NHRA needs to keep its classes healthy? Big outfits have big advantages, but long experience with what you have can also win races. When the big guys innovate, they create fresh unknowns for themselves. We saw this in MotoGP last year, when the 2022 Ducatis were a mystery, while riders and teams with one- or two-year-old bikes had proven setups and could get results from the first race. An example from PSM is veteran competitor Steve Johnson, who remains surprisingly fast because of his experience with what he has, despite not having the latest extreme stuff.