On Your Mark Get Set, MOW!

Feb. 2, 2009
Turning lawn mowers into racing vehicles is the latest and most affordable motorsport out there.

Any organization that decides to be founded on April Fool’s Day must not take itself too seriously. The U.S, Lawn Mower Racing Assoc. (USLMRA), for instance, was founded on April 1, 1992. And even its most accomplished members seem to have a good sense of humor, much of it at their own expense. The association’s founder and president, for example is Bruce Kaufman, better known as “Mr. Mow-it-all,” and most racers and mechanics have nicknames as well, such as “Mr. Mowron,” “Mr. Mowjangles,” and, of course, “The Lawn Ranger.”

Authored by:
Stephen J. Mraz
[email protected]

G Team Racing,

U.S. Lawn Mower Racing Assoc.,

But don’t let the smiles and corny jokes fool you. These folks are serious about their mowers and truly enjoy tinkering and making them faster, as well as racing them. And you know they must enjoy it because there is never any prize money. And sponsorships, which are rare, barely cover travel expenses.

Here’s a look at some of the engineering that goes on behind the brights lights and glamor of BP Class lawn mower racing.

Beefing up the engine
A lawn-mower engine is typically governed to go at a single speed, about 3,650 rpm. So naturally, the first thing mower mechanics and racers do, after removing the cutting blade(s) is remove the governor. Then like mechanic/ driver Don Gienger they overbore and sleeve the piston. This let Gienger turn a Briggs & Stratton 28-in.3, 12-hp engine into a 31-in.3, 20+ hp that tops out at 6,500 rpm. Gienger has the skill and machinery to design and build his own cams, engine components that determine how long and high the fuel and exhaust valves on the pistons will open. His cams keep the valves open longer so the pistons get more fuel and generate more power.

Carburetors must be from a mower, so there are no fuel injectors, yet. Gienger ports the carb and polishes the venturi and throat, letting it deliver more fuel. He also builds an aluminum air cleaner which acts as a velocity stack to straighten out the air as it enters the carb. “This gives the engine better and more consistent performance,” says Gienger.

“Over the years, other drivers would ask where I got my components, and every now and then I would make one for someone else,” recalls Ginger. “So I eventually started taking orders and that has grown into a small business selling racing-mower accessories. (Check out

Michael Formentini, another well-known mower racer, uses a Briggs & Stratton Intek V-Twin to which he’s added a billet flywheel from ARC Racing. It replaces the much heavier cast-iron version that came with the engine. The new flywheel also lets driver and mechanic, usually the same person in mower racing, advance or retard the timing. The flywheel contains a rare-earth magnet that energizes the coil as it spins. According to ARC, this means a 17% increase in coil voltage and a 38% bump in coil output, which could translate to better performance. (ARC Racing is not quite prepared to say a hotter spark guarantees better performance.)

Formentini, who got his vehicle up to a 76.07 mph to set a record for lawn mowers at the Texas Mile, an annual speed event held on an 8,000-ft-long, 200-ft-wide road, also uses billet connecting rods and roller rockers and chrome-moly push rods. He ports and polishes the carb, and removes the choke mechanism to smooth out and increase airflow. The carb is also rejetted, with the size of the new jet dependent on the fuel he used. “I run high octane, anywhere from 100 to 106, a race gas,” he says. “Increasing the octane increases compression.”

Formentini also builds his own headers. “I run a tuned exhaust,” he explains. “The exhaust ports on the V-Twin engine are 1-in. diameter, so I start with two 1-in. pipes. Both pipes are the same length and they join together into a 1.5-in. pipe. This lets one pipe scavenge off the other, helping pull exhaust gas out of it. This technique came from the guys at NASCAR who discovered that with overhead valves, the faster you get the exhaust out, the more power you are going to make.”

Then the tranny
“New guys to the sport often think they need all the horsepower they can get to win races,” says racer Bobby Cleveland, a design engineer for Snapper and long-time winner at USLMRA events. “But it’s really the transmission that wins races.” He points out that USLMRA races use Le Mans starts, so drivers must run across the track, hook up their tethers (dead man switches), then start the engine. “So the more you build your engine up, the harder they are to start. And the start is a big part of the race. Another racer might have 10 even 20 hp more than I do, and I have close to 30, but the tracks we run on are short. By the time they get their torque and engine revved up, I’m already braking for the first turn. My engines also last longer than a high-horsepower, high-compression model.”

Cleveland relies on a Peerless transaxle, a component that once sat in a 5-ft-wide walk-behind mower. But because the transaxle was once standard in a mower, it’s fair game for USLMRA racers to use on their machines. “It has a higher gear ratio than you could get today,” says Cleveland. “Today’s transmissions are about 13:1; the Peerless is 3:1. It’s also got roller bearings instead of brass bushings, four shift keys instead of two, and a 1-in. axle rather than a ¾-in. one. All this makes it more rugged.”

Gienger is another advocate of Peerless transmissions. “Some guys run the right-toleft 700 Series with a belt input drive on the bottom and a chain drive on the side that goes to the mower’s back wheels. Others use the older 350 or 400 Series with an H-pattern three speed and with some pretty sturdy gears in it.”

Formentini, who also uses Peerless transmissions, notes that they usually come packed with bentonite grease, a lubrication grease that won’t wash out and is commonly used if equipment, such as a mower, is likely to get wet. “But I pull all that grease out, put an oil seal on the input shaft, and fill the transmission with oil. It improves lubrication because at the rpms we turn, the bentonite doesn’t get to all the areas it needs to. I also put a breather on the transmission to bleed off pressure as it builds up inside.”

Jayson Mikula, three-time BP Class Champion, also backs Peerless, saying it’s readily available and reliable. “Most new mowers are hydrostatically or fluid driven, and most racers prefer gear-style transmission,” he says. “Racers have tried to use hydrostatic versions, but they are designed for engines that run at a constant rpm, and that keeps the pump for the transmission at a single rpm. But we run our engines at twice the normal rpm, which would cavitate the oil in the tranny and it wouldn’t work very well.”

Chassis and steering
The front end on most commercial lawn mowers is not strong enough to take the pounding racers put them through. So the Association lets racers modify the front and rear axles. “We make them stronger and weld them solid, lower them so they handle better and the machines are more stable, and add caster and camber,” says Cleveland. “We use aluminum go-cart wheels with good bearings, but the rules limit us to turf tires, those built for mowers.”

The Association also lets racers modify brakes. “Since we bumped up the speeds, we also need better brakes,” says Cleveland. “I make my own using motorcycle disc brakes I pick up at swap meets. It is powered by a go-cart hydraulic master cylinder and uses tougher metal than that used for standard mower brakes.”

With faster and faster speeds on the straights, the Association has recognized the need to let drivers install front-wheel brakes to augment the normal rear brakes. “I’ve always rebelled against them because I’ve never seen a lawn mower with front brakes,” says Cleveland. “But if they’re going to allow them, I’m going to have to add them as well.”

Unlike most other drivers, Cleveland still uses a stock steering setup, all the way down to the front axle. “Mine is a little slow compared to those using go-cart setups, but I’ve run it like that for 13 years.”

Gienger, on the other hand, has built a fully adjustable steering subsystem with a centerlink that delivers better Ackerman steering. (Ackerman steering is an ideal setup in which the inside wheels follow a smaller diameter circle than the outside wheels. It reduces scrubbing on the inside wheels which adds friction and accelerates wear.) “My setup lets the mower’s four tires follow four different paths without any of them binding in corners. Some other drivers have steering linkages that also tip one wheel in or out farther than the other, but this can cause that wheel to scuff through corners,” says Gienger. “This means your steering is not right and you’re generating drag which slows you down.”

Most drivers lower the frame to the allowable 4 in. and keep the wheels out at 38 in., the maximum allowable width. But there are no suspensions on these machines, just the padding on the seat. This makes tires one of the critical components. Most in the BP Class use four-ply tires. They are allowed to use two-ply versions, but most want the sidewall strength of a four ply.

Mikula believes he’s found the best tires for his mower — the Turfmaster by Carlisle, a deeper lug, four-ply tire that works well with low tire pressures on wet and relatively soft tracks. For more grip, he switches to Turfpro, another tire from Carlisle. It has shorter fatter lugs, almost like a slick. “It takes a bit more air pressure and has better side bite,” says Mikula.

Mikula also believes he does more to his chassis than most other racers. “I place the engine and other components as much toward the center as possible to cut down rotational inertia and help with handling. For example, one rule says the engine must be put in the original crankcase hole. So I mount mine as far back as I can, putting the 90-lb motor nearer to the center of the chassis. I also mount the battery near the center of the chassis and push the transmission as far forward as I can. I try to get as much weight over the center because when I sit on the mower, my 175 lb goes almost directly over the wheels.”

“Lawn-mower racing is the poor man’s NASCAR,” says Cleveland. Most guys race and build their own stuff. You can work on them in your own garage. You don’t need a big shop. When race-day time comes, you can throw the racer in the back of a pickup truck to haul it to track. The mowers are inexpensive as well. A lot of lawn-mower dealers will just about give you the mower just to get it out of their way.”

Lawn mowers by the class
To keep races competitive and costs down, the USLMRA has set up a variety of di erent classes. The range of classes let drivers start young and with relatively inexpensive machines and progress up through more-capable classes, all the while competing against drivers of all ages. USLMRA events have always been gender neutral and only one or two classes have age limits.

Here’s a quick rundown of the Association’s racing classes:

S-Class (Stock): Engines are governed to 3,650 rpm, tire pressure is limited to 15 psi, and all parts must be stock or exact replacements, with no improvements to power or reliability.

JP-Class (Junior-prepared): Drivers must be 10 to 15 years old; single-cylinder valve-in block engines governed to 3,650 rpm; exhaust can be open; transmission or transaxle must be from a lawn mower, be shiftable, and with a highest gear of no less than 8:1; stock body with a steel factory deck and front and rear axles in stock location with a 39-in.-minimum wheelbase and 38-in.-maximum width; tire pressure limited to 15 psi or less; and all racers must have a kill switch which turns the engine o when driver leaves the mower,

I-Class (IMOW, which stands for International Mower of Weeds): and JP-Class are analogous to IROC, in which drivers have nearly identical vehicles, making it a test of driver skill rather than engineering ingenuity. Top speed for these machines is about 22 mph.

SP-Class (S-Prepared): 8.5-hp valve-in block at or L head single-cylinder engines. Top speed in this class is over 50 mph. CP-Class (C-Prepared): Single-cylinder overhead valve and two-cylinder valve-inblock four-stroke engines with 20 hp or less. Top speed over 50 mph

BP-Class (B-Prepared): Overhead-valve V-twin four-stroke engines with 20 hp or less. Speeds top 80 mph in this class

FX-Class (Factory-Experimental): Maximum engine is a 465-cc, singlecylinder four stroker with less than 20 hp. Centrifugal clutch, extensive frame, and engine modifications allowed. Top speed is over 90 mph.

Racing-Mower Basics
There are a few basic guiding principles behind USLMRA rules. The most important is safety, which is why it is taboo to race a mower with the blade still attached. The Association also mandates safety gear for the racers, such as helmets, boots, and eye protection. But experience has led them to discourage safety belts. It seems the safest place to be in a lawn-mower crash is far from the mower. There are also no bumpers or roll bars, and this is open-wheeled racing where running into or swiping against another mower can be hazardous if the wheels touch in the wrong way. (Up until three years ago, the Association allowed bumpers, but found drivers tend to use them to purposely hit other drivers. So they outlawed them to make the races cleaner.) The rules do, however, call for tethers or kill switches that will turn the mower’s engine o if the driver is unseated. And so far, USLMRA has not had a serious or life-threatening accident over its 16-year history.

Another cardinal rule is that you never race for cash. There are never any purses and the winners get nothing more tangible than trophies. “This keeps the racing enjoyable and a ordable,” says Association Founder and President Bruce Kaufman. “And although the cost of being competitive in mower racing is going up, we try to keep it down as much as possible. For example, if there’s a technology out there that might let a mower go faster, that doesn’t mean we are going to sanction it if it is too expensive. Our mowers seem to be going fast enough already, and our races, which are typically 20 laps of 600 to 800-ft-long ovals, only let drivers go so fast anyhow.” Kaufman estimates a person could purchase a competitive mower in all but the FX class for about $5,000.

The other principle is that the lawn mowers must look like lawn mowers. “The di erent classes let drivers use a variety of engines, which can be souped up,” says Kaufman. “The Factory Experimental Class lets drivers modify bodies, but the racers must still look like lawn mowers with a deck, and use a lawn-mower engine. They can’t look like a four-runner, ATV quad, or a go cart. With our machines, there’s no doubt that they are lawn mowers.”

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