The current mainstay of 4-cycle racing is the Briggs and Stratton 5HP engine. The Tecumseh Products Company is offering the racer engine choices.
Tecumseh’s box stock 5HP engine currently does not have a national class in either IKF or WKA racing but the company is actively pursuing a place for its alternative to the Briggs and Stratton Raptor.
This articles sets out to examine both engines and, as they say, “you pays your money, you takes your choice.”
The Tecumseh is approximately one inch wider than the Briggs. Both have the industry standard bolt mounting patterns, crankshaft sizes and location.. The Tecumseh comes with the attached factory pull-start. The Briggs Raptor does not include a factory-installed pull start.
Carburation for both engines is approached in different ways. The Briggs uses a traditional pulse-jet carburator with modifications made for the Raptor application. The Tecumseh engine uses a float-bowl carburator that features adjustable low- and high-speed jets. The venturi size on the Briggs is .695, while the Tecumseh venturi measures .740 While the Briggs carb pumps its own fuel from a tank located below it, the Tecumseh includes a fuel pump which draws fuel from the tank located on the go-kart.
While most users of the Briggs run their engines on methanol, the Tecumseh is a gasoline engine using regular 87/8 octane.
The flywheels are significantly different. The Tecumseh flywheel weighs 7 lbs. 10 oz., while the Briggs is lighter at 5 lbs. 12 oz.. Both engines feature a similar type of solid-state ignition. The Tecumseh features a specific motorsports ignition deveoped for and sold only for racing.The Tecumseh engineers claim it to have the hotest sark on the market..
Popping open the side covers on both engines, one first discovers that the camshaft on the Briggs rides slightly higher than the crankshaft center line, which the Tecumseh camshaft runs on the same plane as the crankshaft. Both crankshafts are supported by nine-ball bearings on the PTO side of the crankshaft. The Tecumseh uses a larger crankshaft counter-weight that the Briggs and Stratton. Tecumseh uses a much larger camshaft gear, roughly 3.8 inches diameter compared to the Briggs 3.3 inches for the Briggs. The Tecumseh cam has a .270 lift , while the Briggs measures out at .233.
Most racers replace the stock Briggs steel dipper with a cast aluminum or plastic unit. The Tecumseh comes stock with a cast aluminum dipper. The Tecumseh has a thick-wall cast in iron sleeve. Tecumseh is also in the process of deveoping billet aluminum valve spring retainers and steel split-lock keepers. Tecumseh will upgrade the valve springs to go along with the new keeper/lock arrangement.
One final note on the crankcase — the Tecumseh features nine internal crank case bracing ribs, which the Briggs uses five. The bottom of the Briggs crankcase is flat and the Tecumseh has a boss that runs parallel to the crankshaft roughly 1/3-inch high.
Both engines use a similar valve lifter and valve spring arrangement. Where the engines differ is the size of the valves. The Briggs and Stratton intake valve is roughly 1.12 inches wide and the exhaust valve measures 0.99 inches. The Tecumseh engine features a 1.21-inch intake valve and a 1.17-inch exhaust valve.
The cylinder heads also reveal significant differences. The ramp on the Tecumseh head from the spark plug to the cylinder has a gentler angle than the Briggs head. The interior of the Briggs head appears to smooth, while the interior of the Tecumseh head in the area of the valves has a step. Both engines use eight head bolt to secure the head.
The Tecumseh engine is designed to race on gasoline straight out of the box. The racer need only supply an exhaust pipe which has the same mount setup as a Briggs, except for the larger 5/16’s inch bolts and a clutch, which also is transparent to the Briggs. Tecumseh recommends that the racer not blueprint the engine as the company feels it is pretty straight directly from the factory.
Most Briggs racers prefer to run methanol which requires carburator modifications. Camshafts and blueprinting are also necessary to make over 7HP. Claims of 7-plus horsepower from the Tecumseh circulate around the country. Currently the Briggs and Stratton Raptor engine will cost a racer in the neighborhood of $250. The Tecumseh 5hp engine is available for $199. Tecumseh claims to be developing a high-tech plasma coating for bearing surfaces for all future engines.
Briggs and Stratton racing around the country is perhaps karting’s largest engine segment. Tecumseh is actively seeking IKF and WKA recognition and a class for its engine and is also seeking local option classes.