Air, I need more air. You can almost hear the engine in a Legends car begging for more coo
Heat is the number-one killer of racing engines. It is especially deadly to an air-cooled Legends motor, but there are steps the racer can take to minimize the devastating effects of heat. In this article, we will look at changes that build horsepower and increase the longevity of the motor. In addition, we will suggest things the racer can do in the engine compartment to reduce power-robbing heat.
Everyone knows increasing horse-power increases heat. Legends drivers trying to add power can certainly attest to this. With the hard-compound BFGoodrich T/A tires, only so much grip is available. The answer to the age old question of whether to spend money on the engine or on getting a better handling car comes from the suspension side first for the Legends driver. With these lightweight cars, handling will win more races than horsepower. When a stock 115hp engine can spin the tires, any extra horsepower will go up in smoke off the right rear tire.
Most drivers believe their cars handle as well as everyone else's. When the race winner pulls them down the straightaway, they just know he has more power. It can't be that he's hooked up better coming off the turn. But if you're going to add power, do it wisely.
Building a Better Engine PackageThe Legends FJ 1200 Yamaha engine is a strong piece, if it doesn't get too hot. The rules do not allow many changes, but some things, if done right, will add longevity to the engine. The bottom end of this power plant is well-designed. Most engine builders will not balance the bottom end because it doesn't need it and it's illegal to lighten any of the rotating parts. You want to check the rod and main bearings to make sure all the clearances are correct. You can run the bearings a little looser to get some horsepower. If you do remove the rod bolts, it is a good idea to replace them with new nuts and bolts.
Installing the approved Wiseco piston kit, which you can buy from a Legends authorized dealer, can be beneficial. It gives you a forged piston and, some engine builders say, a better ring package. The Wiseco piston is half a millimeter bigger than the stock 77mm cast piston. It doesn't give you more power, just more reliability. Any time you open the case, it is a good idea to put on a new camshaft chain. Chains can stretch. New slotted cam sprockets are another good idea.
Everyone knows if you want more horsepower, you can find it in the head. However, the rules do not allow any port matching or shaping of the combustion chamber. The only thing you can do to the cylinder head is give it a three- or four-angle valve job.
Installing stronger valve springs will allow the engine to turn more rpms. The downside to higher rpms is that the motor runs hotter. These engines produce a lot of torque. Check the power curve of your engine. In most cases, it stops making power at 9,400 rpm. In an attempt to go faster, some racers are popping off the rev limiter, which is set at 10,500 rpm. Proper gearing produces faster lap times, not higher rpms.
More power is available from maximizing the compression. The rules say the maximum compression ratio is 10:1. It is generally checked by screwing a compression gauge into the spark plug hole and checking the cranking compression. The maximum cranking compression allowed is 180 psi. The stock compression is around 150 psi
In order to increase the compression, you can change the cam timing and valve lash. Also, setting the deck height as close to zero as possible maximizes the combustion chamber efficiency. The problem with increasing the compression this way is that it allows no margin for error. If the chain stretches ever so slightly, the valves hit the top of the piston.