| Understanding Horse Power And Torque |
| Mechanical Efficiency Friction robs a great deal of power from an engine. The greatest friction losses are caused by the pistons and piston rings. We overcome this with meticulous cylinder wall and piston preparation. Cylinder blocks that are bored and honed with a torque plate in place always contribute to a reduction in friction. This practice reduces cylinder-wall distortion caused by head-bolt clamping forces. Thus, the piston travels in the same properly sized bore throughout its stroke, and the piston rings are not subjected to changes in tension due to wall distortion. The piston manufacturer's recommended skirt clearances should be followed in most cases, because they have spent countless hours developing a skirt that stabilizes the piston and the ring pack in the bore with minimal friction. A smooth bore generally improves ring seal and reduces friction. The best honing finish depends on the type of rings and the final application. The piston-ring manufacturer's recommendations are your best bet. Rings should be hand-fit with ring gaps set to the minimum recommended clearance. Piston rings should also be very carefully checked in each individual piston to ensure the minimum recommended side clearance. If a ring is sticking due to too little side clearance, friction will soar. If a ring is too loose, it may flutter and drag intermittently while bleeding off precious cylinder pressure. One way to improve mechanical efficiency that most people ignore is through the use of special antifriction coatings for pistons, rings and bearings. These coatings are available in do-it-yourself kits from mail-order houses such as Summit Racing. When properly applied, the coating can get you another 10 horsepower or so. The ideal application would use coated components with optimized clearances and a good synthetic oil for maximum friction reduction. Altogether, there may be as much as 20 horsepower available with the right combination of friction-reducing ingredients. Another component of friction reduction is the preparation of the cylinder-block bearing saddles and the crankshaft. Cylinder blocks should be align-honed to minimize frictional losses. This gives the crankshaft a straight set of bearings on which to run. Likewise, the crankshaft must be straightened to eliminate runout, and the entire reciprocating assembly must be properly balanced to minimize drag created by uneven forces. More torque may be gained if you use a well-designed oil pan with an effective oil scraper and aerodynamic shaping of the crank-throw leading edges. Small-block Chevy builders should avoid the temptation to use a big-block-style oil pump. Use a properly clearanced small-block pump, and set it to deliver only the pressure necessary to provide optimum lubrication. Most small blocks never need more than about 60 psi, even at a high rpm. Excessive oil pressure or a bigger pump with taller gears robs power throughout the entire rpm range. Also consider the pumping losses caused by the induction and exhaust system. This should lead you to careful consideration of each system, because the engine's ability to work efficiently is largely controlled by these systems. See the accompanying sections for further discussion of these subjects. |