8) The Squeeze
The compression ratio equates to power and efficiency and has no drawback to driveability until the point where increased pressure triggers detonation. There is a ceiling on how much compression can be exploited, and that is the engine's detonation limit. Any steps that will allow more ratio to be used will pay dividends in power, but detonation must be avoided at all costs. Employing coatings can allow for greater compression, and that combination can add substantially to output. A carefully designed engine can tolerate an efficient high-compression ratio while living nicely on pump gas. This is an area where the engine builder's knowledge and experience is put to the test, especially when trying to push the limits.
For a great number of engines built after 1970, there's quite a margin for improvement in compression ratio since the factory ratio was very low. When considering increasing the ratio, many factors must be balanced. Key among these factors are cylinder pressure as it relates to the camshaft, or more specifically, the valve events the cam directs, as well as the engine's combustion characteristics. The combination can be skillfully planned, taking advantage of good squish and quench characteristics through piston selection and block machining. This improves detonation tolerance and allows for a practical increase in compression ratio. Cooler running also helps in this regard. Adding ratio will add power without conspicuous external engine changes, but it must be approached with the needed level of execution to the rest of the engine package to avoid dreaded detonation.
9) The Consumables
All the power an engine can develop isn't limited to the internal hardware. Upgrading some of the common maintenance items to those designed for high performance is an easy way to reap power gains. Some items that make the cut here are the engine oil, the spark plugs, and the air filter. Attention to detail on items such as these will benefit output in a very unobtrusive way.
Standard paper-element air filter elements can present a restriction to flow that will cost power. An easy upgrade here is an oiled cotton/gauze element such as the type available from K&N, ACCEL, or Holley. These filters are designed for high flow, and unlike paper elements, they maintain that high flow with use. These filters can be had in OEM replacement specs, fitting the stock filter housing just as the original. In enclosed housing filter cases, the mod is totally invisible.
In the area of engine oil, modern synthetics almost always show a power gain through decreased friction. The benefit here is twofold, since besides providing a measurable power gain, these lubricants significantly reduce engine wear and cut down on internal engine deposits. We strongly recommend synthetics. Spark plugs can also show a small gain in output. It's the small details that add up to a sharper-running powerplant.
One of the most overused and least understood terms in the realm of engines is "blueprinting." Essentially, it means the engine is built with a high degree of precision, making careful measurements of critical clearances and performing corrective steps in machining to set these measurements to the desired specifications. A few examples would be helpful here. Imagine if there's a variation in a connecting rod length of several thousandths of an inch. If the engine is being built to an exact blueprinted spec for piston-to-head clearance, this inaccuracy will make it impossible to set the critical squish/quench clearance. Now imagine there's a variation in combustion chamber volume-not an unusual situation. The compression ratio will vary from cylinder to cylinder, making it impossible to target an exact desired ratio. Now imagine that the block's deck surface is out of parallel with the crank. The cylinders along that bank will vary in both compression ratio and piston-to-head clearance, throwing off both. The examples can go on and on, but the bottom line is that variations in specifications of individual components limit the ability to target accurate and desirable specifications when building the engine.
Blueprinting means measuring and correcting specs in the individual components; then the engine is built with a high degree of accuracy to exact specifications. Those specifications will be at the builder's discretion to optimize the engine's performance. Typically, lower-grade engines are built to conservative targets to absorb the inaccuracies of the nonblueprinted components and clearances. Obviously, if the pistons are about 0.050 inch in the hole, a few thousandths here or there in the rods or decks won't matter. Blueprinting allows the builder to optimize the engine to its full performance potential.
Holley Performance Products
1801 Russellville Rd.
Bowling Green, KY 42101