![]() ![]() The higher the boost pressure, the lower the compression ratio of the engine. Picking up a copy of one of the 60’s- technology forced-induction manuals will highlight their solution. The balance of boost versus compression ratio has been an engine builder’s and tuner’s challenge for years. Of course, the big downside to higher boost pressures is that the likelihood of encountering engine- damaging detonation also increases. In dealing with forced-induction applications, it’s well known that increasing boost pressure on a properly sized turbocharger will increase power production (at least, to a point when the capacity of the turbo or fuel system is exceeded). In dealing with naturally-aspirated applications, high compression ratios are the key to serious power levels. For the same size engine, the older engine would have been more fuel efficient if they had the fuel, cylinder head and ignition technologies of today combined with the high-octane gas of the 60s. Likewise a reduction in compression ratio from 11:1 to 7.0:1 should result in a 12.3-percent decrease in power.īelieve it or not, high-compression engines of the late ’60s, with compression ratios up to 12.5:1, had higher thermal efficiencies than many of today’s engines. Plugging through this equation we find an increase in compression ratio from 8.0:1 to 11.0:1 should result in a 9.2-percent increase in power. These values were obtained using the thermodynamics equation to establish the thermal efficiency of an Otto cycle engine. In fact, more accurate projections can be found in the accompanying DSPORT chart. How much additional power can be expected with a higher compression ratio? The old-school rule of thumb is that each additional point that the compression ratio is raised will deliver an additional 4 percent power. In basic terms, higher thermal efficiencies translate into additional horsepower and better fuel economy. This means that the engine is able is turn more of the heat generated from the combustion process into horsepower instead of wasted heat. So how does an engine’s compression ratio affect performance? All other factors being equal, an engine with a higher compression ratio will deliver a higher thermal efficiency. A 10-to-1 compression ratio means that the air- fuel mixture gets squeezed down from the full volume of the cylinder to a volume that is just roughly one tenth of the cylinder’s size. THE BALANCE OF BOOST VERSUS COMPRESSION RATIO HAS BEEN AN ENGINE BUILDER’S AND TUNER’S CHALLENGE FOR YEARS Compression RatioĪs the name indicates, the compression ratio of an engine indicates how much the air-fuel charge is compressed during the compression stroke of the four-stroke process. An engine’s thermal efficiency is highly influenced by the engines static compression ratio. How well an engine can convert the heat (thermal energy) into power (kinetic energy) is quantified by an engine’s thermal efficiency. The engine’s second task is to convert this thermal energy into kinetic energy in the form of horsepower at the flywheel. Using a four-stroke cycle, a fuel-and-air mixing strategy and a spark for ignition, the internal combustion engine’s first task is to convert the chemical energy stored in the fuel into thermal energy (heat) through a process called combustion. Without going into a lengthy explanation of internal combustion engine dynamics, your vehicle’s engine is a machine designed for energy conversion. Understanding how both compression ratios and boost pressures affect performance is a key to maximizing performance from your street or race vehicle.īy Michael Ferrara // Photos by DSPORT Staff Today’s performance engines are running at higher boost pressure levels and higher compression ratios than ever before. This reality includes the leading-edge forced induction and engine-management technologies that make power production the easy part of building a racecar. You can return any new or unused item within 90 days of the date your item was shipped and we will refund the full purchase price.One-thousand horsepower, four-cylinder engines are today’s reality in import drag racing. Visa/Mastercard, Discover, American Express, Pay Pal, and Pay Pal Credit, Gift Cards, Summit Racing SpeedCard. Have questions? Our customer support team is available 7 days a week to help you. We’ll beat any advertised price on an in-stock product. We're confident our prices are the lowest. Over 1 Million parts from more than 1000 trusted brands, more parts added all the time. We ship in-stock parts via ground shipping the same day if ordered by 8:00 pm EST. Just place an order over $109, and we'll drop the shipping and handling charge. ![]()
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