Selecting the proper turbocharger for your engine involves many considerations.
Not only are the facts about your specific engine necessary, but equally important is the intended use for that engine. The most important approach to these considerations is a realistic mindset. In other words, if you’re turbocharging an engine that is presently rated at 200 hp in its naturally aspirated form, you’d probably love to have it produce 600 hp. However, that may be unrealistic inside of the additional collection of modifications you intend to do. If you’re looking for a nice power increase for all-around street driving, a 50-percent increase is more realistic and matching a turbo to this level of increase will produce more satisfactory results. A 300 percent power increase (200 to 600 hp) is possible in many engines, but increases like that are reserved for competition engines that have an array of additional modifications, both internal and external, that all work together to achieve this level of power. One of the most important factors in determining which turbocharger is most appropriate is to have your target horsepower in mind. But you have to be realistic about what you’re shooting for.
The application and intended use of the vehicle is extremely important as well. An autocross car, for example, would require a rapid boost rise for fast acceleration, whereas a Bonneville car running long straights is more concerned with horsepower at higher engine speeds. Indy cars frequently adjust the turbo for short tracks versus long tracks because of how critical the turbo match is to optimize flow at specific engine and vehicle speeds. Tractor pull applications will likely see the highest engine speeds right at the start of competition, and as the pull progresses, the load is progressively increased much like a prony brake until the engine is maximum loaded down by the pulling sled. These different uses require different turbo matches.
The term Volumetric Efficiency, or VE, is a very important term and concept to understand. Maximizing engine VE raises it’s potential for horsepower and RPM. With the exception of fuel and ignition modifications, most of the traditional aftermarket high-performance engine parts essentially raise the engine’s VE. Forced-air induction is all about increasing VE. But what is Volumetric Efficiency exactly?
An engine’s VE is a comparison of an engine’s calculated, or theoretical, volumetric flow rate of air, versus its actual capability. An engine has a fixed displacement, for example, 300 cubic inches. That displacement will theoretically flow 300 ci every two engine revolutions (a four-stroke engine must rotate twice for all cylinders to complete all four cycles). In theory, there would be a linear relation to airflow and engine RPM where doubling the revolutions per minute would double the air displaced by the engine. If an engine were able to flow exactly as much air during operation as the theoretical calculation says is possible, that engine would have a VE of 100 percent. However, in reality that rarely happens.
While there are some engines that achieve 100 percent or higher VE, most do not. There are many factors that impede the engine’s ability to meet 100 percent volumetric efficiency, some intentional, some unavoidable. For example an air cleaner housing and filter will typically impede intake airflow, but you don’t want to operate your engine without air filtration.
The reason turbocharging has such a dramatic impact to engine performance can be better understood using this concept of volumetric efficiency. In a turbocharged engine, time still limits how long the intake valve is open, but if the intake pressure is greater than atmospheric pressure (boosted), then we can force more total air volume in during the valve opening. The quality of that air is improved for combustion purposes because its density has also been increased. The combination of boost pressure and air density compensate for the time-limiting aspect of the valve events and allow boosted engines to achieve well over 100% VE. But when maximizing total horsepower output, even turbocharged engines will benefit from many of the very same design improvements done to enhance VE on naturally aspirated engines.
As mentioned above, a given engine will have better or worse VE over the RPM band. Every engine will have its sweet spot, which is the point in an engine’s design where, at full throttle, the volumetric efficiency is at its highest. This is typically the point where peak torque will be found on the torque curve. Since VE will be at its highest point, maximum fuel efficiency or BSFC, measured in pounds of fuel per horsepower, per hour, will also be at its peak efficiency. When calculating the proper turbo match, VE is an important element to consider, as it is an important contributor to determining the airflow demand of a given engine.
Shanghai SHOU YUAN is an experienced supplier of aftermarket turbochargers and parts, which attracted large quantities of customers from different countries in international market. There are many clients who are satisfied with our products and repurchase regularly every month. Our 20 years of experience in turbo industry can provide you with high-quality products and attentive after-sales service. We have a wide range of product categories, including turbine wheel, compressor wheel, compressor housing, CHRA, etc. Therefore, you can contact us if you want any parts of turbochargers.
Post time: Apr-12-2023