Efficiency islands are the concentric regions of the map and identify compressor efficiency at any point. This is not an option for our example since we are limited to 12 PSIg due to our stock engine internals and pump gas fuel.Įfficiency range can also be observed by knowing pressure ratio. In order to reach the 3.0 pressure ratio, you would need ~26 PSIg at sea level. This turbo has a max flow of 80 lbs/min at 1.95 PR, whereas 3.0 PR can flow 95 lbs/min. If your operating point is outside of the choke line you need a larger compressor. It is also called the choke line and represents the point where efficiency drops below 58% and turbo speed is approaching the allowable limit. The right boundary of a compressor map identifies the maximum air flow we suggest at any pressure ratio. The 1.95 PR is below the widest part of the map (~3 PR) and the widest part of the map is where a turbo can produce its maximum air flow which is only necessary if you need it. We can observe the corrected air flow potential (horsepower) associated with this PR is about 80 lbs/min by following the red line to the right boundary of the compressor map then down to the air flow scale. At 12 LBS of boost at sea level your compressor will be operating in the 1.95 pressure ratio range (red dot). If you look at the left vertical axis or Y Axis of the map you see a scale for pressure ratio. Now that Pressure Ratio is calculated let’s look at a compressor map and see what it tells us. P2c (12 gauge + 14.7 atmosphere) / P1c (14.7 atmosphere – 1 depression).We only make the depression adjustment to the (P1c) part of the equation because P1c is Absolute Inlet Pressure. Also known as depression, this can result in -1PSIg or more in some intake systems. This is because the air filter or ducting adds resistance to the air flow resulting in a pressure loss. System Depression: An air filter or a restrictive ducting system will often result in LESS than the ambient pressure, especially at higher RPMs. If you are not at sea level you can substitute a value from the chart below for PSIa. This is standard atmospheric pressure at standard conditions. PSIa refers to absolute atmospheric pressure. Having a boost target is necessary for determining pressure ratio. Stock engines usually have lower ability to handle boost, while highly modified engines can handle much more. Depending on the build of the engine, your gauge pressure limits will vary. A boost gauge pressure reading of 12 means the pressure in the manifold is 12 psi above atmospheric pressure. PSIg refers to gauge pressure and measures the pressure above atmospheric. P1c = (PSIa) Absolute Atmospheric Pressure (PSIa) – 1 System Depression.P2c= (PSIg + PSIa) Boost Gauge Pressure (PSIg) + Absolute Atmospheric Pressure (PSIa).Additionally, pressure ratio is not an indicator of horsepower but we will get to that in another step. PR is identified on the Y (vertical) axis of the compressor map. Knowing pressure ratio is a key component to selecting the correct turbo for your application. This identifies where the compressor will perform its max duty cycle. Pressure ratio is a variable equation that combines ambient pressure with gauge pressure divided by ambient pressure. Get ready to turbo any engine! Calculating Pressure Ratio ( PR= P2c / P1c ) Get your calculator ready because this may get complicated, but remember at any point you can click the Boost Adviser link above and it will take you to the automated system. In this article we look at Volumetric Efficiency, Brake Specific Fuel Consumption (BSFC), Engine Speed (RPM), Elevation, and we deep dive into the equations that are used to behind the scenes of Boost Adviser to match a turbo for your vehicle. You can always ask an authorized Garrett distributor or use our Boost Adviser application to help narrow your search results even further. Horsepower and engine displacement are the two main inputs needed for selecting a turbo and will allow you to get a rough idea of what turbo is right for your build while the quick sort feature on the turbo product page can be used to eliminate non matches. In part one of this how to series we explained how to identify target horsepower, why turbos are rated for crank horsepower, how to calculate wheel horsepower to crank horsepower depending on drivetrain. How To Select A Turbo Part 2: Calculations
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |