Enter the crank pulley diameter, supercharger pulley diameter, and the engine RPM into the calculator to determine the supercharger RPM. If you’ve ever wondered how much hp a supercharger adds, wonder no more; this boost horsepower calculator will help you calculate it in seconds! If you know how much power your naturally aspirated engine produced, you can calculate how much hp a supercharger adds with various amounts of supercharger pressure.
- It compresses the air, allowing the engine to consume more fuel, which results in higher possible power output.
- Our boost horsepower calculator is extremely easy to use.
- The following example outlines the steps and information needed to calculate Supercharger RPM.
The supercharger diameter for this problem is measured to be 3.5 inches. For this example, the crank diameter is measured to be 4.5 inches. Both of them compress the air and inject it into the engine. The engine is fed with more air, so it can use more fuel. If it can use more fuel, it can produce more power.
Calculating Pulley Size Ratio
Superchargers usually run at a boost pressure between 6 and 9 pounds per square inch (psi). The default value in our calculations is 6 psi, but you can adjust it to your preferences. A supercharger really is a horsepower gain cheat code for your machine.
This based on the same reasoning used to calculate needed carb CFM. The principle is that an engine is an air pump and it is easy to calculate how much air it pumps if you know the displacement, speed (rpm) and efficiency (VE) of the “pump”. The 0.9 factor is the ~VE for the typical intake tract under non-boosted conditions. The number 3,456 is just a mathematical factor to make the units come out properly. To calculate supercharger RPM, divide the crank pulley diameter by the supercharger pulley diameter, then multiply by the engine RPM.
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The following equation is used to calculate the Supercharger RPM. I’m looking at a mercedes supercharger for my project as well.
Have you got any references to calculating pulley size based off absolute pressure ratios? I’m just interested to read more as running the calc I did above based off absolute pressure yields a massively different pulley result. When you are stepping pulley sizes on positive displacement chargers you need to do the ratio of target absolute pressures (not just boost) to diameters. So you would add atmosphere to both the current and desired boost before doing the ratio to get the correct new pulley size. Calculating max boost depends primarily on three variables. The max CFM of the blower, rpm where you want the boost to peak, and the displacement of the motor.
Calculating Actual Air Requirements at Desired Boost
Using current and target absolute pressure ratios for pulley sizing is the same as using the engine and blower displacement which are absolute. Currently I have a 6 inch serpentine pulley that fits onto the front of a 77/78 crank pulley. I’m planning to start with a 2.75 inch blower pulley (2.18 ratio)…
Based on some quick calcs on my 3 liter motor it looks this will yield 6.7 pounds of boost. Our boost horsepower calculator is extremely easy to use. You only need to know your naturally aspirated engine’s current power output and the pressure you want a supercharger to create. The output is presented in the last field of the calculator. Curious about what changing your upper and lower pulleys will do to your boost levels on your 1.9L LSA supercharger? Use the following boost calculator/estimator as a rough guide to see how to right-size your boost for your desired power level.
Word of caution with too big of a crank pulley, a 2.5 ratio puts the supercharger rpm past it’s “redline”. Remember that our boost hp calculator operates on a simplified model. Real-life results might be a bit different from those predicted by this tool, especially if your engine is very large or uses fuel different than petrol. Both calculations are real close for a 2.21 ratio. I have a 3.5″ Diameter pulley on the Mercedes SLK supercharger and with the electic cluth would be difficult to change. It is good to know that the pulley size that I am looking at will work. Divide the desired air flow (13132L/min) by the swept volume of the supercharger (SC14 from the 1G-GZE is 1.42 litres per revolution).
When you initially size a blower you are using absolute displacement/VE of blower and motor. To approximate ideal generated pressures, due to blower VE and charge heating having counter effects in terms of outlet pressure/volume it gets pretty close to ideal volume/pressure. Note that boost levels depend on a variety of variables (including temperature and humidity) and this is simply an estimate based on a linear math relationship between stock boost and upper/lower pulley adjustment.
How to use this boost horsepower calculator?
Note that it assumes that the engine is operating at 100% volumetric efficiency. It’s interesting to note that if your engine has less than 100% VE (i.e., it doesn’t breathe very well), your resulting boost pressure will be higher than what the equation predicts. So, you should be able to use your measured boost pressure to give you a rough idea of what your VE actually is. Explore the rest of our boost hp calculator and this article to learn how a supercharger works and how much hp it adds.
You select pulley sizes to spin the blower to close to max impeller speed at the rpm where you want the power peak (primarily determined by the cam). Anything which increases VE will increase power but decrease boost. Anything that interferes with the blower output (especially inlet restriction) will decrease blower CFM and decrease boost and hp. An engine with a larger CID will see less boost and make about the same peak power as a smaller motor if the same blower is used and maxed out in each case. However, the larger motor will have a fatter torque curve and go quicker.
Increased air density (cooler, drier, higher barometric pressure) will increase hp, lower air density will decrease hp. I’ve used the gauge pressure calc above in 2-3 instances and have generally come out bang on my target. My thought process here is that the supercharger is working at a pressure ratio with ambient pressure at the inlet.
The 1.9L LSA supercharger came stock in the 2nd-gen CTS-V and 5th-gen Camaro ZL1 and is a popular addition to both modern and resto-mod LS motors. I just recently had a problem with my crank pulley. I’d like to hear what you guys have done to mount your crank pullies. Hey guys, just want to make sure i have this right. Its an eaton m90 and im going off those specs down below. The following example outlines the steps and information needed to calculate Supercharger RPM.
This calculation assumes NO OTHER MODS beyond pulleys. Any pulley changes will require a tuner to get the most of our your aftermarket mods. A supercharger RPM is the rotational speed at which a supercharger moves when subjected to a given RPM and a given crank to supercharger pulley ratio.
This will tell you the maximum speed the supercharger rotors must be run at to produce the volume required. Add the boost pressure desired (5 Psi) for the engine to 14.7 Psi (atmospheric pressure). Both superchargers and turbochargers can yield similar results in adding a lot of power when properly installed and tuned.
It compresses the air, allowing the engine to consume more fuel, which results in higher possible power output. The supercharger is connected to the engine by a belt. Some energy is required to run a supercharger, but it produces much more power than consumes. You can learn more about supercharge vs turbocharge differences below. Then how much air is needed to run at a set boost level
The volume of air the selected Supercharger makes. The size of the PULLEY need to make that Boost level etc.