Net horsepower was attained from engine dynos with the accessories, OE air cleaner, and factory exhaust system present on the test subject engine. To make horsepower numbers more accurate to what you would actually see from your engine when installed in your car, for the 1972 model year, American car manufacturers started using "net" horsepower figures. Between the lack of power-robbing accessories and restrictive exhaust systems, the advertised horsepower numbers were quite inflated when compared to today's power figures. Also these power figures were typically attained with a very unrestrictive open exhaust system, along with the lack of restrictive OE air cleaner assemblies. These gross horsepower figures came from engine dyno results in which the tested engine had no real-world accessories attached such as power steering pumps, smog pumps, and or A/C compressors. "Net" HorsepowerĪs for American carmakers, previous to the 1972 model year, the horsepower figures you typically saw in car manufacturer literature and car magazines were "gross" horsepower figures. One horsepower is equal to 745.7 watts, watts being a unit of power that James Watt also came up with, and the same unit you see everyday associated with things like light bulbs and electrical devices. One horsepower is equivalent to the amount of force needed to lift 550 lbs of weight within a period of 1 second. Watt would call this new unit of measurement "horsepower". Back in the 18th century James Watt was developing steam engines and wanted to come up with a unit of measurement that would indicate the amount of workhorses the steam engine would replace. The car has a turbo from the factory so increasing the boost at 6500rpm would be the easiest solution.Horsepower is a measure of the ability to move a certain amount of weight a certain distance, within a certain amount of time. What power would the car make if we move peak VE from 5500rpm to 6500rpm? Turbo/Supercharger, camshafts Ford Focus ST If we move the power band of the engine to higher RPM with a camshaft or turbo upgrade for example, how much power would the engine make at 6000rpm with 110% VE?īolting the numbers into the VE calculator we getġ15bhp, an increase of 36bhp or 45%. The engine, even though it is normally aspirated, is making over 100% VE at 4000rpm. With the Honda, not a lot we can do because the peak VE is already close to redline. Nissan Micra 1.2, 2009 – Normally Aspirated (Non Turbo) Honda S2000, 2004 – Normally Aspirated (Non Turbo) If we can move the peak VE to a higher RPM we can increase the power of the engine while theoretically not increasing stress on the engine.īelow is a list of three cars, we look at the RPM of the peak VE and see how much tuning potential these engines have (without increasing engine stress) NA EnginesĪ normally aspirated engine which is designed for torque will have a low VE at high RPM because cylinder filling at low RPM is the priority Turbo/Supercharged EnginesĪ turbo engine can have a VE of over 100% because air is being forced into the engine under pressure by the turbo ie the amount of air in the engine is more than the actual capacity of the cylinder because the air is pressurized above atmospheric pressure (by the turbo) The better the VE the more power the engine has. In other words, how easy is it for the air to enter the engine. In simple terms, volumetric efficiency is how filled the cylinder is, (immediately before the compression stroke starts), compared to the actual capacity of the cylinder.
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