The 310 horsepower rating of a 1973 Pontiac Trans Am SD 455 may seem quite dismal if you're comparing it to something like the 370 horsepower rating of the 1970 Pontiac Trans Am RAIV 400, but the actual difference in the power output of these two engines is much smaller than the 60 horsepower discrepancy indicates. 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. Install an aftermarket intake manifold - A performance intake manifold can improve air distribution to the cylinders, increasing horsepower.Horsepower is a measure of the ability to move a certain amount of weight a certain distance, within a certain amount of time.Upgrade the engine's valvetrain - Installing stiffer valve springs, stronger pushrods, and lighter rocker arms can help the engine rev higher, increasing horsepower.Lighten the flywheel - A lighter flywheel can help the engine rev faster, improving throttle response and increased horsepower.Install a larger throttle body - A larger throttle body can allow more air into the engine, increasing horsepower. Running Boost from a blower, turbo or other device, then you will want to try the Effective Compression Ratio calculator.Improve the engine's cylinder head - Porting and polishing the cylinder head can increase airflow into and out of the engine, improving horsepower.Upgrade the engine's cooling system - This can help dissipate heat more efficiently, increasing horsepower by preventing heat-related power loss.Replace the engine's stock pistons with high-performance pistons - This can increase compression and improve engine efficiency, increasing horsepower.Install a high-performance ignition system - This can improve spark timing and voltage, increasing horsepower.Upgrade the engine's camshaft - This can change the timing and duration of the valve openings, increasing horsepower.Install a nitrous oxide injection system - This can temporarily boost horsepower by introducing highly oxygenated gas into the engine.Upgrade the engine's fuel injectors - This can improve fuel delivery and combustion, increasing horsepower.Add a turbocharger or supercharger - These devices force more air into the engine, which increases horsepower.Install a performance chip or programmer - This can adjust the fuel-to-air ratio, ignition timing, and other engine parameters to increase power.Upgrade the exhaust system - A performance exhaust system can help reduce back pressure and improve exhaust flow, which can increase horsepower. Install a performance air intake system - This allows more air to flow into the engine, improving combustion and increasing horsepower.
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