Re: Had engine tuned and "jerk before stop" is gone
Pulled from
Horsepower: Making it Add Up
SAE Net Horspower
In 1972, American manufacturers phased in SAE net horsepower. This is the standard on which current American ratings are based.
This rating is measured at the flywheel, on an engine dyno, but the engine is tested with all accessories installed, including a full exhaust system, all pumps, the alternator, the starter, and emissions controls. Both SAE net and SAE gross horsepower test procedures are documented in Society of Automotive Engineers standard J1349. Because SAE net is so common, this is the standard we will use to compare all others.
SAE Gross Horsepower
This is the old process that American manufacturers used as a guide for rating their cars. It was in place until 1971. SAE gross also measures horsepower at the flywheel, but with no accessories to bog it down. This is the bare engine with nothing but the absolute essentials attached to it; little more than a carb, fuel pump, oil pump, and water pump. Because the test equipment on the engine is not the same as in SAE net, it is impossible to provide a mathematical calculation between SAE net and SAE gross. As a general rule, however, SAE net tends to be approximately 80% of the value of SAE gross. SAE J245 and J1995 define this measurement.
DIN Horsepower
This is a standard, DIN 70020, for measuring horsepower that very closely matches SAE net. The conditions of the test vary slightly, but the required equipment on the engine and the point of measurement (flywheel) remains the same. Because the test conditions are so similar, it is safe to divide DIN horsepower by 1.0139 to arrive at SAE net. This value is so close to equal that for all but the most technical purposes DIN and SAE net are interchangeable.
Brake Horsepower
Often road test magazines will list horsepower as "bhp".
This is just another way to talk about SAE net horsepower.
Kilowatts
Kilowatts, or kW, is not a different way of measuring engine power; it's just a different unit of measure. Countries that use kilowatts instead of horsepower typically use a rating system very close to SAE net horsepower (usually DIN). To convert kW to SAE net hp, divide the kW value by 0.7457.
Advertised Horsepower
Surprise! Those horsepower numbers presented in advertising and brochures aren't always accurate. Though manufacturers are supposed to base their horsepower ratings on SAE net standards, they are not completely beholden to it. They often fudge the numbers. Ford and Mazda both recently got in trouble with the Mustang Cobra and the MX-5 Miata, respectively, when they delivered a car that had less horsepower than what they advertised. Ford ended up doing considerable warranty work to bring the numbers up where they belonged, and Mazda re-rated their car and offered to buy back any offended customers' cars. General Motors regularly underrates their engines, most notably the GM LS1 5.7L engine as installed in the F-body (Camaro and Firebird) cars. Mechanically almost identical to the engines installed in the Y-body car (Corvette), the engine mysteriously "lost" 40 advertised horsepower in the F-body chassis. Although this technically is as fraudulent as selling a car with less than the advertised horsepower, no one seems to complain when they get a car with more horsepower than what appears on the spec sheet.
Based on my stock case, is it technically correct to say that motor power is horsepower at the crank + lost power (power lost through drive-trains, temp, humidity, etc) = the advertised horsepower that BMW made?
Therefore, 126.7 + 25.4 = 152.1 which is very close to 156 (advertised)?
