Alright, I need some help clearing this up.

Everything I've ever seen on the output of the z's always shows the 240's at 150hp and the 260 and 280's dropping more untill the arrival of the turbo zx's. Is this true? I now doubt this due to a recent post that shows multiple VIN tags that show a 260 at 162 and a 280 at 170hp. What's the deal? Can someone set me straight.

thanks

Nate

Nate,

My understanding is that somewhere between the 240's and 260/280's there was a shift in either how or where the horsepower readings were taken. Thus causing the misunderstanding that the later models actually made less power(or not as much). Or something like that......it's really late as I'm writing this and my brain my be malfunctioning....:stupid:

Yes I have heard this before...

read from crank was advertised first

then...

they started reading from the rear wheels

that would make sense.

Nate

Horsepower is basically an imaginary number derived via torque with this calculation:

bhp = torque x rpm/5252

Being an imaginary number there are various methods of calculating it, with some methods more liberal then others.

Until 1972 most US auto manufacturers used an old SAE standard method develop the so-called "gross" horsepower numbers. This standard was designed to measure the horsepower output of the basic block, cylinder head, and internals. The standard did not specify intake, exhuast, and accessory configurations.

The Japanese used a more conservative version of that standard in their JIN measurement system. In 1972 the state of California, as part of their Clean Air act implementation, required all auto manufacturers to specify horsepower ratings using the SAE J245 (now SAE J1349 and J1995) standard. Somewhere the term "net" was thrown in by the automotive marketing folks, but there's nothing "net" about that standard. It measures crank horsepower with the engine as configured in the car including complete exhaust and intake systems.

The current overall measurement systems are SAE (the most liberal), JIN (the moderate), and DIN (the most conservative). So, when you see the horsepower ratings for an American car you can assume they are a little optimistic, for a German car they are a little conservative, and for a Japanese car probably exactly correct (until you get to the mandated 280hp limit imposed by the Japanese government.)

yes 150hp "gross" but as of todays standards ("net" if you like) it's around 137hp

I think that in the U.S. the insurance industry began to get into the picture in the mid 70's as well. The insurance rate for high horsepower cars became artifically prohibitive.

At least that is my impression, since I owned some late 70's U.S. cars that clearly had way more horsepower than was advertised.

You just can't push 5000 LBS as fast as some of those cars went with the insignificant amount of power that G.M. claimed the engine delivered...