When you talk to the old fellows for whom American muscle cars were the peak of automotive performance, they can sometimes get lost in the moment and the love they had for these vehicles. They remember fondly how fast and powerful their muscle cars were, and lament that so many cars now lumber around with underpowered four-bangers in the engine bay.

By the mid-70s, automakers didn’t even bother with power ratings. It was that bad.

But as Hagerty Insurance company explains, automakers had a lot more leeway in those days when it came the horsepower ratings of their engines. And as it turns out, they were being pretty generous with those numbers. Just how generous?

Well as Hagerty explains, there can be as much as a 100 horsepower difference between actual engine performance and automaker ratings. How can that be? Because back in the day, American automakers dyno-tested their engines using the “net” horsepower method.

These engines lack air cleaners, exhaust systems, or power-draining front accessories, providing higher output numbers than was actually possible on a production car.

In 1972, new government regulations kicked in requiring automakers to regulate engine emissions, leading to lower compression ratios and engine gimmicks that cleaned up exhaust fumes, but killed power. Automakers also began supplying gross power ratings, with the air cleaner, exhaust, and accessories all attached.

The differences between net and gross ratings could be quite dramatic; Hagerty cites as an example the 1970 through 1972 Corvettes as a prime example. In 1970 the LT-1 350 V8 was rated at 370 “gross” horsepower, but lower compression ratios dropped that number to just 330 gross horsepower in 1972.

And the net rating, with all the intake, exhaust, and accessory equipment attached? Just 225 ponies, which mean at the wheels you were lucky to put down 190 ponies. Yikes!

Other cars didn’t fare much better; the 1971 HEMI 426 V8 had a 425 gross horsepower rating, but just a 350 horsepower net rating, and on a dyno it might make 300 horsepower at the wheels. So next time an old timer starts ranting about emissions this and government that, remind him that automakers were up to some shenanigans too.