US cars and engine power on the 60s and 70s

When I was a teen in the 90s I was briefly a car buff, spending time with friends street racing and trying to improve our shitbox cars. Mine was a 73 Ford Gran Torino with a 302 V8 engine.

The lore at the time to explain why 70s cars like mine were so slow compared to 60s muscle cars was that government emissions rules changed significantly and cut available engine power by huge amounts around 1970. So engine power ratings for big block V8 engines went from 250-300 HP in the 60s to 150-200 HP in the 70s.

I’ve since heard that it was more the way engines were tested than emissions, and the true power for those engines hadn’t changed much at all.

Which story is true? Or is it a combination?

Engines went from being rated with gross horsepower (nothing attached to the flywheel) to net horsepower that factored in power loss from the accessories and drivetrain.

It’s a combination. The switch from gross to net horsepower happened around 1972, but from the late 60s to the mid-70s, automakers were having to dramatically de-tune their engines to meet emissions standards.

Link to article per above post:

Manufacturers did reduce compression ratios as well in an effort to improve emissions, so that played a role in reducing net horsepower as well.

Steronz got it. The shift in how HP was calculated caused the listed numbers to decline, but the attempts by auto manufacturers to meet emissions regulations caused the decline in performance. It wasn’t really until the widespread use of fuel injection that auto manufacturers figured out how to get better performance and reduced emissions.

it’s definitely both. Emissions requirements caused horsepower to drop. They were taking lead out of gas so as not to poison the catalytic converters (or poison the air), which meant higher compression engines had to go. They also changed the ratings so a 300 gross horsepower engine (tested with no alternator, power steering pump, water pump, etc.) was detuned to perhaps 220 gross horsepower for emissions, and then rated on a net basis (with all those accessories) to maybe 170 horsepower. Then they strapped on very heavy 5 mph bumpers. The '70s were not a good time for performance cars.

You are also talking about a 1973 car as experienced 20 years later. Any chance that car had failing valve seats and worn rings causing it to lose a lot more power? I’m not surprised your Gran Torino felt dog slow.

I still remember that car fondly, even though it was a piece of crap. It was very low mileage for its age at the time – when I got it in the mid 90s it only had about 20K miles. I ended up driving it until it died my freshman year in college.

I think the engine was in pretty good shape – I actually put in a new carburetor and intake manifold and got the 0-60 time down to 8 seconds. It was slow compared to the real muscle cars, but it wasn’t too bad compared to my friends cars (90s compacts and pickup trucks, for the most part).

That thing could go toe to toe with my granny’s 2015 Camry! :wink:

This reminds me of one of my favorite SDMB threads, from 2006:

Muscle Car Shootout: Would today’s fastest cars shut down the ‘60s-'70s muscle cars?

This thread, however, is more relevant to the OP (from 2003):

Did Detroit ‘Muscle Cars’ Really Have Higher-Than-Rated Horsepower?

How badly was the headliner sagging?

In order to keep things in perspective, we need to keep things as apples to apples and oranges to oranges. I’m a real statistics nut when it comes to engine power and torque figures and remember them throughout history like a sports fan might recite batting averages.

1971 was a transition year and in many cases both the gross and the SAE net figures were given.

Let’s take your 302. In 1971, the last year it was rated in gross HP, it made 210 gross HP. Free breathing on an engine dyno, and sans any parasitic accessory drag. That same engine dyno rated ( not a chassis dyno showing rear wheel hp…that’s a whole different enchilada ) at 150 NET HP. All the accessories, breathing through single exhaust. I’ll bet a set of dual exhausts would boost that to about 160-165, but given the same exhaust configuration, both engines would give the same SOTP ( seat of the pants ) feel in the car whether it’s rated as gross or net. Peak power was 4000 to 4400 rpm. Not high, but typical for a base 302 with 2 barrel carburetion.

Next year in '72, the compression ratio was reduced from 9:1 to 8.5:1. Net horsepower now at 141, though I doubt that half point compression reduction accounted for the loss of 9 net HP of a small engine like that. I’d chalk that up to more conservative tuning for emissions reduction. Even so, unless one winds it over 4000 rpm through the gears, most wouldn’t really notice the loss anyway; it would still have a night torquey feel at more sedate driving conditions.

By 1977, things took a dark turn. More restrictive head/combustion chamber design and even more mild camshaft timing for emissions reasons, and now that single exhaust is also equipped with a restrictive catalytic converter. Those early converters ( 1975 to 1983-ish ) were the next worst thing to having a potato wedged in your exhaust system. power was ( depending on the vehicle ) 129 HP, or in some applications, 134. Strangled as it was, it made its peak power at 3400 RPM. Though still possessing a decent amount of off-idle and low end V8 torque, it was also working against insane high rear axle gearing.

Oranges to oranges, in the realm of high performance, the net ratings were mainly just paper, but the lower compression caused a required shift to milder cam timing. Decent runners they were, but by the time catalytic converters hit in '75, forcing all single exhaust, high performance free-breathing engines were dead anyway.

Somehow not too bad, from my memory.