What exactly happened

[Automobile Maniac]

After 1971 engines pretty much turned into garbage. What specifically on the motor made the power drop? I hear all the time people saying "smog equipment" what the hell do they mean exactly?

For example:

1971 corvette LS5 454 V8 365 bhp
1972 corvette LS5 454 V8 270 bhp

What parts are draining this much power???
Can't you just remove these parts and make the motor have exactly as much power as the years before???

Thanks for any help

[71Cnet]

engine designs also changed. different internal components were used also. like different pistons push rods even the heads, intakes and exhaust manifolds. compresion ratios changed. it really has nothing to do with the emisions stuff.

[Madcat455]

Didn't they also switch from a Gross HP measurment to a NET HP measurement??? Or was that later on??

[PeteRR]

Lower compression was the biggest reason for the drop from '71 to '72, at least for Mopars. One of the performance Dodge dealerships, Grand Spaulding Dodge, tried to get around it by offering as an option a Paxton Supercharger to get the HP back in the 340 SB. It was known as a GSS. The Feds shot that down after '72.

[MagicRat]

Originally Posted by Madcat455

Didn't they also switch from a Gross HP measurment to a NET HP measurement??? Or was that later on??

Madcat is correct, the measurement changed, mostly in 1971, I believe. This change alone usually cut the HP numbers by approx. 30%, without actually changine the engine at all.
Furthermore, the old 'gross' measurement was notoriously inconsistent.
There are many examples where gross power figures just did not add up, given the equipment used. (We all have heard stories how they did so to 'fool' the insurance companies and/or senior management at the car manufacturer)

For example the plain jane '68 429 v8 4bbl was rated at 360 hp.
The Cobra Jet option, with better heads, manifolds, bigger cam and more compression was rated at 370 hp. Now there is no way that all those excellent high performance parts just got 10 more hp. You could get 10 more hp out of a base 429 just by flipping the lid on the air cleaner.
Furthermore the 'Drag Pack' Super Cobra Jet, (pretty much a race only option) was rated at only 375 HP. Its true output was more like 450.

Other reasons for the reduction........

Compression ratios, as mentioned earlier were dropped. This allows the engines to run better on unleaded and also reduced the NOX emissions.

Cam shafts and Cam timing.......most of the more radical cam shafts were eliminated. Also, a trick that just about everyone used was to retard the cam shaft timing a few degrees. This reduced power, but helped clean up emissions.

For example, the ford 460 4bbl used in Lincolns was rated at 365 hp from '68 through '70. But through '72 to '79, it was rated at 208 to 212 hp.....and it was the SAME engine as the 365 hp version. If you drive them back to back, (I have) they 'feel' almost identical.
The only difference was a 2 point cut in compression, adding an EGR valve and retarding the camshaft timing 4 degrees.

Therefore, 2 modest engine tuning changes, an EGR valve and using a different rating system lost 153 hp......on paper, but only about 25 hp in reality.

[GTStang]

Like everyone said it is "smog equipment" in a way but more trying to meet new smog/mpg laws through cam retarding, CR drop through less stroke/bigger CC heads/ and different pistons the big 3 used all of these to lower emission but HP drops also came.

[swi66]

Speaking as a guy who remembers it well. It was not only the government and emissions.
It was the insurance companies as well. Huge tariffs on cubic inches as far as costs of policies. Car companies wanted to "under-rate" the actual horsepower as who would buy a car you couldn't insure. And shortly thereafter costs of gas skyrocketed, further causing the car companies to tone it down so they could sell cars..............

Could you imagine if insurance companies, the government, and the oil companies didn't due what they did! We'd all be driving 1000 horsepower cars...............

swi66

[terzmo]

H.P doesn't seem to be a factor now ??? 500 hp corvettes....over 300 on alot of other models....what excuse will they use ???