So... I just purchased a '72 440/727 out of a Newport Custom.

I was doing some research and found the difference in hp between the model years to be impressively large... from 335hp in '71 to 245hp in '72. I know that HP started to decrease as emissions standards became more strict, but what EXACTLY was changed that caused that unfortunate decrease in power?

 

WELCOME -- How about Ralph Nader, and the insurance companies ?

 

What year did manufacturers go to "net" horsepower? That might have been "it." HP did not change when manufacturers went to "net" ratings, but rather the way engines were rated.

Bear in mind there WERE constant changes from the first (federal) smog infested engines in 68 clear up until of course now. EG the first year or two Chrysler used EGR, there WAS no external valve, which has lead to arguments "there is no smog equipment anywhere on this engine." Oh yes, "there was" First couple of years Ma used EGR, "she" just "drilled two holes" in the bottom of the intake manifold (floor jets) and coupled exhaust gas leaking right in.

Until you go through the individual service manuals for each year and in some cases "more" (service bulletins you or I may not have) you won't know what all changed.

And bear in mind there were ratings differences between car lines in some cases, and certainly 1/2 vs 3/4 and heavier trucks, etc.

 

Thanks for the insight!

 

EG -

A couple of things, the increased emission control requirements and reduction in compression (kinda went hand in hand). Then there was how the HP was being measured (that's where some of the insurance pressure came in).

Archer

 

1....Compression reduction
2.......Induction type
3...... Exhaust played its part also

But now days... if you want to get it all back and then some..... Stroker kits are the way to go..Oh and a decent set of heads...

Just my 2 cents

 

an other smog change that happened on some U,S. cars in the late 60s was the grind on the cam. i remember a story about Olds found out that low RPM the race cams had better emissions than a reg cam. but i dont know which cars had that change. so the phrase smog cam is true.

 

Bob -

Only problem with the crank and heads is the price tag - basically a full rebuild + "good" parts. Gotta tell ya, my first engine was a 1974 318. Cam, intake and exhaust really woke that puppy up. Going to 340 heads finished the package.

Still kinda sorry I parted it out when I got the 440.

Archer

 

And to think there is 500 H.P. now days out of them 318's....
BUT
Like we say.... "Horsepower cost".....

 

As others said, one factor was change from gross to net hp. But if you dig more into it, the gross power ratings usually had little relationship even to the gross ratings of the engines. It was essentially lying hp, or wishful hp. The marketing department inflated the numbers so that they look good. In some places in the net you will find stories about the hp being under rated for insurance purposes. I don't buy that.


Good news is that Chrysler made the best large scale production engines, and towards the end their ratings were reasonable. The 375 gross hp 440 was good for about 350 hp net. Many engines from GM and Ford had similar ratings, but not as good performance.


Going to the smog engines. Based on what I have found out is that a low compression 440 (8.2) equipped with the high performance cam was good for about 280 hp net. The engines with the small cams and single exhaust were further taxed by the lean carburetion (plus the EGR? don't know much about that, I would think that EGR would go to zero at WOT, plus you should be able to plug it). The bump in compression ratio should be all it takes to take you to the 69 and before specs. I suspect that the iron crank should be OK as long as you don't rev it too high. The "HP" exhaust manifolds were just a gimmick.