Ok, I've been told that these /6's are all pretty much the same in stock form up through 1974 and then a few things changed. So, I'm looking at this spec sheet I found on the web which says that my original 1969 /6 I had in my Valiant before I blew it up should have had a 3.40x4.125 Bore/Stroke 8.4:1- Comp Ratio 145@4000- HP@RPM and 215@2400 Torque@RPM. Now it says the 1974 /6 is 3.40x4.125 Bore/Stroke 8.4:1- Comp Ratio 105@3600-HP@RPM and 180@1600-Torque@RPM. So, with that being said, is there a 40 hp loss and a 45 loss of Torque on the 74 /6 or is it made up in that RPM difference? If they are the same, why would they list the HP differently? I put a 1974 /6 in the Valiant and was woundering if I should have searched for an older one with more stock horsepower or is all this just a case of "fuzzy math"?
Thanks guys!!!!!!!!!!!!!!!!!!!!!

Apples and Oranges...

Both engines have the same head (hardened seats for unleaded in the '74), same crank, pistons, etc...
The 1974 will have a slightly better stock camshaft in it, about the same time that cam came into play, the Auto Industry decided to change the way they measured HP and Torque...on the '69 it sometimes was measured from the crank with no accessories on it...the NET measurement required the Alternator and sometimes the A/C to be hooked up for a "more accurate" measurement...

Also starting in 1973 EPA required things to be hooked up like the EGR, the change to a different leaner carb and setting in 1974+, and more smog stuff in years after that...

So in the simplest terms, it's fuzzy car math, lots of power robbing stuff, and a different measuring standard which doesn't make comparing a 60's mill to a smog 70's mill easy.

-D.Idiot

So in reality, when you put the newer /6 into the older application and eliminate the evil, power robbing extras, they'll basically come out to the same thing if you measure the HP and tourque with the same tecnique for both motors, 69 and 74, and so there isn't really that noticeable a HP difference, or an advantage to the 69 /6 or the 74 /6, right?

Right.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

If you look at ANY American engine and compare factory horsepower ratings before 71 to after 72, you'll see huge differences. The main reason is that the automakers adopted the SAE "Net" horsepower rating procedure for (I think) the 73 model year (or maybe it was 72). At any rate, many of the engines that had NO mechanical changes magically lost as much as 100 horsepower. The 318 dropped from 230 to 145, IIRC, and that was with the GAIN of a dual-plane manifold that actually helped its low-end power. Now some engines DID have mechanical changes that cost power- the higher performance v8s like the 440 4-barrels lost a good bit of compression in that era too. But *most* of the change was just due to the change in the measurement procedure, which now was done with all the accessories installed, a full exhaust system, etc. The ratings process has changed a few times since then as well, but never such a big change in one year's time.

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It propably had a little to do with commercialism as well. In the 60s the more HP you could record sold more cars. In the 70s, the opposite effect, with more government intervention, smog policing, and gas shortage, the lesser readings kept the 'pinkos' happy. Nowadays its reversed again, everybody wants the HP back to get people to buy new cars every three years. You might get 290+HP out of some new car whatever that be, but it doesn't translate on the road like it did in the 60s.

That's right. 290 horsepower claimed today is a lot closer to an actual real-world value than 290 horsepower claimed in 1968 was!

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Now they just have to get their MPG ratings more accurate and believable!but thats a whole different story.

Yeah, but that rating procedure is set by the EPA and law, not SAE or the manufacturers.

There was recently another change in the horsepower rating procedures. It cost some of the manufacturers several HP - but led to a GAIN by some.

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"When you find a big kettle of crazy, it's best not to stir it." - Pointy-haired Boss

1964 Valiant V200, 225/Pushbutton 904
BBD, CAI, HEI, LBP, AC, AM/FM/USB, EIEIO