Hi, new member with a question regarding horsepower and torque ratings. I have a 1974 Dodge Dart Swinger Special in need of restoration. The engine is a 225 cu in slant six with an auto transmission.

I have noted that engines from 1970 / 1971 are rated at 145 HP / 215 FT LB, while the 1974 is rated at 105 HP / 180 FT LB. I believe that some of the difference can be attributed to a different method of measurement, and it stands to reason that emissions controls would contribute to a loss of power also. However, I wonder if there are additional reasons for the lower ratings. Were smaller carbs specified in order to increase fuel economy, and / or more restrictive exhaust to meet stricter noise standards?

If anyone has any knowledge on this subject, please educate me.

Thanks -- GS

I think the biggest impact on the performance of these cars were safety measures. Along with the bigger bumpers came the added weight and the accompanying performance penalty.
The ratings went from Gross to Net starting in '72. I don't know the exact difference but it involved engine dyno numbers gained from tests without accessories attached vs the power robbing accessories attached, hence Net.
exactly what was being run off the engine is going to require a more knowledgeable person to explain.
'75 year was also when the federally mandated catalytic convertors were put into use on cars.....they were in their infancy as well as the other emission controls and the learning curve definitely impacted performance.
With all that said....I have a relatively heavy '74 duster with a stock 198 slant 6 and it runs out pretty decent.

1974's that we owned were gutless, cantankerous safety hazards if all the NEW emission stuff wasn't working exactly and tuned exactly. And it rarely was. Very dangerous engine when between cold and up to normal heat. The unleaded fuel didn't help. 1975 had the new "peanut" heads and the emission system worked better, so a good improvement in DRIVABILITY & power. I think the distributor curve and vacuum advance was different in 1975 too??? One 74 we got rid of as soon as we could (for other reasons also), and the other we put a 1976 Aspen /6 in. We have owned 74,75,76 Darts & Valients. We stay away from '74 engines & emission systems. I'm sure that if you change carbs & mess with the EPA stuff, you can get back to 145 HP. Our 74 Sport project is getting a 1978 Volare engine & 1980 trans. BTW- The wife's daily driver 1975 Dart SE has good power, 277,000 miles, and never had the heads off. That's our experience.

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"Louise", a 1976 Dart Custom project, (now sadly reverted to being just an "organ donor" to our other project Darts.)

Welcome to the forum Sasquatch! Please come back often. Tell us more about your project. Read all the articles here to get a good background on what you have and best practices. There is much good information, and literally hundreds and hundreds of years of practical experience when taken collectively. Folks here are happy to help.

Previous answers summed it up, there is little essential slant six difference between various years besides tuning add ons:, ignition, carbs, timing etc. There might have been a cam change, but not one of serious impact. They were never high compression from the factory, so that did not get bumped down as happened on the performance V-8 engines.

Sam

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1975 federal distributor still had the 15L governor and similar vacc. advance can like 1973 and 1974, but was dialed with a slightly different curve (but not much better than the previous years...1976 model year is the year of real change in governors, curves and vacc advance...

The SAE ratings are typically an optioned engine run on the dyno...so to get the gross HP ratings back, you will also have to take off the alternator, and other "standard" accessories... Emissions packages didn't change much on federal cars from 1974, 1975, 1976.... (They all had EGR, and the Holley 1945...1975-1976 adds a catalytic convertor).... Mopar also changed the EGR orifice size and/or plunger depth on some later years as well (Feather Duster being a prime example).

The killer on the 1974 was the carb was jetted real lean, standard jetting was a #58...1976+ jets with a #612 close limit jet, so that will take the gumption out of the car in a big way (much like the mid-60's Holley 1920's that came with #54-55 jets...).

That all being said...you can easily get back some power on a stock engine with some standard improvements: degree the cam so the Intake lobe centerline is 4 degrees advanced, rebuild the carb and check the jetting, clean up the ports in the head with a die grinder (with the head off, especially if you are doing a gasket change, going to a 2 1/4" head pipe and exhaust to the muffler like the Feather Duster and later super six F-bodies....use a late 70's federal/super six distributor and dial in more initial to give the engine a little help.

Those cars were gutless and ran poorly even when everything was in perfect condition and adjustment. That is because the American auto industry at that time complied with emissions regulations in the most cynical ways they could get away with, evidently in an effort to spur a public and/or Congressional backlash against the very concept of regulating vehicle emissions. They did the same thing with safety regulations, and had a few minor successes, but while they were busy fighting those stupid wars of their own making, automakers in other countries were doing a much better job of making cars that ran well and put out clean exhaust, and that were safe and pleasant to drive. For some strange reason I'm sure is totally unrelated, in the 1970s and '80s a great many Americans stopped buying American cars—permanently.
That is a myth without basis in fact. The removal of lead from gasoline made things massively better, not worse, and not just from the standpoint of pollution, public health, and crime rates (yes, really)—but also in terms of engines running better for longer periods of time. Gasoline lead and its associated chemistry makes an awful mess inside engines. There was a brief period of time during which the only unleaded gasoline generally available was of regular-level octane, but that was addressed by 1979 or so.
The peanut-plug head doesn't run any differently than the previous type, and the '75 emission systems (and driveability, and performance) were closely similar between most '74s and most '75s. Some of the '75s with catalytic converters ran better than those without, because instead of trying to squeak past the standards with a strangulation-tuned engine, the engine could be tuned to run reasonably well and the resultant filthy exhaust cleaned up by the converter. Also keep in mind Chrysler's quality control was piss-poor at that time, so how well or poorly the cars ran, drove, and stayed together was all over the map. If you happened to get a good one, great. If not, sucks for you.
The distributor advance curves were different for most every year/emissions/transmission/altitude package.
The biggest problem with the '74s was the new-that-year Holley 1945 carburetor. Lots of engineering revisions were made to the 1945 and it was quite a bit less godawful by 1976, but the engines still gasped and wheezed, stumbled and stalled, didn't like to wake up on cold mornings or get back to work on hot afternoons, etc.

There were good, dependable, working fuel injection systems readily available off the shelf in the early 1970s. They gave excellent driveability and much cleaner emissions without all the hang-on-and-pray added widgets, but the US automakers decided that rather than spend a small mountain of money changing from carburetion to fuel injection they'd rather spend a giant mountain of money on widgets and TSB campaigns and stalling-related safety recalls and part reissues and futile service training and futile warranty work and customers lost forever.
That "145 hp" figure was always fictional. See here.
How many heads does it have?

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

Dan:

Can be said for other big two and AMC in those days, and some European junk that landed on these shores now conspicuous by their three decade plus absence from showrooms.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

I wouldn't place too much emphasis on the rated numbers as I would seat of the pants feel. My '72 Valiant (225/904) made 80HP and 140 LB/FT of torque when I dynode it with the one barrel and stock compression. I put it on a dyno to see what I was really dealing with. The added 2 barrel/milled head and opened up exhaust and electronic ignition has made it a much different (quicker/better) car.

Dan, you may have hit the answer why OUR 74's were so crummy to drive. It may have been that "new" 1945 carb, as you said. How many heads? One head. I looked around, but I guess the other one was just my blockhead.

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"Louise", a 1976 Dart Custom project, (now sadly reverted to being just an "organ donor" to our other project Darts.)

Ford and GM, definitely. AMC actually made a pretty good effort (by the standards of the day) at building their cars carefully in a push to promote quality/warranty they started in '72. But it is interesting to note what happened to new-car warranties pretty much across the industry around that time. In 1963, Chrysler shocked everyone with their 5 year/50,000-mile warranty. By 1972, warranties were back down to 90 days or maybe a year, maybe 12,000 miles.

(An acquaintance who spent his career as an application engineer for chassis dynamometers and had a front-row seat for several decades' worth of ups and downs in the US auto industry says "Ford does a great job of building a lousy design, Chrysler does a lousy job of building a great design, and GM does a mediocre job of building a mediocre design". With exceptions in all directions, that's a pretty accurate summary.
Oh, definitely. Fiats come to mind first, though there were others. There were some good French cars being made, but not many of them were sent here; mostly France sent over their junk. And there were some relatively large Japanese sedans, Dart/Valiant size or a little bigger, with stout 6-cylinder engines that probably would have found a lot of happy buyers in America, but weren't sent. The '71 Toyota Crown, for example (though it must also be said the Japanese, like the Americans, kept futzing around with carburetors long past their best-before date).

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

Wow, thanks for all of the responses to my question regarding HP & torque. It appears that the basics are responsible for the different ratings, as opposed to any significant internal engine changes from 1970 to 1974.

I purchased the car in not running condition. The owner stated that after an oil change, the oil pressure light came on. (The car had been sitting for at least a couple of years.) I found the oil pump seized and the OP drive gear missing, which was later found in the oil pan (and on top of the oil pickup!). While cleaning oil pan gasket from the bottom of the block, I noted a couple of teeth missing from the OP / distributor drive gear on the cam. It was obvious that a new cam was needed, and a few unsavory words slipped out. In the end, it was a good thing, as once the head was off, cylinder scoring and ridges were found. So, the engine is now at a shop for a full rebuild.

Hence, my questions. I figured this would be the time to make any internal changes. But, I have decided to stick with the stock cam profile and the only internal engine change will be the slight overbore of the cylinders. I am more concerned with retaining ‘drive-ability’ and reliability, than significant increases in performance.

The impetus for my question was the fact that I reside at 6,000 feet elevation in Colorado. Thus, engines already make less than rated power than due to the thinner air. This also makes for many carbureted engines running far too rich. Therefore, I want to be sure that I will be able to jet a new carb to run reasonably well between 5,000 and 8,000 feet. Any suggestions in this realm will be greatly appreciated.

Thanks again for all of the feedback.

-- GS

I lived at 5,500 feet in Colorado for a lot of years. Climbed mountains (with the accelerator on the floorboard and not at 70 mph!) in 1bbl-carbureted slant-6 A-bodies. Yup, they get gaspy up there!
A Motorcraft 2100/2150 conversion would be a very fine way to go. You might write to 2100-specialist Michael Ehrmann michael.ehrmann@hotmail.com and ask him for a Motorcraft 2100/2150 conversion setup for a 225 Slant-6 engine. Tell him you live at 6,000 feet, you want an electric choke, and you need ported spark advance. Once you've got the carb and adaptor on the way from him, start shopping for a suitable air cleaner. You'll want the thermostatic type (like the stock air cleaner), not a plain open-element type. The Motorcraft 2100/2150 takes an air cleaner with a standard "4 barrel" sized neck, so that shouldn't be hard to track down on the used-parts market.

Before carb-shopping, though, you'll want to decide what kind of intake manifold to use. You can use a stock '77-up 2-barrel intake, which will require an adaptor plate because the 2100/2150 uses a larger mount pattern than the Carter BBD that came on the 2bbl slant-6 engines. Or, See the parallel 2bbl setup article. In your car you don't face the rod-type throttle linkage issue pre-'67 owners have to contend with, but there's still something to be said for putting together a parallel intake manifold (you could modify your existing 1bbl intake, since you already have it in hand). Or if you want the easy-peasy-lemon-squeezy method and have money, buy an Offenhauser 4bbl intake manifold (aluminum, nice), slap an adaptor plate on it, slap the 2100/2150 on the plate, and off you go.

If you're doing a full rebuild with breathing in mind, you'll want to put in the Engnbldr oversize valves (1.70"/1.44") and a better-than-stock torquer camshaft such as the Dutra RV-10RDP grind -- I have a new one on shelf; send me a PM if you'd like to buy it. You'll also want to improve the engine's exhalation by putting in a thoughtfully-specified exhaust system. The stock '74 system is undersized (Chrysler never met half a cent they didn't work to save). If you have the budget for it, get Dutra Duals.

Good ignition's a good idea, too; see HEI upgrade.

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