(first posted 10/13/2016) 1971 was something of a watershed year for the great performance/muscle car boom that had been building ever since the “horsepower wars” of the mid fifties. Two very large factors were to change the braggadocio that had been building for decades: insurance industry backlash and a switch lower compression across the board for 1972, in order to comply with the mandate that all engines be able to run on unleaded regular gasoline. And then in 1973, the industry agreed to only advertise SAE net hp ratings, which reflect the actual installed output of an engine rather than the SAE gross hp ratings in use for so long, which measured an engine’s potential output without any engine-driven accessories, maximum ignition advance, no air cleaner, open exhausts.
While GM and Ford stayed with gross ratings for that final high-output year in 1971, Chrysler went a different route, and either just didn’t show any hp numbers in their brochures (in the case of Dodge) or showed them both (gross and net) in the case of Plymouth and Chrysler. Which makes for some interesting musings.
Let’s take a closer look at these engines from the 1971 Satellite brochure. What stands out? How about the disparity between the gross and net hp ratings among the various engines. The two extreme examples are the 318, whose net rating is only 67% of its gross, and the 440-6, whose net is a whopping 86% of its gross rating. What does that tell us? That the 318 was over-rated, and the 440-6 under-rated, neither of which are surprising. I never could quite see (or feel) why the 2-barrel low-compression 318 had any more hp than say a comparable 327 Chevy (210 hp rating). Or had 30 more hp than a Ford 302 or Chevy 307. Realistically, the 318 should have been advertised with no more than 200 hp, based on its 155 hp net rating, if not less. Meanwhile, everyone knew all too well that the 440 six pack was a monster, and underrated at 385 hp.
The other equally obviously underrated engine is the 340, whose 235 net hp is a whopping 45 more than the 383 2V, although both are rated at 275 hp gross. That the 340 was underrated was no secret at the time, and this makes it clear just how much.
What is surprising is how low the net rating for the 225 slant six is. 110 hp is pretty modest given that the serious de-smogging era had yet to come. And it had only 5 hp more than the significantly smaller 198 six. As a point of comparison, my Ford 240 six was rated at 150 hp gross, and 129 hp net. But that was in 1966, before any emission controls were required.
Which brings up an important point: emission regulations began in earnest in 1968, and were generally tightened every two or three years, with California having its own more demanding requirements. That means that by 1971, emission regs already had an effect on these engines, generally the result of modified ignition advance curves (generally less advance), as well as running air injection pumps (“smog pumps”) that promoted further combustion of unburned fuel in the exhaust manifolds.
The reality is that many/all of these 1971 engines weren’t making the same power as they had previously. This shows up in comparisons of gross/net power outputs for those where these are available in the pre-smog era. For instance, by 1971, Chevrolet’s 250 six was rated at 145/110 hp. Back in 1966, it was 155/125. My point is that although Chevy did lower the gross rating by 10 hp, Chrysler stayed pat with its gross numbers for 1971, even though they had been similarly affected. It does show up in the net numbers, especially in the case of the 225 six, which undoubtedly had a net output of some 120-125 hp in the pre-smog era. But the gross numbers (“advertised hp” stayed the same for all of these engines in 1971. We will have to speculate how much the 426 hemi really made back in 1966. By 1971, it was 350 hp net, still a considerable number.
Of course, much worse was yet to come: by 1980, the 225 six was down to a paltry 85 net hp. As were all of the other engines, and not just Chrysler’s.
The Chrysler brand also showed both ratings for their big cars in 1971, so here’s a couple of 440s that weren’t on the earlier chart. The interesting comparison is between the 383 4-barrel and the lower-output 440, which although rated at 335 gross hp, made only 220 net hp, significantly less than the 383 with 250 hp. How to account for that? It may mostly be a combination of wanting to show a higher number for the larger engine, as well as the significant effect that an open exhaust has on an engine that comes delivered with a restrictive single exhaust.
One good source of net hp ratings are the Vehicle Information Kits at the GM heritage Center. Chevrolet showed both gross and net ratings, and often dyno charts, for many of their engines, up to a point. meaning that their top output engines were typically shown only with the gross numbers, as the net was probably giving away too much for either competitive reasons or maybe because the gross number were either too high or low relative to the net number. These are from the full size ’65 Chevy kit.
The last year Chevy showed net and gross hp numbers (and a dyno chart) for a top-performance engine was in 1959, when the hi-po fuel injected 283 was rated at 290 gross, 245 net. And the dyno chart clearly shows the key difference: the gross peak happens at 6200 rpm; the net peak at 5600 rpm. The way engines are set up to run on the gross test, with ignition advanced as much as the engine will take, no mufflers, and no drag from driven accessories allows the engine to rev higher, the key to more hp. Unfortunately, the 315 hp version of the FI 283, which appeared in 1960, did not have net hp shown, and for that matter all of the hi-po 348/409/327/396 and 427 engines starting in 1959.
But then Chevy also clearly manipulated the rpm at which it advertised the peak gross hp. For instance, the L30 version of the 327 had been rated at 250 gross/210 net for some years. That 250 gross peak was given at 4400 rpm. For some reason, in 1966 the same L30 engine was got a 275 gross hp rating, although the net was the same at 210 hp. The only apparent difference was that the gross peak was now given at 4800 rpm, although the dyno charts do show the peak at those corresponding rpm.
The same machinations are also evident with the 325/350 hp L79 version of the 327. And undoubtedly others too. It is accepted wisdom that manufacturers just plain lied about their hot engine’s gross hp, as in made up the numbers. They presumably just chose the rpm level where the engine made the amount of power they were wanting to advertise. Or?
I spent way too much time delving into all kinds of obscurities at the GM vehicle Kits, but here’s just one odd example. The 1969 truck kit shows the 292 High Torque six, with two dyno numbers and ratings, depending on whether they were equipped with air injection systems or not. Both are rated at 170 hp gross, but the net numbers are 125 and 130. Now this is common throughout, and another example of how the gross advertised number was misleading. But that’s just part of the story.
Here’s the same basic engine, but as installed in the larger C50 series trucks. Same 170 hp gross rating, but now the net numbers are 140 (with air injection), and 153 (without emission controls). A little digging showed that back in 1966, prior to any emission controls, the 292 was rated at 170 gross, 153 net, in all applications. Again, this shows that manufacturers were mostly no lowering gross ratings, while emission controls were eating away at the net numbers; 28 net hp in the case of the 292 with air injection. Or the emission control systems were just completely stripped off when the gross dyno test was run.
Well, it would be a mammoth project to to correlate all of the variations between gross and net hp numbers, especially in the period of 1968 through 1971, the last year gross numbers were used, and the game was finally over.
I always read about the Mopar 340 being such a specially potent engine, allowing Dusters to dust Corvettes and pony cars.
What made it so special and why was its run ended while the 318 seemed to go on and on.
Don’t really have a definitive answer for you on that, but all I know was the ’68 Formula S that I had wailed! It had a four speed, which specified a hotter cam, and you could shut the door on pretty much everything at the time. That and the heat riser counterweight jangling away made for one memorable machine 🙂
Regarding the 340 – maybe something about the whole being greater than the sum of it’s parts. Chrysler just hit a perfect balance.
340’s were just giant killers.
The 340 evolved into the 360, didn’t it? The 360 certainly wasn’t anywhere near as potent as the 340, even in 4-barrel form.
IIRC, the 360 was originally engineered as a torque-specific truck engine and adapted for use in low-performance big cars like the Fury, then on to replace the 340 when it was no longer viable for the times. The 360 was still okay, but certainly not in the realm of the high-performance 340. Those V8 engines with big valves were just too difficult to meet emissions and get decent fuel economy
Nevertheless, some might consider 1971 the pinnacle of the high-performance small-block V8. Not only was the 340 in its best state of tune with no emission controls and the first year of the stellar Carter Thermoquad carburetor, but the magnificent Ford Boss 351 made its debut, as well. It’s just too bad it had taken Ford so long to finally get a decent performing small-block; it would have been perfect in the 1967 Mustang fastback and really altered the ponycar dynamic. A 351C-4v (of any sort) in the earlier car would have moved the bottom-feeder GT (with its 390 slug engine) to the top of the pecking order, besting even the hottest Camaros.
The compression was dropped 2 full points on the 72 340 and intake valves went down from 2.02 to 1.88 in 72 . I think that had more to do with the net horsepower drop by the way no the net horsepower of the 72 340 was 240 not 235 . Now the 360 never got the compression or big valves that the 340 did in the pre 72 years. The first high performance 360 didn’t come out till 74 and it had a net horsepower rating of 245 that’s 5 more than the 73 340 with basically the same stuff. If you read my any of my replies know this I not trying to make you look stupid. It wouldn’t be fair if I was because the both of us would be making you look stupid.
The 360 first appeared in passenger cars in 1970, for sure Dodge but unsure if there were others.
They are similar in appearance only. The important internals (cam, valves, ports, pistons etc.) were all different.
The 340 was a hot rod…period.
The 360 was intended for regular duty in larger heavier cars and trucks with no real performance ambitions.
It really had to do with when they peaked. A 360 built to the regulations of 1968-1973 would have been that much better than a 340. Instead, the performance version wasn’t introduced until 1974, when compression ratios were low, fuel was unleaded, airflow was restricted both in and out of the combustion chamber, and carburetion was hobbled by efforts to reduce emissions. If you look at the ’78 L’il Red Express Truck, you’ll see that the 360 in E58 trim had little to apologize for performance-wise when liberated from passenger car emissions regulations. They were rated at 225 net hp, and various tests suggested they produced at least that much. A teenage neighbor had a ’76 Volare squad car with a free-breathing 360 that was simply faster than anything else on the streets of my hometown in the early ’80s. By the mid-’80s, Dodge St Regis and Plymouth Fury squad cars with 318s were about as fast as mail trucks, but there was a time when the 360 showed its potential in versions unavailable to car buyers.
Although the 360 had almost the same diameter bore as the 340, it had an approximately quarter-inch longer stroke (the 340 was pretty much a bored-out 318 block with better breathing heads, hotter cam, 4v carb, etc.).
Someone else more knowledgeable than I can better explain the pros/cons of stroke versus bore but I suspect that, generally speaking, the longer stroke 360 produced more torque (desirable for large cars and trucks) at the expense of higher rpm of the shorter stroke 340.
Yet…with regular-gas compression and a mild cam, it made 300hp. The best smallblock heads were used on the 360. (308 castings, 1987-91.)
Thanks Rudiger and Robert for clarifying. The 360s in my parents’ ’77 Fury wagon and ’78 Crestwood wagon were no performance monsters!
The ’70 340 6-Pak always impressed me as high performance engine.
Multiple carburetor engines ran great when in tune, but it was a pain to keep them that way. With that said, the 1970 340-6v engine was otherwise the high-point for the series as there were some substantial internal upgrades (stuff like thicker webbing and four-bolt mains, IIRC) which made it the most sought after block for high-performance duty.
Well, it wasn’t exactly magic. It was a very well sorted out small block, and made power roughly analogous to the 350 hp 327 Chevy. It was clearly underrated at 275 hp gross. Probably closer to about 33-350 gross. An dit was commonly installed in the rather light-weight A bodies. So yes, a light Duster 340 could take a bigger engined heavier car. But I wouldn’t ascribe unnatural abilities to it.
It had to be de-smogged, and it morphed into the 360, which never pretended to be a true hi-po engine.
Here it is:
The Amazing Mopar (Dodge/Plymouth) 340 V8 Engine
One of the best engines of the 1960s and 1970s for performance enthusiasts was the 340 V-8. It had high-flow heads, big ports, a two-level intake manifold, and a six-barrel option (three two-barrel carbs). The package allowed for high speed with the light weight helping handling.
The 340 cars gave away nothing to the 383 cars in a straight line, and were ahead of the 383 cars on anything involving turns — and spark plug access.
When the 340 came out in late 1967, it was a street fighter from the start. Separating the 340 from the standard-performance 318 were not just 22 cubic inches, but also:
a dual timing chain with a windage tray to improve top end engine RPM by keeping the crank counter weights from ‘churning the oil’ in the pan.
2.02 inch intake valves and 1.60 inch exhaust valves
a high-rise dual plane intake
an 850 cfm carburetor (from 1971 to 1973)
a forged steel crank (through 1972’s engine #39118000, when a cast iron crank was used)
high-performance heads
a revised oil pump with a 90 degree adaptor
a special carburetor and cam
Mopar ActionThe 340’s best power rating was 290 horsepower; even in 1973, it still managed 240-245 net horsepower. A good-running, early 340 in a lightweight A-body or Road Runner embarrassed many big block engines. Though relatively few were made, many parts interchange with 318s and 360s….
http://www.allpar.com/mopar/mopar340.html
…According to CAR LIFE Magazine, “Rated at 275 bhp, Mopar’s 340 may have had 325 or more” and that it was “as cleverly engineered as the 426 Hemi, just not so fussy.” CAR and DRIVER called its 340 Dart GTS (4 speed, 3.91:1 gears, 14.4 ET @ 99 mph) “a giant killer.”,….
http://www.tunakiller.com/340_Engine.html
An 850 cfm carb is pretty substantial on a 340, even the 351C in the 1971 Falcon GT-HO Phase III had a 780 and was supposed to put out 360-380 hp depending on who you believe (300 hp officially).
“So yes, a light Duster 340 could take a bigger engined heavier car. But I wouldn’t ascribe unnatural abilities to it.”
The thing that made the Duster 340 special was the price. At $2547, MSRP was over $250 less than the 1968 Road Runner, and it was just as fast (if not faster). $250 was nothing to sneeze at in 1970. At that price, you didn’t get a lot, but you did get the 340 engine, 3-speed floor-shifted manual, 3.23 open differential, HD drum brakes, and full gauges (minus a tach), and that was enough.
Frankly, in terms of going fast for the lowest possible price musclecar, the Duster 340 may be at the very top of the list, beating out such worthy contenders as the Road Runner and Fairlane Cobra with the the 428CJ engine..
I can’t remember which magazine it is right now ( it’s at home) but in 71 they tested a Duster 340, Nova 350 SS, AMC SC360 and a Comet GT. If I remember correctly the Duster was second fastest after the SC 360. I’ll look when I get home.
Dude you don’t know enough about any engine to giving advice . I don’t think you are a Mopar fan but the 1970 Duster 340 came with a 3:55 rear gear standard. Go to YouTube there is a race in the pure stock class you need to checkout a 71 Duster 340 against a 69 zl1 camaro the Duster won 2 out of 3 races he red lighted one time or he would have won all three he had the quicker time ever race. If the 426 Hemi is such a dog why did the Hemi cars of the day run some of the fastest quarter miles. I also noticed that all the basic rules of net horsepower rating could be apply to the Hemi engine but for some of the Chevy the rules couldn’t be used you had to go back to 1966 hearsay to get some of what you consider their engine ture horsepower number are.
did you read what the zl1 owner said about the race…thats what I thought the duster has a blueprinted motor and the guy in the zl1 was taking it easy
The 340 was fast but it would never outrun the ZL1 from the factory
Also look up what blueprinting is for a motor then you will understand.
If you bore out a 360 to accept 340 pistons,this can be done then put the 360 rods on the pistons you will need the help of a machine shop then add 340 he ads and cam from a six-pack 340 an 850 Holley with eldabrock manafold add a set of good headers you,ll have a real monster small block for kind of small investment
No need for all that…keep the overbore to a minimum, use either a Magnum engine or the 308 truck heads on a roller block…400hp is easy.
I see you’re like most everybody that has posted you don’t know what you’re talking about. First of all I don’t know why you would want to 340 pistons in a 360 but that doesn’t matter because you would have to have cut the top of the piston down, the rods are the same length.
Just read this & here is some personal experience from 1968 — ran my buddies dart with a 340 4 speed rear gear unknown but not a low gear – my 66 chevelle 396 4 speed with 3: 41 rear gear beat his ass approx 3 cars —- he was pissed —- he had just ran his brothers 1968 chevelle 396 w/ 325 hp engine with 3:41 and beat it approx 1 car —– the 340 was not a world beater but a quick little inexpensive car . may have taken a 300 horse corvette automatic with a poor driver somewhere sometime . I should that while I was in the Army from 1969-1971 THE MAIN STREET SMALL AMERICA CAR WORLD CHANGED FROM BALLS OUT RACING ON ANY GIVEN NIGHT IN ANY LITTLE TOWN TO JUST A HANDFUL OF PEOPLE EVEN OWNING A MUSCLE CAR . BUT RATHER LOW PERFORMANCE CARS WITH A/C P.S. ETC HAD BECOME POPULAR AS WELL AS MARIJUANA — I THINK WHEN THEY TOOK LEAD AND COMPRESSION OUT OF CARS THEY ALSO TOOK TESTOSTERONE OUT OF AMERICA . IMO . THE 1971 SATELLITE 383 -2 BARREL WOULD NOT SPIN A TIRE ON WARM BLACK TOP 275 H.P MY ASS . HAD TO LOCK UP THE BRAKES AT 80 MPH FOR ANY EXCITEMENT OUT OF THAT CAR.
Paul, I dug up a GM full-line brochure with their own text about gross/net, and then the specs for their whole line, if of interest. Apologies for so many separate postings:
Interesting; never seen that one before, obviously. Thanks for the addition.
Chevrolet (1971)
Pontiac (1971)
The Ram Air IV HO 455 was down some 40 hp from the 426 hemi (310 vs 350 net hp).
More Pontiac (special Firebird ratings):
Olds (1971)
More Olds (maybe duplicates above 100%)
Cadillac (1971):
Those Cadillac net numbers are very low; the net for the Eldo is 64% of the gross. That’s the lowest I’ve ever seen. Typically, it’s in the 75-85% range.
Would Cadillac’s low net HP values be due to higher parasitic losses from accesories like the AC compressor, larger power steering pumps etc?
Looking at the example of the Imperial 440 above, just as likely a very quiet exhaust was the cause
I’m not so sure the Imperial’s mufflers robbed much horsepower (if any). Seems like I read somewhere that they flowed so well that they were actually the same mufflers used on Hemi cars, too!
Again not that it matters but gm product quite exhaust stole robbed horsepower.but Chrysler product even though it’s also a top of the line luxury car they put Hemi mufflers on it . How loud do you think they were and again you don’t know enough about any engine to be giving out expert apinion. People with a little knowledge will you don’t know what you’re talking about , people hoping to learn something from this might think you know what you’re talking about.
On the Eldo, I recall that due to the low hoodlines, those cars used a very-short air filter assembly…that couldn’t have helped.
Also note that, in 1971, GM dropped compression about two full points across the board.
It jumped out at me that the ’71 New Yorker could be had with the 440 and dual exhausts but the more upmarket Imperial could only be fitted with single exhaust. So this was because the dual exhausts are noisier?
I would argue that the luxury cars such as the Cadillac would have a greater percentage in horsepower drop due to more restrictive (quieter) exhaust and air breathers, and more standard engine accessories.
It wasn’t the air cleaner assembly it was the “low riser” intake manifold. When I had my Eldorado I researched ways of waking it up. I did some research and found that in order to get more power I had to get a mid to high rise intake. The problem was that the hood would not close unless you cut a big hole for the carb. I gave up on that idea altogether and sold the car.
What the hell, here’s Opel for ’71:
When I sold my ’70 C10 I gave the new owner the original owners manual, (wish I kept it) it had all the engines offered in pickups listed in gross and net hp. My 307 engine was rated at 200 gross hp, and the book said 157 hp net if California, which it was, and 162 hp net for the rest. 1970 was the last year of high compression in GM engines.
I just subtract 20% from gross ratings to get net hp, seems to be pretty close. But as Paul points out, sometimes the gross output seems to be way overstated.
I wouldn’t mind having a C10 with a 292. Plenty of torque and lots of room to work on it. Is there a difference in the block between that and the 230/250? Putting one in a Nova would be a neat trick for a car show, especially with 292 engine badges.
Yes. The 292 block is quite a bit taller than the 230/250, due to a longer stroke, and I’m not sure it would fit in a passenger car, at least one with a stock hood.
The 292 block is probably one inch taller, reflecting the longer stroke. It might require a non-stock air filter, but I can’t see it not fitting under the hood. I know it’s been done numerous times, like this one below.
It has seemed to me that in the days of SAE gross, horsepower figures were calculated more by the advertising department than by engineering, which seems to have changed in the SAE net era.
These are some interesting comparisons.
My take is that the SAE gross numbers for a long time seemed quite reasonably accurate enough, and were typically about 120% of the net number, which makes sense. The disparity seemed to come about for two reasons: the impact of smog devices not being accounted for, but then perhaps the SAE gross test allowed them legitimately to remove them. And there were certain engines that were obviously manipulated for both insurance and marketing reasons. The ’66 425 hp 427 Chevy was known to make 450 hp, and was going to be advertised as such, but the backlash from insurance companies made Chevy lower that to 425 hp at the last minute. And Pontiac had a habit of having the same engine have a higher rating in the GTO than the Firebird, presumably to maintain a sense of pecking order.
The 275 hp rating on the Chrysler 340 was also clearly understated in order to slot in below the bigger 383.
But I still think that the manipulation was not quite as egregious and common as is often thought. If the net is roughly in that 75-85% range of the gross, than it suggests the gross number has a high degree of validity. And that was quite commonly the case before 1966-1968 or so. In fact, it would surprise me to find an example of an engine well outside of that range prior to that period.
Pontiac rating the same engine higher in the GTO than the Firebird might have been more than a mere fib. I recall that they actually installed a limiting screw on the Firebird carburetors so the throttle plates wouldn’t actually open all the way. Once this became known, it was a simple trick to increase the speed of a Firebird by simply removing the screw.
I have never seen advertised gross horsepower in the 60’s to be SAE Certified gross horsepower.
Age old argument with gear heads and 60’s/70’s car fans. Some just never understood the different ratings and assumed that “HP was cut drastically in 1972”. And we never hear the end of it.
Even today, young car fans will ask “what happened to the HP?”. In new Hemmings Muscle Machines, a kid asked that, and editors had to explain.
The change to net ratings made it hard to advertise horsepower in the seventies. Even where it was creeping up to 220 net as it did for the L82 Corvette and the Pontiac 400 Trans Am in 78-79. The cars were quite fast again, sub 7 second 0-60, but dare not quote hp because it just sounds so much lower than 10 years before.
Ford rated their 200 six at 120 gross. Starting with a 67 chassis dyno by Ak Miller in a Hot Rod magazine 6 cylinder hop up article up to modern day chassis dyno on Classic Inline’s website a 200 built to stock 60’s spec put 65hp to the ground with the stick shift and 58hp with the C4 automatic. In a 1970 Maverick the 200/auto took 14.5 sec to 60 and the 200/stick did it in 12.3. Now after emission controls really hit by 73 the six cylinder Ford’s did take a major nosedive. The 200/auto in a 74 CR test took 17 sec to 60 and in a 76 4dr CR test with stick it took 17.6. Of course weight also factor’s into it as well. The poor old 250 that did 0-60 (with auto) in 10.8 in a 70 Grabber was even slower in most road tests than the 200. In a 75 Granada it took 21.5 sec to 60. That’s the same as the 144 in a 60 Falcon! I say however that the reason the 250 was slower was because the WWII era stroke added reciprocating weight that takes longer to wind up, the 250 basically breathed thru the same size exhaust as the 200, and the 200’s Carter 1bbl flowed 187 cfm whereas the 250’s only flowed 215 cfm which is 35 cfm less than displacement versus the 13 cfm difference of the 200. Also the 250 had the same size valves as the 200 in spite of 50 extra cubes. Of course there’s no denying it made more torque although Classic Inline’s dyno tests prove it ain’t much more at the wheels. So I prefer the 200. And as a side note Four Wheel Drive magazine also used to do chassis dyno figures on the 4×4’s they tested and a 80 something Bronco with the FI 302 that was rated by Ford at 180 hp only put 103 to the ground. Only 38 more than a non emission 200.
Don’t forget that the 73-on cars gained significant weight. The 75 Granada weighs 50% more than a 1960 Falcon.
The 250 did have a slightly longer stroke crank but I don’t think it could take the blame for being so slow. Apparently 70 net horsepower! The 250 in Australia made 120 hp when the emissions hit, but they developed the cross-flow cylinder head to address things.
Well the longer stroke would have higher internal frictional losses. I would think that would figure into the equation also. And yeah, the increasing weights of the cars did indeed make a major difference.
Also, by the mid-70’s, everything was getting super-tall axle gears.
It’s important to note that net ratings are at the flywheel, NOT at the drive wheels. If you have 58 to 65 hp at the drive wheels, that probably means roughly 100 horsepower at the flywheel, which sounds about right.
This got me wondering how the true HP ratings of 30’s & 40’s stack up. They must be pretty accurate even for the faster cars as a 400 to 500 ci engine putting out between 125 and 150 hp.
interesting that the 426 Hemi made less power than even the basic truck-spec modern Hemi (350 VS 390 net HP)
Ive always been more of a 440 Wedge fan than the Hemis, its a much better engine for the street
The 426 Hemi’s ratings were pure fiction. Actual dyno tests with 480-500HP of stock Hemis have shown that. The 426 Hemi and the 340 were probably two of the most-underrated engines of the era.
The same is true for the LS6 454, which will handily make 500HP in stock trim.
Great post! Gross vs net horsepower is probably one of the most misunderstood concepts in the car enthusiast world.
I have a few points though that should be mentioned though.
In 1971 General Motors also advertised gross and net horsepower figures, not just Chrysler. Off the top of my head, I recall 1971 Chevrolet literature even showing a difference for net horsepower ratings due to exhaust (fullsize wagons couldn’t get factory duals, and had lower ratings compared to coupes/sedans with duals). Ford only listed gross figures in 1971.
For 1972, all domestic manufacturers switched to SAE net horsepower ratings exclusively. This was as set out in SAE J1349 standards. While GM and Chrysler rated the same engine regardless of platform, Ford had different power ratings for the same engine in different platforms. For example a 1972 351 Q-code was rated at 266 hp in a 1972 Mustang, but 248 hp in a 1972 Torino, even though engines were the same. There would be differences in exhaust, but if anything the Torino had a less restrictive exhaust than the Mustang. This also occurred for more pedestrian engines, with the LTD generally having higher horsepower ratings than lower lines with the same Engine. Ford only did this practice for a couple of years. Ford also did not overtly advertise horsepower ratings or even print them in brochures.
SAE J1349 standards introduced in 1972 had specific guidelines to follow, and I would argue are not comparable to earlier net ratings that manufactures listed. We have no idea what GM or Ford’s idea of “net” horsepower was when they listed their figures. I am sure they are much closer to the SAE net figures but are not directly comparable because there was no standard to follow. It would be like comparing SAE net to DIN figures, while close, they aren’t the same.
This is further reinforced by the SAE’s revision of horsepower ratings again in 2005 under SAE J2723. This was a revision to the practice of obtaining SAE horsepower ratings. The first engine to be tested was the Corvette 7.0L Z06 and it actually saw a small increase in power, going from 500 hp to 505 hp. While many engines lost power, such as the Toyota 3.0 L 1MZ-FE V6 which went from a 210 to 190 hp rating. The J2723 standard was designed to prevent manufactures from fudging numbers and end up with more consistently comparable ratings. My point is, even under the SAE guidelines there is some big variations, so there is no way that we can expect the pre-1972 net horsepower ratings to be at all consistent with the post 1972 ratings.
I also think it’s a bad practice to apply a “formula” to convert gross to net ratings. First off, the gross figures had very poor standardization especially with hi-po engines. Secondly, the parasitic losses vary wildly from car to car. A 1969 340 Dart, will have free flowing exhaust and air breather, possibly no engine accessories other than an alternator and water pump, while a 1969 Cadillac will have a restrictive quiet exhaust, a restrictive air breather to reduce noise, power steering, air condition, possibly an AIR pump. So the Cadillac will obviously have far more parasitic losses.
Although emission related engine design changes may have had an effect of the horsepower ratings in this era, many engines still had few if any emission controls even by 1972. I doubt the 1971 Hemi was one that was much affected. There were few changes to the street Hemi made throughout its life, other than some minor camshaft revisions, with the last being the 1970 switch to a hydraulic cam. I don’t believe any Hemi ever had an AIR pump. I am no Hemi expert, but as far as I can tell the 1970 and 1971 engines are pretty much identical. And based on the performance of the cars of the time, a 350 hp net rating does seem to be appropriate.
One last point, the Chevy 283 engine does have some differences in the peak hp RPM gross to net. I would account much for this for the exhaust and the air breather. These items may have maxed out their CFM causing the engine to be unable to breathe beyond that point and thus not make any more power. Further, I doubt that there would be much difference in the ignition timing between the net and gross figures. There were no emission standards in 1957, so for Chevy’s top engine why would they not run the optimal advance curve in the distributor? But again, it all comes down to speculation because we really have no idea of what Chevy’s definition of net horsepower was at that time.
The reason 1971 was the last year for gross ratings in the U.S. — and I actually only found this out about a month ago while researching something else — was a California state law requiring SAE net ratings for MY1972 and beyond.
While California obviously can’t regulate advertising in, say, Utah, the law meant that any nationwide ad campaign had to use net figures. Also, while California engines often did have lower output due to stiffer emissions requirements, continuing to advertise gross ratings in other states would have been asking some consumer or consumer group to sue or file a complaint with the FTC. (“Your ad says this car has 50 more horsepower than the ones in California and I don’t think that’s true!”)
I do know that Cadillac published an article in the SAE Journal about the new OHV 1949 V8. The gross HP was rated at 160 and the net was rated at 133. I would assume that there were some standards for both numbers.
The SAE J1349 standard wasn’t developed until 1971 and came into full effect in the 1972MY. It has been revised since and now superseded by a new standard that allows for even less loopholes. Like I said, while “net” power ratings were published by manufacturers in the past, there was no standardization on what “net” horsepower was until this SAE standard was introduced. Manufacturers played pretty fast and loose with numbers, and we have no idea what method they used to test these engines beyond speculation. Here’s a quote from David Lancaster from GM powertrain also a chairman of the SAE committee:
“Since 1971, when the [J1349] standard first was instituted to improve on the widely abused SAE gross horsepower ratings that gave rise to some exaggerated ratings of muscle cars, J1349 has been revised several times, says Lancaster.”
If you read the chart on the Chevy 283 above, how they went about gross and net is somewhat clear, although what fuels they used is not made clear.
It gives some of the basics of the test conditions, but SAE J11349 is a 23 page document (2004 edition) specifying all the parameters of the test. Like I said, I am sure these old OEM net ratings are close to SAE net, but I doubt they tested as per SAE J1349. And like I originally posted, even with SAE J1349, there were still manufactures that tested differently than others that resulted in some big horsepower changes when J2723 was used (see Toyota losing 20 hp in their rating).
I think (as I posted below) that gross ratings in the mid 50’s were probably based on very high octane gasoline (probably aviation fuels) which allowed for the spark advance to be much higher than possible with the actual automobile fuels available to most drivers. As a result the gross ratings are bogus. Net ratings were either not done, or were not advertised.
One thing that is obvious to me is that the gross ratings do not translate into net ratings, nor can you take the net and translate that into a gross rating.
What is meaningful is quarter mile performance comparisons.
“One thing that is obvious to me is that the gross ratings do not translate into net ratings, nor can you take the net and translate that into a gross rating.
What is meaningful is quarter mile performance comparisons.”
I agree with you wholeheartedly on these points.
DIN ratings, so far as I know, have always been net, although some of the procedures are different, as are the correction factors for temperature and pressure. Not that U.S. automakers used DIN figures in the States, but there was some specific precedent.
Interestingly, the California law I mentioned specifically refers to J1349.
The 225 cube slant six was gone in 71 here but had been wearing 2barrel 160hp badging for several models, did they just dream up a catchy number and call it good?
Since the pre-smog 225-1V claimed 145 gross, claiming 160 hp for a version with slightly more venturi area than a drinking straw (and perhaps warmer cam timing?) wasn’t outlandish as gross ratings went. Of course, that probably still amounted to something like 120 net hp.
But wait, there’s more.
The 225 1bbl Slant-6 engine’s published rating was 145 bhp and 215 lb·ft from 1960 clear through 1971. That’s with nominal compression ratios that varied from 8.2 to 8.5, three different camshafts installed with various timing, dozens of significantly different ignition advance curves, dozens of significantly different carburetors, and several significantly different emission control packages (yes, even before 1972).
Given that the 170 Slant-6’s published power changed from 101 bhp to 115 bhp in 1967 when it was given the slightly upgraded camshaft the 225 had received for 1965 as well as a carburetor with a ø1-11/16″ throttle bore rather than ø1-9/16″ (both sizes were used in various applications on that “145 bhp” 225) those numbers start to look a lot like they were pulled out of a hat, or thin air, or a fabled dark part of someone’s anatomy.
As for the 160 bhp rating of the export-only 2bbl package launched in ’67: it might or might not have been a realistic absolute number, but it is realistic in ratio to the 145 number for the 1bbl engine. The 2bbl package had a much more reasonably engine-matched carburetor flowrate and, yes, a slightly hotter camshaft (which was applied even to the 1bbl engines starting in ’71). The driveability of the 2bbl engine was very much better than that of the 1bbl, and when a 2bbl package was released for the domestic market—the “Super Six” setup of ’77—it, too, gave about the same 10% bump in advertised horsepower and large improvement in driveability.
(Then there’s the 190 bhp figure on the South African ChargerPower version of the 225 with higher compression, a hotter cam, and a 4bbl…and the 175 bhp figure on the Australian Pacer 225 package…)
A comment on the Chevrolet gross ratings vs net from the 50’s: the spark advance is adjust to optimum, which means that they probably used the highest octane fuel available, possibly aviation fuel. What this really means is that the gross ratings are bogus in term of what sort of actual power/performance you might expect. The net ratings (not advertised) are realistic.
After World War Two I think gross ratings were probably done without a lot of “tweaking”. But the horsepower race starts, and I think power ratings are tweaked. As we get to the 60’s, the horsepower ratings may be exaggerated.
Buick for example rated the 401 @325, then the 425 is rated @340 or 360 (dual carbs). The new 430 is rated @360. Then for 1970 a 455 engine is rated @370. I think the 455 might be underrated, but if the 401 was overrated, then the late sixties number make more sense if they are trying to rate the engines as installed without super premium fuels and “optimum spark advance”.
By the late 1950’s high-octane gasoline made from aviation components, mostly Alkylate, became available. On the west coast it was Chevron Custom Supreme. As I recall it was advertised as 104 (research) octane. It still had far less lead than 100/130 aviation fuel. 115/145 was the ultimate. As jet planes entered first military and then airline fleets, more alkylate was available for automotive fuel.
I don’t remember what we had at the end of the 60’s. My 69 GTO liked premium, probably about 100 octane. I do remember that Gulf Oil came in with cheap gas, but the GTO burned it faster than other stuff. I switched to Standard (which became Amoco and then BP) which the GTO did better on, something like 12 MPG instead of 10.
I have gone to GM’s Heritage site and looked at the Chevy charts. While the 327 rated @250 and @275 Gross with the same net horsepower rated @210 look the same, they are different. The charts could be better, but the net torque curve is different. The gross torque curve on the 275 HP engine is tuned to move the peak torque to 3200 RPMs from 2800. The net torque curve changes, but the peak is still at the lower speed. The net (from 1964) was 315@2600, while the 1966 engine is 310@2800. So there is some difference. Remember that the net was not made public as far as I know, so the gross ratings are what mattered (not that they should have).
I think I see the difference: for 1963 the 250 HP 327 got dual exhaust standard; for 1965 single exhaust, and the chart shows 200 net; for 1966 the exhaust is still single, but now the horsepower is up to 210. Dual exhausts may have been optional.
The translation from SAE gross to SAE net is painful enough for my brain, but then if you go outside the US, it gets a lot worse.
You have to contend with DIN, CUNA, JIS, PS and nowadays the kW… not to mention the “fiscal horspower” thing in many countries too. And there is no way to accurately translate engine output from one system to another, unlike, say, MPG to L / 100 km or cc to ci.
I recommend AUWM’s article on this confusing mess, though keep the aspirin handy.
http://ateupwithmotor.com/terms-technology-definitions/gross-versus-net-horsepower/
Makes me consider the Rolls-Royce power rating (“sufficient”) as a wise way to measure these things.
0.75 kW is approximately 1 horsepower. I like computing in MKS units.
One mechanical horsepower is 745.7 watts, but one metric horsepower (often abbreviated PS, for the German pferdestarke) is 735.5 watts, which creates further opportunities for confusion.
We lucky… people who have strapped on a 440 Belvedere or 392 426 Cuda Etc… would never ever ask and you also would know when several people are feeding each other silly statistics. Have a blessed day
I’m just amazed that several Chrysler Corp. cars offered the entire range of engines they made, from the 1bbl 198 slant 6 to the 4bbl Hemi 426.
Amazing today! That surely was the case in the larger models. One of a number of Chrysler corp. daily drivers I’ve owned over the years, was a ’73 Fury 2dr. As I recall from the shop manual there were about 8 engine options. The slant 6 was only available on fleet orders in that car. The others (from memory) were a 318 2bbl, 360 2bbl, possibly a 360 4bbl(?), 400’s, both 2 and 4 bbl, and 2 or possibly 3 different 440’s.
I remember for the 1971 model year, GM began listing both the gross horsepower rating and the net horsepower rating in their sales brochures. I remember the 307 Chevrolet V8 was rated at 200 gross horse power and 140 net horsepower.
My thought as I read about all these inconsistencies is that that the Big 3 were then doing what VW did. with both mpg reporting and emissions certification with their diesels.
They were cheating.
Ford later got caught in the mid 1970’s manipulating carbs and other engine aspects on certification vehicles, and paid a then record fine and ended up setting up the APTL outside the main Dearborn engineering campus to promote independence (or reduce interference), in emissions testing and certification, as part of the settlement agreement.
My god I hate the timed edit function that cuts off an in process edit when the clock runs out. So frustrating.
According to the table the 340 had 10.3 to 1 compression ratio. That says everything on why it had such high net power. The question is why did it get to keep the high compression when the other engines like the 318 got theirs lowered for emissions reasons?
The lowering of compression ratios was not, in the short term, for emissions compliance, but to prepare for unleaded gasoline (which would, aside from the benefits of not having TEL in engine exhaust, help to prepare for future emissions controls). So, whether to drop compression ratios on high-performance engines was still, at this stage, a matter of individual corporate policy rather than regulatory compliance.