360-2 ratings

But it remains unclear how the 10 hp uptick in the ratings between 1973 and 1974 should be accounted for.
You're way overthinking this Poogey. A memo from the VP of Marketing is all it takes to add 10 hp to the rating. The techs down in the dyno lab calculating multiple testing results from the same engine came up with 10 hp with the tweek of a pencil.
 
See what the NHRA "factored" ratings are.

CBODY67
 
A memo from the VP of Marketing is all it takes to add 10 hp to the rating.

If it's more a question of (ill-advised) marketing strategy than of measuring then, yes, what are we talking about?! Inflating the 1974-75 figures made the later drop-off look all the more dramatic.

On a more general note, advertised engine ratings are mentioned in almost every motoring article, as if it were some sacred (or should I say secret?) formula. But they are more like names, as in "you know, the 1974-75 360-2 engine they called the 180 hp".

See what the NHRA "factored" ratings are.

I'm not quite sure how to read the tables. From 1974 on, should I read the 360 180 HP column or the 360 A 180 HP column? The A is explained as "P5007140, P5155469 replacement head for SS only". These two columns contain different factors in the years 1974-1976: 270 as opposed to 250. From 1977 to 1980 there are no differences between the factors in the two columns.
 
Thank you for these detailed comments! Maybe I did not understand every aspect of it, but that's my problem.

So we should get away from the idea that the AIR and EGR affect the power ratings negatively. And the power-robbing effect of the catalyst would be only mild. So far, so good. Lower compression ratio sure left its mark on the ratings, as it was lowered from 8.8 to 8.4 from 1972 to 1973, exactly where you see a 5 hp loss.

But it remains unclear how the 10 hp uptick in the ratings between 1973 and 1974 should be accounted for. The compression ratio remained at 8.4, for instance.

Here's the table once more:

year power torque compression
1971 175@4000 285@2400 8.7
1972 175@4000 285@2400 8.8
1973 170@4000 285@2400 8.4
1974 180@4000 290@2400 8.4
1975 180@4000 290@2400 8.4
1976 170@4000 280@2400 8.4
1977 155@3600 275@2000 8.4
1978 155@3600 270@2400 8.4

Looking at the tune-up specs, the 1973 timing was set at TDC. The 1974
Thank you for these detailed comments! Maybe I did not understand every aspect of it, but that's my problem.

So we should get away from the idea that the AIR and EGR affect the power ratings negatively. And the power-robbing effect of the catalyst would be only mild. So far, so good. Lower compression ratio sure left its mark on the ratings, as it was lowered from 8.8 to 8.4 from 1972 to 1973, exactly where you see a 5 hp loss.

But it remains unclear how the 10 hp uptick in the ratings between 1973 and 1974 should be accounted for. The compression ratio remained at 8.4, for instance.

Here's the table once more:

year power torque compression
1971 175@4000 285@2400 8.7
1972 175@4000 285@2400 8.8
1973 170@4000 285@2400 8.4
1974 180@4000 290@2400 8.4
1975 180@4000 290@2400 8.4
1976 170@4000 280@2400 8.4
1977 155@3600 275@2000 8.4
1978 155@3600 270@2400 8.4

Starting in 1972, horsepower and torque are SAE net figures. They are measured at the rear of the transmission with all accessories installed and operating. Since the figures vary when a given engine is installed in different models, some are representative rather than exact.

Would be easy to increase HP & TQ if the SAE figure were measured with an engine without A/C versus an engine having A/C.

The advertised power band can also be adjusted. This was a neat trick in the 1960's and early 1970's. Manufacturers under rated the HP & TQ levels for insurance reasons and to meet Federal HP/Weight ratio's.

Camshaft specs can be changed to increase cylinder pressure (Dynamic Compression) even though the actual (Static Compression) is low, at 8.4-to-1. The closing rate of the intake valve can increase cylinder pressure and thus HP & TQ numbers. So an 8.4 compression engine can be made to perform like a 9.0 compression engine.

Looking at a Chilton's Tune-Up Manual, the initial timing from 1973-1979 varies. 1973 is TDC. '74 is 5degrees BTDC. '75 is 6 BTDC. '76 is 2 BTDC. '77 is 10 BTDC. '78 is 20 BTDC (Lean Burn Engine). '79 is 16 BTDC. Timing changes can pull a few more HP, but it also would indicate cam specs have changed.

Comparing valve spring pressures at their measured height, these are different throughout the years - indicating a possible cam difference. Installed heights are the same, but spring pressures are different.

Head chamber cc's can be varied. As pointed out, the minimum chamber cc's were to work with NHRA class rules. So a 63 cc chamber may be the NHRA minimum, but the factory chamber was more like 75 cc's. You would have to mill the head to get the NHRA class minimum. So although the advertised compression ratio is 8.4, it may actually be 8.2 instead.

With that, you would need to have in hand the AMA specifications for each year to do a better and more accurate comparison of each engine itself, ie cams specs/valve type/spring rates, carb info, timing, and other engine changes.
 
Those AMA specs could keep me off the streets for quite a while. Trailing the web, I found the 1971 and 1972 Plymouth Fury specs. The others will have to be collected in a time-consuming manner.

For the moment I can serve with some cam specs.

years camshaft nr. lift in/ex duration in/ex
1971-1974 3512589 410/412 252/256
1975-1978 3830025 410/410 252/252

They went from split lift and duration to equal right between 1974 and 1975, with those oh so identical and enigmatic ratings. What would have been the theoretical effect, all other things being equal?

There just does not seem to be a relation between advertised ratings and specs, which reinforces the creative-marketing argument.
 
(First I'd heard that horsepower was measured at the transmission yoke than at the flywheel.)

In a pre-emissions era, "Gross" horsepower figures were allegedly more optimized for most power on the dyno. Yet there were SAE specs of how that would be done, just as there were SAE specs for the later "Net horsepower/torque" figures.

Remember, too, that until the earlier 1980s or so (possibly later), running an engine dyno was "an art" as the load on the engine was varied to get the horsepower/torque figures. NOT like the newer computerized dynos that do it all by themselves, once the throttle on the dyno control panel is moved to WOT. So two different dyno operators, which respectively different "feels" for the engine, might come up with different numbers. An article at Allpar stated that the Chrysler dyno operators took great pride in getting repeatable and accurate numbers. There's a YouTube video at Nick's Garage when an original 440/375 and carb are both rebuilt to OEM specs and it produces 375 horsepower on his computer-run dyno.

It was known that there was a "window" of power ratings for any given production line engine. Variations on head castings (relating more to combustion chamber size/deck height), minor differences in ports, etc. Cam changes can be tracked via the particular-year parts book and Chrysler service manual. There were also SAE specs of how cam lobes were measured, too! Even different for intake lobes than exhaust lobes! NO "Lift at .050" specs existed in the OEM, just the SAE method of measurement. Yet the "max" number was what was advertised. ONLY factory operatives at the engine plant knew of how wide that window might be, but it related to the numbers a new engine produced after it'd gone through it's 30 minutes of "Run-in time" at the engine plant dyno room. A "stack" of normal build specs could result in an engine that produced 10 horsepower less than advertised, for example. If everything was "dead-on", then advertised power resulted. In those times, these differences didn't matter too much as long as they "ran like we wanted them to run".

The NHRA specs were monkeyed-with to ensure "more even competition". If one brand's engine is rated at 300 horsepower, yet doesn't perform equal to another brand's engine in an equivalent vehicle, they might "factor" that 300 horsepower down to 280, which might put it in a lower class where the car would be more competitive. By the same token, if they observed the opposite, that 300 horsepower could be factored UP to 320 horsepower, which might put it in a higher class and "make it work for its trophy", so to speak. I think the Chrysler 340, in the earlier years, was factored from 275 OEM rating to 290 NHRA rating?

Now, when we got to the NASCAR years, with 427 Fords and 426 HEMI Mopars, it was highly obvious that the factory ratings were "low" for those motors. In the later '60s, there were various formulas the insurance industry used to put rates on "muscle cars". Cubic inches and weight, for example. GM had their internal rule about 400cid being the largest engine in a mid-size car, BUT that didn't keep dealers from putting larger engines in themselves. Other manufacturers kind of tended to follow that rule, but not completely. That tended to generate a LOT of 400cid engines in GM brands, in their smaller cars. As the full-size and larger cars still had larger engines from the same engine families. Tis was also the era that generated the Chrysler 340 and Ford 351 "Cleveland" small block V-8s. NOT related to why the 302 Z/28 Camaros existed, per se. Smaller engines that, with a few tweaks in chassis equipment (axle ratio, tire size, etc.) could perform with their larger siblings on the street or drag strip.

Many OEMs usually rated their engines one way, regardless of the transmission it was hooked to. In the mid-'60s through early '70s, in the World of Pontiac, there were many variations of 389 V-8s whose only difference might be a "smaller 2bbl carb" for allegedly better fuel economy, a manual transmission, or some "economy" calibration. End result was that one engine size and carb type might have 5 or 6 possible build variations AND different power ratings. Otherwise, other OEMs would put a different distributor in for manual transmissions than automatics (different base timing, but very similar total 4000+ rpm total advance specs (base timing + distributor timing) for the same flywheel horsepower.

Now, I've seen where people have obsessed over a 5 horsepower variation from year to year on the same-spec engine. That power difference only happens at 4000+rpm levels, NOT at the more normal 2000-2500rpm levels normally seen on the street or highway. Where throttle response matters much more than sheer power/torque ratings. How responsive the transmission might be to part-throttle kickdown.

Where it might matter is on the measured drag strip. But then, too, if a TorqueFlite Mopar puts 86% of rated power to the ground, that 10 flywheel horsepower becomes 8.6 "ground horsepower". Any differences in performance could well be due to driver skill, track conditions, and how much power might be absorbed by particular tires rather than other tires. When I arrived at those figures, it was in the later '60s when bias ply tires had the vast majority of the tire market.

So, with all due regard, these minor power differences from year to year might make good "bench racing" discussions (in general or in particular situations of particular engines), but for the vast majority of vehicle customers, "not that important" as long as it "drives well". By the same token, there has to be an engineering-based reason for it. Most might well relate to emissions specs for the particular model year, or a body platform that allows for a better under-car exhaust system (in the case of '95+ Pontiac Grand Prix 3.8L cars and similar Buick Regal LS cars with the same engine . . . Pontiac had a dual outlet muffler and got a few more horsepower as the Buick had only a single muffler and a few less rated horsepower, for example).

Now, also be aware that in modern times, if what's advertised is not really there, that OEMs can be fined for false advertising. If 320 horsepower is rated, but most engines only produce 310 horsepower, for example. Happened in the case of 5.0L Mustangs about 10 years ago! Which can be why "SAE Certified" labels are on some engine power ratings now. I suspect there's an SAE spec for that too!

LOTS of things to consider.
CBODY67
 
Those AMA specs could keep me off the streets for quite a while. Trailing the web, I found the 1971 and 1972 Plymouth Fury specs. The others will have to be collected in a time-consuming manner.

For the moment I can serve with some cam specs.

years camshaft nr. lift in/ex duration in/ex
1971-1974 3512589 410/412 252/256
1975-1978 3830025 410/410 252/252

They went from split lift and duration to equal right between 1974 and 1975, with those oh so identical and enigmatic ratings. What would have been the theoretical effect, all other things being equal?

There just does not seem to be a relation between advertised ratings and specs, which reinforces the creative-marketing argument.


Consider that, especially in the case of exhaust timing and lift, that when "ports flow poorly", a good bit of that can be compensated for with more duration on that side of the cam, plus a little higher lift. End result, more exhaust flow from the port.

As I recall, the '75 and up cars had larger exhaust pipe diameters than most of the earlier cars tended to. That's what I remember seeing in the make ready section of our local dealership, back then. So, with those larger pipes (2.25" OD vs 2.0" OD, or something like that), less exhaust timing could produce the same flywheel "net" power ratings.

It could well have been that if Chrysler changed camshaft manufacturers, they made a very minor change to cam specs at the same time, just so they'd know where the cam came from, should that ever be necessary to track. Just a changed part number would not do it, possibly. As by the time the failed cam got to where it was being investigated, any tags of ID could have been gone.

To me, there's not enough difference in the stated specs to make 5 horsepower difference.

Digging around in the Hamtramck Registry website can yield some AMA specs for particular model years of vehicles, but not all. Otherwise, downloadable Chrysler service manuals can e an option, too.

Just some thoughts,
CBODY67
 
The Service Manuals can't always be trusted as a definitive source for engine specs. Have the '73 manual in hand and it lists the compression ratio as 8.7, not 8.4 for 1973 - so looks to be a carry over from 1972. Cam specs look to be correct, however.

Pontiac engines used combustion cc's to adjust compression. Often advertised as 10.75 to 1, they usually were not because the combustion chambers were larger than advertised. They also offered different head gasket thicknesses on some of the high performance engines. Different head designs were also used, the standard mom & pop car with press-in rocker studs, the high performance screw-in stud heads found on GTO's and other models having the same GTO engine. Then you have the Ram Air series of heads to include D-port and Round-port exhausts. Early 70's produced the 455 HO head and the Super Duty heads used on the 455. Camshafts were also a specialty at Pontiac. Generally the lift was kept at .406", but the higher HP & TQ engines saw more duration and Lobe Separation Angles (LSA) changed. The Ram Air II cam was .469" of lift and to that, Pontiac added 1.65 ratio rockers to get .516" of lift used as the cam for the Ram Air IV.

Pontiac had to keep to a HP to weight ratio and when the lighter Firebird was offered, The Firebird 400 was the same engine used in the GTO but rated less to pass GM's mandate. Example, 1969 GTO had 366 HP while the same engine in a Firebird was 345HP. The difference? Pontiac installed a stop on the secondaries that did not allow them to fully open. Remove the stop, as most did, and you got your 366 HP back.

Pontiac rated their high performance engines lower on the HP/Torque scale by selecting a lower RPM to represent the engine. NHRA however factored the engines higher - more like what they really produced. The 1969/70 Ram Air III engine made 366HP. The Ram Air IV was rated at 370HP, just 4 more HP. It has smaller/lowered roof combustion chambers, round port exhaust, .516" lift vs .406", forged pistons, and a few other goodies. It made over 400 HP @ 6,200 RPM's, but Pontiac listed it at 370 HP @ 5,500 RPM's.

So to unravel the answer as to why one year is 10 more or less HP than another year could be a number of things OR reasons.
 
As I recall, the Pontiac combustion chambers were machined rather than "as cast"? After flow benches became more common, some people finally flowed the round port heads and found out they really didn't flow more than the normal-shape port heads did. Although it looked like the round port heads would have flowed much better. I believe I saw that in "Pontiac Enthusiast" magazine?

It was also known that the reason that many of the factory cams seemed to hover in the low .400" lift range was that not much higher than that was where port flow "stalled" going higher with more lift. The only other alternative was to increase duration as much as they could. Buick used that same trick on their '59 401 engines. Which gave them a notorious rougher idle, as a result.

What I was seeking to illustrate was with the basic 389 from the middle '60s or so. Where the "synchromesh" engine had one rating. The similar automatic had another rating. And the "Economy" version had another rating. And there might have been a "high compression 2bbl" version, too? Other brands covered their basic 2bbl motors with one-spec engine. Or a low compression and higher compression motor (as Olds tended to do on their big cars circa 1960).

So we get back to a prior post where I noted that in order to make an informed determination of power output, comparing one model year with another model year, you really need a spreadsheet with all of the engine camshaft specs, compression ratio, valve sizes, cylinder head numbers, and exhaust system specs for pipe diameter and muffler inlet/outlet specs. NOT to forget about carb numbers and distributor advance curve specs.

Enjoy!
CBODY67
 
Yes, Pontiac chambers were machined versus cast. The round port heads did flow better than the D-port heads as cast, but you can get the D-port heads to flow just as well if you do porting work.

Pontiac sometimes used a different cam for an automatic and stick. Both engines could be rated at 350HP but the automatic got a step milder cam while the stick got a slightly hotter cam. Other times, the automatic & stick were exactly the same. There was not set pattern to why they did this as other times the auto & stick got the same cam.

Pontiac heads were not designed to flow big numbers unless you get into the exotic engines which were essentially race engines. So .406" on the lift produced the best flow numbers overall. The lower lift kept intake velocity up and one of the reasons Pontiac's use torque over HP. Flow benches say that the heads will flow up to about .460" in stock form, but then fall flat unless you do port work. So the longer durations and increased valve overlap did as you stated, rough idle and some were not really streetable and were sold only with 3.90 or 4.33 rear gearing.

The 2 Bbl 400 was an economy engine with 8.6 to 1 compression. I believe these engines used a dished piston to get compression that low versus a special head with a large combustion chamber. It was an optional engine and for someone who liked the look of the GTO but did not want the performance aspect of it nor the thirsty 400 that went in most. The B-body cars list a 7.6 compression 400 rated at 293HP. Most were advertised as 10.5 or 10.75, but in actuality, you can drop each by about .25 as the heads had a couple more cc's than advertised.

To truly find the differences in the listed Mopar engines, you would have to sit down and study each and every engine to include the different models across the board. Then you might be able to pinpoint what factors made the difference, however small it was.
 
Just found an interesting note in the 1972 AMA Plymouth Fury Specs. Regarding the ratings for the 400-2 and 440-4 engines it says: "With California emission package subtract 9 horsepower and 5 lb. ft. torque." The Californian emission package consisted of an air pump and floor jet exhaust recirculation.
 
Since the "new" "SAE net" ratings started in '72, I doubt that '71 rating is correct.
Someone "disagreed" with what I wrote here, so I looked it up.

According to the 1975 Chilton's Auto Repair Manual, the '71 360 was rated at 255 HP and 360 TQ. The 175/285 rating did start in '72.
 
Actually we are both right. In 1971 Chrysler and GM published gross and net ratings:225 hp (gross) = 175 hp (net). Only Ford did not do this and stuck with gross for 1971.

This may convince you: https://www.hamtramck-historical.co...etBook/1971/71_Fleet_Gross_Net_HP_Ratings.jpg

Here is the 1971 AMA published gross/net figures for Pontiac and here is the HP numbers for the 4 Bbl 400CI & 455CI as my example. All engines for 1971 do show both Gross & Net figures with the Net figures broken down further based on single or dual exhaust systems. 400CI gross-300HP@4,800 RPM. Net-200HP@4,000 RPM with single exhaust and 255HP@4,400 RPM with dual exhaust. 455CI gross- 325@4,400RPM. Net-260HP@4,000 RPM with single exhaust and 280@4,400 RPM with dual exhaust.

My engine list also includes the Gross & Net numbers based on the engine having single or dual exhaust. For example, the 400CI - the Gross is the same for either exhaust system, .

Here is a note at the top of the AMA engine spec page,"Gross HP and gross TQ corrected to 60 degrees Fahrenheit and 29.92 in. Hg atmospheric pressure. Net HP and net TQ corrected to 85 degrees Fahrenheit and 29.00 in. Hg atmospheric pressure."

I would assume being the AMA spec, that this would be an across the board measurement for all manufacturers. So in addition to the change in NET horsepower and torque ratings with all accessories installed and in use and measured at the transmission output, the atmospheric conditions were also changed. Any drag racer knows that heat is your enemy and power drops. So some of the HP & TQ losses would certainly be due to the hotter temps used to formulate the NET numbers.

It is also interesting to note that axle ratio's are included with footnotes such as 3.55 ratio on the 455HO was not available with A/C - yet there is no difference in any of the Gross/Net numbers which you would assume would be increased.

I just found a neat little guide and explanation about Gross & Net HP. I stated earlier, based on the Chilton's Note on the SAE Net measurements, that the numbers were measured at the output of the transmission. This seems incorrect as I found this piece online that seems very credible that states the HP & TQ Net numbers are taken off the flywheel, not the back of the transmission. So here is the article: Understanding Gross Versus Net Horsepower Ratings > Ate Up With Motor

Something to think about.
 
After some homework on the 1973 and 1974 AMA Plymouth Fury Specs a list with differences between the two years emerged. Here are some highlights:

- as far as emission controls is concerned, the 49-state 360-2 had no air pump and an EGR valve only in 1974. And this:
Crankcase Emission Control:
Type, Location
1973: Closed Induction System, Rocker Arm Cover
1974: Induction System, Valve Cover

- exhaust system:
Valve Rotator Type
1973: Low-friction lock on exhaust
1974: Low friction lock: std.

Exhaust Muffler
1973: One, reverse flow
1974: One, reverse flow, one resonator

Exhaust Pipe Dia. Main
1973: 2.25 x 0.067
1974: 2.25 x 0.038

- carburetor:
1973: Holley R-6452A
1974: Holley R-6731A

- ignition:
Distributor Model, Timing
1973: 3656780, TDC
1974: 3755475, 5 BTC

Distributor Centrifugal Advance
Start, Intermediate, Maximum
1973: 2 to 13@1100, 20 to 25@1600, 27 to 32@4100
1974: 1 to 8@1100, 16 to 21@1600, 23 to 18@4000

Distributor Vacuum Advance
Start, Maximum
1973: 0 to 5@9, 19 to 24@15
1974: 1 to 5@7, 20 to 24@12.5

Spark Plug
1973: Champion N-13Y
1974: Champion N-12Y

The camshaft specs are identical for the two years, with more duration and lift for the exhaust valve.

Now, is there a smoking gun among these data to explain the 10 hp rise in ratings?
 
My money is on the timing advance curve. If you know anything about timing, advancing the initial and bringing it in earlier can gain you more HP. Notice the 1974 spark plug is also cooler - can get a little more out of that as well. Now we are talking small gains, but when added up, your totals can become very noticeable - so 10 HP just from this alone would be my smoking gun.
 
Let's settle for that then, and I'll give you guys a break. Thanks for the tremendous input on my nagging questions!
 
Back
Top