horsepower ratings of engines

[WZ JUNK]

I am curious about the ratings of engine horsepower in the early 70's.   There was a change in the ratings about 1972.  The change was meant to reflect a true horsepower rating that accounted for a realistic situation instead of an engine on a test stand.  As a result when you look at the figures after this change all engine horsepower claims are lower than the previous year.  During this time period emissions requirements were also being implemented.  Is the lower horsepower rating due to the change in the way that horsepower was measured ?  Did the change in design to accommodate the government regulations cause and additional drop in power?    I can not remember what was going on but I bet I knew at the time.

John

[wayne petty]

as far as i know..   the horse power testing was changed to require all the accessories to be on and operating while  the engine is being tested

instead of just the crank spinning with nothing attached...

i also seem to recall that the tests were also done through the transmission.. but that seems false to me..


but there are a lot of people who will know more...

[jaybee]

I never heard of any government regulated change, think it's just something the SAE agreed on.  The old method (gross hp) was just a bare engine.  Net hp is on the engine dyno but with all normal accessories.

[kb426]

I remember people talking about government enforced but it may have been people talking. I don't remember reading anywhere that I would call accurate. It seems like 72 was the second year of compression drops for emission purposes. That and the accessories and possibly some honesty were the reasons for such low ratings as I remember.

[WZ JUNK]

Here is some data I took from an old Motor's repair manuel for a 500 cubic inch Cadillac.


1970    compression ratio 10-1        400 hp @4400

1971    compression ratio 8.5-1       365 hp @4400

1972    compression ratio 8.5-1       235 hp @3800

1974    compression ration 8.25-1     210 hp @3600

So it looks like when they dropped the compression ratio the engine lost about 35hp in 1971.  In 1972 they changed how they rated the horsepower of the engine and they also changed the RPM that they measured the horsepower.  I think these years are all the same bore and stroke.  Other than changing the camshaft design, I wonder what they did to detune the engine.  It looks like the 1971 engine would be the best choice for street use.

John

[Uncle Bob]

All the elements are here, maybe just need to rearrange a little.  From the manufacturer point the decision was made (as jaybee mentioned) to go from gross to net rating, or from an unloaded engine to a loaded one would be another way of looking at it (see Waynes comments).  This took place at the same time more stringent government controls on pollution came into effect, so it might appear as a "mandate" though not.  The manufacturers had comparatively little time to develope new methods to meet the new standards, so did the things necessary with then current technology and knowledge to get the required results.  One of the mandates was to reduce NOX (oxides of nitrogen).  The quickest (and relatively cheapest) known way at the time was to lower compression ratio.  So we got lower compression ratios, and the resultant lower hp, which appeared even "worse" because the way it was measured changed too (gross to net).  

Another misconception of the time was that lower octane fuel was "mandated".  Just as in the period right after WWII, as manufacturers began the hp race and raising compression ratios, the fuel suppliers began offering higher octane fuels to the general public to go along with the new engine designs.  Likewise, in the mid '70s, as engine octane requirements went down, so did the octane levels in the fuel.  Again, this overlapped the government clamp down on lead in gasoline (tetraethyl lead being the most cost effective way to boost octane rating), and the approaching technology of catalytic converters (which were killed by lead deposits), and the rational responses to market conditions (which may or may not be rational depending on your point of view) become mixed with misconceptions

[jaybee]

Good discussion.  I think Uncle Bob's explanation sounds about right.  New government regulation, technology not up to the task, a change in procedure, rapidly increasing car weights, building the wrong cars when the oil embargo hit, and idiot bean counters instead of car guys running the companies.  No wonder we were all so wild about the cars built in those days.

[WZ JUNK]

I did a little more reading on the net about these earlier engines without the hardened valve seats.  It seems there is some controversy over whether the hardened seats are needed in all engines.  Some people swear that engines that are not under heavy load constantly do not need the hardened seats.   I always thought that the hardened seats were necessary with the unleaded fuels in any engine.  Any thoughts on not using hardened seats?

John

[Uncle Bob]

Well John, this is one of those no win discussions.  Folks have their opinions and that's that.........similar to recent discussions about zddp in motor oil.  Similar to the discussion above, a partial fact here, a partial fact there, then some mixing of them to come to another conclusion.

Back in the early '70s a lot of research time and effort went into the study of valve seat recession, exhaust valve to be more precise.  Automotive engineers, petroleum engineers, mechanical engineers, yada yada.  Dyno cells, actual fleets of several kinds, test, test, test, all looking to define what was the mechanism of "failure", the cause(s), and potential cures.

What came out of that was the observation that under extreme heat at the valve seat/valve face interface, when the temperature got hot enough micro welding would occur.  Of course the valve opening again would tear the weld and the errosion proceeded, receding the valve into the seat.  Why the lead had an effect will make sense to an experienced welder.  Dirty workpieces won't weld well, the lead "contaminated" the valve seat/valve face and prevented or reduced the potential for micro welding.  That wasn't the intent of course, the lead compounds were there for comparatively cheap octane rating boost.  But the lead depositing on the exhaust valve after combustion had an effect. The engineers of the time (when lead compounds were the norm in nearly all fuels), spec'd whatever material got the job done.  A more cynical view would be that they used the cheapest material they could get away with.  Spun the other way, they used what worked and got no benefit from higher grade material.  The result of all the testing led to the use of induction hardened valve seats, the difference in metallurgy (a hint as to why some prefer stainless seats) was sufficient to prevent micro welding in most cases.

The list of what caused much higher exhaust valve seat temps is somewhat long, but high load, high ambient temps, lean fuel mixtures, are among the more common.  In the mid '70s I remember having a discussion one day with a shop foreman for a construction fleet that had gasoline powered dump trucks.  He was having valve recession issues with a couple trucks that were doing a lot of freeway time driving back and forth from Idaho and Washington.  He was convinced it was that "new fangled" unleaded gas crap.  Only thing was he was being supplied leaded fuel that was still available at the time.  But he just "knew" the fuel was the problem so stopped looking for other causes.  As diplomatically as I was able I asked him if during "the good ol' days of leaded fuel only", did the parts suppliers make and sell replacement valves?  Well, yes, of course they did.  Why would that be?  Well, everyone knows that valves get burnt.  Okay, what caused that?

Once we got around to a good discussion based on his considerable good experience he started to evaluate how the vehicles were operated and serviced.  In the end it was found these trucks were having a high rpm lean condition that was causing high enoiugh temps that even with lead contaminated valve seat/faces they were erroding.

If I remember correctly there were a number of SAE papers written on the fleet/dyno cell evaluation/result process but that was 35 or so years ago.

[Carnut]

Heh, heh, about all I know about the subject is that I've been driving a 67 Dodge 383 since new and so far I dosen't seem to need a valve job. Also my 61 Chrysler still has the original 383 in it and seems to be doing fairly well in operation.

Now admittedly they both haven't been driven hard or very often but they've been using unleaded now for years.

Now some would say they had been using leaded long enough to be covered on the seats so no problem and that a new engine build wouldn't have the lead covering. dunno about that one.

Also 'back in the day' there were was some premium gas available that never had lead in it, at the moment I forgot the brand, but many folks say no one ever had problems with that gas. So one does wonder how much lead was ever really needed.

[enjenjo]

Also 'back in the day' there were was some premium gas available that never had lead in it, at the moment I forgot the brand, but many folks say no one ever had problems with that gas. So one does wonder how much lead was ever really needed.

Amoco "White" premium unleaded, I used to run it in my L79 Nova.

[Crosley.In.AZ]

HP ratings ... lol

my Silverado truck picked up extra 15 hp  rating  from earlier trucks with 5.3 engine. Gee I wonder if it is the electric  cooling  fans and removal of the mechanical fan that let 15 hp free up?

[Carnut]

As has been discussed the HP ratings changed to a harder system around 72 or so, showing lower HP ratings for nearly identical engines. So it would then kinda mean most all pre 72 HP ratings needing to be reduced by some percentage to bring them into line with current readings.

Which then takes me to the current ratings of Camaro, Mustang and Challengers with HP ratings in 400+ HP range being somewhat equivalent to even higher ratings 'back in the day'.

This is astounding to me. Not just that engines like with that HP can be built but that in this day and age of Greenies and Insurance weenies, they can actually be available to be purchased by anyone. Even from Government Motors.

Seems to me if you have the money this is another golden age for high HP engines.

[GPster]

I always thought that it was manufacturers trying to fool insurance companies  and it went clear back to the early '60s when Chevy was rating dual quad 409s at 425 HP. GPster

[39deluxe]

Back then engine gross output figures were filtered through the marketing dept before they were published. Not only did they decide what sounded best in the advertising but they were known to be more than a little optimistic with their advertised horsepower ratings and compression ratios. There were a few examples of under estimated ratings to appease the insurance industry such as the '67-'69 Z28 302 rated at 295 but actually around 400 gross and the '67-'69 L88 rated at at 430  but actually just over 500 gross.  

The SAE net rating that started in '71 was SAE's attempt to more accurately publish what the real world hp was of an engine as installed in the vehicle. With the insurance companies surcharging everything that even looked like a performance car in the early '70s it was an easy choice for the manufacturers to go along with the new lower ratings if they wanted to continue selling performance type cars. Of course the actual horsepower did fall due to the lower compression ratios and tuning that was forced on the manufacturers to meet the new emission requirements.

Some odd situations resulted. Published road tests from the day show that the '71/'72 Corvette LT1 with the new lower compression 350/330 horse engine actually out performed the '70 car with the 350/370 horse high compression engine in both 0-60 and quarter mile runs. In this case the cars were identical and the engines were identical except for the cr. I'm sure the higher compression '70 would have shown it's stuff on the top end but normal driving and acceleration wasn't hurt by the lower cr.

By the middle '70s the marketing people were back at it so as to not sound like their cars were total wimps. My wife had a '77 Trans Am Special Edition that she bought new. It had the Pontiac 400  and an auto trans. I tried every tuning trick I could to get a little more umph out of it with very limited success. I even tested it with the cat off and 0-60 and quarter mile times didn't improve hardly at all so I just left what made it more drivable and forgot about going any further with it. This was basically just the secondary metering rod change and timing mods.

A few years ago when Edelbrock introduced their alloy Pontiac heads I found out why from a build article in one of the magazines. It seems that even though Pontiac was still claiming about 8.5 cr on these engines they were actually only about 7.2. No wonder mid 70s cars were such slugs.

Tom