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Nailhead HP ratings


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Can anyone explain the different hp / cubic inch ratios of the three big Buick nailheads?  Cams, compression ratios, head design, carburetors, etc. are pretty much the same so where does the difference come from. (And yes, I did end that sentence in a preposition.)

300 hp 364 cubic inches = .825 hp/ cubic inch

325 hp 401 cubic inches = .810 hp/ cubic inch

340 hp 425 cubic inches = .800 hp / cubic inch

 

If the same ratio for the 364 was to be applied to the 425, the 425 would produce a little over 350 hp. Were these hp ratings just estimates? Or pencil and paper calculations?

 

Man oh man, can you tell this Covid "stay home, stay safe" is beginning to wear on me?  

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Ed, THE DEVIL IS INTHE DETAILS.  Tom T calculated my 20/1000 over bore with forged pistons gave me a  10:1 compression ratio in my 401 63 Riviera engine. Tom went on to say with the pistons and 10:1 compression ratio I would have more power. Tom tried to explain a lot regarding how the calculations were made and  how things Like quench add power. The engine was balanced and the ports polished with some new cam and main bearings. The list of things that was done to the engine all sound familiar to me. Without hesitation I was more than surprised once the engine was completely installed the engine started right up. Now, Tom T did put in electronic ignition and Tom rebuilt my carburetor. 
When I turned the engine over and it started you could have knocked me over with a feather.

Turbinator

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Another question I have regarding the horsepower ratings is why do the big Buick's using nailheads, 430's and 455's with single exhaust have the same horsepower ratings as the Riviera's with dual exhaust?  Just curious!

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Ed, I’m probably way outside my comfort zone with this stuff but have you done the same engine analysis based on their rated  torque? Since the calculations of horsepower are based on torque, I would think the latter would be easily measurable then the H.P. becomes a simple calculation from the torque results.

 

If the internals are fundamentally the same, but the torque is different I’m at a loss. Might be a chicken/egg thing either way, but they were “selling” the torque rating more than the H.P. might be an answer somewhere there.... or not.😊

 

Later,

 

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1 hour ago, MikeJS said:

Ed, I’m probably way outside my comfort zone with this stuff but have you done the same engine analysis based on their rated  torque? Since the calculations of horsepower are based on torque, I would think the latter would be easily measurable then the H.P. becomes a simple calculation from the torque results.

 

If the internals are fundamentally the same, but the torque is different I’m at a loss. Might be a chicken/egg thing either way, but they were “selling” the torque rating more than the H.P. might be an answer somewhere there.... or not.😊

 

Later,

 

I'd try that but if you look at the single four barrel 425 and the dual four barrel 425, the single four barrel is rated at 340 hp and the dual four barrel is rated at 360 hp. BUT, both are rated at the same 465 lb ft of torque. 

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Found this on-line, not sure if it helps, but interesting nonetheless...

 

 

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In the early to mid 1950's the American Automobile Manufacturers were in fierce competition for market share with one another. They were making all but complete model changes ever year! In 1952 the Chrysler Corporation had introduced it's now famous Hemi... as an answer to GM's Caddy and Olds offerings. By 1954 Chrysler reported to the public that the upcoming "Chrysler 300" was thus named because its Hemi engine produced 300HP.

 

If there was a single starting point for the HP Race.. that was most likely it. That announcement however seems to have left several Automotive Engineers squirming in their seats and looking somewhat sheepish. They could not publicly refute their bosses in Sales and Marketing because after-all that's who they actually worked for in the long run. When you get Sales, Marketing and Advertising People together.. new limits to how far the truth can be stretched are all most always found.

 

So what to do?.... Let's publish a paper through the Society of Automotive Engineers that will divulge the truth to anyone interested enough to find and read it. We also know that none of the Automotive Press nor Magazines would be included in that first group, so good PR can be maintained.

 

Thus the SAE Gross HP ratings were defined.... and anyone with any technical understanding of the subject would see at once that as written, it left all manor of loop-holes wide open. It is just my personal opinion, but shared by many that it was simply a way for the Engineers to tell the truth... the truth was all Gross HP ratings were no holds barred and lots of marketing hype! Nonetheless the truth was out there... and the engineers could squirm a little less, give a knowing wink and nod to each other.. and go on with their lives with a little less guilt.

 

All this worked well.... "until".... the Federal Government got involved. Emissions Control because the marching orders of the day around 1964 and by 1967 all automobiles produced for sale in the USA had to start controlling specified emissions.... So standard Compliance Testing had to be established for all makes and models.... thus standards that much more fully defined the test conditions had to be developed. Thus the SAE HP Rating was defined, and it closed all manor of loop-holes intentionally left open in the initial SAE Gross HP rating system....

 

Once the Federal Government gets involved in anything, there is endless growth ahead... by 1971 the manufacturers knew that the Emissions Standards would be greatly increased in the years ahead, and they started planing accordingly for their 1975 models. With the fuel shortages of 1973/74... they also knew that Emissions Tests would be used to estimate and report fuel mileage to the consumers. What is it they say? "you get what you measure"!...

 

Thus the SAE Net HP rating standards were developed..... The task at this point was to define a testing standard that yielded the lowest possible amount of the federally controlled emissions, while yielding the highest possible estimated fuel economy. It also had to be rigidly applied across all brands/makes and models!!

 

"Houston We Have A Problem!" reported the Engineers ..... the criteria that gives us todays goals, will clearly show that the rating systems we had in years past - was a partial or complete falsehood. No problem replied the Sales and Marketing People, the consumers don't remember anything for more than two years... lets tell 'em what they want to hear!!... "Our engines are clean and fuel efficient!"

 

In summary:

SAE Gross HP - any thing goes. Any grade of fuel, no accessory loss, no water nor oil pumps attached, One Run Wonders OK. Most of the engines used to hit their Peak HP ratings were junk after one run. They were also special built, set up loose etc. Very few of them would have ran over 1000 miles in actual use... But They Did Hit, at least once, the Numbers As Advertised.

 

SAE HP - required a standard production engine be taken at random off the engine line, equipped with oil pump, water pump, fan, distributor, and generator/alternator. It also had to have standard exhaust manifold and header pipe in place.

 

SAE Net HP - all the above, PLUS all standard accessories found on the average model the engine was installed in. It had to have a full exhaust system, standard air cleaner in place, coolant in circulation and be measured at standard operating temperatures as found in the average model it was installed in.

 

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That all makes sense, but Buick didn't try to sell cars based on hp.  They "advertised" their engines based on torqe ratings.  The 445 and 465 nailheads for the single four barrel 401 and 425.  I'm just wondering if the 364 had a hotter cam, a bigger carb, better exhaust, or ????? to get the better hp / cubic inch ratio.  Or did they just pick a nice round number - 300, 325, 340, 360.  Why not 302, 323,337, 365.5? In the Skylark series in 1966, there were a couple of engines that weren't that basic 325 hp 400 (401). They had one with an 11:1 compression ratio, and another with the Rivera's Quadrajet carb and intake. Those two engines had higer hp ratings that were not evenly divisible by 5. 

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21 hours ago, RivNut said:

That all makes sense, but Buick didn't try to sell cars based on hp.  They "advertised" their engines based on torqe ratings. 

Bigger numbers always sound good and a more "sophisticated" performance message as opposed to Buick being on the horsepower sales bandwagon like the lowly Chevs, et al.. ??

 

Other than that I got nothing, except this kinda interesting data (once you get past all the ads)

 

https://www.automobile-catalog.com/curve/1965/88520/buick_riviera_425_v-8.html

 

Later,

 

 

 

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