Would anyone happen to have the GM/Chevrolet TSB (technical service bulletin) regarding complaints of pinging/detonation and a second head gasket for the 1962 model year for 340-360 HP Corvette and 409 pass cars? Supposedly this TSB went out to dealers in early/mid 62 production.

A little later in production, these new engines were assembled with two head gaskets instead of one. Also, on a "customer complaint basis", two gaskets could be installed to correct the problem.

Did this revision continue into the 63 model year?

 

Yes, it continued into 63. I need to look for a copy of the bulletin.

 

Michael, I have one. I'd have to search for it. I'll do that if no one comes up with one that's handy.

Seems strange there were complaints of detonation in 1962 with 95-100 octane gasoline available almost everywhere yet the same engines seem to run just fine on "today's" 92-93 octane that many complain about.

I think the Owner's Manual calls for 100 octane on all 1962-63 engines, doesn't it?

 

Never got to work on a 340-360 horse Vette engine back in the day, but I helped three guys who had 409-409 62 Impalas jerk the extra head gasket off of the motor. Didn't know it was a service bulletin change. Just thought they all had em. We never had a problem with pinging/detonation, but we ran the good gas, too.. 33 cents a gallon as I remember.

 

I wonder what those "old" 62-63 vintage octane numbers would translate to in today's octane rating system?

 

Even my 63 250hp Owners Manual says something to the effect that all motors should use premium fuel. I'd have to dig it out to check confirm for sure.

 

Frankie, I'm sure you are right. I can remember a guy who had a 250-327 62 Impala 4 speed car, and he was notorious for running regular. It rattled like it had beans in a hollow can when he would stand on it.

 

Not sure about today's octane rating system, but the gasoline back in the day even had lead in it which was great for anti knock and valve/seat wear.

 

Chuck,
In the old days, we used RON (Research Octane Number)
Today we use PON (Pump Octane Number), which is an average of RON and MON (Motor Octane Number)
RON and MON simply use 2 different ways to test octane number on a calibrated test rig
MON is typically 8-12 points lower than RON.

Conversions/Comparisons:

http://www.pencilgeek.org/2009/05/oc...nversions.html

Pump High Test, in most states, 93 PON = 97.4 old RON octane

 

Thanks, Joe.

I knew that the old "Research" method was higher than today's average RON/MON number.

Referring back to Frankie's post, I'm reading the chart as saying RON of 100 = 95.75 today's pump high test.

 

"As the subregular and middle grades of gas came to market in 1962, the average octanes of gasolines in the U.S. now stood at 93 for regular, 99 for premium and 102 for the few super-premiums still left on the market. Those numbers would increase only slightly in the next few years to around 94 octane for regular, and 100 for premium by 1967."

 

I think 240 Sunoco was 97-98 octane. Almost every car on the road would run on that stuff back then if it was supposed to have premium fuel. That included all the high performance Chevy stuff back then except for the L 88.

Brief history of octane. I'd give credit but I don't know who wrote it.

The History of Gasoline Octane

As the high compression engine era was gaining steam in Detroit during the early to mid 1950s, the need for higher octane gasolines was becoming more and more apparent. When automobile production resumed in 1946 following World War II, gasoline octanes in the United States averaged at 79 for regular and 85 for premium and those numbers climbed year after year until 1954, when premium gasolines were rated as high as 94 octane and regular at 86. Oil companies were promoting their gasolines, especially their premium grades, with claims that their fuels increased power and gas mileage while cleaning out the carburetor and other engine parts to wash away accumulated carbon and other deposits while regular usage prevented the future buildup of such. Among the additives widely promoted by leading oil companies were Texaco Sky Chief with Petrox, Super Shell with TCP, Mobilgas Special with a Double Compound ingredient and Sinclair's Power-X featuring a nickel additive.

As Detroit continued the horsepower race unabated in the mid-to-late 1950s, the oil industry responded by continuing to increase the octanes of their gasolines, and a few even went the extra mile by introducing "super-premium" fuels which were even higher in octane that the premium grades. In 1956, Sunoco introduced its "Dial A Grade" blending pumps that could dispense five different grades of gasoline, later increasing to eight, ranging from subregular Sunoco 190 to superpremium Sunoco 260. That very same year, Esso introduced a third grade of fuel called Golden Esso Extra, which came in a gold pump and had an octane rating of just over 100. That was followed in the spring of 1957 by Gulf, which introduced its super-duper Gulf Crest that was dispensed from a purple pump, and Chevron debuted its Custom Supreme grade in the western states.

By 1958, oil companies generally took a position concerning the number of gasoline grades offered with the greatest majority choosing to stick to just two (regular and premium) and simply increasing the octane ratings of both grades of gas with the premium fuels coming very close in octane to the super-premiums offered by some competitors. That year, regular gas averaged at about 90 octane and premium hit the 98-99 mark. With compression ratios on Detroit's hottest engines reaching the 10 to 1 plateau and higher, nearly half of all 1958 automobiles were powered by engines requiring premium fuel. And that included virtually all medium and higher-priced automobiles, leaving only a few lower priced cars powered by engines capable of using regular fuel including most Ramblers and Studebakers, as well as Ford, Chevrolets and Plymouths with standard six-cylinder or small V8 engines.

But the advent of smaller compact cars with more economical engines, both domestic and foreign, along with detuned engines in some larger cars, slowed down the octane race a bit and by 1961 only one-fifth of new cars were powered by engines that required premium or super-premium gasolines. Motor Trend magazine noted the trend toward economy that year by pointing out that Chrysler Corporation had reduced compression ratios across the board on standard engines to burn regular gas, a move that may reduce miles per gallon fractionally but give you more miles per dollar. "Five years ago, new car buyers swallowed premium gas as a necessary evil; today a salesman has to have a good reason for specifying it."

With a smaller proportion of new vehicles on the road requiring high-octane gasolines and the octane ratings of both regular and premium grades continuing to climb, demand for the more expensive super-premium grades, never really that high, dropped dramatically. In the fall of 1961, Esso and Gulf both discontinued their super-premium grades of fuel in favor of lower octane fuels to supplement their regular and premium offerings. Esso increase the octane of its premium Esso Extra and introduced a new middle grade of gas, Esso Plus, which was inserted in price and octane rating between Extra and their regular fuel. Gulf took a different direction by replacing its super-premium Gulf Crest with a new sub-regular product, Gulftane, which was priced about one or two cents less than its Good Gulf regular - and also designed for vehicles that could use gasolines with octane requirements lower than regular grades. In the process, Gulf created a subregular product that was priced on par with regular gasolines offered by cut-rate independent gas stations that generally sold gas for a few pennies less than major-brand stations - sparking off "gas wars" in many areas of the country where prices often dropped as low as 18 cents per gallon for regular and subregular grades (compared to the prevailing normal regular fuel price of 25-26 cents per gallon).

As the subregular and middle grades of gas came to market in 1962, the average octanes of gasolines in the U.S. now stood at 93 for regular, 99 for premium and 102 for the few super-premiums still left on the market. Those numbers would increase only slightly in the next few years to around 94 octane for regular, and 100 for premium by 1967.

By this time, other oil companies jumped on Sunoco's bandwagon by offering blending pumps dispensing several grades of gasoline from one pump to tailor fuels to a particular vehicle's octane requirement. Signal Oil Co. offered seven different grades of gasoline through its blending pumps at its Hancock and Norwalk stations in the Western United States. In the Mid-Continent region, Conoco began testing four-grade blending pumps in some markets in 1965 and introduced the concept throughout its marketing area two years later. In addition to Regular and Premium, Conoco offered its sub-regular Conotane (similar to Gulftane) and a Super grade between Regular and Premium similar to Esso Plus. A similar four-grade pump setup was offered by Skelly that included Skeltane (sub-regular), Regular, Special (intermediate) and Keotane (premium).

The development of true high-octane gasolines came to a screeching halt (along with the musclecar era) as a result of the Clean Air Act of 1970, which stipulated many federal mandates for automakers to reduce emissions of their engines. With that, General Motors President Ed Cole announced that his company's engineers found the answer to meet these ever toughening standards - a catalytic converter, which got the job done but required the use of unleaded gasoline. As a first move toward the 1975 models that would be equipped with such devices, GM reduced compression ratios on all of its 1971 engines to permit the use of low lead, regular leaded or unleaded gasolines and other automakers soon followed. This move spelled the end of the "octane race" and as unleaded gasoline was being phased in at most U.S. service stations during 1974 in time for the 1975 and later models that would require such fuels, the higher-octane premium and super-premium leaded fuels gradually disappeared from most stations - leaving only lower-octane leaded regular and unleaded grades. By the late 1970s/early 1980s, the last of the leaded premium grades disappeared as oil companies introduced new premium unleaded fuels that were higher in octane than the unleaded regular fuels (91-83 vs. 87) - but still lacked the moxie of leaded premium fuels, leaving drivers of older cars with engines requiring high-octane gasolines with few options to keep their classic rides intact without undue engine knock, creating a cottage industry for octane boosters and, with the recent phaseout of leaded gasoline altogether, additives to replace lead as a lubricant against valve recession.

 

Neat stuff. Interesting to note that most gasoline was unleaded until after WW2, when compression ratios started to go up to 8:1 and higher. The early cars ran unleaded gasoline, had 3.5 to 6.5 CR, and needed their valves ground every 40k miles or sooner. I'll also add that adding another head gasket to lower compression is the absolute worst way to do the job...not even a good band-aid. Any quench qualities are destroyed, and due to this, often pinging is actually increased. Dished pistons or bigger chambered heads are the right fix.

 

Once upon a time my original 1962 340/327 needed a new piston (detonation?). My mechanic suggested he replace the two shim steel gaskets with one per side. I agreed. It was not many miles later that each head gasket blew, at separate times. He then put TWO gaskets on both sides and the engine never had another problem for me or the next owner.

My current 340 (clone) uses run of the mill FelPro non shim steel gaskets going onto 20000 trouble free miles.