[giles]

I'll solve your "who designed the engine" argument for you. Chevrolet engineering ceased to exist on 1/1/85. The divisional engineering staffs were folded into 2 super groups; CPC (Chevy Pontiac Canada) and BOC (Buick Olds Cad). There were still very small divisional engineering staffs after this date but they supported motor sports and show cars, but did not design any production parts. Engine design and development was split off from CPC and BOC in 1990 to form "GM engine division" and it became "GM powertrain" a year later when Hydramatic was added. The LS series shares the bore center with the old small block and nothing else and was designed by "GM Powertrain". If it makes anyone feel any better GM Powertrain HQ and design work is performed on the site of what was PMD, in Pontiac, MI.

[Sirrotica]

Originally Posted by giles

I'll solve your "who designed the engine" argument for you. Chevrolet engineering ceased to exist on 1/1/85. The divisional engineering staffs were folded into 2 super groups; CPC (Chevy Pontiac Canada) and BOC (Buick Olds Cad). There were still very small divisional engineering staffs after this date but they supported motor sports and show cars, but did not design any production parts. Engine design and development was split off from CPC and BOC in 1990 to form "GM engine division" and it became "GM powertrain" a year later when Hydramatic was added. The LS series shares the bore center with the old small block and nothing else and was designed by "GM Powertrain". If it makes anyone feel any better GM Powertrain HQ and design work is performed on the site of what was PMD, in Pontiac, MI.

TY Giles, for clarifying who designed and who is responsible for the LS engine manufacturing, it is a true corporate V8. Chevy has no more input in it than any other of the GM divisions. I assume you have ties to GM and this is coming from an insider that knows the timeline and people that are responsible for one of the great pushrod V8s ever manufactured.

Any GM fan can take away that many of the good engineering points for all of the division engines were incorporated in to the LS design. That being said, none of the divisions had a hand in the final product.

[se428bandit]

I think regular gas was 91 octane back in '74.

[north]

Yup, regular leaded gas was 91-93 octane in the 60's and 70's. Unleaded (super unleaded came later) was lower at about 87, same as today. Super leaded was typically 98-100 with speciality brands like Sunoco 260 at 104.

I remember a trick in the 80's was to mix super unleaded and regular leaded (before it was discontinued). Even though both were 91 octane the blending of the lead with the better quality super unleaded resulted in higher overall octane.

[Sirrotica]

In 1974 regular leaded gas was 89 octane which would be the leaded fuel the factory would recommend, unleaded was 87 which would be the alternative unleaded fuel . This is using the Research Octane Number, R+M/2=RON.

A 74 GP has an maximum compression ratio of 8.0:1 with a 98 cc combustion chamber. It will run fine on most anything that comes out of a gas pump, providing the tune is correct.

Research Octane Number (RON)
The most common type of octane rating worldwide is the Research Octane Number (RON). RON is determined by running the fuel in a test engine with a variable compression ratio under controlled conditions, and comparing the results with those for mixtures of iso-octane and n-heptane.

Motor Octane Number (MON)
Another type of octane rating, called Motor Octane Number (MON), is determined at 900 rpm engine speed instead of the 600 rpm for RON.[1] MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern pump gasoline will be about 8 to 12 octane lower than the RON, but there is no direct link between RON and MON. Pump gasoline specifications typically require both a minimum RON and a minimum MON.

Since US fuels were previously rated by the Motor octane number the Motor number would be higher than the Research method.

This is how the 2 numbers are added together and divided by 2 to get an average number between the 2 methods. This is the current method used and is the number posted on gas pumps currently.

When comparing octane ratings it is important to find out what method was used to rate the fuels since there are 2 different rating methods, and the Motor method uses higher numbers than the Research method. The averaging method is currently the one used in the US.

87 octane RON rated, or regular unleaded is plenty sufficient for a stock 74 400 in good tune.