Why is it advised to keep cr at 9.5:1 max, when using iron heads in a performance build? These engines had above 10:1 cr back then, with the same iron heads.
I don't get it?

 

Without getting into details the most simple answer is, gas that was used back than had a higher octane rating.

 

Seriously, that's it? :-)
I know alot about this, no need to go into detail on that subject. I was just curious :-)

 

The highest normally-obtainable pump octane back in the sixties was equivalent to a pump marking of about 98 today.

See any Sunoco stations selling 98-octane 260 lately?

- Eric

 

Yes, that's it. Back in the 1960s it was easy and inexpensive to increase octane in gasoline by adding lead. That's not an option today. Aluminum heads have better heat transfer than cast iron, which is why you can typically run a little more CR with aluminum. If you want to pay for racing gas, feel free to run higher CR with iron heads.

 

I don't think they had it very long but I remember Esso (now Exxon) had some super high octane gas that I think they called Esso Golden Extra or something like that and it was north of 100 octane (103 I think). Here is a link. Too bad it does not show the price. ON second thought maybe that is a good thing.

http://www.bing.com/videos/search?q=...B1A395A5A8E986

 

Remember these?



I used to run Sunoco 260 in my 442s. The advertised octane rating was about 98.

 

The other thing that happened in the early 1970s was that the feds required all gas stations to start selling unleaded gas. Most stations took out the premium pumps and replaced them with unleaded pumps. The trick at the time was to run about 3/4 tank unleaded (preferably unleaded premium if you could get it) and 1/4 tank leaded premium. The unleaded premium was more refined than the leaded to get the same octane rating, and the added lead from the 1/4 tank boosted the combined octane rating higher than either of the fuels alone. That was the theory published in the magazines of the time, anyway.

 

I thought I remember Sunoco 260 and Crown marked at 104. That is what we filled the late model with. When we added a handful of mothballs the exhaust blew out a very pretty blue flame the length of the straight!

 

I remember those days Joe except I thought it was a 50/50 mix.

 

The lead additive was tetraethyl lead, which is a liquid.


It was used as a cheap octane booster and a valve seat lubricant.


Gas back in the day looked and smelled much differently than the gas you buy today.


I used to buy Sunoco 260 for my 1971 Charger R/T, and it was 104 octane.

 

Still is. You can buy it from several sources under the name Octane Supreme.


Which is 2 points higher than I recalled, so revise my earlier statement up to say that a modern pump would have to be labelled 99 or 100 to give the same octane as that old Sunoco 260 (and the highest I see routinely these days is 93).

- Eric

 

The upside of getting lead out of gasoline is spark plugs last much longer now. It used to be after 12,000 miles or so the ceramic insulator was coated in a lead based deposit that would make plugs misfire.
Platinum tipped plugs came on the market here when leaded gas was still what most cars used. They were good for maybe 1000 miles before they packed up, maybe a hundred mile on old points ignition engines with a worn carburettor.

Roger.

 

Keep in mind that there are two different octane rating scales, Research and Motor. Today, advertised octane is the average of the two (R+M/2). Earlier advertised octane levels may have been one or the other. Kinda like comparing gross and net HP ratings.

Not to mention the whole improvement to global health thing...

 

Exactly. In the sixties, the oil companies used the Research octane number, which, in the range of production gasoline, runs about 4-5 points higher than the AKI number that Federal regulations require that we use in the US now.

In Europe, they still use the Research number, so European gasoline appears to be higher octane than ours is, but it's not. Their pump may say "97," but the gas that comes out is the same as our 92.
Engines have been destroyed because of misunderstandings arising from this difference in numbering systems.

- Eric

 

In Europe low octane is called 92, average octane is called 95 and high octane is called 98/99.
All gasoline powered cars are designed to run 95 and it is said that the tanks for the 92 pumps also has 95 in them. Shell offers their Vpower fuel rated at 99 octane.

 

In the US, pump octane is labelled from 87 to 93 or 94 AKI (depending on location), which is exactly 5 units lower than the European range of 92 to 99 RON, so that fits together nicely.

- Eric

 

Yup. Back in the days, high octane was rated at 98 here.
What was it rated at over there? 93? That must have been premium, right?

 

93 or 94 is Premium in the US now.

In the 1960s, Premium was about 100 and Super Premium was 102 to 104.

- Eric

 

Only two grades of gas are offered in every UK gas station I've come across since leaded fuel was withdrawn from sale. Known as unleaded and super unleaded, next time I get gas I'll check what octane rating is claimed.

Roger.

 

102-104! phew! that's like jet-fuel :-)
What numbers would that translate to in todays ratings?
rustyroger: they dont sell Vpower at the Shell stations over there?
I am beginning to think they only have that in the scandinavian countries plus germany :-) That's weird though...

 

They sell it in the US - it's usually rated at 93 octane [equivalent to about 98 in Europe] (though I have also seen 92 [equivalent to about 97 in Europe]).

- Eric

 

Technically, that's like Av Gas, not Jet Fuel. JP-1, I think it's called, is for turbines and is akin to kerosene. Av Gas is for reciprocating engines like ours, in planes.

The interesting thing is that new cars run high compression. My 4 banger Tacoma sports a spiffy 10.5 to 1, and that's done with variable valve timing and computerized spark timing to not knock on low octane.

The low comp thing is to be able to run 87. An original motor, to my knowledge, will do just fine on some premium with a lead additive. If one rebuilds their engine, I believe that, if you harden the valve seats, drop the compression, and put a roller cam in, you can run modern gas, no lead additive, and modern oil no issue. I think I'll keep the original cams in my old ones and run Valvoline VR1 or a ZDDP additive. Not sure what I'll do for compression.

 

Beat me to it.

Jet fuel is super-refined kerosene with special additives, not too different from diesel fuel. And JP-1 is long gone. JP-4 is common. JP-8 is what modern fighters use. JP-10 is for cruise missiles. And then there's JP-7, which is the special high-temp jet fuel used by the SR-71.

 

V power is sold at Shell gas stations, petrol (as we call gas over here ) and diesel fuel are both available as V power. I used to drive a Mercedes diesel van, my boss insisted I only put V power in it. I could detect no discernable difference to supermarket fuel in either mileage or performance.
I think V power is Shell's version of super unleaded.

Roger.