Re: Which fuel is recommended?

Posted by Rusty O\'Toole On 2008/7/23 17:35:50

Not a silly question at all.

Leaded gas was first made in the late 1920s. Octane levels and lead levels remained low for many years. In the 1930s most cars used gas from 50 to 65 octane, special high compression engines use gas of 75 octane.

Until the early 1950s low lead gas of 60 to 75 octane was the rule. Cars had hardened valve seats and were made to run on low lead, low octane gas.

With the advent of the new high compression, overhead valve V8's compression ratios and lead requirements rose rapidly. Octane levels in the 80s for regular, and in the 90s for high octane were the rule.

Fuels of up to 103 octane were sold in the 50s and 60s for special high performance models.

The rule is, the octane should look like the compression ratio.

Older flathead models of 6:1 to 7:1 compression, require gas of 60 or 70 octane.

High compression engines of up to 9.5:1 require 95 octane. Compression ratios of 10:1 require 100 octane.

Naturally this is not an exact law. But the octane should be similar to the compression ratio.

Unleaded gas, or low lead gas is fine for engines before 1954 and after 1970. Those made from 1954 to 1970 may benefit from an additive like Redex or Bardahl in the gas to protect the valves.*

95 or 98 octane is plenty high enough for all production engines.

Here in Cobourg Ontario Canada today gas is $1.29 for one litre of 87 octane regular. 91 octane is $1.39

$1.29 = $4.88 a gallon. $1.39= $5.25

Latest news flash, today July 24 gas dropped to $1.21 reg, $1.29 hi test

*Note, this refers to American cars. The heavily leaded high octane gas came in around 1954. The first car I know of that had NO exhaust valve seat inserts or valve guides, was the Chev V8 introduced in late 1954 as a 1955 model.

Unleaded gas became available in 1970 for 1971 models, the first cars with catalytic converters.

All American cars from 1971 model year up, are built to run on unleaded gas.

I know in Europe the heavily leaded high octane gas did not become available until later, and unleaded gas did not come in until the 80s. So for European models you will have to consult the maker to find out what type gas is suitable for your car.