Which Octane Should I Use?

On Sat, 31 Jul 2010 17:18:13 +0200, John Stafford >
wrote:

> In article
> >,
> Jim Ed > wrote:
>
>> > Anything above 87-RON, the 73 will run both leaded and unleaded.
>>
>> Does 87-RON = 83 octane U.S.A. pump gas?
>>
>> > Even the pre -67 cars can run unleaded these days as the lead has
>> been > replaced with calcium(Sp?).
>> >
>>
>> Is this lead substitute, calcium(Sp?), used in U.S.A. gas or is it
>> used only in Norway?
>
> In part of the USA where there is a winter, it is difficult to know what
> kind of gas we are getting because it changes seasonally. Gas would be
> less expensive to distribute and manufacture if they would stick to one
> formula.

The Calcium content would still be there though, as it is a lead
replacement to lubricate the valve seats and guides.

J.
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I used to run high-octane in my tired old 1500, trying to get as much
oomph out of it as I could to get up the occasional hill.
After putting in a factory fresh zero-mile 1600 I eventually
downgraded mid-grade then to lowest octane. Didn't seem to notice much
diff in performance so stopped spending the extra bucks.

On Jul 28, 4:35*pm, Jim Ed > wrote:
> I have a stock 1973 Beetle with 1600cc Type I engine.
>
> Which octane, U.S., should I use?
> TIA!

griff wrote:
> I used to run high-octane in my tired old 1500, trying to get as much
> oomph out of it as I could to get up the occasional hill.
> After putting in a factory fresh zero-mile 1600 I eventually
> downgraded mid-grade then to lowest octane. Didn't seem to notice much
> diff in performance so stopped spending the extra bucks.
>
> On Jul 28, 4:35 pm, Jim Ed > wrote:
>> I have a stock 1973 Beetle with 1600cc Type I engine.
>>
>> Which octane, U.S., should I use?
>> TIA!
>


Higher octane fuel does not give you any more power. If anything, it
burns slower and doesn't ignite as easily.

The good thing about high octane fuel is, you can compress it more than
low octane, and get more power THAT way. But if you do not compress it
any more mechanically, then you don't get any more power. The only way
to get more power out of it is by raising the compression ratio or
dynamic (actual) compression, or by installing a turbocharger or
supercharger to pre-compress the mixture outside of the cylinder, so to
speak.

Modern cars have knock sensors in them, which retard the ignition
advance when knocking or pinging is detected. With higher octane fuel,
there is less pinging or knocking, and thereby less retarding... which
results in more power, because the computer doesn't hold the advance
back. Some engines show a "noticeable" power increase, while some don't
seem to run any different.

But our old carburated non-computerized engines don't know what goes on
around them and they don't make any more or less power on different
octane fuels, unless you mechanically modify the engines to utilize the
potential of higher octane. Then you can't go back to low octane
anymore. Unless...... you lived near sea level and decided to move
somewhere up in the mountains, like 5000 ft above sea level
The less dense air at high elevations reduces actual compression
pressure, so you can run lower octane OR higher compression.