Classic Mustangs List Archive

This read-only message was archived from a public mail list.
Mail From: Rick Pargeter (email redacted)


I was reading the re-printed owners manual that I just received, and
looking at the fuel requirements, the manual stats that the 351C-2v needs a
"regular fuel - 91 octane or above". Well, you're lucky to 91 in the
supreme grade today.

Has the way octane is rated changed from the 70's? Seems I remember a
change back in '80 or so.

What does 91 octane in 1972 equate to today?

TIA

Rick
72 Mach1


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This read-only message was archived from a public mail list.
Mail From: mr fomoco (email redacted)

Rick Pargeter wrote:
>
> I was reading the re-printed owners manual that I just received, and
> looking at the fuel requirements, the manual stats that the 351C-2v needs a
> "regular fuel - 91 octane or above". Well, you're lucky to 91 in the
> supreme grade today.
>
> Has the way octane is rated changed from the 70's? Seems I remember a
> change back in '80 or so.

I believe through the early 1970s, Ford measured octane
via something called the "research method". Basically,
this measures the gasoline’s ability to resist knock at
low speed - meaning city type driving.

Nowadays (and, I think, by the mid-70s) manufacturers
switched to what's called the "(R+M)/2 Method". (You
have probably seen it on the gas pump, right?) This
formula expresses a simple arithmetic mean using two
uniquely-derived measurements.

"R" is the aforementioned "Research Octane Number" and
the "M" is a "Method Octane Number". The latter figure
measures a fuel's ability to resist knock under severe
conditions...like high speed or towing heavy load, etc.

Obviously their mean produces a more realistic measure
than either, alone. (R+M)/2 results will always to be
lower than the "R" numbers used when your car was new.
--
MrF
Allen Cross
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This read-only message was archived from a public mail list.
Mail From: Paul Prince (email redacted)

There is a good article at
mustangworks.com/articles/faqs-n-tech/gasfaq.shtml

that discusses gasoline and goes into some good stuff about octane ratings.
BTW, the M in (R+M)/2 is 'motor'
Paul Prince
1965 Mustang 2+2
1989 Mustang GT Convertible
-----Original Message-----
From: mr fomoco <(email redacted)>
To: (email redacted) <(email redacted)>
Date: Tuesday, July 21, 1998 2:36 AM
Subject: Re: [CM:12498] Octane ratings - then and now


>Rick Pargeter wrote:
>>
>> I was reading the re-printed owners manual that I just received, and
>> looking at the fuel requirements, the manual stats that the 351C-2v needs
a
>> "regular fuel - 91 octane or above". Well, you're lucky to 91 in the
>> supreme grade today.
>>
>> Has the way octane is rated changed from the 70's? Seems I remember a
>> change back in '80 or so.
>
>I believe through the early 1970s, Ford measured octane
>via something called the "research method". Basically,
>this measures the gasoline’s ability to resist knock at
>low speed - meaning city type driving.
>
>Nowadays (and, I think, by the mid-70s) manufacturers
>switched to what's called the "(R+M)/2 Method". (You
>have probably seen it on the gas pump, right?) This
>formula expresses a simple arithmetic mean using two
>uniquely-derived measurements.
>
>"R" is the aforementioned "Research Octane Number" and
>the "M" is a "Method Octane Number". The latter figure
>measures a fuel's ability to resist knock under severe
>conditions...like high speed or towing heavy load, etc.
>
>Obviously their mean produces a more realistic measure
>than either, alone. (R+M)/2 results will always to be
>lower than the "R" numbers used when your car was new.
>--
>MrF
>Allen Cross
>------------------------------------------------------------------------
> The best Mustang decoder money can buy, $29.95 !
> voicenet.com/~fomoco
>Your online source for 1960-1973 Ford & L-M info
>
>------------------------------------------------------------------------
>All the list info you'll ever want: antler.moose.to/~server/cm
>


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This read-only message was archived from a public mail list.
Mail From: Mr Fomoco (email redacted)

Paul Prince wrote:
>
> There is a good article at
> mustangworks.com/articles/faqs-n-tech/gasfaq.shtml
>
> that discusses gasoline and goes into some good stuff about octane ratings.
> BTW, the M in (R+M)/2 is 'motor'

> -----Original Message-----
> From: mr fomoco <(email redacted)>
> To: (email redacted) <(email redacted)>
> Date: Tuesday, July 21, 1998 2:36 AM
> Subject: Re: [CM:12498] Octane ratings - then and now

Oops - my slip!

By the way, Paul, please note the time of my post (above).
You try typing "motor method" several times at 2:36 AM. ;-)
--
MrF
Allen Cross
------------------------------------------------------------------------
The best Mustang decoder money can buy, $29.95 !
voicenet.com/~fomoco
Your online source for 1960-1973 Ford & L-M info

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This read-only message was archived from a public mail list.
Mail From: Paul Prince (email redacted)

Are you kidding? I need my beauty sleep. No way I would be up that late.
Paul Prince
1965 Mustang 2+2
1989 Mustang GT Convertible

-----Original Message-----
From: Mr Fomoco <(email redacted)>
To: (email redacted) <(email redacted)>
Date: Tuesday, July 21, 1998 10:43 PM
Subject: Re: [CM:12512] Octane ratings - then and now


>Paul Prince wrote:
>>
>> There is a good article at
>> mustangworks.com/articles/faqs-n-tech/gasfaq.shtml
>>
>> that discusses gasoline and goes into some good stuff about octane
ratings.
>> BTW, the M in (R+M)/2 is 'motor'
>
>> -----Original Message-----
>> From: mr fomoco <(email redacted)>
>> To: (email redacted) <(email redacted)>
>> Date: Tuesday, July 21, 1998 2:36 AM
>> Subject: Re: [CM:12498] Octane ratings - then and now
>
>Oops - my slip!
>
>By the way, Paul, please note the time of my post (above).
>You try typing "motor method" several times at 2:36 AM. ;-)
>--
>MrF
>Allen Cross
>------------------------------------------------------------------------
> The best Mustang decoder money can buy, $29.95 !
> voicenet.com/~fomoco
>Your online source for 1960-1973 Ford & L-M info
>
>------------------------------------------------------------------------
>All the list info you'll ever want: antler.moose.to/~server/cm
>


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