87,89,93

In looking to fill up wife's new Ford Focus,
we used the premium 93 stuff.... but then did some web surfing.
It appeaes that the octane rating does not improve mpg,
but is merely aimed at timing and engine knock.

I could swear I got better mpg in our 2001 Jeep GC with 93 or 89..
but maybe just an illusion or wishful thinking.
Ok... I am going to only use 87 in our son's car, and see how things go.

---- he said ----
Most engines have a knock sensor and spark retard.

More spark retard means more compression and more power.
If the car senses a knock then it will back off the spark retard.

So in theory, they all provide the same power at the same compression.
Really only matters in tubo/supercharged cars or with really high
compression piston (like my Ninja sportbike)

ps56k wrote:
> In looking to fill up wife's new Ford Focus,
> we used the premium 93 stuff.... but then did some web surfing.
> It appeaes that the octane rating does not improve mpg,
> but is merely aimed at timing and engine knock.
>
> I could swear I got better mpg in our 2001 Jeep GC with 93 or 89..
> but maybe just an illusion or wishful thinking.
> Ok... I am going to only use 87 in our son's car, and see how things
> go.
> ---- he said ----
> Most engines have a knock sensor and spark retard.
>
> More spark retard means more compression and more power.
> If the car senses a knock then it will back off the spark retard.
>
> So in theory, they all provide the same power at the same compression.
> Really only matters in tubo/supercharged cars or with really high
> compression piston (like my Ninja sportbike)

Best to use what the manual says to use.

Higher Octane simply means the fuel is less likely to
self-ignite under pressure and temperature.

I run a supercharger in the ZJ and it needs 92 (10% ethanol)
or 93 pure gas to avoid pinging under full throttle.
Ethanol is actually a very good knock preventer.

--
-- DougW -- 93 ZJ 4.0 http://revbeergoggles.com
HESCO Supercharger - 300W Stereo PPI/Audio Control - Bilstein HD Shocks
Flowmaster Exhaust - rear DCpower - custom gauge install - Brembo Rotors
Banks Header - and BEER, in the fridge! Who says old=slow.