better mileage with higher octane?

51_racing wrote:

> Eeyore wrote:
>
> > It pretty much invariably improves performance.
> >
> > Graham
>
> Absolutely could not be more WRONG here.
> I race(d) in a class that limited compression to 9.5:1.
> We could run any fuel we wanted, and time after time, people would put
> race gas (Sunoco 110 or Turbo 110) then have to crank their ignition
> timing way up only to come close to getting the same performance that
> they did using 92 octane pump gas.

That's hardly typical though. I thought we were talking about road cars ? Also
modern cars don't have manual timing adjustment., the ECU does it.

Graham

Eeyore wrote:
> 51_racing wrote:
>
> > Eeyore wrote:
> >
> > > It pretty much invariably improves performance.
> > >
> > > Graham
> >
> > Absolutely could not be more WRONG here.
> > I race(d) in a class that limited compression to 9.5:1.
> > We could run any fuel we wanted, and time after time, people would put
> > race gas (Sunoco 110 or Turbo 110) then have to crank their ignition
> > timing way up only to come close to getting the same performance that
> > they did using 92 octane pump gas.
>
> That's hardly typical though. I thought we were talking about road cars ? Also
> modern cars don't have manual timing adjustment., the ECU does it.

His point was that if the engine was optimized for lower octane fuel
then you have to resort to work arounds like bumping the timing way up
with little if any bennefit. There are no absolutes but it has been my
experience that the higher octane fuel has a slower flame speed for a
given temperture/pressure. Increasing the compression ratio will
increase the temp/pressure. Without the compression increase you
resort to advancing the timing to get the temp/pressure back up where
you need it. But that works against you because the engine has to
overcome the rise in cylinder pressure before the piston gets to TDC.
So even if the ECU advances the timing to take advantage of higher
octane you get little if anything extra for your money. If you have a
turbo you can crank the boost up and make more power, but that's not
the same thing as mileage, which is what this thread is about.

Bruce

if it help anyone at all my camaro on regular gets 24-25 mpg and pings
and what not and on higher octane gas it gets 30-32 and never pings and
seems to run better but thats just my car my dads built 350 in his s10
gets 14 mpg on regular and 15 on higher octane but it doesnt seem to
run better so i guess it just depends on your vehicle.


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rscamaroboy89 wrote:

> if it help anyone at all my camaro on regular gets 24-25 mpg and pings
> and what not and on higher octane gas it gets 30-32 and never pings and
> seems to run better but thats just my car my dads built 350 in his s10
> gets 14 mpg on regular and 15 on higher octane but it doesnt seem to
> run better so i guess it just depends on your vehicle.

Makes perfect sense. If you have a Camaro that gets that kind of
mileage, its obviously an LS-1 or LT-1 with full digital engine
management and knock sensors, plus a pretty high static compression. The
engine managment system is having to pull back the timing to let the
engine survive on regular octane gas, but can use its optimal settings
on premium. An old carbureted HEI ignition 350 can't tell the
difference in fuels because it doesn't have knock sensors and digital
engine management. You could *manually* set the timing up to use
premium, but then you couldn't run regular at all without risking damage.

Bruce Richmond > wrote in article
.com>...
>
>
> Some how I just can't see a circle track racer saying. "We can get
> along fine with less power."

I had one tell me exactly that at Oxford Plains Speedway a few years back.

He was running a NASCAR Busch North Series car and he said, "Man, I wish we
could put my little Pro-Stock engine in. This track is so hard to hook up
to."

The more circular and the flatter the track is, the less power and the more
chassis - "handling" - is needed.

Too much power breaks the rear wheels loose all the time, and the car
certainly does not "handle" well.



Even if some were to take that aproach in
> the interest of reliability, I am sure some would have opted for dual
> quads if they were allowed. There's no question they were a factory
> item. And there is still the matter of the Fords being allowed to run
> dual quads which were not stock.
>
>