Why does my Loyale run poorly on 93 octane?

[Decimal Cat]

Hey folks,

This one sure has me scratching my head. Every now and then I've decided
to try running my 91 Loyale wagon (Fuel injected, SPFI, EA82) on 93 octane
gas as opposed to the 87, and there's a noticeable loss in power with 93.
Not too much (my butt dyno estimates about 5-10 HP), but it's there.

I'd have expected it to be no different or a little better, but after I
got a faulty O2 sensor replaced in the y-pipe a while ago, last night I
decided to see if there was any change. . nope. . car is still sluggish
(well more than usual) on 93.

Any thoughts? The manual for the car says to use 87 octane *or higher*.

 

[Fuzzy Logic]

Hey folks,

This one sure has me scratching my head. Every now and then I've
decided
to try running my 91 Loyale wagon (Fuel injected, SPFI, EA82) on 93
octane gas as opposed to the 87, and there's a noticeable loss in power
with 93. Not too much (my butt dyno estimates about 5-10 HP), but it's
there.

I'd have expected it to be no different or a little better, but
after I
got a faulty O2 sensor replaced in the y-pipe a while ago, last night I
decided to see if there was any change. . nope. . car is still sluggish
(well more than usual) on 93.

Any thoughts? The manual for the car says to use 87 octane *or
higher*.

http://www.canadiandriver.com/articles/pb/premium.htm

 

[Rick Courtright]

This one sure has me scratching my head. Every now and then I've decided
to try running my 91 Loyale wagon (Fuel injected, SPFI, EA82) on 93 octane

Hi,

IF (and that's a big word here) there's going to be any benefit to going
with a higher octane gas, you'll probably have to drive the car for a
while so the ECU can figure what you're doing. I've gone the "higher
octane cuz it's pinging" route in my '90 version of your car (mine's
4wd, 5 spd--yours?), and the best I've ever done on fuel economy was to
break even, and that took a month to do (about 3000 miles.) It did so
little WRT to the pinging I couldn't justify it there, either.
Concerning power loss, I didn't really notice it, but my "butt-dyno"
says a loss of 10 hp from the 90 hp engine in my Loyale wagon would
almost result in me sitting at the stop light unable to get going again!

As the article referenced by another poster puts it, don't waste your
money.

Rick

 

[Decimal Cat]

http://www.canadiandriver.com/articles/pb/premium.htm

Good article and all true from what I've seen, but I'd like to see a bit
more in-depth technical explanation as to why some cars just don't need it.
..

 

[Decimal Cat]

octane

Hi,

IF (and that's a big word here) there's going to be any benefit to going
with a higher octane gas, you'll probably have to drive the car for a
while so the ECU can figure what you're doing. I've gone the "higher
octane cuz it's pinging" route in my '90 version of your car (mine's
4wd, 5 spd--yours?), and the best I've ever done on fuel economy was to
break even, and that took a month to do (about 3000 miles.) It did so
little WRT to the pinging I couldn't justify it there, either.
Concerning power loss, I didn't really notice it, but my "butt-dyno"
says a loss of 10 hp from the 90 hp engine in my Loyale wagon would
almost result in me sitting at the stop light unable to get going again!

As the article referenced by another poster puts it, don't waste your
money.

Rick

Thanks for the response Rick. My dad (used to be a professional auto
mechanic in the pre-computerized-cars days) made an interesting suggestion
regarding this which was that a small engine such as the one in my car
doesn't need high-test because 93 octane actually burns more slowly than 87.
87 goes off like TNT, he says. That sounds reasonable. (Anyone well-versed
in chemistry feel free to jump in and expand upon or contradict this. )

As for my car, it's a 4wd 3AT (that AT is going on the scrap heap and being
replaced by the Subaru 5MT for that car if/when I can afford it - even for
an automatic it's pretty bad) wagon.

As for breaking even on the fuel mileage, I get about 24-28 MPG depending on
the average speed and type of driving. At ~55 MPH I get around 28 MPG, but
at 75 MPH it drops down to about 24. ( I can live with that, so yeah. ) I've
done mileage tests with high-octane before and found it's not any better
even in the mileage, partially, I think because you're more tempted to press
that gas pedal harder to make up for the loss of power. Every time I've gone
from the 93 back to the 87 it's been a relief.

In that same vein, though, is there any truth to those commercials for Shell
gasoline claiming that their gas gives your car better mileage? I tried the
Shell 93 once, but that wasn't any better than the other stuff.

Thanks again.

 

[JaySee]

Thanks for the response Rick. My dad (used to be a professional auto
mechanic in the pre-computerized-cars days) made an interesting suggestion
regarding this which was that a small engine such as the one in my car
doesn't need high-test because 93 octane actually burns more slowly than 87.
87 goes off like TNT, he says. That sounds reasonable. (Anyone well-versed
in chemistry feel free to jump in and expand upon or contradict this. )

This and ONLY THIS is why you need higher octane for high compression
engines. Octane is the amount of OCTANE vs HEPTANE IIRC. Octane is
slow burning stable fuel while heptane explodes. Fuel is supposed to
burn, not explode. Under high compression, heptane becomes even more
likely to explode, thus you need higher Octane percentage. Those
explosions are called KNOCKING and PINGING.

As for my car, it's a 4wd 3AT (that AT is going on the scrap heap and being
replaced by the Subaru 5MT for that car if/when I can afford it - even for
an automatic it's pretty bad) wagon.

As for breaking even on the fuel mileage, I get about 24-28 MPG depending on
the average speed and type of driving. At ~55 MPH I get around 28 MPG, but
at 75 MPH it drops down to about 24. ( I can live with that, so yeah. ) I've
done mileage tests with high-octane before and found it's not any better
even in the mileage, partially, I think because you're more tempted to press
that gas pedal harder to make up for the loss of power. Every time I've gone
from the 93 back to the 87 it's been a relief.

In that same vein, though, is there any truth to those commercials for Shell
gasoline claiming that their gas gives your car better mileage? I tried the
Shell 93 once, but that wasn't any better than the other stuff.

Haven't seen those commercials. I have seen TV shows claiming all gas
at all pumps is the same. My mileage says otherwise. Here in US,
California I only buy 76 or Chevron because they give me the best
mileage. Mobile and ARCO give me bad mileage. I haven't tried Shell,
Texaco or Exxon (which I would guess is the same as Chevron)

 

[Walt Kienzle]

[snip]
There is, but only slightly. It doesn't necessarily apply to most cars, and
IMHO boarders on false advertising. I haven't seen that from Shell, but in
my area Amoco (before they became BP) and Mobil had commercials like this.
Their claim for better gas mileage centers around the premium detergent
ingredients that they use. The detergents will clean dirty fuel injectors
and clean fuel injectors give better gas mileage (and performance) than
dirty injectors. This assumes that :
- everyone that is listening to the commercial has a car with dirty fuel
injectors.
- other brands of gasoline don't contain detergents that are as effective
- additives for fuel injector cleaning are not effective or are not used
Any one of these is a long shot in my opinion. Even if you have been
using gasoline with a less effective detergent formulation and your
injectors are dirty, you need about 3 tankfulls of "the good stuff", before
the fuel injectors are sufficiently cleaned. In my opinion, an occasional
dose of fuel injector cleaner is a better solution.

Walt Kienzle

 

[Rick Courtright]

California I only buy 76 or Chevron because they give me the best
mileage. Mobile and ARCO give me bad mileage. I haven't tried Shell,

Hi,

Another California driver here... and, yes, I've noticed significant
differences between brands. Not so much with overall mileage, but more
with the power/pinging thing (my Loyale's got 354k miles, the engine's
never been opened up, so I'm sure there's plenty of carbon in there!)

76 does the best for me, but is the most expensive in my area and we
don't have many stations, so I usually use something else. Chevron,
though highly rated, is all over the chart--one tank will be great, the
next one runs like it was drained from some Third World tank (oddly, it
seems to be dealer dependent.) Shell is neither here nor there. Arco
does as well as the others mileage wise, but I can't run it past about
80 deg F without serious pinging on the hills (I'm at the edge of the
mountains), even jumping a grade or two.

So there is a difference in my experience, at least with our CA
"boutique" gas. Going across the border and buying gas in AZ (probably
more a 49 state blend) makes the car run much better! Guess that's part
of where they get "YMMV!"

Rick

 

[oothlagre]

That makes sense that it would burn slower. My buddy has a Chevy Lumina that
has to have higher octane fuel, the reason is his engine has a 10:1
compression ratio whereas a lot of cars have an 8:1. Well, with the lower
octane gas, the fuel is burning too rapidly causing an explosion, which is
where the pinging noise comes from. Burning the fuel at a slower speed keeps
it from "detonating" and allows smoother operation of the engine. The engine
pinging I am told can wear on the piston heads over time.

Henry

 

[name]

[snip]

Shell

the

There is, but only slightly. It doesn't necessarily apply to most cars, and
IMHO boarders on false advertising. I haven't seen that from Shell, but in
my area Amoco (before they became BP) and Mobil had commercials like this.
Their claim for better gas mileage centers around the premium detergent
ingredients that they use. The detergents will clean dirty fuel injectors
and clean fuel injectors give better gas mileage (and performance) than

There's also some kind of friction modifier gas additive out there.

 

[T]

It's already been answered mostly;

Hi compression motors (10:1) need a slower burning gas. The flames
front propagates slower across the cylinder volume due to the
additives they blend in to make it higher Octane.

Low compression motors (8:1) can get by on something more likely to
burst into flame.

They are the opposite of diesel engines which make use of the really
highly compressed fuel that it detonates with an additional charge of
air being introduced at the right moment in the cycle.

If your gas motor is getting preignition then the force of the
explosion is fighting against the upstroking piston, hence loss of
power and potential (inevitable) damage.

They way to make use of the high octane is to turn your distributer
forward a bit, so as to advancing the timing. This will also serve to
move away from suitability for lower octane fuel.

Really, if you are getting pinging it'll pay to fix the problem vs
buying higher octane fuel to solve the symptom.

Investigate seafoam, B12 Chemtool and other detergents/solvents like
Techrolene, MMO, naphtha, etc.

Conventional wisdom is high test in low compression motors does
nothing much worth the extra expense.


TBerk