Why does my Loyale run poorly on 93 octane?

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*.

Reply to
Decimal Cat
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"Decimal Cat" wrote in news: snipped-for-privacy@giganews.com:

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Reply to
Fuzzy Logic

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

Reply to
Rick Courtright

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. .

Reply to
Decimal Cat

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.

Reply to
Decimal Cat

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.

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)

Reply to
JaySee
[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

Reply to
Walt Kienzle

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

Reply to
Rick Courtright

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

Reply to
oothlagre

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

Reply to
name

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

Reply to
T

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