MPGs run, Aspire SE

[rmoltis]

Hey tom I don't know about you.

But I've always gotten better gas mileage with premium fuel.

One time in my current aspire when it was completely stock and I had it for a few months.

My avg mpgs were 34mpg.
Consistant.

Then I decided to try one tank of mid grade fuel.
My mpgs went down to 28mpgs.

After seeing the results i never tried 89 octane.
I just went back to premium. And back to my 34 mpgs.

Have you ever experimented with premium fuel for mpgs?

[mikeyjd]

OK, understood. Anyone doing MPG runs with just the first pump shutoff would get very inconsistent results; I can always add another 1/2 gallon or more after the first shutoff.

I just get annoyed that people are still criticizing my methodology, without reading my earlier threads to see what I am doing, and criticizing from the comfort of their computer chair, without doing any testing themselves. Every run is a couple or three hours of time, or more in some cases, when I could be doing other things, and I've made a lot of runs. Not to mention the expenses of gas, cam, cam gear, FPR, header, etc. At this point I easily have over $1K in testing, including gas and parts. Luckily I have the time and inclination.

Word

[TominMO]

Hey tom I don't know about you.

But I've always gotten better gas mileage with premium fuel.

One time in my current aspire when it was completely stock and I had it for a few months.

My avg mpgs were 34mpg.
Consistant.

Then I decided to try one tank of mid grade fuel.
My mpgs went down to 28mpgs.

After seeing the results i never tried 89 octane.
I just went back to premium. And back to my 34 mpgs.

Have you ever experimented with premium fuel for mpgs?

As I understand it, the only advantage premium fuel gives you is permitting more advanced ignition timing. This will increase HP, and therefore may give you better gas mileage at a given speed, because it takes slightly less gas to maintain that speed. But if you don't advance the timing, putting premium in the tank does nothing but cost more.

[rmoltis]

So the fuel by my house is $3.53 for unleaded.
And $3.83 for premium.

And for a 10 gal fill up it is a $3 difference.

$3 isn't that much more to pay for premium.

Even if it gained me 6mpgs the time I was referring to in washingon

For a 10 gal tank of premium its $38.3

And if hypothetically it netted you 340 miles on 10 gals.

And unleaded netted you 28mpgs per 10 gals.

And you divided the 340 miles on premium by 28 mpgs.

It would cost you 12.14 gals of unleaded which would cost you $42.86 worth of unleaded.

As opposed to 38.3 for premium.

Theoretically it would cost more for unleaded.

Now this is only my experience based on past results

And by no means am I a gas mileage conniseur.

I just drive my car normally and keep track of mileage for reference of mechanical/maintenance stability.

I just feel like some factors may not have been accounted for?

Just wondingering if you've ever tried a full tank of premium to compare your mileage results with?

I mean if I got 34mpgs with premium and 28mpgs with mid grade as a normal day to day driver.

You as as a gas mileage officianado May gain substantially more.

I'm just curious.

I just like to provoke thoughts.

[mikeyjd]

So the fuel by my house is $3.53 for unleaded.
And $3.83 for premium.

And for a 10 gal fill up it is a $3 difference.

$3 isn't that much more to pay for premium.

Even if it gained me 6mpgs the time I was referring to in washingon

For a 10 gal tank of premium its $38.3

And if hypothetically it netted you 340 miles on 10 gals.

And unleaded netted you 28mpgs per 10 gals.

And you divided the 340 miles on premium by 28 mpgs.

It would cost you 12.14 gals of unleaded which would cost you $42.86 worth of unleaded.

As opposed to 38.3 for premium.

Theoretically it would cost more for unleaded.

Now this is only my experience based on past results

And by no means am I a gas mileage conniseur.

I just drive my car normally and keep track of mileage for reference of mechanical/maintenance stability.

I just feel like some factors may not have been accounted for?

Just wondingering if you've ever tried a full tank of premium to compare your mileage results with?

I mean if I got 34mpgs with premium and 28mpgs with mid grade as a normal day to day driver.

You as as a gas mileage officianado May gain substantially more.

I'm just curious.

I just like to provoke thoughts.

As Tom already pointed out ,you won't benefit from higher octane without adding timing, if the engine was originally designed to run on 87 octane fuel. Any increase in fuel economy from using the 91 octane without adding timing would have to do with a myriad of other contributing factors, but it wasn't the increase in octane. Based on several studies done (I can find them if you're interested), most report worse fuel economy when using higher octane fuel with stock timing.

[rmoltis]

I understand theory.

But I never did anything special or different when this occured.

Also with the 08 corolla.
When my fiances corolla used to run on unleaded it got 35 mpgs.
Now that it uses premium it gets 40mpgs.

No change In driving style.
Just a difference if mpgs.

Theory and application are 2 different things.

Have you guys ever compared the 2 different octanes In real life
Rather than relying on other studies???

[sketchman]

When I had my Neon I tested it with premium. I wasn't doing it very scientifically, so I just noticed my monthly gas $$ output went down. Then I read up on it and decided it was all in my head. Time to try again, I guess.

Doesn't higher octane slow down the burn as well as making the unburned mix more det resistant? That could help explain things possibly. Maybe at low RPMs the slow piston speed and worse cylinder filling works better with a slower more det resistant burn?

[jason_]

I've read numerous articles higher compression burns faster, and makes higher nitrogen oxides (double check me on this) left over from burn.

Reason EPA/manufacturers whacked all road vehicles in the 70s.

The terrible truth and side effect....

My older Chilton books (the 400/500 page "real" repair manuals) shows horsepower and torque nearly cut in half on some same displacements/carb/manifold/application ..... Several pages and charts, all side by side, flywheel and rear wheel ratings.


So naturally to battle higher compression/heat and encourage an electrical ignition, octane is added, which can be a combination of chemicals, to the fuel. I remember reading hexane is one.

Whether or not octane slows the burn, I'm not sure. Compression does speed up the burn process, makes more bang for same amount of fuel/air compressed, also naturally generates more heat,, and mechanically more power.


After driving 9 years/same 52mile route, on my 1.3 odb1 @ 9.7:1/87 octane, and now 10.5-11:1/93 octane.
I've gained milage. No 2nd thoughts.
Mind you, I believe I gained from higher compression, not octane. I'm pointing out they need to both work hand in hand, one by itself is a waste, the other by itself will destroy the engine.

On a note, I couldn't finish the week on a tank. Now I have a couple gallon left over every Friday evening.

Sent from my rooted HTC Supersonic using Tapatalk 2 Pro

[TominMO]

When I had my Neon I tested it with premium. I wasn't doing it very scientifically, so I just noticed my monthly gas $$ output went down. Then I read up on it and decided it was all in my head. Time to try again, I guess.

Doesn't higher octane slow down the burn as well as making the unburned mix more det resistant? That could help explain things possibly. Maybe at low RPMs the slow piston speed and worse cylinder filling works better with a slower more det resistant burn?

Gas $$ putput means nothing, as I think you understand, because fuel prices fluctuate. You are correct about what higher octane gas does, but it doesn't explain rmoltis's claims. Modern cars have knock sensing capability so that they can retard ignition timing to protect the engine, but I don't believe they have the capability to go the other way--i.e., they can't "detect" higher-octane gasoline and advance the timing, and give you better mileage.

@ rmoltis:
Anecdotal claims mean nothing too. You have to do the kind of disciplined testing I am trying to do, running at a given speed for a decent distance, carefully filling the tank the same way every time, even if possible trying to minimize atmospheric situations like wind and temp. Without that, you can't expect people to get excited about your claims. I have great difficulty believing that the difference between 89 and 91 octane is 6 MPG, all other factors being equal. Not to mention the differences between summer and winter gas. I have found that winter gas costs me 10% or more in fuel economy.

@ jason:
Makes sense that higher compression yields greater power via a faster burn--which is controlled by using higher-octane, slower-burning fuel, thus preventing knock. And with higher compression/more power, your foot is less into the fun pedal, so better mileage results.

I think (but haven't proven via testing) that advanced ignition + premium gas will give similar results, since burn will start earlier and therefore be more complete. So again, the driver's foot is not as close to the floor.

[Spike]

Without doing anything else but filling with premium (Chevy Sprint) .. 3 tanks in a row my MPG (same horrible driving style ) went down. I was averaging about 41 at the time, premium tanks went down to 35 35 36 over 8-gallon spans.

Never tried midgrade, though.. maybe I should do that.

[TominMO]

Without doing anything else but filling with premium (Chevy Sprint) .. 3 tanks in a row my MPG (same horrible driving style ) went down. I was averaging about 41 at the time, premium tanks went down to 35 35 36 over 8-gallon spans.

Never tried midgrade, though.. maybe I should do that.

I could see you losing mileage with premium because it burns slower--therefore your foot is farther down to compensate, and you use more gas. If you want better mileage, try premium with a slight advance in timing, like maybe 3 degrees.

[jason_]

@ jason:
Makes sense that higher compression yields greater power via a faster burn--which is controlled by using higher-octane, slower-burning fuel, thus preventing knock. And with higher compression/more power, your foot is less into the fun pedal, so better mileage results.

I think (but haven't proven via testing) that advanced ignition + premium gas will give similar results, since burn will start earlier and therefore be more complete. So again, the driver's foot is not as close to the floor.

You'll find the limit. There's a point ignition will be holding back the piston to complete the up stroke.

I personally think i have gained with higher ratio, more octane, and only 8* advance. I can't go further, I shaved so much material, belt walk compensation goes beyond slot on dizzy, hehe. I need to Dremel the dizzy plate so I can turn it further.

And I've been reading, and I think I'll do a 4 wire o2 purchase and install on odb1.

Sent from my rooted HTC Supersonic using Tapatalk 2 Pro

[rmoltis]

There's no anecdotal claims.

I reset my trip meter every fill up to the neck of the pour spout.

And use the miles collected vs the fuel filled up.

I did a 2500 mile round trip in the corolla from Pittsburgh to Miami and back on premium.

Cruise control the whole way at between 60-75 depending on speed limits.

It was 40 mpgs the whole way.

A few years back driving to Arizona when I first met my fiancee she was still using unleaded.
And it was a 5000 mile round trip to which we achieved 35-36mpg using cruise control the entire way at the posted speed limits.

There are no claims to anything other than what I've experienced in real life.
And if it works for me why does everyone say it doesn't work?


From what I've read knock sensors are designed to keep the engines advance right on the "hairy edge of knock" on any fuel to provide peak efficiency.

Assuming there is an upper and lower limit of timing the knock sensor can adjust based on 87-93 octane fuels. Since its only obdII


I guess it depends a lot on the people and what cars they are driving.
Older vehicles don't seem to respond as well to higher octanes as well as newer vehicles

[Spike]

Plus, the Sprint has no computer, no vacuum hoses, nothing. The only way to adjust how it drives it via carb or timing. So what I'm saying is, on a normal (not even OBD 1 anymore) earlier car, that has no way to compensate aside from tuning to the gas you're using, premium didn't help. If anything, it seemed to slow it down (though the engine sounded smoother).

I have no experience with OBD2 cars. We've never owned anything newer than 1993, haha.

-Joe

[TominMO]

Well, poop.

Yesterday I had backed off the ignition timing to 12. Went to visit a friend today, ~20 miles mostly hwy, the car starts hiccupping and then losing power. CEL comes on and it goes into open loop. Tends to die when coasting to a stop sign.

After my visit I drove home. Before driving it, I warmed it up and set the ignition slightly lower, ~10 (didn't have timing light with me). Feels low on power. Wondering maybe if I burned one or more exhaust valves? What do you think, from this description? Gonna do a compression test in a little while.