Best octane fuel for fuel eceonomy? (5.3L only)

[curtis ronci]

Just recently getting rid of a V-10 f-250 I love the mpg on my 5.3.
Having said that I do find on any car or truck the best way to get or to regain good mileage is to look at yourself.
Driving style for one is important and even more so how are you about maintenance?
Plugs,coils,wires,tire pressure,clean filters,brakes and even extra junk in the car can kill mpg

 

[GreyStone]

Are there areas that still actually put a sniffer up the tailpipe?

Around here, any OBD2 vehicle ('96+) just gets plugged in to the OBD port and the ECU readiness monitors are read. Vehicles older than OBD2 are emissions exempt, just a visual for required equipment (cats, smog pump, etc.)

I live in NorCal - and they check every damn thing - crazy strict!

 

[cfmistry]

does the cost difference even out to the mpg difference? it may get better mpg, but how is the cost difference? which is actually cheaper to run?

No place on this earth would switching to 93-octane (a factory tune) make sense from a financial standpoint. In general it costs 40% more than regular 87-octane, and you would be lucky to get 10% improved MPG. I was getting about 5%.

But that was not the point. I knew it was not cost-effective, but I wanted any increased range I could get. Less trips to the gas station = convenience = worth something. I may have gotten a little more range, but I'm not convinced.

 

[George B]

Just recently getting rid of a V-10 f-250 I love the mpg on my 5.3.
Having said that I do find on any car or truck the best way to get or to regain good mileage is to look at yourself.
Driving style for one is important and even more so how are you about maintenance?
Plugs,coils,wires,tire pressure,clean filters,brakes and even extra junk in the car can kill mpg

This is true.
clicking off the cruise and allowing a long slowdown roll on off ramps and up to stop signs will gain back some mpg.

 

[91RS]

I wonder which octane is better for emissions/smog testing?

Whatever the stock required octane is with the stock tune. Many people don't understand that manufacturers are much more concerned with emissions output than they are with MPG (they are to the extent that customers are because that's all they see). Emission output is what killed of the fabulous 3.8L.

 

[swathdiver]

I wonder which octane is better for emissions/smog testing?

The highest octane you can get. We had gutted cats and all kinds of other mods on our Buicks way back when and all we had to do to pass the sniffer test was to turn the fuel pressure way down and run high test unleaded.

Not too long ago there wasn't such a spread in prices between grades of gasoline. As such, it was easy to benefit cost and performance wise from running higher octane versus lower octane fuels. Even on the stock tune mine delivered better economy on 93 versus 87 and until the direct-injected engines came out, we proved this on every auto driven since the 1970s.

Now here's a wrinkle for ya, I now mix fuels for even better fuel economy, about 6-8 gallons of E85 mixed with E15 or 93 and the truck gets even better gas mileage than if she was burning straight 93. The motor (computer system) loves ethanol and if mixing with E15, costs less than a tank of 87.

 

[donjetman]

We do mostly hwy driving. She gets 15.5 mpg on 87 octane, 16.5 on 89, and 17.5 on 93 octane. Right now around here, 93 octane cost 31% more than 87 octane, but she only gets 13% better mpg.

 

[GreyStone]

Whatever the stock required octane is with the stock tune. Many people don't understand that manufacturers are much more concerned with emissions output than they are with MPG (they are to the extent that customers are because that's all they see). Emission output is what killed of the fabulous 3.8L.

My dad had an El Camino with the Conquista package - it had a 3.8 with a stick shift, lots of torque in that little engine - but it hated high RPMs.....lol.

 

[George B]

So far I am getting my best mileage and cost per mile on 87. It does not run as well as on E85 which only returns 10-11 mpg.

Going to try a blend of E85 with 93 to see where I land.

 

[swathdiver]

My dad had an El Camino with the Conquista package - it had a 3.8 with a stick shift, lots of torque in that little engine - but it hated high RPMs.....lol.

Those were low rpm torque motors, the cams were dead by 4400 rpms, raced them for years. Must've been fun to drive, any pics?

 

[GreyStone]

Those were low rpm torque motors, the cams were dead by 4400 rpms, raced them for years. Must've been fun to drive, any pics?

No pics unfortunately - it was fun to drive but had a crazy stiff clutch - I honestly cant remember if it was a 3 speed or 4. It definitely ran out of breath early in the rpm band - but could pull like a tug boat!

 

[swathdiver]

No pics unfortunately - it was fun to drive but had a crazy stiff clutch - I honestly cant remember if it was a 3 speed or 4. It definitely ran out of breath early in the rpm band - but could pull like a tug boat!

They came with both, most of them 3-speeds, gone by 1981 if memory serves. Fun stuff!

 

[gpracer1]

What is responsible for better fuel mileage at the same * light throttle opening during cruise* ??........TIMING
The more timing without knock/detonation the more torque the better the mileage.
What allows more timing without KR? (Knock retard)
Cooler intake air.... IAT , allows more timing.....look at a tune map timing vs IAT
Higher octane fuel....allows more timing to be utilized
Lower engine temp ECT ....less prone to knock/det

Your highest amount of timing will be at the lightest load/throttle like cruising at 40 mph.

OEM tuning is for the minimum fuel octane available everywhere, or for performance vehicles they stipulate in the manual the minimum requirement.
Aftermarket tuning can give you more timing if you are dedicated to using high octane fuel, add a real cold air intake and its even better.

PS, you cant really do MPG comparison with gas vs E85 as it has ~27% less energy than gas....the only good thing is the higher octane rating. You would have to do a price comparison with total miles driven.

 

[donjetman]

Now here's a wrinkle for ya, I now mix fuels for even better fuel economy, about 6-8 gallons of E85 mixed with E15 or 93 and the truck gets even better gas mileage than if she was burning straight 93. The motor (computer system) loves ethanol and if mixing with E15, costs less than a tank of 87.

2+ yrs later:

I am again occasionally mixing in about 5 gals of e85 when filling up w/e10 93 octane.

Cost is $2.60/gal for e85 and $3.65/gal for 93.

I can't notice a mpg hit to my local driving, so its a win.

But the station is 20 miles away so I don't get the chance to do this very often.

And everyone here shoukd know by now "I take it easy on the ole beast".