Regular vs. Premium Gas - a perspective

I guess this debate will rage on forever.

Some guys cite tuning companies that write tunes and run these trucks on the dyno claiming that even on the stock tune the truck pulls timing, i.e. power, when running 87 octane.

Then you've got the AAA study where they did things in a slightly more scientific way, and saw back to back losses of power with 93 octane on a 5.7 Tundra. The 87 performed better.

The average guy has no idea what to believe. But at $4.00+ per gallon it sure helps sway the decision toward 87 when I grab the pump nozzle.

 

93 does not help in Houston.

before blower, I ran a couple tanks and saw no diff. NONE.

now, I'm stuck using 93...in a good way.

 

I need to follow your route. I just drove from Alabama to Ohio and trip total was 970 miles. (granted it was Ft. Morgan to East Central OH)

 

This. My understanding is that octane is a measurement of resistance to combustion. So a higher octane number requires more compression before it ignites and pushes the piston back down. So a higher compression engine will ignite a lower octane fuel before the piston reaches the top of the compression stroke, even without a spark aka dieseling. So the sweet ass 69 Camero doesn't shut off.
Same reason the valves ping and knock with a lower octane. The valves have not reached their closed position before the fuel ignites. Fuel ignites, slams the valves closed, loses some of its umph in the process and we hear the 'ping'.
1) somebody correct me if I am wrong.
2) my 2018 FFV 5.7 Tundra definately runs quieter on 91, but my major concern is the pre-ignition causing wear and tear on my valve train when I run 87.
3) with a FFV the computer has to adjust to account for the %of alcohol in the system, I would think that would help protect the components from pre-ignition damage. Right?

 

You are correct that octane is an index of a fuel's propensity to knock but if your truck, which is designed to run 87, is knocking, I'd say it's indicative of a bigger issue that burning premium is just masking.

 

What's the net elevation change between the two locations?

 

The AAA article showed a highway increase with premium. Now even 1 mpg its still tough to say whether you’re offsetting the cost unless the entire tank is on the highway

 

Premium costs at least 20% more here. So I'd have to go from 18 mpg highway to 22 to justify it.

 

First I've heard about the valves being pushed shut. Both should have been closed way before the plug fires. How else would the compression be naintained. Not sure resistance to combustion is the best term but higher octane fuel burns slower. The detonation is caused by the flame front traveling fast enough to trap unburnt fuel and air in an area of combustion chamber and compressing it to the point it explodes instead of burning. Since this flame front travels slowly at first having the spark fire BTDC gives time for the fuel to start burning before the higher pressures are reached.

 

Stumbled upon this video today, and it made me remember this thread. I'll be sticking to 87 from now on.

https://www.youtube.com/watch?v=ryqyTPfNj1Q

 

After reading this entire study, I do not understand why this is not referenced and cited more often in these threads/debates. Is there any opinion out there questioning the validity and/or results of this AAA study comparing Regular vs. Premium usage in the 5.7 engines?

 

I saw about a 10% increase in fuel economy when I’d use premium on a cross country road trip - didn’t quite pay for itself but almost. FWIW I run 87 95% of the time.

 

When i use shell premium nitro i get 50 more miles per tank before the light comes on.

 

I was told that when running 87, the ECU sucks about 13 degrees of timing out, that the OEM fuel rails are ineffecient, etc. This was after I did a DAP Tune on my 2012.

 

i have to opt for the premium also. My old F150 I just replaced, would bog and hesitate on acceleratations until I started running premium through it. No other change in the equation, and the bogging/hesitation stopped. For now I'm running premium through my 2019 tundra, based on my experiences with my F150.

 

The benefit to higher octane is probably going to be dependent on how the truck is used. scooting around towing is one thing, but towing or very high speed highway are another. Towing, the engine is going to see very high cylinder pressures and temperatures continuously and the higher octane will likely improve timing there. The PCM is fully capable of adding timing in real time and over a long term average.