Thinking about gas prices and weather to use regular or premium fuel in my gasser RV

[Rosy]

Have you guys ever watched the show on TV called Engine Masters? There is an episode where they used a big block Chevy motor on the dyno to find out if octane made any difference in HP. They also monitored fuel/air ratio all along the power curve. If I remember correctly they used 87 Octane as well as 91, 93, 116 Octane Sunoco race fuel and E85 (which is 85% alcohol). Know what they found? Their engine would run on 87 octane without knocking. It was making 500 (?) HP. After running the 87, 91, 93 and even the 116 octane fuels through it they overlayed the graphs on top of one another and there was virtually no difference in any of them! The HP didn't fluctuate more than about 2 HP no matter what fuel they ran. The E85 alcohol blend boosted the HP about 50 (?) extra HP because of all the extra available oxygen in the fuel. But obviously your engine has to be changed over to all the equipment necessary to run E85.

Moral of the story? If your engine will run good on 87 and not knock, then you are wasting your money on using any of the higher octane and more expensive fuels. Obviously if your engine requires 91 octane to not knock you should stay away from 87 but again you are wasting your money buying any higher octane fuel unless you want to switch to E85 but then you have availability issues to deal with.

I assume they were running the engine flat out at full throttle? I know that's a stupid question but I watched a very biased and unscientific show one time where they idled a Civic at 10 mph on both 87 and 91 octane to prove that advertising premium means oil companies are evil, or something.

 

[TheLooks]

How about an acceleration curve? How will it respond from low rpms to ramp up for that big hill? Fuel mileage while doing so?

 

["EZ"]

I assume they were running the engine flat out at full throttle? I know that's a stupid question but I watched a very biased and unscientific show one time where they idled a Civic at 10 mph on both 87 and 91 octane to prove that advertising premium means oil companies are evil, or something.

No, they start the pull at about 2500 RPM and run it up through the red line, which on this engine was about 7000 RPM. No matter which fuel was used the graph looked almost identical every time.

 

[Rich W.]

A. Fuel mileage will drop when you open it up and put some demand on it no matter what fuel you are running.
B. As long as it isnt pinging you have enough octane.

So, if it works on 87 octane there is no benefit to running more expensive fuels. If it pings under load, then yes, make an adjustment.

 

[FL-JOE]

A few months ago we took a motorcycle trip from our leased lot in Florida to Austin TX. About 50 miles outside of Austin I stopped at a rural Shell station and filled up with 93 octane. The next day I started having all kinds of issues with high idle and the bike not running right. Dealer determined it was old fuel. He said they had several come in recently with the same bad fuel issue because lower traffic stations were not selling their expensive high octane fuel and it was sitting for a long time in the tanks.

For the rest of the trip I used 87 octane and added octane booster. Even though my manual says I should run 91 or higher the bike ran great. I'm now back to using Shell 93 octane but only at stations that are high volume.

 

[Little Bitty Zitty]

If I don't feed my 8.1L Vortec 91 Octane she's not happy. Not worth the trouble IMHO

Some food for thought based on my experience as an ASE master mechanic since 1974.

The Ford v10 uses an electronic control system which on the first indinication of ping will retard the timing. This will happen nanoseconds after the ping, long before the human ear can distinguish it.

Premium fuel has additives on it to raise the self combustion point, reducing its tendency for preiginition,( ping). Lower octane fuel has a lower point. Premium fuel does not contain more Energy than the lower octane fuels only that temperature at which self combustion occurs.

The v10 was designed to operate on lower octane fuels.

So do this, scan the engine while driving on the lower octane fuel and graft the advance. If the ECM is not retarding the timing there is no need for the more expensive fuel.

Case: I run my 2019 Georgetown GT5 at 70 and constantly get around 9 mpg. But I don't horse it on the hills, keeping the RPM to around 3800 to 4000. And I use Costco lower grade fuel. Save money using Costco and on not using Premium.

Another thing, Premium leaves move deposits on valves and pistons which rob your engine of power. This is why almost all the good grade fuels have an additive to clean the injectors and engine operating.