91 octane

[L31MaxExpress]

Bone stock 5.7 Vortec on the stock tune in my Express van had knock retard on 87. Ran 91 top tier, had better power and mileage. Then later tuned it for the 91. Huge difference in torque between stock timing map with 87 octane and knock retard vs 91 octane with the timing cranked up.

 

[CrustyJunker]

Your truck should run just fine on your available 87 octane. We've been forced to have E10 in my area for many years now. I heard all kinds of bad stuff from ethanol vs. the Vortec poppets, but I was fortunate to never have a problem.

Top Tier gas is actually good stuff. It yields best fuel economy on my 87 octane powered vehicles. One Chicago performance/dyno shop recommended Shell 93 octane exclusively in one boosted build. -I asked why and was basically warned with a wordy "trust me, don't do it."

Octane tests are pretty strict and must meet or exceed certain values. Those doing the bare minimum get bare minimum results.

 

[BNielsen]

Something that helped me deal with certain gasoline was running a fuel stabilizer/additive.

Now I know some people are "fUeL aDdItIvEs R sNaKe OiL" and some of them are.
But I've had great luck with Amsoil Upper Cylinder Lubricant. The truck definitely felt peppier after 2 or 3 tanks were treated and run out, even with my fuel pressure issue I've been battling.
https://www.amsoil.com/p/upper-cylinder-lubricant-ucl/

That's just me though. My truck has been 0411 swapped and I believe tuned for 89; it's a 454 so I don't expect 20 miles to the gallon, but I did pick up 5 or 10 more miles per tank on the additive. And the only major reason I even started running the stuff was because I got it heavily discounted with a motor oil order.

 

[Insert Quarter]

I was under the impression that the octane number wasn't necessarily better or worse for the engine when comparing 87/91. What was better about 91, or the "premium" grade, was that it contained additives and detergents not used in the "regular" gas 87 octane.

 

[Rob7233]

is there any harm in running 91 octane (top tier shell) fuel in a stock 5.7 vortec motor? I only buy ethanol free fuel for my small engines, and lately that seems to only be available in 91 octane. the small engines love it and so I put 5 gallons of it in my farm truck and it loved it. friggen tonnes of power. I understand the benefits of top tier gas and how it cleans the fuel system but is there any drawback other than the price? my burb has a 42 gallon tank, i dont think I would want to pay the premium price to fill that sucker up!

Al

https://www.shell.ca/en_ca/motorists/my-fuels/shell-v-power-nitro-plus-premium-gasoline.html

Maybe we got into the weeds here. I think that the original poster realize his boost in power NOT actually by any octane boost but by the fact he used Ethanol Free (pure gas) in his vehicle.
Some state up to 30% more power per gallon over the corn alcohol version fuel. Just my 2 cents..

 

[thegawd]

Rob, that is probably 100% true, that and possibly the additives cleaning out any possible dirty deposits. I bought this truck off of a buddy and know everything he did to it. the shorter list is what he didnt do, he didnt touch the fuel system at all or the transmission, but he did a tonne of work to it.

thanks for your input guys!

Al

 

[thinger2]

None of the above is true.
Higher octane fuels have a reduced tendency to spontaneously combust - which prevents the last of the charge self igniting when it encounters the pressure wave from initial combustion before it encounters the (too slowly) advancing flame front which should be it's ignition source.

All of the above is true, you have just stated it in a different way.
And a more complex way that arrives at the same conclusion.
We are saying essentially the same thing but I dont think it helps a newbie to overly complicate things.
The moral of the story is that high octane will not help and can actually make it worse.
My statement is a simplification of the process that I put forth to keep someone from wasting his money.

 

[thinger2]

Pre-ignition and detonation are two different things although extended detonation can also cause pre-ignition. Pre-ignition is caused by a hot spot igniting the fuel before the spark gets there. Higher octane burns slower not later.

Read it again, slowly

 

[Frank Enstein]

Yep. It wont help.
A fuel octane rating is basically its resistance to igniting.
The higher the number, the longer it takes before the burn starts.
Higher octane is used in high compression engines to give a fraction of a second of delay before the fuel ignites.
This allows the cylinder to reach full compression before ignition.
That is why running low octane in a high comp engine causes "pinging"
The low octane fuel ignites before the cylinder is at full compression and before it reaches the correct point in the timing sequence.
The opposite happens when you run high octane in a low comp engine.
The high octane ignites after the cylinder has reached full compression and that ignition happens late in the timing sequence.
And of course these engines were not designed with ethylated fuels in mind so that adds another little kink into the theory

With all due respect you are mistaken. The octane rating is a measure of Antiknock i.e. preignition. It does not burn slower due to octane rating. Race gas burns fast because the engines turn lots of rpm. Aviation fuel burns slower even at the same octane. AV gas is designed to not boil/percolate at altitude and piston aircraft engines don't generally turn very high RPM. Octane is only one facet of the fuel. If you tune an engine for best performance with each fuel sometimes you will get a mileage increase. And sometimes that increase pays for the difference in price (not too much nowadays though).
More octane than the engine can use will simply waste your money but with some fine tuning it might help.

 

[F4U-1A]

I read the F4U-1A Navy Fighter ran on 100AKI (anti knock index). I think that would be $$$ for a GMT 400. Can I start tail gating yet?