92 Octane

91 has no ethanol in my area while 87 has up to 10%, so I fill up with 91. Ethanol-free is supposed to be easier on the fuel system components over the long term.

 

The Tacoma manual says to run "87 or higher".

 

Lulz

 

I typically run premium to guard against detonation which will not only cause a loss of power but will damage the engine.

The 2GR-FKS engine is 11.8:1 and the reason it can run pump gas at all is that it's aluminum which pulls heat from the combustion chamber quicker. Aluminum engines typically run higher compression ratios because of how efficiently they shed heat. The direct injection aspect of the engine also has a charge cooling effect similar to water injection that has been used to combat detonation. The need for higher octane is probably most prevalent at higher engine rpm and load where the engine is allowed to take a full breath. I would definitely recommend using premium while towing to guard against detonation.

So here's the thing, premium has no more power in it. Gasoline energy density is what it is regardless of octane. If you are detonating and switch to premium and feel you got some more power or mileage out of it, is because the engine is now running as it should. GM has used detonation sensing to retard timing when necessary. I don't know if Toyota uses anything like this. If so, it would allow your best running potential with mid-grade or premium. The biggest factor, however, is probably alcohol content. Alcohol has higher resistance to detonation or uncontrolled burning, but only has about 2/3 the energy density of gasoline; it burns cooler. When running gasoline with an alcohol blend, it does not produce as much heat as non-blended fuel. That heat expansion is what drives the piston down on the power cycle and makes the truck go. Less heat expansion, less go. When California would up the alcohol content, I would see the milage drop in my old truck by about 1MPG, however, in that truck that only got 10 MPG it is a drop of 10%. Once they switched the blend back, it would go up. Alcohol content equals less power in engines not specifically built for it. It will likely always equal less fuel efficiency.

Someone mentioned the use of E85 in performance cars. Typically, it's used in supercharged or turbocharged applications with a fuel injection system that can manage it. Because alcohol produces less heat and power than an equal volume of gasoline, it requires more alcohol for the same output. Cars that can run E85 have injection systems that can push enough fuel for stoichiometry, have O2 sensors that can read it, and computer that can manage it. Stoichiometry for spec gasoline (no additives) is 14.6:1, for ethanol it's 9.0:1 and methanol it's 6.4:1. Because of the AFR requirements of blended fuel, it simply requires more of it to produce the same power. Yes, I know alcohol-fueled turbo or supercharged engines produce tons of power, but that is in a use where the engine is designed both mechanically and in management to use that fuel. For passenger car engines, it's like a filler, it's like drinking a diet coke if your blood sugar was low.

In So Cal, I think all our fuel is blended. However, I just got back from Montana and I noticed a lot of the gas stations advertise their premium is not alcohol blended. That alone would be worth buying premium as you may see a small increase in mileage. Besides, the difference in a tank of Regular vs. Premium when putting in 20 gallons is only about $4.00 (here). The price difference is negligible especially when considering the long-term effects of detonation if you are pinging along.

 

Did you take what you last ate into consideration for calibrating that?

 

My truck runs better the higher the octane. Especially under loads either towing, hauling or inclines. I primarily use 90 non-ethanol.

 

Forgot that allowance. Mucho borito . Plus 10 hp and 20 lb tq

 

Is that from "rocket assist"?

 

I was always against the idea that switching to premium would make a difference. I finally made the switch a couple of tanks ago, and the difference is noticeable. I get slightly better MPG and the engine seems to run smoother. I haven't noticed any power difference, though.

 

Thanks all for your responses.

I ran through two tanks of 92 before our trip and not sure if I noticed much of a difference and power v.s. 87 but it did seem to do better with shifting.

However, on another note, I was about 400 lbs heavier on this trip (estimated 4500 lbs) and 3 Kayaks on the roof acting like sails. So the 92 could have made more of a difference then it seemed.

 

Science says it won't make a difference so I'm not going there. But if new evidence shows it does, I'll have to weight the cost vs benefits.

Hope that helps
Cheers!

 

What science?

My truck drives significantly better running premium (90 up here) vs 87. Modern ECUs have the ability to make significant changes away from the “base” tune to stop knock and detonation; this is what allows high compression naturally aspirated engines like the 3.5 in our trucks and allows all the cars running turbos from the factory to run 87 now. With higher octane the ECU has to compensate a lot less, letting the truck run better especially at partial and transitional throttle. It won’t make more power but it fixed a lot of drivability issues on my truck and drives much smoother.

Try three tanks of 89 or 91 in a row, see if it makes as noticeable a difference in your truck as it did in mine. If you don’t notice it, you’re only out $20. If you do, like i did, you get to choose if the extra $5 per fill up is worth it.

 

Manual states "87 OR higher." "Testing done with 91.

Lexus engine yalll