[N0EsBuen0]

You are playing with fire. The dealer doesnt give a shit and puts in what is cheap for them. The owners manual and manufacturer of your very high compression engine say it should have 93 octane fuel. It can get by with 91 and even that is a sacrifice. Man, if you you cant afford the gas, dont buy the car. You are doing the car and yourself a disservice.

In all of the high compression cars I've owned, I've never experienced catastrophic engine failure from using 89 octane instead of 91 or 93.

 

[SkyDog]

I put 93 in all my cars as safety cushion, but could be snake oil?

If those cars have engines designed for 87, using higher-octane gas isn’t giving you any benefit. You won’t need the anti-knock properties of higher-octane gas. Save yourself some money and put 87 in the tank.

Then again, half my cars have about 115k miles on stock engines, one being 230k miles, so I don't think it wouldn't hurt?

It doesn’t hurt, but it doesn’t help, either. There are plenty of other things you’re probably doing right to keep engines running for a long time, like regular oil changes.

 

[dudecris]

If those cars have engines designed for 87, using higher-octane gas isn’t giving you any benefit. You won’t need the anti-knock properties of higher-octane gas. Save yourself some money and put 87 in the tank.



It doesn’t hurt, but it doesn’t help, either. There are plenty of other things you’re probably doing right to keep engines running for a long time, like regular oil changes.

I get the saving money part but giving it's about 8 dollars difference to fill a tank from empty, I don't see much issues against not doing so.

 

[TRU-BOOST]

Most newer cars can adjust for it. Any ecoboost engine or offering from VW or nissan all can accept any fuel. They can control how much boost goes into the engine and tweek the timing to keep it safe. Some high compression vehicles like the mazda skyactiv engines are also fine on regular 87 octane, but they use a system that mimics a diesel engine and actually creates compression ignition. Our engines dont do that. Our compression is not variable like a nissan either. High compression needs high octane. The ecu might be able to get away with it but you are absolutely sacrificing power. With only 228 to begin with there isnt much to spare and seems like an absolute waste to buy a car like this then neuter it with poor fuel.
Read you manual and look inside the gas cap. When it says "premium fuel REQUIRED" It means just that. You must use premium. If you see the words "premium fuel RECOMMENDED" that means you will get better results with premium than you will low octane but it will work with whatever. If something goes wrong and the dealer pulls the ECU history to find out its been pinging and pulling timing for the last 3 months, don't expect warranty coverage. When you willingly put lesser grade fuel in a vehicle that requires it, they have every right to void your powertrain warranty.

 

[SkyDog]

I get the saving money part but giving it's about 8 dollars difference to fill a tank from empty, I don't see much issues against not doing so.

It’s eight dollars buying you nothing. Or, with weekly fill-ups over the course of a year, over $400. I’d like to put that money back in your pocket. Put it toward tires or something. 👍🏻

 

[removedonut]

I put 93 in all my cars as safety cushion, but could be snake oil? Then again, half my cars have about 115k miles on stock engines, one being 230k miles, so I don't think it wouldn't hurt?

Filling a car with higher octane than it’s tuned for has zero effect. The only measurable benefit (for an older vehicle specifically) would be that premium fuel is more commonly ethanol-free

 

[AR86]

So I went today and they didn’t have 96 or 93 like it stated so I put in some 98 and filled the rest with 91. Should be close to 93 right lol

 

[TRU-BOOST]

It’s eight dollars buying you nothing. Or, with weekly fill-ups over the course of a year, over $400. I’d like to put that money back in your pocket. Put it toward tires or something. 👍🏻

🤦‍♂️
you wont need tires. The car will be too weak to spin them. You can however save it to replace the bent valves you get from trying to be cheap.
This car has a steak appetite and you are feeding it ramen. Its not snake oil. The car needs higher octane. This is what happens when prius drivers buy a sports car. If the 8 bucks is breaking the bank, the decision to buy the car at all wasnt right.

 

[SheperdX]

I’ve thought about doing this, but any thoughts on how completely the mix blends in the tank? I think octane stability is pretty vital for engine tuning and longevity, especially with the way knock adjustments work on these cars (or at least did for the 1st gen car).

It mixes just fine. The best way to go about it is to add the 1-2 gallons of E85 first. Then just by pumping in the other gas, it will agitate and blend it up. I do this all the time in my SHO.

Use this nifty calculator for calculate the exact amount you need (scroll down to the advanced one for our cars): Octane Calculator

 

[SkyDog]

🤦‍♂️
you wont need tires. The car will be too weak to spin them.

To be clear, he and I were talking about other cars; ones that were designed for 87 octane fuel.

If a car calls for premium fuel, give it premium fuel. If it’s designed to run on 87, putting premium fuel in it is a waste of money.

 

[BRZerker]

Use this nifty calculator for calculate the exact amount you need (scroll down to the advanced one for our cars): Octane Calculator

Thanks! Wish I had seen this yesterday haha. I spent an hr making an excel sheet that calculates ethanol content and overall avg octane for blends, based on existing fuel in tank and added 91 and e85 over the first 7-8 fillups. Also calculates expected cost per fill.

If anyones curious, I found that:

- 2 gallons e85 per fill (plus 7 gal of 91) will eventually net you an average octane of 94.x. Total ethanol content of 27 percent. Fuel trims should rise approx 6.7 percent (well within the brz's adjustment range of +25 percent). Cost savings of $6/fill.

- If I step it up to 3 gallons per fill, octane is 96, total e content of 35 percent, fuel trims at +9.9 percent, and cost savings of $9/fill.

All figures are approximate and will vary based on a number of factors (actual e85 ethanol content, fuel prices, fuel added, etc.)

 

[LacroixDP]

You are playing with fire.

Agreed, 89 is way too low for this engine. The ECU can compensate some, but it’s not meant for long term usage like this. Petrol is expensive, a new engine due to a denied warranty claim costs even more.

 

[Jtclabaugh]

That would likely be beneficial if you drive hard often. 91 is a sacrifice. Even if there isnt noticable power gain the added knock resistance is just a safety cushion. You could do thr same thing but blend in some E85 for much less $$ if it is available. That is over 100 octane. The stock fuel system and computer is perfectly capable of using low ethanol blends. Once you go to higher ethanol blends or pure E85 is when tuning is needed.

So given CA only sells 91, would you recommend adding an octane booster each time when filling up? Looks like it would only cost ~$3 to do so. I ordered a small bottle to try with one tank so will see if I notice power or MPG improvements

 

[Blighty]

So given CA only sells 91, would you recommend adding an octane booster each time when filling up? Looks like it would only cost ~$3 to do so. I ordered a small bottle to try with one tank so will see if I notice power or MPG improvements

You are unlikely to really notice outside of a dyno, even then its not going to drastic. I wouldn't stress too much. Just keep on filling up and enjoying the car.

 

[TRU-BOOST]

Octane boosters are sketchy. Some have been tested to be quality and provide the results stated on the can. Others raise the octane in a full tank by 0.3 octane. You would be better off doing an E85 blend similar to what is shown above if you have access. I wouldnt count on the "savings" so much though because you will lose some MPG. 91 is perfectly safe but less than ideal. I would definitely not go any lower ever in this engine.

 

[mike d]

I live at altitude and can't get anything easily above 91. Higher altitude = lower octane. I've never had a problem with vehicles I've owned that required higher octane (some 93). I think the manufacturers build in some leeway. I'm suprized that at a low altitude locations you can't get 93.

 

[Jtclabaugh]

Octane boosters are sketchy. Some have been tested to be quality and provide the results stated on the can. Others raise the octane in a full tank by 0.3 octane. You would be better off doing an E85 blend similar to what is shown above if you have access. I wouldnt count on the "savings" so much though because you will lose some MPG. 91 is perfectly safe but less than ideal. I would definitely not go any lower ever in this engine.

Octane boosters are sketchy. Some have been tested to be quality and provide the results stated on the can. Others raise the octane in a full tank by 0.3 octane. You would be better off doing an E85 blend similar to what is shown above if you have access. I wouldnt count on the "savings" so much though because you will lose some MPG. 91 is perfectly safe but less than ideal. I would definitely not go any lower ever in this engine.

hmmm. I work for an oil company lol, but no idea if it's safe to put e85 in our cars.

 

[LacroixDP]

91 in high altitude is perfectly fine. It's frequently used in states like CA where sulphur levels are restricted in petrol. 91 I have no concerns over than reduced performance, but that is the floor for this engine where I'd feel comfortable.

hmmm. I work for an oil company lol, but no idea if it's safe to put e85 in our cars.

You can't put E85 in these without mixing them with regular petrol. I believe the manual cites E15 as the ceiling for our cars.

 

[Jtclabaugh]

91 in high altitude is perfectly fine. It's frequently used in states like CA where sulphur levels are restricted in petrol. 91 I have no concerns over than reduced performance, but that is the floor for this engine where I'd feel comfortable.



You can't put E85 in these without mixing them with regular petrol. I believe the manual cites E15 as the ceiling for our cars.

I'm close to sea level. Car seems fine so not going to worry about it.

 

[Jtclabaugh]

91 in high altitude is perfectly fine. It's frequently used in states like CA where sulphur levels are restricted in petrol. 91 I have no concerns over than reduced performance, but that is the floor for this engine where I'd feel comfortable.



You can't put E85 in these without mixing them with regular petrol. I believe the manual cites E15 as the ceiling for our cars.

Living in CA definitely has its negatives.