Ok calling all experts. I live couple blocks from the mexican border so I decided to take the little drive over there with an empty tank to fill up with their gasoline. They sell premium 91oct (the red pump) for 7.80 pesos/litre that equates to about 2.90 dollars/gal. The savings in a full tank are 20 dollars US vs Mex Gasoline so its worth the bridge toll and everything. I can fill up my roadster with 35 dollars NO KIDDING!

My problem is that when I got there,the attendantdid not let me know that he had already sunk half a tank of regular 87oct in the car.Long story short I told the guy to just fill it up with that and I boughtsome STP octane booster once I got back to the states (3 milesofslow driving). Do you guys think thats enough? The tank in my roadster is really full of that stuff and I can feel a drop in performanceeven with th booster. It used to put me up against the seat at the stock 11 psi now it feels even more pigish.

I have a vent boost gauge installed and no chip, no diode, nothing. What do you guys recommend doing? Should I wait for the tank to go down a quarter and put more octane booster?

 

Just run the tank down to less than half and fill it back up with 91. You'll have some loss in power, just stay out of the boost so you don't ping to heavily.

 

what about those octane booster things. Do you guys trust any of them to actually raise octane a bit?

I bought the cheap one (STP octane boost 3-4 bux i believe). I'm gonna baby the car like I have with the expensive US gasoline.
Difference is that now I will be babying it for the sake of the engine and not so much for economy.

 

You should not have any problems the car will cut boost if it sees any misfires, just fill up as soon as possible. I have yet to see a car explode/catch fire/die with the improper grade of gas in it...

~just my .02

 

I have not seen that happen either.

Im familiar with the thermodynamics, combustion sciences (fuel grades and combustion cycles), and mechanics of materials enough to know that it would be highly unlikely.

What is not unlikely is that the rod bearings start shearing off in layers because of the super high stresses involved in compressing an exploding air fuel mixture. That, I have experienced first hand from the last engine I built for my eclipse. The dang thing ran lean because of my awesome fuel pump rewire job and then I just left all the engine pieces clinking away from me on the highway and oil spattered all over the windshield. It was spectacular, but scary, and costly.

Thanks for the replies guys. Just wanted to know if it was really really bad with this engine especially because it runs a little hotter. Maybe theres someone out there that has done the same and added a little booster or not and drovejust fine.

Yeah for sure im going back to Mex to fill up again when I get to the half way point. The 91 octane this time tho.

 

You should be fine I ran a tank of regular through my car w/o octane booster nothing happened didnt ping or knock under full boost think my gas mileage was worse then normal

 

.....personal experience narrated from a trustworthy source...

exactly what I joined the forum for. Thanks alot. Thats reasuring and exactly what I needed to hear.

Im still going to baby the car through that half tank tho.

 

Your label inside the gas tank says you only have to put a minimum of 91 RON. That is not the same as 91 octane rating you see on the pumps. The US uses the AKI systemwhich is a different system than theRON you see in European countries. AKI is what you see on the pumps.91 RON is the same as 87 AKI here in the states. You won't hurt your engine, but you might see a decline in power from your ecu pulling timing to accomodate the lower octane gas. I don't see any difference between 89 and 93 octane in terms of gas mileage or performace in my 225. So I put midgrade in mine.I'm sure a dyno would be a different story.