Regular gas for the US spec STI

With knock sensor technology you would probably "get away with it" but the difference in cost over even a long trip is not a lot of money. Say you go

1000 miles and get 25 mpg, that's 40 gallons at 20 cents more per gallon for an additional cost of $8 not even accounting for better gas mileage using higher octane and better performance. Is $8 that big of a cost assuming you can afford to take a trip in the first place?

That's a very bad ideal. You can damage your motor. I have a '04 WRX. If you check your manual it says wrx must run a min of 91 octane and the STI must run a min of 93. On all the WRX(sti) site people have tried to use cheap gas in our WRX they all report a lose of on min 2 mpg and a lose in power. Also the knock sensor only hears a knock after it happens. So you will still damage the motor. I live out in Cali and we only have 91 octane gas I add octane booster to every tank full just to give it that extra margin. Turbo motors are very sensitive to quality of gas since they force hot air into the motor they need help to control knock under boost. If you use cheap gas all it can do is reduce timming and try to cope. You are only talking a differance $1.50 a tank full(15g tank) . Is your car not worth an extra $1.50 a tank. Depending on how you drive you should be getting around

22 +mpg on the highway anyway. I also have a '64 Pontiac Grand Prix that has a 389 w/tri-power (three 2bbl carbs) that the manul says needs a min of

You'll probably end up getting worse gas mileage... I've found this to be the case with cars that recommend higher octane fuel.

So you might hurt your engine without any savings to show for it.

Nick

Philip Procter wrote:

Or switch to coffee instead of lattes and buy a water filter and lose the bottled water. That will pay for your premium gas.

Carl

1 Lucky Texan

Edward Hayes wrote:

The knock sensor will probably prevent any major damage from happening to your engine, but you will probably get *worse* gas mileage. The knock sensor is an inherantly passive device, meaning that it waits for a ping to actually happen before cranking back the timings, it doesn't proactively try to adjust the timings. It'll keep your engine safe, but it won't make it efficient.

Yousuf Khan

I was thinking give up fries with the Famous Star and switch to a medium Coke at each fill up, but the thought is the same. I had connections with a gas station at one time and it's amazing how people react when the gas prices go up.

It is my understanding that 100 octane unleaded (not avgas) is still available to the public at a number of pumps in the so cal area. The only caveat is they may not want to pump it directly into your street car so bring a couple of 5 gal cans.

You could always investigate adding 1-2 gallons of toluene at each fillup.

Carl

1 Lucky Texan

John Emdall wrote:

That's not the only caveat.

Avgas is *leaded*, so plan on replacing your cats after a few tanks, too.

Steve

Okay, I'll ask the obvious question: why did you spend $30K+ on a performance car like the STi if you don't want to spend the coin on premium gas to protect your car's engine? The answer to your question is pretty simple: use premium gas; don't screw around to save yourself a buck here and there.

Jen :: killing people and burning down trees ::

Google "bore wash timing pinging" and decide for yourself if this is a risk you *really* want to take, to save a few bucks on each fill up.

Steve

Ok, let me explain about forced induction (turbo or supercharging) and how it relates to octane ratings. First of all the octane rating of gas is it's resistance to what's called detonation. Higher rating=more resistance=better burn When you're running any forced induction application this becomes critical in that you start running a lot more air into the engine. Remember, all that a turbo does is force more air into your engine so that there is more air to burn. Now if you run any gas with too low of an octane rating you are basically now running too lean on the engine. It's just as if the engine wasn't getting enough fuel. Hence detonation. Very bad juju. Too much air+not enough/wrong fuel=BOOM! Forget knocking, we're talking about destroying your pistons, and blowing the head on the motor. Trust me, this information came very painfully to me.

Philip Procter wrote:

Want to hear a good one? My wife and I test-drove 2 wrx's at a local dealership. The first one drive like a top but was the wrong color. The second one was the right color, but in the showroom. They took it out and it ran terrible. We left, not buying the car. They called back and said it had been filled with regular. They filled it with premium and give it to a saleslady to drive around. We came back a couple days later, test-drove it and bought it.

Damn near lost a $23,000 sale for a 1/4 tank of regular gas.

The shortened version is; too low an octane with highly compressed air = detonation while your piston is on the way up the cylinder. Snap, crackle, pop!

I thought that was pre-ignition.

Not quite, but same results. Detonation is where the air/fuel charge basically explodes instead of burning with a nice even flame-front pattern. It's caused by too lean of a mixture, or poor fuel (lo octane or other). Pre-ignition is where you have a hot spot in the combustion chamber that ignites the mix prematurely, causing excessive pressure in the combustion chamber. That is caused by too hot of a spark-plug, glowing hot carbon deposits on piston crown or combustion chamber, etc. They _are_ closely related, however, Detonation frequently leads to pre-ignition. It's a vicious cycle that can destroy an engine in a few cycles.

ByeBye! S.

Steve Jernigan KG0MB Laboratory Manager Microelectronics Research University of Colorado (719) 262-3101

It is.

Steve