I couldnt have said it better myself, listen to this guy

 

I agree, and to put it in simple terms, If you get behind my friends 69 Firebird with the crate built 350, what do you notice? It smells like a refinery no matter how well the car is tuned. If you stand behind a 2004 Lancer and smell, you may get a slight sense of a gas odor but no where near the intoxicating levels from the Firebird. It's all in how much fuel is combusted and how efficiently. Also using a higer octane fuel is, broken into terms even a moron can understand, EXPENSIVE! why the hell would you use it if you didn't have to? just dollars and cents there.

 

yes 87 is good enough

 

Since I bought my 05 RA I've been putting in 92 octane. I plan to install an ecu and exhaust system before summer though (6 months or so), should I bother changing back to 87 or just stick with 92?

 

I'd switch .. it's a waste of money.

 

Switching to 87 will help you save money faster to get the piggy. Don't run 92 until you have an actual need to.

 

OK, I have the ECU Piggyback, and in California, they only sell 91 octane gas at the pump. Therez this Union 76 in Orange county that sells racing fuel (100 octane) at $5.49 / gal. If I took my car to the track, would I get any better times in the 1/4 mile with this gas, or should I just stick with 91 octane?

 

Probably not, as the piggy was mapped to run with 91 octane. Many of the Evo guys who run those high-octane racing gases have special maps in their ECUs just for it.

Give RRM a call, they can probably tell you whether or not there'd be a benefit with their mapping.

 

Eh, higher octane is only bad if you drive your car like a grandmother. My car has never seen anything lower than 91 octane, never, not once. I'm at almost 25,000 miles and my engine runs strong. I redline the car in just about every gear, and the car sees 100mph+ on a daily basis, so, I think 91 octane is ok for my car. You just need to make sure you run your engine hard enough that the gasoline's flashpoint is met.

- Jason

 

It doesn't work that way. Running your engine harder doesn't increase your compression ratio or air/fuel mix, which is what it would take to meet the flashpoint of the higher octane fuel. As explained in posts up above, you're still not burning as much fuel as you could in your cylinders, sending more unused crap through your exhaust system, and wasting money.

 

That guy's correct, running the engine harder doesn't do much. The reason why running an engine hard every ONCE in awhile is good is to try to get rid of the deposits (or at least some) before they build up. Driven like a grandma, ANY car will get build up in the cylinders. Run 87 and give the engine a WOT acceleration every once in awhile. Don't do it all the time though, carbon doesn't build up in 2 weeks. It takes miles and miles to build up.

 

um... gasoline's flashpoint... you don't run hard on your car to meet the standards. There is two things that can meet the gasoline's flashpoint: compression ration (CR) or fuel/air ratio. You can't alter your CR unless you install a forged piston with higher CR. You can change the fuel/air ratio via fuel management unit. CAI or short ram wont do the trick because all you are doing is adding more air into the cylinders which then the computer adds more fuel to correct to the fuel/air ratio. So final say, NO, run hard on the car won't make it meet flashpoint.

Using higher octane fuel than the manual indicates will result in a big gas bill for each month. An engine that is designed for 87 octane can only burn that much. If you add in 91, the engine will be unable to use up all the fuel during the combustion stage. The excess fuel will leave the cylinders in the exhaust stroke of the engine. Then if your exhaust gas is hot enough, you might get flames (or spark plugs in your exhaust XD). Higher gasoline = higher price. If you dont need it, you dont need it.

 

remind me to post pics of the internals of my spare engine. I'm porting the head and there's carbon EVERYWHERE!!! All over the pistons (it's flakey), all over the head, on the valves (exhaust AND intake) some of the valves are so crusty that I don't know what the hell I'm gonna do to get it off and there's evidence of buildup in the intake chambers, too. I doubt the owner was getting moderately good power. I'll post comparison pics of the engine that's in my car currently when I do the head swap. I rarely shift before 4K RPM, only ever use 87 octane and take her to the track a couple times a month, so I'm pretty sure that any buildups are kept to a minimum (because I use the proper fuel) and then blown out (because I allow the car to rev in to the higher RPM range regularly).

 

Here is a simple rule:
Lower than car manual recommended gasoline: BAD
Higher than car manual recommended gasoline: OKAY (nothing bad to it, you just throw money out)
Same as car manual recommended gasoline: GOOD

Except with old car engines because they have lots of carbon buildup over the years. They need a little higher octane than normal.

 

OK, I get the point thanks to this thread, thanks, I'm switching to 87 from 92+. But I have been running at least 92 octane since I have had my RalliArt, and it now has 13000 miles on it. Did I screw up my engine already? I know I have carbon build up in my exhaust because I can see it at my tailpipe (even though before this thread I thought that black stuff was normal

Thanks,
Dan