redpoint

How does a lower octane increase carbon buildup? Is there a link you recommend I read to learn about octane caused deposits?

moneyfornothing

Just bought an 07 TSX with 24k miles on it. Been researching this issue over the past few days. Been reading posts from people who say 87 is ok, and those who don't.

I did run across these, which basically make my mind up. I am going to go with 87. It is a .40 a gallon difference here (I can only find 93). This equals about $400 a year or so for me.

http://www.aboutacura.com/2007/12/ca...-my-acura.html

http://usatoday30.usatoday.com/money...emiumgas_x.htm

elsaic15

wow i never realized how much that really adds up to

Iceman

When I'm in the city, I can find cheap (8 cents above regular) premium gas, so I use it. 8 x 15 = $1.20, which is chump change no matter how poor you are. When I'm on a road trip, the price of premium can be astronomical, but the price of 89 octane is usually pretty close to regular, so I use it. My gas mileage has been fine with 89 octane.

My question for everyone is, when do you think you are putting the most load on the engine? Stop-and-go driving, or highway driving? When do you put your foot to the floor, and want that extra horsepower that 91 octane gives you? I say it's when you're driving around town. When I pass cars on the highway, I usually don't bother downshifting from 6th gear. You need 91 octane in the city in order to get the most out of this engine.

redpoint

In the PDX area, Mid-grade is 89 octane and sells for 10 cents above regular 87. Premium is 92 octane and sells for 20 cents more than regular. So you can spend 10 cents more than regular to get 2 more octane, or 20 cents more to get 5... If I could find 89 octane for only 8 cents over, that is what I would use all the time.

Engine load is mostly a function of throttle opening. The further the skinny pedal is pressed, the greater the throttle opens, and more air enters the engine. The denser air is hotter, and requires a higher octane to resist premature detonation. Since octane requirements are largely dependent on air density, a lower octane may be used at higher elevations. In Colorado, "regular" gasoline is only 85 octane.

Since air densities are only high near full throttle and at lower elevations, most of the time lower octanes are sufficient. Burning premium just to cruise on the interstate is a waste. That said, if you are at lower elevations and punch the throttle frequently, then higher octanes are appropriate.

I tend to give 80% throttle and shift early (3100 RPM) while accelerating to maintain a high engine load. This is an efficient way to accelerate. Since the load is high and I live near sea level, I stand to benefit from higher octanes.

mrdre78

Would using 87 octane cause your check engine light to come on?

redpoint

Not likely. What code is being thrown?

thoiboi

Sure

mrdre78

P0420 but I found out it's the catalytic converter. Now my airbag light is on FFS

BROlando

I know that this is an ancient thread.

93 (or 91 for some) does return better MPG. Even on the highway. This is a modern car that will take advantage of as much timing advance as possible.

However....around here, 93 is ~30% more expensive than 87. I'm not going to get 30% better MPG. So....I use 89.

I use 89 octane for ONE reason. 87 causes quite a bi of pinging at many load/RPM scenarios.

89 causes some small amount of audible pinging too. But I have to lug the engine pretty hard to cause it. In winter, its a bit worse. Seems like the coldness does not make up for the denseness.

My "commute" is like 5 miles per day now. In summer, its even less because I ride my bike more. So its not that I can't afford 93. 93 just doesn't make any logical sense.

kurtatx

Thanks for clarifying