Originally Posted by rsdeo

The use of higher octane fuel will not harm your engine at all.

Yes high test has a higher flash point, but this will not hurt your engine. Most modern engines incorparate a knock sensor which will retard an engine igniton if detonation is sensed. This then reduces your performance.

Over the last 20 years of driving I have always filled with 94 octane fuel in my fathers Maxima, my three Supras and Tacoma. That is a lot of driving and no engine problems at all. A few friends have switched between fuel grades and found that most modern engines lose a little bit of power, hesitate a little and lose mileage when on a lower grade fuel.

I have never heard of or seen carbon build up because of the use of high test.

Originally Posted by Red Dragon

getting the higer octane is better. My parents have this old shagon wagon and it is a peice. they manuel say 89 octane which they use and they were complaning they van moves so slow and i told them to get 91 octane gas and YES you do feel a differance the car feels like it is brand new.

Originally Posted by Jesse00

Car manufacturers add a line to your manual about RECOMMENDED FUEL for a reason. That octane (or aki) is there so that people will know which type of fuel to use. Higher octane, more combustion it gives. But if your car suppose to run 87 and you give 92, your engine will not use up all the fuel, therefore, carbon buildup inside your cylinder. BAD THING TO HAPPEN. Its like a cancer, you wont notice anything until your car fails on you. So please use the recommended fuel as directed in your manual for the sake of your car.

Originally Posted by engineerboy

rsdeo- you won't ever get knock if you're using too high of an octane. Please take the time to read my explanation in my previous post (and follow the link for a nasty picture of carbon buildup in the cylinder head). I'm also interested to learn of your engine building/tuning background that you've never seen carbon buildup in an engine... I'd like to know the secret feel free to make corrections to what I wrote, as I'm really here to discover "truths" and to learn how to better extract performance and longevity from my car.

Originally Posted by thesreviceadvisor.com

WHAT IF I PREFER TO USE GASOLINE WITH HIGHER OCTANE RATINGS?

You can, but there are no real benefits, other than the gasoline manufacturers making more money off of you. When you use a fuel with a higher octane rating than your vehicle requires, you can send this unburned fuel into the emissions system. It can also collect in the catalytic converter. When you over stress any system, it can malfunction or not do what it was designed to do properly. In the early 90's, an early warning symptom was a rotten egg smell from the tailpipe. Easy fix, go back to using regular 87 octane gasoline. The rude odor usually disappears after several tanks of gasoline.

Originally Posted by canadiandriver.com

Many drivers believe that using a premium grade fuel is better for their vehicle and produces more power. Not true. As long as the fuel does not pre-ignite, any grade of fuel will produce the same amount of power. Save some money at the pumps and optimize your fuel economy by selecting the correct grade of fuel for your operating requirements.

Originally Posted by leeric.lsu.edu

Higher octane fuel contains more POTENTIAL energy but requires the higher heat generated by higher compression ratio engines to properly condition the fuel to RELEASE that higher potential energy. In the refining process, fewer gallons of higher octane fuels are yielded from a barrel of raw crude.

If fuel octane is too low for a given compression ratio, the fuel prematurely and spontaneously ignites too early and the fuel charge EXPLODES rather than BURNS resulting in incomplete combustion. The net effect is a loss in power and possible engine damage. The operator hears an audible "knock" or "ping", referred to as detonation. Detonation may vary from a faint noise on light acceleration to a constant, deep hammering noise while driving at a constant speed. Improper timing adjustments, vacuum leaks, or excessively lean fuel mixtures may also cause detonation.

Many vehicle owners believe that higher octane fuels are better for their vehicles since they are labeled "PREMIUM." The logic is that since it is a premium fuel it must be better. In reality, the premium label originates from the higher cost to refine and the resultant higher retail cost. Some refiners label their high octane fuels "SUPER." Some owners think that these fuels will make their vehicles more powerful. Only engines with high compression ratios can deliver all the potential energy from higher octane fuels! Always consult the manufacturer's octane recommendation to determine the proper octane requirements for any given vehicle. Generally, engines with compression ratios of 9.3 : 1 or less will safely operate with unleaded 87 octane fuel. Engines with higher compression ratios usually require higher octane fuels.

Originally Posted by engineerboy

Silly- What are you talking about? "I heard this lady did this".... you're not making any sense... But that's fine. If you want to spend the extra money on nothing, hey, you do what you want.
I started datalogging on my auterra today, and yes, the timing does advance, but BFD- it's advancing on my 87 octane, too.
when I'm done with this tank I'll go to 89oct. I'll do dyno runs, and timing datalogging.

It's been shown that the extra "power" you're feeling is more from the weight reduction caused by your wallet getting smaller than any real performance gains. It's psychological. But, like I said, I'll do dyno runs on 89 (because octane is octane, right and even a little more should produce some kind of result) and we'll see what happens. I'll also monitor the EGT and AFR (although I can't log them to post).

Where are your datalogs, seeing as how you've basically demanded mine? I'll show you mine, but I doubt I'll ever see yours.

rsdeo- Everything you said is true, but lancers, and most economy cars, do run really rich. The fuel may not "live" in the cylinders, but that extra carbon does get the chance to build up on its way back out of the engine. The intake and exhaust valves get equal exposure to the exhaust... if that much black can accumulate on the bumper of a car, why can't performance hampering carbon buildup in the cylinder? I guess we start to discuss break-in methods and ring clearances at this point ......
In Washington all of our gas is mandated to run at least 10% ethanol so we get the benefits you mentioned.

Originally Posted by sillypuddy

if you want to talk, back it up with data logs, not "i heard this lady did this" ****

Originally Posted by rsdeo

Once the fuel ignites from the spark all of it will burn. Nothing is left unburned because it is not compression ingniting the fuel. The only instance I have seen unburnt fuel is on some turbo modded cars were the fuel mixture was set excessively high. You will see a flash of flame out the exhaust especially if there is no cat.


I was talking about my own engines. They are not perfectly clean, but a lot better than what I've seen from others. I don't do engine rebuilds for others. Most people treat their engines really rough (lack of oil changes with poor quality oil, hard driving on cold engines, etc.) and you know what that means.

A lot of carbon build up on a lot of older engines is from burnt up oil. Blow by from rings and worse worn valve stem seals. Oil does not burn clean.

Try using gas with an ethanol mixture added. It burns cleaner (less emissions), raises octane and the alcohol absorbs moisture which is good for your tank.