Whay type of Gas?

Status
Not open for further replies.
Joined
Nov 16, 2002
Messages
37,903
Location
NJ
Most cars can run on regular, like mine, but I notice improvements using higher octance. I recently tried Sunoco Ultra 94 and it is really good. Anyone else try this? Also, is there any negavtives to using a higher octance? thanks
 
There really are no negatives in running a higher octane gas than you need, other than the extra cash that is lifted out of your wallet. The old stories of valves getting burned out from too high of an octane is just that, a story.

I will say this though, if your engine calls for 87 octane, there is no need to put in the higher stuff, since the engine is tuned to run on the lower stuff and won't take advantage of the higher octane with any more MPG or power. The spark curve of the car is set up from the factory to run on the lower octane, and unless you modify that curve (through an aftermarket computer program or chip) you won't see more power. And even if you did get an extra MPG or two, the money you spend on the premium would negate any gains in that regard.

Another thing that many people don't know is that if your engine calls for the higher octane stuff, due to being a turbo or supercharged application, or simply a higher compression engine, you can take advantage of some savings by stepping down to a midgrade fuel in the cold winter months. I do this every year in my LT1 Firebird, which runs 10.5 to 1 compression and definitely needs the high octane stuff in warm weather. But cool weather equals a lesser need for the high octane since the colder ambient temps mean less chances of the computer backing off the timing due to sensing spark knock. I have used a scan tool on my Firebird in cool weather which proves that 89 octane produces no spark retard all the way up to the legal speed limit (beyond that it kicks in a couple of degrees, but nothing major)
 
There is negatives to running higher octane fuel in a engine designed for low octane.

Low octane fuel burns easier, thus faster. High octane burns slower thus not as efficient.

When an engine designed to run low octane fuel, starts to rattle/knock upon acceleration, this is an indicator of carbon build up in the cyl which acts like a piece of charcoal does and stays hot, so when the fuel is injected into the cyl, instead of the fuel burning or igniting at the time when the plug sparks, the carbon, which is like the piece of hot burning coal, will set off the fuel prematurely thus blowing against the piston when it is traveling up to top dead center. This will severely affect you fuel mileage as well as power.

So, now, the mechanic/dealer says, well, use the prem high octane fuel. OK, now when the higher octane fuel comes into the same hot cyl with the coal like carbon, it again starts to ignite but it is much slower to burn so, it won't blow until it gets much hotter than the lower octane, so then the piston has time to make up to the top where it should be before the spark ignites the fuel, thus you get better mileage because you get the fuel to ignite at the correct time.

The down side to all this, since the higher oct fuel doesn't burn as efficiently it leaves more residue which adds to the existing carbon, so now if you decide to switch back to the lower octane fuel, you have more "coals" and it really starts to knock harder than it did before you switched. This is the down side.
 
Another negative to running too high an octane would be lost power. Many (most?) engines still don't have knock sensors. If they're designed for 87-89 octane (retarded timing) and you run 100 an excess portion of unburnt mixture will go right out the exhaust.

Have to mention the gasoline faq here again. More than you ever wanted to know... waitaminit, that doesn't apply here.
smile.gif


David

Edit: Whoops! Bob beat me to it, and then some.

[ December 07, 2002, 04:26 PM: Message edited by: OneQuartLow ]
 
My car can run Ok on 87 regular, & I did that almost exclusively for the first 88,000 miles or so. It can also take advantage of ~93 octane, *If* given enough warm-up cycles for the computer to finally adjust. Mileage, most of the time, is very close. I've run Chevron 93 almost exclusively now for 30,000 miles or so. The "Fun Factor" is much greater w/93 octane.
grin.gif


I've been told that late model Chevy & GMC V-8 pickup owners manuals specify 87 octane fuel *Only*, & that when people decide to give them a "treat" of Super unleaded, they start to give trouble within a few miles. Does anyone have any further information on this?

One last octane factoid: if all else is equal, theory says a vehicle should get best fuel mileage with the lowest octane that does not cause pinging. Why? short version, like Bob pointed out, lower octane burns easier, thereby giving up more stored energy.
 
some guy did a test that i know of with a dyno chart. he used 86 that was reconmended with his car. then used 89 and 91. he found that there is a loss of power of use of the gasolines.

his things were

new oil, and oil filter every time.

ran the car through 2 complete drains and filled it with the required gas..so you wont have a mixing

after 3 weeks dyno the car

found that he had less power. but it burned more cleaner.
 
my saturn seems to start better and run more smoothly on 3 octane gas than on 87. Can having higher mileage on the engine affect the type of gas you use?

--Matt
 
Have to agree with Bob on this and from personal experience. I have a '99 Kawasaki Vulcan 1500 Classic that is recommended fro 87 octane. Anything more and not only does the engine lose power(it doesn't ignite as fast) but carbons up real fast. Most all the Vulcan forum guys know this as gospel.
Perhaps the MC engine is more sensitive but the principles are the same. Running i.e., 93 octane in an engine calling for regular 87 will lead to carbon buildup and associated power loss and problems. It just burns too slow for an engine tuned for faster burning fuels. IMHO.
 
yea i agree with you...i feel a little power in my car, but thats what others say when they put higher octane in....when dyno charts come then it shows. i guess the car feels smoother casue its not igniting that fast, unless u have a vehicle wiht a advanced timming or high compression over 10 then it should be using high octane..if not then why waste money??
 
I ran my car on regular, low octane from the beginning and noticed an engine ping while excelarating at 2500 to 3000 rpms. When I switched to a higher octane, 93, it went away. I have been using a high octane ever since and I now have 100,000miles on it. Car and Driver wrote an article awhile back talking about the differences in fuel. A friend of mine read about it. He claims they did find a difference in power even if the car only called for low octane. So I guess if i switched back, i can tell if there is carbon deposit build up? I also never understood the differnce between and engine knock and ping? My manual refers to a ping sound. It sounds like metal rattling. It is a light sound and only occurs at a particular rpm. My old car did the same thing on low octane gas.
 
Yes, low rpm can exaggerate the effect. If the computer/vacuum advances the timing under throttle but rpm is still low then a cylinder will get spark too early and ignite the fuel when the piston is still rising. That's pre-ignition. Higher octane burns slower, so will reduce this problem at all rpm's. It usually goes away as rpm's rise because the piston gets to the top more quickly, before the fuel burns significantly.

So if you need higher octane to get rid of the pinging, use it. (Someone already said use the lowest that doesn't cause pinging.) Or see if you can't retard the timing somewhat if you'd like to run lower octane.

Errant firing may be called detonation, knocking, preignition, pinging, etc. Really, there are probably better explanations but here are the three causes I know of:

1) the normal spark ignites the fuel, but the mixture burns too fast.
2) deposits in the cylinder heat up (like little glow plugs) and ignite the a/f mixture early. (sometimes happens at multiple points or along with normal spark causing multiple ignition points and flame fronts collide - kaPing!)
3) or the mixture ignites spontaneously from cylinder heat and compression. (Under compression, gasoline changes (ask Mola) and has a much lower ignition temp) This may also happen at multiple points, likely from hot deposits and triggered by rising compression. Basically, if it's happening and changing octane fixes it, you're probably getting it from a combination of factors. They're all bad on the engine. Pistons pit, valves burn, rod bearings die (extra compression), spark plugs come apart, etc.

As I recall the gasoline faq I posted earlier has tons of info on this from smarter guys than I. Check it out.

3rd-cup-of-coffee-David
 
Mine calls for 91-octane. But I noticed 98-octane has less vibrations at idle and slightly quicker acceleration compared to 92-octane fuel.

Shell Extra 92: 0~100kph in 12.31secs
Shell V-power 98: 0~100kph in 12.15secs
 
quote:

Originally posted by OneQuartLow:
So if you need higher octane to get rid of the pinging, use it.

Isn't this treating the symptom rather than the disease? The engine was designed to run on 87 octane, if it pings excessively with it, to the point where a higher octane is needed to make it stop, there is a problem. Whether it is deposit buildup or a slight error in one of the components that controls timing, something isn't right and should be fixed.
 
The timing on these newer engines seems to be so precise that using a different octane than what is required can cause damage. My owners manual on an '02 Ford Explorer 4.0 SOHC V6 says to run 87 ocatane only, and that if it knocks excessively to bring it to a service center. It says using higher octane gas can damage the engine. I'm happy to save the extra $$ by not filling up with a higher octane gas. On all of my older cars, running a higher octane improved my gas mileage and therefore was justified.
 
Never heard of damaging the engine using a higher octane gas. Interesting....I wonder how this could be? With engines becoming more and more advanced and computerized, i guess it should be no surprise.
 
Status
Not open for further replies.
Back
Top