Why Cheap Gas Doesn't Pay In The Long Run [Archive] - GrandAmGT.com Forum

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PhantomLover007
10-07-2007, 05:47 PM
Mike Rosania
Clean fuel injectors are a must for peak engine performance, fuel economy and emissions. If the injectors are dirty and can't deliver their normal dose of fuel, performance, fuel economy and emissions are all going to suffer. Dirty injectors can't flow as much fuel as clean ones, nor can they delivery the correct spray pattern that is so essential for clean, efficient combustion. The fuel feedback control system will compensate for the leaning effect once it is in closed loop, but it can't correct the underlying condition that is causing the problem.

Where do the deposits come from? Mostly from the fuel itself. Gasoline is a mixture of many different hydrocarbons, including oilfins, which are heavy, waxy compounds. The heavier the hydrocarbon, the more energy it yields when it burns. When the engine is shut off, the injectors undergo heat soak. Fuel residue in the injector nozzles evaporates, leaving the waxy oilfins behind. Because the engine is off, there is no cooling air flow through the ports and no fuel flow through the injectors to wash it away, so heat bakes the oilfins into hard varnish deposits. Over time, these deposits can build up and clog the injectors.

The formation of these deposits is a normal consequence of engine operation, so detergents are added to gasoline to help keep the injectors clean. But if a vehicle is used primarily for short-trip driving, the deposits may build up faster than the detergents can wash them away.

Now here is the potential problem with purchasing cheap petroleum. To save a few pennies per gallon and to increase the competitive and/or profit margin of gasoline, some suppliers have cut back on the amount of detergent they add to their fuel or have switched to cheaper and less effective additives. Commonly used deposit-control additives include polysibutylamine, polyisbutylene succinimide and polyisobutylene phenylamine. But these same additives also can build up on intake valve stems causing them to stick. To prevent this from happening, additional additives called "fluidizers" must also be added to the fuel. But, over time, these can contribute to the formation of combustion chamber deposits that raise compression and the engine's octane requirements.

Dirty injectors lean out the fuel mixture and contribute to lean misfire, hesitation and even detonation. Cleaning should restore like-new performance. One of the best additives is polyetheramine. It keeps injectors, valves and combustion chambers clean without the help of any additional fluidizers - but it costs more than twice as much as the other commonly used additives. How much additive does it take to provide an adequate level of protection? Industry sources say the recommended level is about 1,000 parts per million (ppm) of dispersant-detergent in the fuel - which costs the gasoline supplier less than a penny a gallon. Even so, as much as 85% of the gasoline that is being sold contains only one-tenth of the recommended dosage, or only 100 ppm of additive. Consequently, using cheap gas contributes to the formation of injector deposits.

The benefits realized by injector cleaning obviously will vary depending on the condition of the injectors prior to cleaning and how badly they were clogged. Injectors that are really dirty should show more of a noticeable improvement in performance than ones that have only a light accumulation of deposits. Either way, performance, fuel economy and emissions should all be better after a cleaning. Most high-mileage engines as well as engines that are used mostly for short trip stop-and-go driving are the most likely prospects for injector cleaning. Some experts recommend cleaning the injectors every 25,000 to 30,000 miles to keep them flowing at peak efficiency.

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Next time your fuel gage hits “E,” realize that saving a few pennies at the pump could ultimately cost you the price of new Fuel injectors. If you are concerned with getting better gas mileage, consider installing a SCT Tuner. Performance tuners can reprogram your car’s factory settings, delivering fuel mileage gains of up to 2 MPG. –Mike Rosania


But isn't it not good to run a GA on 91 octane?

Sprucegagt
10-07-2007, 07:20 PM
Notice it says "cheap petroleum" not low octane gas. It basically explains why Shell and a few other companies are a little more expensive than others.

Grreen99GT
10-07-2007, 08:09 PM
i run my grand am on 91 octane

nickofcourse
10-07-2007, 08:32 PM
unless your car has a turbo or super charger or you are running nitrous, there is no reason to run anything but 87 octane which is what the factory suggests.

Grreen99GT
10-07-2007, 08:36 PM
idk, my car runs better being on 91

AaronGTR
10-07-2007, 09:02 PM
idk, my car runs better being on 91


And you have some kind of proof of this? :rolleyes: Sorry, but the placebo effect doesn't count. Unless you have conducted some sort of testing that showed evidence of improved performance or milage with 91, which I doubt, you should only be running 87 octane. The only reason to run higher octane is running boost, running nitrous, or using a tuned pcm with advanced timing.


Basically what the article is saying is don't buy the cheapest 87 octane you can find. Spend the extra 2 cents per gallon or whatever and buy some higher quality 87 octane from a larger reputable retailer. You are more likely to get those detergents that will keep your engine clean and running well over the long run.

Grreen99GT
10-07-2007, 09:07 PM
i have read something on this forum somewhere about the benefits of higher octane (even without being turboed, supercharged, etc). i really have never been sure, but you know more than i do about this so i will listen to you

rocketfast123
10-08-2007, 06:01 PM
89 is just right for me. 87 equals 12Mpg in the summer, 89 equals 14Mpg.

I never turn my a/c off in the summer.

Panacea
10-08-2007, 10:58 PM
89 is just right for me. 87 equals 12Mpg in the summer, 89 equals 14Mpg.

I never turn my a/c off in the summer.

Wow, either your car sucks, or you just suck at driving... My GT would get 17mpg during the winter time, and that's driving like a mad man...

DomesticFreak
10-09-2007, 01:58 AM
i have read something on this forum somewhere about the benefits of higher octane (even without being turboed, supercharged, etc). i really have never been sure, but you know more than i do about this so i will listen to you

Octane rates the fuel's resistance to ignition. The higher the octane, the higher the resistance. Therefor, if you're using lets say 91 Octane as you are, on a engine designed for 87, you actually making the engine work harder to burn that fuel. It can cause pre-mature ignition, knocking, and detonation problems, and in the long run (I've seen this first hand) all that knocking (and so on) will cause your engine to die sooner. I've seen a fried piston come out of a car from a guy who was using 93 octane on an engine designed for 87. Car had 100k and needed an engine re-build because he usedg such a high octane from day one.

Now, if your boosted/Nitrous injection, you WANT that higher resistance, because your forcing more Air(NOS) into the engine and you don't want the fuel igniting too early.

That should clear up a few things...

AaronGTR
10-09-2007, 04:54 PM
Wow, either your car sucks, or you just suck at driving... My GT would get 17mpg during the winter time, and that's driving like a mad man...


Yeah, no kiddin'. I still got better milage than that even after I added the SC. The car is rated for 20mpg city/32mpg highway from the factory. Either there is something wrong with his car, he's not measuring his milage correctly, or he's flooring it everywhere he goes.

nychris83
10-10-2007, 04:21 PM
Yeah, I get 28 mpg on 87 octane w/ my GT consistently, and I do very little highway driving. Oh, by the way I'm new here, nice site.

nickofcourse
10-13-2007, 08:27 PM
anyone use speedway, and where does speedway get its gas from?

nickofcourse
10-13-2007, 08:28 PM
Yeah, I get 28 mpg on 87 octane w/ my GT consistently, and I do very little highway driving. Oh, by the way I'm new here, nice site.

wanna trade cars? i get way less than that and i just do city driving

fo44rd
10-19-2007, 06:12 PM
wanna trade cars? i get way less than that and i just do city driving

I get around 28 MPG mostly city driving, but I do drive like an old man pretty much cracking off shifts in the 1,700 to 2,200 range and locking up the torque converter at 38 mph or so, except when its cold out the computer wont release the torque converter until the car reaches a set operating temp.

cardude007617
10-01-2008, 02:49 PM
alright well this is the first octane thread i saw thats somewhat close to my thought here. every week i take a trip home from college and its about 110 miles or so, all freeway. i know there are no gains from putting in higher octane fuel, but would i gain any mileage (i have the cruise set at 73-75 usually) by putting in mid grade? or would i just waste my money and hurt my mileage?

eric99gt
10-01-2008, 06:53 PM
waste. Refer to domestic freaks post above

Mike Jung
10-01-2008, 08:15 PM
waste. Refer to domestic freaks post above

Octane rates the fuel's resistance to ignition. The higher the octane, the higher the resistance. Therefor, if you're using lets say 91 Octane as you are, on a engine designed for 87, you actually making the engine work harder to burn that fuel. It can cause pre-mature ignition, knocking, and detonation problems, and in the long run (I've seen this first hand) all that knocking (and so on) will cause your engine to die sooner. I've seen a fried piston come out of a car from a guy who was using 93 octane on an engine designed for 87. Car had 100k and needed an engine re-build because he usedg such a high octane from day one.

Now, if your boosted/Nitrous injection, you WANT that higher resistance, because your forcing more Air(NOS) into the engine and you don't want the fuel igniting too early.

That should clear up a few things...
I would take that with a grain of salt.

Higher octane gasoline causes pre-mature ignition, knocking, and detonation problems ?

FuriousG
10-01-2008, 11:21 PM
I switched to 91 octane after installing my new ECM since PFYC recommended the change. I'm assuming the new programming was better suited to 91. I know that a stock engine is better at the recommended octane but what about those who have the performance tuned ECM? Are we wasting our money buying 91 octane?

Rich
10-01-2008, 11:23 PM
no. if youre tuned for 91 or 93, thats what youre supposed to use.

99GTCoupe
10-02-2008, 08:29 AM
Mike, I think he meant in reference for a car not designed for it, but I dunno lol


I run 89 and my engine sound smoother than running at 87. There have been many posts on it and a decent amount seemed to say the same thing. I figured I'd try it out, and it works for my car. As for gas mileage, I dunno on that. All I know is I hit up BP, only change to that is the three times in the past year I had to hit the Marathon (Mobile? I think Marathon, though) by my house. Midgrade all the way

peshields
10-02-2008, 09:38 AM
I put in the expensive stuff at the pump. I figured it out one day to see if i was losing money or not, and with the mileage change from 87 - 93 octane, I'm actually saving a little. My average city mpg on 87 was around 18.5, on 93 its 20. Now there is a $0.30 difference between 87-93 where I live, so if you figure that on a tank, (12 gallons) I'm getting 240 miles @ 93, and 222 @ 87, thats a difference of 18 miles. since 18 miles is nearly worth 1 gallon of octane 87, thats $3.75, (give or take depending on gas prices)

Now, compute $3.75 x 12 for octane 87 = $45
$4.05 x 12 for octane 93 = $48.6
Difference - $3.60

I can also break it down by price per mile,
87 octane - $0.2027 / mile
93 octane - $0.2025 / mile

Same mileage cost, but with 87 octane I have to fill up more often, and with 93 octane, my car FEELS like it runs better. Like eating steak vs ramen noodles, if they cost the same, why not eat steak?

350rs
10-02-2008, 04:11 PM
dont forget that higher compression motors need that higher octane as well. my camaro was around 11:1 and ran terrible on 87. and best on 93 obviously. so thats all i ever ran in it. i tore that motor apart a month or so ago and its clean as a whistle. no fried pistons, nothing out of the ordinary for a 35k mile engine ( i wanted more power, thats why i tore it down). of course i had a warped head and fried seats when i hit about 330 degrees.. ;crap

however. i run nothing but 87 in my GA and im gettin mid or upper 20's city and low 30's highway. Thats at around 70. i baby this car though, my toy is well. most of you know what my toy is..

AaronGTR
10-02-2008, 04:20 PM
I put in the expensive stuff at the pump. I figured it out one day to see if i was losing money or not, and with the mileage change from 87 - 93 octane, I'm actually saving a little. My average city mpg on 87 was around 18.5, on 93 its 20. Now there is a $0.30 difference between 87-93 where I live, so if you figure that on a tank, (12 gallons) I'm getting 240 miles @ 93, and 222 @ 87, thats a difference of 18 miles. since 18 miles is nearly worth 1 gallon of octane 87, thats $3.75, (give or take depending on gas prices)

Now, compute $3.75 x 12 for octane 87 = $45
$4.05 x 12 for octane 93 = $48.6
Difference - $3.60

I can also break it down by price per mile,
87 octane - $0.2027 / mile
93 octane - $0.2025 / mile

Same mileage cost, but with 87 octane I have to fill up more often, and with 93 octane, my car FEELS like it runs better. Like eating steak vs ramen noodles, if they cost the same, why not eat steak?

You have no idea what you are talking about. You can't just fill up at the station with twice with different kinds of gas and measure how much you put in and figure out your gas mileage by that. That is not a scientifically accurate method. There are too many variables like driving different routes, different amounts of throttle for traffic conditions, even weather... You'd have to run the car on a dyno at the same throttle position, for the same amount of time, with the same atmospheric conditions, and completely draining the tank when switching fuels to make sure they don't mix and change the octane. THEN, you could test to see if the octane changes your gas mileage.

Or you could just do some research and you'd find out it's already been tested and octane has absolutely NO affect on gas mileage... so you are wasting money.