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Raging gas prices..what octance are you running?


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Hey guys,

Since I just got my tahoe I filled her up with supreme. Well that cost me nearly $60. :driving: I was wondering if running 89 octance would be that bad?? What are most of you running since gas prices have soared?? On a side note, it looks like they are starting to slowly come down here. :thumbs:

 

Thanks,

Chad

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Here in Colorado we can buy 85 octane which is the cheapest so I've been fiiling up with that. I hope that doesn,t hurt anything. I think the owners manuals say to use at least 87 octane because of "spark knock". I haven't heard any so far so I think I'll still use the 85 octane and save a few bucks til prices come down more (hopefully) Does anyone know if I may be damaging my engines using 85????

 

:driving:

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If you don't have an aftermarket tuner or custom PCM (advanced timing), you don't really need to run high octane...at least I never did. In fact, when I ran 93 octane on my stock tune, I got 1 MPG less, on average for 3 tanks worth. 87 octane did fine, no pinging or anything unusual.

 

Now that I have the PCM tuned though, I gotta run the 93 octane. It's only about $4 difference for me @ 20 gallons, and since I'm getting 2 MPG better than stock, I'll keep buying it. :-)

 

:driving::thumbs:

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Here in Colorado we can buy 85 octane which is the cheapest so I've been fiiling up with that.  I hope that doesn,t hurt anything.  I think the owners manuals say to use at least 87 octane because of "spark knock".  I haven't heard any so far so I think I'll still use the 85 octane and save a few bucks til prices come down more (hopefully)  Does anyone know if I may be damaging my engines using 85????

 

:thumbs:

 

 

 

I personally wouldn't run 85 octane in a vehicle. The lowest I would go would be 89 probably. But, thats me.

 

 

On a side note, I just realized I mis-spelled "octane" in the thread title. :driving:

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I'm on my final tank of a six tank comparison of mileage / drivability between 87 and 93 octane gas in my truck ('04 5.3l Silverado Z71 ECSB w/3.73 rear end).

 

I've posted about what I'm doing in one or two other topics here, but this is as good a place as any to post my updates (actually better- thanks to the octane question).

 

Basically, I have been buying my gas from the local Sam's Club since I bought my truck, and I usually have bought their cheapest. They only offer 2 grades- 87 and 93, which btw is a minor correction from what I posted before where I said I thought their lowest was 89, for anyone wondering about the discrepancy. I started my test mostly because my father has been complaining that his '04 is getting poor mileage unlike my own, despite being mechanically the same (engine, gearing, 4wd drivetrain, etc.). He also happens to swear by name brand high octane gas only in his vehicles, to the point of ribbing me that I'm running "that crap" in my truck. This got me interested in whether or not the octane of fuel he's using has anything to do with the mileage he's seeing, and so I decided to see if it had any effect on my truck..

 

Note that while I have a DIC, I always manually calculate final mileage when filling up, and thanks to the same father that got me started on this I've ALWAYS done so. I'll use the exact numbers from that log once I'm done with my experiments. The ones below are rough estimates off the top of my head (in other words, probably within .5 mpg at worst :driving:).

 

So far:

3 tanks of 93 (I'll post more exact numbers once I finish the complete test, but these are close)

lowest mpg tank: low-mid 18's. (I attribute this more to bad weather than the gas- I usually see better mpg on sunny windless days and worse on rainy / cold / windy days.)

highest mpg tank: mid-19's (19.5 or 19.6)

rough trend of high 18's low 19's.

Pretty much the same as what I'd observed on prior tanks of 87. But since I'd just put my new Fold-a-Cover on right before starting the high octane test, I had to run three tanks of 87 with the cover, just to factor any effect that might have out..

 

2 tanks of 87

lowest mpg tank: around 19.2

highest mpg tank: 19.3

guesstimate of the mpg for the current tank (I'll find out this evening..): 19.5+ (DIC reads 20.3 right now. Read 19.5 for tank 1 and 19.7 for tank 2. Allowing for the optimistic numbers it has been providing..)

 

Since I decided to compare low octane to high octane, I've since decided to also include name brand gas vs. generic gas (with Sam's Club representing the generic stuff). This is partly to test my father's theory, and partly because I recently found a GM TSB covering multiple vehicle lines that suggests using only gas stations that have certain cleaning additives in their fuel. Techron, maybe? I don't recall the name- but the TSB in question was nice enough to list all the current brands / stations that carry fuel with the additive, among which Shell was one. There just happens to be a Shell station right on my route to and from work. So my fillup tonight will be there (and I'll record the results for this final tank of Sam's 87 while I do it). I'm going to do 3 tanks of the Shell low octane and 3 high octane again, just to see if maybe being a name brand AND high octane makes a difference. My gut instinct is that it won't though. (I'll most likely stick with shell for the cleaning agent though, which is supposed to be in ALL of their fuel grades.)

 

My results at this point lead me to believe that the octane of the gas has little effect on the mpg and performance of my truck, so long as it meets the minimum spec GM has placed in my manual. I haven't noticed any difference in power, and the mileage numbers haven't changed enough to be really significant (could just be slight variations in traffic, etc. to produce the slight changes I'm recording so far). If I WERE to think they were significant, I'd have to say that the low octane actually was higher more consistently than the "good stuff" though.

 

BTW, asilverblazer. I understand what you're saying about the cost (45 already, what's 5 more..). Multiply that $5 by the number of tanks of gas you'll pay for in any given year and try to repeat that though.. ;)

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Guest chevydeerhunter

I've got the 4.8 in my truck and if I'm not mistaken, the manual recommends using at least 87 octane. Personally, I use 89 octane which is the middle of the three around here. I filled up a couple of months ago with 86 and I definitely noticed a knock so for that tank, I ended up buying an octane booster and away went the knock.

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Im useing 89 right now due to a slight spark knock when climbing the hills around town with a load.

 

I do think I get a about 1mpg better with shell than anything else.

 

Also you can get away with 85 in your truck in the higher elevations like the rockies of Colorado. You can hardly never find that stuff unless your way up there. And I don't fully remember why you can use a lower octane in a higher elevation...........so I'll leave it to someone else.

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I know everyone will swear I'm wrong, but running the lowest octane rating without causing detonation will yield the best fuel economy and power. Without being able to change the timing the extra octane does nothing to your performance or efficiency. The only thing it may have are additional additives to keep things clean. To be more scientific, higher octane gas is more resistant to igniting. This lets you increase cylinder pressure raising volumetric efficiency, i.e. making more power. A gasoline that is harder to ignite does nothing to make your engine perform better if it will run on a lower, faster burning fuel without detonating.

 

I run strictly 87 on my stock truck. Got 19.8 outta my last freeway trip, 4.8l 3.42 gearing regular cab truck, 05'. I run 93 in the vette, but I have the timing advanced pretty far to take advantage of that fact. No computers there to mess with.

 

Controversial I know, but there's no scientific basis to it making more power in a stock engine. *flame suit on* I look forward to the mileage results in the above mentioned test. Even a 10mph headwind significantly impacts gas mileage on a freeway trip.

 

-Matt

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We bought fullsized vehilces with a 26 gallon tank and a V8 listing around $30,000 give or take, why do so many bitc* about the gas price issue. Yes, I know it is high and it is getting higher, with slight dips, but I knew that when I bought the truck.

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We bought  fullsized vehilces with a 26 gallon tank and a V8 listing around $30,000 give or take, why do so many bitc* about the gas price issue.  Yes, I know it is high and it is getting higher, with slight dips, but I knew that when I bought the truck.

 

 

 

 

 

I don't think anyone was more or less complaing about gas prices. The question in a nutshell was what octane is worth it.

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With the Hypertech Power Programmer I tuned it to run on premium so thats what I run,Either Sunoco 93 (Not the Ultra 94,thats a waste of $$ for sure) or Exxon 93.

We don't have any Chevron gas stations around here but there is quite a few on my way down to N.C. so when I go down there I'll fill up with there premium also since its on GM's "Top-Tier" gasoline list.

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We bought fullsized vehilces with a 26 gallon tank and a V8 listing around $30,000 give or take, why do so many bitc* about the gas price issue. Yes, I know it is high and it is getting higher, with slight dips, but I knew that when I bought the truck.

 

 

I think Dennis Miller put it best. "What is the big deal with paying $2 to move a 6000 lb SUV 15 miles down the road? Sounds like a bargain to me!"

 

 

Personally, I run 89 octane in both rigs. Around here, 89 octane is now CHEAPER because Illinois decided to increase the fuel tax on NON-ethanol gasoline. I have always run 89 octane, which contains 10% ethanol and in the past paid 3 cents per gallon more for it.

 

I will also put my flame suit on too, but I have had NO adverse effects from running the ethanol and have gotten great milage from it too. Besides, I am a farmer. If I can not help use the product I produce, what good am I???

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