Premium in a 5.3?

Colossus · December 9, 2016

It's a big debate here regarding 85 Octane.

Their thinking: 85 Octane is offered in many places above 4000 ft in place of 87. 85 Octane here at altitude translate to 87 Octane at sea level. 87 Octane here at altitude translates to 89 at sea level. 91 Octane at this altitude translates to 93 Octane at sea level. Air is thinner up here. That means gas burns differently. Now. All that has been the rule of thumb since the 60s and 70s and 80s. Before the days of fuel injection.

Now a days with computers controlling various things in the fuel and ignition system, It probably does not apply as much. Knocking isn't as big of an issue up at higher altitudes above say 5000 ft. The thinner air cuts down on knocking considerably. That has not changed. But given the computer controlled fuel and ignition systems - it will take all that into account. As I stated previously either on this thread or another- most modern vehicles, especially direct injection models, will take advantage of higher octane and adjust things accordingly which is why there have been many on here reporting noticeable performance gains when running premium grade fuel. I've noticed it myself on several of my gasies.

But, read for yourself and decide for yourself.

http://www.denverpost.com/2006/10/16/some-knock-states-lower-octane-levels/ (2006 Article)

http://mechanics.stackexchange.com/questions/6920/can-i-use-lower-octane-fuel-at-high-elevation

https://www.fueleconomy.gov/feg/octane.shtml

Dixon700 · December 9, 2016

I read a few posts here and there, I don't feel top tier gas is any better than anyone else. The bp at my work place, claims top tier gas, but I don't get better performance or economy than the snappys gas station by my house. My neighbors had a speed shop mostly for dirt track cars and sold race fuel, sunoco leaded 114 and 118 octane. Their fuel distributor tested gas from gas stations and only 2 of the ones he tested was even 87 octane with others being below that, so it seems at most gas stations you're buying garbage anyways??? So my question is wouldn't a bottle of octane booster be cheaper with each fill up?

Colossus · December 9, 2016

Octane booster is not really meant for modern fuel injected engines. Top Tier fuels are not meant to increase performance but rather to keep the fuel system/injectors and what not clean. Read: http://www.toptiergas.com/why/

Dixon700 · December 9, 2016

Octane booster is not really meant for modern fuel injected engines. Top Tier fuels are not meant to increase performance but rather to keep the fuel system/injectors and what not clean. Read: http://www.toptiergas.com/why/

So, top tier is just supposed to be cleaning inside. it's not supposed to be a better performing fuel. Why is octane booster not designed for newer engines? Would it not be the same as just running a higher octane fuel? If not, why?

TJay74 · December 10, 2016

octane booster in a bottle wont raise a tank of gas enough to even notice, at most it will take 87 octane to maybe 87.5 octane. for the cost of that bottle you could buy a whole tank of 91 and be a lot better off.

applewoodsb · December 10, 2016

More octane does not give more power. It is simply the anti nock rating. Once the octane level is high enough to prevent engine detonation or nock any more octane is useless. Similar to pouring 10ozs into a an 8oz cup. The extra 2oz were wasted. But it is possible that too low of an octane could reduce power. This would be because the knock sensor would detect knock and retard timing to prevent knock. Thus a loss in power, mileage etc. Once you have enough octane to prevent knock any additional does nothing.

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TJay74 · December 10, 2016

Correct, but as we are saying. The 5.3 trucks knock on 87, ALOT. hence why we are saying run 89 or 91. The compression ratio isnt that far off from the 6.2l trucks which require 91+ octane. While the 5.3 trucks will run on 87, the warmer it is outside the more time they spend in the low octane table and losing performance.

GMC2015 · December 10, 2016

Not trying to thread hijack, but I'm guessing that I should also run 89+ in the ecotec 4.3? They have the same compression ratio as the 5.3 (11:1).

Cowpie · December 10, 2016

When I lived on the front range of Colorado during the mid 70's to early 80's, there was 85 octane around then too. Nothing new and original. I had just been released from Fitzsimons Army Medical Center in Aurora, CO after being transferred there from overseas and I decide to go home to Iowa and bought a new ride. When I came back, I noticed 85 octane at the pumps and I pitched a fit about it. That is when, after talking with several folks in the know, that the altitude does not require as much octane to prevent knock due to lower air pressure at altitude that has a subsequent lower compression ratio in the cylinders.

That is counter to higher compression ratios building up in cylinders due to carbon buildup. If folks find they are getting a knock problem and have to run higher octane to counter it, it is just putting a bandaid on the problem. De-carbon the cylinders and the problem generally will go away.

Colossus · December 10, 2016

Ahh Fitzsimons. Had the pleasure of going into the old main hospital there after UofC HSC took over that part of the the old campus. <sigh> I hated seeing all the old stuff torn down but nice to see Children's Hospital and UCHSC get out of Denver and out to Aurora. Now if they can just get the new VA hospital finished up. Which they are.. thanks in large part to the Bridge & Dam builders, aka the good folks at Army Corps of Engineers.

DTOMKIDD · December 10, 2016

After running premium even more I love the benefits but I feel like these trucks don't like the cold. Not that it's very cold in California but it seems to me that as the temperature falls so does my mpg. Has anyone else noticed the same thing?

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diyer2 · December 10, 2016

IMO

If you live say below 5000 ft in elevation you may need to run a higher octane fuel. But I believe that's not neccessary for higher elevations. My truck yea a 2012 non DI engine lives from 5k ft. to 10k ft.

I may try a higher octane fuel for a comparison but I feel it's not necessary.

Colossus · December 10, 2016

Cold weather will always reduce fuel economy.

kstruckcountry · December 10, 2016

IMO

If you live say below 5000 ft in elevation you may need to run a higher octane fuel. But I believe that's not neccessary for higher elevations. My truck yea a 2012 non DI engine lives from 5k ft. to 10k ft.

I may try a higher octane fuel for a comparison but I feel it's not necessary.

Maybe not needed. But I prefer the way my pickup runs tuned on 91 in the mountains. If it's noticeable in an "old" engine, I'd think it'd be very noticeable in direct injection engine.

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Colossus · December 10, 2016

What mountains are you talking about. The little piddly hills like the smoky mountains out east, or REAL mountains above 7000ft? (No offense to you folks out east, I LOVE the Smoky mountains, beautiful, beautiful, beautiful!)