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Premium Unleaded Gasoline(91-93 Octane)


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#1 Jeff7353

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Posted 28 November 2006 - 04:50 PM

Just out of curiosity, how many of u guys are running 90 or above octane in your truck? I have recently switched to 93 octane and know for sure that I can tell a difference in acceleration and in engine noise. I know this subject has been beat to death, but give me your comments or suggestions on why u switched to high octane or not..... :confused:

#2 Jimmy J

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Posted 28 November 2006 - 04:58 PM

I've yet to try anything over 87 in my rig. Only 4200 miles on her. Our area only has 87, 89, and 93!!! What exactly do you mean by..."engine noise"? Good or bad?

Edited by Jimmy J, 28 November 2006 - 04:59 PM.

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#3 Scyry

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Posted 28 November 2006 - 05:07 PM

More octane means less energy per gallon of fuel. For example, E85 has a lot higher octane rating than premium gasoline, but it gives you lower mileage because it doesn't produce as much energy when you burn it. Therefore, the only thing you gain going to 90+ octane, is less chance of detonation. Factory tuned vehicles run so rich, that going to 90+ octane is worthless, performance wise.

Only benefit I could see, is most preiumn blend fuels have more detergents in them, so you can stave off carbon deposits longer. Also if you have pinging in your engine, going to a higher octane could lessen it, because the higher octanes basically don't burn as violently.
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#4 Jeff7353

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Posted 28 November 2006 - 05:11 PM

I've yet to try anything over 87 in my rig.  Only 4200 miles on her.  Our area only has 87, 89, and 93!!!  What exactly do you mean by..."engine noise"?  Good or bad?

<{POST_SNAPBACK}>

By engine noise I mean it seems to have quieted down a whole bunch from the normal ticking i usually hear..

#5 DSengineer

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Posted 28 November 2006 - 06:26 PM

I've yet to try anything over 87 in my rig.  Only 4200 miles on her.  Our area only has 87, 89, and 93!!!  What exactly do you mean by..."engine noise"?  Good or bad?

<{POST_SNAPBACK}>

By engine noise I mean it seems to have quieted down a whole bunch from the normal ticking i usually hear..

<{POST_SNAPBACK}>


Octane should not have any affect on CSK if that is what you are referring to. Mine ticks like a mother regardless of octane.

I use to strictly run 87 but now use 89 because I have to with my Wait4Me tune. Never even tried 91. No 93 here in Cali.....

#6 MustGoFaster

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Posted 30 November 2006 - 03:30 PM

More octane means less energy per gallon of fuel.  For example, E85 has a lot higher octane rating than premium gasoline, but it gives you lower mileage because it doesn't produce as much energy when you burn it.  Therefore, the only thing you gain going to 90+ octane, is less chance of detonation.  Factory tuned vehicles run so rich, that going to 90+ octane is worthless, performance wise. 

Only benefit I could see, is most preiumn blend fuels have more detergents in them, so you can stave off carbon deposits longer.  Also if you have pinging in your engine, going to a higher octane could lessen it, because the higher octanes basically don't burn as violently.

<{POST_SNAPBACK}>


You may want to recheck your source for the information that higher octane has less energy. You got it right later on - octane is more a measure of resistance to detonation of pregnition. Higher octane fuel allows you to run more compression/timing/boost etc.

the loss of energy is from the Ethanol - Ethanol has an extremely high octane rating - something like 118 or so, but the trouble with Ethanol is energy density - Ethanol has much less energy per gallon than gasoline, that's why the gas mileage goes down when you use alcohol fuels. You simply need more ethanol to produce the same power as gasoline.

as for factory tuning - I agree, often the stock computer is set way rich to prevent any detonation or spark knock. The car maker has to make the car usable in the widest range of areas, and often that means that they have to assume that the owner will use the cheapest gas available. therefore they have to set it rich so that it still can run even when you beat on the engine with cheap gas. That being said, the computer is able to adjust, within certain limits, how rich it runs, and it will run better on premium.

the bottom line - I did the math on my truck over 8,000 miles. filling up with premium gave me on average about 1 mpg better, it costs me about $2-$3 more to fill the tank with premium and I get about $5 worth of mileage out of it when compared to regular gas - it's fairly minor - but over the course of the life of the truck, even if I save $1 per tank - that's $250 by the time I hit 100k. 250 over 8 years is a pretty pathetic number I agree - but hey. it is what it is.

Edited by MustGoFaster, 30 November 2006 - 03:31 PM.


#7 clm7214

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Posted 30 November 2006 - 03:38 PM

My 6.0 runs much better on 89 than 87 octane. It is very noticeable. Going from 89 to 91 i cant even tell a difference in mpg or performance. I guess 89 is the upper limit of what my engine can adjust to. Therefore, i always run 89.
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#8 dewfpo

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Posted 30 November 2006 - 07:43 PM

I switched from 85 RUL to 91 PUL (high altitude octane) in my 8.1L to see if there was any noticeable difference in mpg, performance or anything else. I've run 5 tankfuls thru so far and experienced no change in performance or mpg (keeping close records). The only noticeable change is that when I warm start my engine there is always a noticeable single knock on startup with RUL and it is gone 95% of the time with PUL.

Just my observations.

For those of you stating these engines are set rich..... that makes absolutely no sense to me and is counter to everything I have heard. It's my understanding that modern engines are set to run as lean as they can go and the knock sensor(s) back off the timing if the engine knocks. Perhaps at WOT they may run a little rich to build max power but I seriously doubt they run rich most of the time. Just my 2 cents.

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Edited by dewfpo, 01 December 2006 - 11:27 AM.

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#9 Jimmy J

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Posted 30 November 2006 - 09:10 PM

Jesus...am I confused now! So which is it? Increased performance running higher octane or not? If there is any increase, does it justify the added expense per gallon?

Edited by Jimmy J, 30 November 2006 - 09:12 PM.

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#10 DSengineer

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Posted 01 December 2006 - 12:02 PM

For those of you stating these engines are set rich..... that makes absolutely no sense to me and is counter to everything I have heard.  It's my understanding that modern engines are set to run as lean as they can go and the knock sensor(s) back off the timing if the engine knocks.  Perhaps at WOT they may run a little rich to build max power but I seriously doubt they run rich most of the time.  Just my 2 cents.

DEWFPO

<{POST_SNAPBACK}>



Just talk to any of the custom PCM programmers (Jesse at Wait4Me, Nelson, Westers) and they will all tell you that they do indeed come set very rich from the factory.

Knocking is an indication of detonation, not necessarily a lean condition. You can be running dangerously lean with premium fuel and not have any knocking or other signs that your motor is on the verge of meltdown. Therefore relying on a knock sensor is not what I would call safe.

#11 Mattt

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Posted 01 December 2006 - 12:07 PM

I agree with clm7214 on this point My HD has the computer re-tuned, and there is a slight increase in power and mileage when I run 89 instead of 87. I see another 1-1.5 mpg with 89 vs. 87. Power wise, it accelerates better getting on the fwy. & I hear way less pinging with 89 in it. I think the 2 additional octane points is enough to keep it off the knock sensor. My understanding is whenever the knock sensor senses a ping it retards the timing instantly to combat that. Retarded timing = less power = getting on the go pedal harder to maintain accleration. Not really a noticable difference between 91 & 89. I only run 91 when towing my 10k lb. toyhauler trailer or 7k lb. boat.

And I agree with dewfpo on this point. I have Never heard of any factory program being set up rich. In fact, I've heard it is the opposite. The factory sets them up as lean as possible to meet their emissions goals. That is why they tend to ping on cheap gas, because they are so lean. I *think* when you have the computer re-programmed they also play with the fuel curve. More fuel = more power.

Now, I dont know much about the fuel that is available in CO, but I've heard it is different. Here in SoCal, we have std. 87, 89, & 91. Any way you cut it, pinging is bad for the long term health of a motor. So, in that case, if you have constant pinging you would want to run a higher octane fuel to combat the ping.

On a side note, my brother has an 01 1500 w/ 4.8, and his truck used to ping like a mother! After a throttle body clean, most of the ping went away while running the same fuel.

#12 MustGoFaster

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Posted 01 December 2006 - 12:12 PM

DEWFPO - what you've heard is correct - these engines are set as lean as they can be. my reply was probably a bit confusing. they are tuned out of the box to run as lean as they can on the minimum octane they spec out (usually 87) without knocking.
PUL is something that I have no idea about though - didn;t know they had high altitude gasoline for cars - I knew the stuff for planes is different - that' pretty cool info. Also, if you're at a very high altitude I'm guessing the effects of changing octane will be minimized for you. I have no scientific data to base this on other than when I was working with the supercharger on my buick, those doing the same modifications at higher altitudes had way more problems than those working closer to sea level. My only guess is that octane indexes are determined at or near sea level pressure conditions - lower pressure will undoubtedly alter the tests.

Jimmy J - gas stuf is mega confusing - there are opinions all over the board on it, and there always will be because everyone's car/truck is run different than others. Therefore it will always be subject to personal experience. some notice a difference, some don't. My sisters toyota is like that - the thing runds on 87 exactly the same as it does on race gas. (tested it with a scanner) same timing, spark advance, O2 readings - everything. My guess is that the eingines' running as efficient as it can get considering it's age, and the way it's configured. Most testing of octane and it's effects take place in a lab or other controlled environment. and for the most part, with such a small difference in octane ratings, you would have to have access to a scanner or other measuring tool to determine what any differences are taking place. seat-of-the-pants measurements are at best - just more opinions.

The important thing to consider is that 91 octane gas does have more potential than 87. but you have to have certain things in place to take advantage of it. Frmo what I have determined from talking with people who have worked with custom tuning for our trucks, the stock computer is capable of advancing timing and other settings within a limited extent. custom tunes simply take more advantage of that and in a simplified manner of speaking, give the base programming more "room" to work with" as well as taling off or remobing other limitations inherent in the stock system.

bottom line, day-to-day environments are so variable, that most people will only see a positive change in a small portion of their routine. It really comes down to personal preference, and trying it out. my numbers that I posted earlier were under certain conditions, primarily highway driving, and pulling loads. in day-to-day city driving, I admit that I see no real difference in mileage or power over regular gas. In the end, I suppose it'll be nearly a dead wash - but there's the mental factor, and for me I can afford to put in premium, so I always do. sometimes I come out ahead, sometimes not. This is the first time I've ever had a new vehicle, so we'll see how it ends up after the first 50,000 or so.

#13 DSengineer

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Posted 01 December 2006 - 02:07 PM

I *think* when you have the computer re-programmed they also play with the fuel curve.  More fuel = more power.

<{POST_SNAPBACK}>


Cutting out torque management and actually leaning out the fuel curve along with increasing timing is where most of the PCM tuners get more power out of a custom PCM tune. I get the same if not slightly better fuel economy with my Wait4Me as I did with my stock tune. So they are not just dumping more fuel into the equation to get more power.

I'm telling you guys the stock PCM's are set rich from the factor. Just pick up the phone and talk to any of the PCM programmers. They sit all day looking at these fuel curves. If anybody knows they do......

#14 lagrange151

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Posted 01 December 2006 - 02:38 PM

6.13 Can higher octane fuels give me more power?

On modern engines with sophisticated engine management systems, the engine
can operate efficiently on fuels of a wider range of octane rating, but there
remains an optimum octane for the engine under specific driving conditions.
Older cars without such systems are more restricted in their choice of fuel,
as the engine can not automatically adjust to accommodate lower octane fuel.
Because knock is so destructive, owners of older cars must use fuel that will
not knock under the most demanding conditions they encounter, and must
continue to use that fuel, even if they only occasionally require the octane.

If you are already using the proper octane fuel, you will not obtain more
power from higher octane fuels. The engine will be already operating at
optimum settings, and a higher octane should have no effect on the management
system. Your driveability and fuel economy will remain the same. The higher
octane fuel costs more, so you are just throwing money away. If you are
already using a fuel with an octane rating slightly below the optimum, then
using a higher octane fuel will cause the engine management system to move to
the optimum settings, possibly resulting in both increased power and improved
fuel economy. You may be able to change octanes between seasons ( reduce
octane in winter ) to obtain the most cost-effective fuel without loss of
driveability.

Once you have identified the fuel that keeps the engine at optimum settings,
there is no advantage in moving to an even higher octane fuel. The
manufacturer's recommendation is conservative, so you may be able to
carefully reduce the fuel octane. The penalty for getting it badly wrong,
and not realising that you have, could be expensive engine damage.

This is from FAQ.org
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