Foo - Octane levels and temp.

I've been told that lower octane levels burn more cleanly at a certain cold temperature. I need to know first of all if this is true, and second if it is, what temp is it where you want to switch to 87?

I disabled my EGR valve, so this is important.

Get rid of that FORD and get a Chevy. Heeey. Ford, Furd.............heh.

Fords always screw me over.

Fords always screw me over.

Thats because you have a ford car. Mine may as well be a truck the way its built. And ford trucks are built to last.

Ok. So mich. You're deep in the heart of the funzone, and siu is going to the funzone. What the heck is the funzone then.

Is it like the discovery zone? if it is, I want in.

Ok. So mich. You're deep in the heart of the funzone, and siu is going to the funzone. What the heck is the funzone then.

Is it like the discovery zone? if it is, I want in.
More like Chuck E. Sleaze. :rolleyes:

Ok. So mich. You're deep in the heart of the funzone, and siu is going to the funzone. What the heck is the funzone then.

Is it like the discovery zone? if it is, I want in.

DZ is for small kids. Us grownups have fun, like in the funzone.http://www.thehighroad.org/images/smilies/fce32f95.gif

Don't know about a "funzone," but I know "I can't stop messing with danger zone...." :rolleyes: *thinkin' she-bop*

DZ is for small kids. Us grownups have fun, like in the funzone.http://www.thehighroad.org/images/smilies/fce32f95.gif
For some reason when I think back to when I was like 10, I get the most awesome warm feelings when I think about DZ. That place was so much fun.

Lowers temps allow more heat to flow from the radiator, and consequently, from the engine block. How much? Who knows, it depends on the specifics. I wouldn't suggest dropping below the manufacturer's rating unless not going to flog the engine for that tank. And reconnect your EGR valve, it may increase the intake charge temps, but it also reduced pumping losses at low load, which increases mileage. Not to mention the emissions side. Disabling the EGR valve in order switch to 87 octane gas for financial reasons is... eh, kinda pointless. Not that you're doing this, but if you are, don't. And a few cents is not worth risking high load detonation, and your engine...

That, and many ECUs will run the vehicle very rich if you disconnect the EGR.

That, and many ECUs will run the vehicle very rich if you disconnect the EGR.


I told him that. Thank you for the back up. :)

Get rid of that FORD and get a Chevy. Heeey. Ford, Furd.............heh.

Chevy:D , i have a cavalier. Runs very well indeed.

Chevy:D , i have a cavalier. Runs very well indeed.
I have a chevy cavalier too. The spark plug wires like falling off while I'm driving. :D

I installed them myself.

The spark plug wires like falling off while I'm driving. :D

Did you ins...


I installed them myself.
nevermind :rolleyes:

Did you ins...

nevermind :rolleyes:
Hey. I installed the push button starter too.

I got skills.

I've been told that lower octane levels burn more cleanly at a certain cold temperature. I need to know first of all if this is true, and second if it is, what temp is it where you want to switch to 87?

I disabled my EGR valve, so this is important.EGR lowers the combustion-temperatures in the chamber by diluting the air-fuel mixture with exhaust. This serves to lower NOx emissions. If you disconnect it, you may gain a little power from hotter-combustion. I have no EGR or air-pump in my car at all and tune for emissions with the laptop.

As for octane, ther's A LOT of misunderstandings and misconceptions on what "octane" refers to. Please review the Gasoline FAQ (http://www.repairfaq.org/filipg/AUTO/F_Gasoline.html) for background info. I also wrote up a summary of what octane is and isn't here: CornerCarvers - Mixing Race Gas and 91 Octane, What do you get? (http://corner-carvers.com/forums/showthread.php?t=10704#post120353) (post#18 halfway down page).

As for lower-octane burns "cleanly at cold temps", it's actually a side-effect of the change in gasoline blend during the winter months. Typically, 92-octane is the highest you get at the pump. In the winter, alcohols and other oxygenates like MTBE are added to provide extra oxygen in the fuel. Up to 10% is usually added. This has the effect of lowering gas-mileage because you have fewer hydrocarbon atoms per gallon (oxygen molecules are damn BIG!). It also has the effect of increasing evaporative volatility (Reid Vapour Pressure) of the gasoline, something you actually don't want in the hot summer months. And it lowers octane of the gasoline to 91-octane.

So yes, the 91-octane gas with alcohol/MTBE DOES burn cleaner in the winter (as in lower HC emissions during the warm-up). But that's not because of the lower octane, it's because of the additives. It's also possible to add other additives along with the alcohol like toluene/xylene and actually raise the octane to 93 and still have a cleaner burning fuel than the summer blend.

As for 87 vs. 91 octane, there's no difference as far as the additives package. It's changed at the refinery depending upon the weather. Only two concoctions are delivered to the gas-stations, 87 & 91. These are blended 50/50 to give the 89-octane blend in the middle. They ALL burn equally "clean" in terms of emissions.

I should also add that EGR increases intake charge temperature, but limits peak combustion temperatures. Just so those two don't get confused.

When the engine is running cold, your exhaust combustion won't be that clean. I have a carburetored car, and in the morning the fumes smell like burned gas. After it's warmed up, it smells clean or at least not bad. Anyways back on subject, octane level will not have anything to do with how clean it burns. Higher octane just burns at higher temps then lower octane gas. So with higher octane, the engine creates more compression, that's pretty much it.



P.S. Octane mostly has an effect on how the engine is running, not how clean it burns the fuel. A well tuned engine will burn gas properly and will be clean.

Burned gas? Uh oh. Mine smells like condensation. During high idle warm up it seems like your air/fuel mixture might be off. Unless mine is not rich enough.....

When the engine is running cold, your exhaust combustion won't be that clean. I have a carburetored car, and in the morning the fumes smell like burned gas. After it's warmed up, it smells clean or at least not bad. Anyways back on subject, octane level will not have anything to do with how clean it burns. Higher octane just burns at higher temps then lower octane gas. So with higher octane, the engine creates more compression, that's pretty much it.
Higher octane actually = lower flash point with hotter and more even flame front from the detonation in the cylinder as well as a greater release of energy from the same volume/mass of fuel air mix.

Kind of like the difference between ammonium nitrate/diesel fuel vs propane/O2(Pure) mix

Burned gas? Uh oh. Mines smells like condensation. During high idle warm up it seems like your air/fuel mixture might be off. Unless mine is not rich enough.....
Yea...when your car warms up at 2500rpm it smells like that. My car is run completely by vacuum. There is only the slow heater choke that is electronic, otherwise it's all vacuum. Honda designed this engine to ruin very rich during warm up. It will only smell like burned gas when its warming up at 2500rpm. After about 5 minutes, tap the gas and the idle will go down to 1500rpm and everything smells fine. Then when the engine has warmed up completely, the idle goes to 950.

Higher octane actually = lower flash point with hotter and more even flame front from the detonation in the cylinder as well as a greater release of energy from the same volume/mass of fuel air mix.

Kind of like the difference between ammonium nitrate/diesel fuel vs propane/O2(Pure) mix
c`mon im 16, give me a break.

c`mon im 16, give me a break.
Arm...or leg?:D ;)

Higher octane just burns at higher temps then lower octane gas. So with higher octane, the engine creates more compression, that's pretty much it.That's completely NOT TRUE. Back to the Gasoline FAQ (http://www.repairfaq.org/filipg/AUTO/F_Gasoline.html) for you! ;)

Here's the pertinent section: Chapter 6) What do Fuel Octane ratings really indicate? (http://www.repairfaq.org/filipg/AUTO/F_Gasoline6.html#GASOLINE_001). The ONLY thing octane indicates is AKI-anti knock index. There's even disagreements on how to quantify knock. Regardless of that, octane is NOT:

- combusion temp
- flash-point (ignition) temp, actually radical akyl-group formation is what causes knock
- flame-front propagation speed
- combustion pressure
- power (87 will yield exact same power as 91 on same engine)
- emissions
- smell, taste or any other perverted uses you have for gasoline.

All the above factors can be custom-tailored in gasoline independent of the octane-rating.

my truck "pings" with 87 so I usually put in the 93 Supreme or whatever it is.

Yea...when your car warms up at 2500rpm it smells like that. My car is run completely by vacuum. There is only the slow heater choke that is electronic, otherwise it's all vacuum. Honda designed this engine to ruin very rich during warm up. It will only smell like burned gas when its warming up at 2500rpm. After about 5 minutes, tap the gas and the idle will go down to 1500rpm and everything smells fine. Then when the engine has warmed up completely, the idle goes to 950.


I'm talkin' 70 Chevelle here. No FI.

I'm talkin' 70 Chevelle here. No FI.

:beer: .

I've been told that lower octane levels burn more cleanly at a certain cold temperature. I need to know first of all if this is true, and second if it is, what temp is it where you want to switch to 87?

I disabled my EGR valve, so this is important.

OK, a lot of things here. First, does the manufacturer of your car/truck recomend premium fuel? If not you are wasting your money putting it in (unless you experience knocking). Also burning more cleanly and what you heard are probably incorrect, but here is some information to think about.

An increase in ambient air temperature of 5.6 degrees Celsius increases the octane requirement of an engine by 0.44 - 0.54 MON. When combined with air temperature and humidity, it is possible to use one octane grade in summer, and use a lower octane rating in winter. The Motor Octane rating has a higher charge temperature, and increasing charge temperature increases the tendency to knock, so fuels with low Sensitivity ( the difference between RON and MON numbers ) are less affected by air temperature.
At most we can change only a point or 2 of octane on say, a 30 degrees Celsius difference which is definately possible. If you factor in the average RON and MON for octane ratings (MON is typically higher), the effect of temperature is probably less than that.

I'd say that it's definitely possible that you could move down a grade in cold conditions. Especially since "most" drivers will "take it down a couple notches" in the winter when there is snow and ice around.

That being said, the price between grades is not all that much relatively speaking, so why not give yourself piece of mind if you can afford it.

Unh-unh, people. <incomprehensive Vega look>


Check this. :D

This, fellow Foo'ers...is a ride. <said with quiet Vega reverence>

Unh-unh, people. <incomprehensive Vega look>


Check this. :D

This is a ride. <said with quiet Vega reverernce>
Here is a hot Vega! Remember this car from the 70's?
http://www.draglist.com/artman/uploads/daily_stories/d7_panic.jpg:D

Um no. This is a car.

http://www.geocities.com/wilson_j182/67.jpg

I promised Mich I'd give him a ride in this.


http://i123.photobucket.com/albums/o286/Flycrow/ta.jpg

I promised Mich I'd give him a ride in this.


http://i123.photobucket.com/albums/o286/Flycrow/ta.jpg

Nice:D .

Or we could cruise in this.


http://i123.photobucket.com/albums/o286/Flycrow/car001.jpg

We should roll through east oakland in that green one.

Awwww Hell NO. And come back with what? Door handles? That's all Im gonna be left with after they jack us.

Maybe I should get that shotgun Mich was telling me about......... hmmmmmmmm.



So Jon, shall I post the red one you saw that I brought to the mall that day?

You should get a shotgun. Next load of money I get I'm either buying a fork or a shotgun.

Yea, post the red one. I have a thing for that car, it's totally sexy. Red baybuh.

Aw crap. No red car pics. Ehhhhh. It looks like the black one. Just photoshop it red and there ya go.

Goat Farmer

http://www.oldride.com/rustyphotos/174_1.jpg

I'm talkin' 70 Chevelle here. No FI.
Still, you have a V8? Comparing to an inline 4 with the 2 barrel that runs on one barrel until past 4000rpm's:)

So i notice you guys flashing your cars. Lemme flash my recent.
http://i37.photobucket.com/albums/e58/russian03rustler/DSCF0007-2.jpg
http://i37.photobucket.com/albums/e58/russian03rustler/DSCF0005-3.jpg
Almost 144k miles.....weee


P.S. My hubcaps are going back on soon after i get them painted. Later on i will have some Integra rims on on her, aka Fat Fives.

Here's the one I'm lusting after:

http://www.norcal-saac.org/archive/images/cobra_daytona.jpg

1st of 6 ever built
390bhp weighing in at a portly 2300 lbs

no one ever sells one and the last one that did kinda went for $4-mil....

Here's the one I'm lusting after:

http://www.norcal-saac.org/archive/images/cobra_daytona.jpg

1 of 6 ever built
390bhp weighing in at a portly 2300 lbs

no one ever sells one and the last one that did kinda went for $4-mil....
Is that a race version of the Cobra?

no one ever sells one and the last one that did kinda went for $4-mil....

Whoah! 4 mill? Christ, definitely not a driver... I guess I don't see the point in museum pieces outside of a museum. :p

What is that, Siu? A '68 or a '70 SS?

BTW, in the end, 'Vettes rule. Give me a '76 Buckskin or '78 Light Beige. :D <droooool>

Here is a hot Vega! Remember this car from the 70's?
http://www.draglist.com/artman/uploads/daily_stories/d7_panic.jpg:D
'73 GT?

So i'm the only import loser here? Ok..i feel special.

Whoah! 4 mill? Christ, definitely not a driver... I guess I don't see the point in museum pieces outside of a museum. :pYeah, they found it lost in a storage unit where it had been sitting for decades. Here's the story:


Car & Driver - Death, Deception, and the $4 Million Cobra (http://www.caranddriver.com/features/3406/death-deception-and-the-4-million-cobra.html)
CarMemories.com - CSX2287 - The long lost Prototype Daytona Coupe (http://www.carmemories.com/cgi-bin/viewexperience.cgi?experience_id=87)
NorCal Shelby Club - Missing Daytona Coupe found! (http://www.norcal-saac.org/archive/csx2287.html)

What is that, Siu? A '68 or a '70 SS?

BTW, in the end, 'Vettes rule. Give me a '76 Buckskin or '78 light beige. :D <droooool>

70 SS 396 all original. Custom order. Build sheet. Matching numbers. Never been hit. Bought it at 89,000 miles (not too many more, probably about 3k more) and only drive it to car shows. :)