Went to Glenwood Springs / Carbondale (flew to Denver, rented a car).  When I filled it, the cheapie gas (hey, it's a rental) is 85 octane.  The owners manuals for my cars are 87 and 91.  So, my question is: do you guys run 85?  Is there an additive for anti knock (the rental Toyota Camery LE ran fine)?

p.s. of course I visited Doc's grave!

I noticed that, my Crown Vic ran it, Ethanol gas gave it knocking in NY later though.


I run 93 Octane here in GA

The thinner air. I figured that I should fill up in the mountains (in NV) with 87 octane, cause I was gonna end up running flat out in the desert and I didnt think it would be enough octane once I got out of theh mountains.

Octane is fuel retardant , the higher the number the slower it burns and the higher the flashpoint is . In the less dense air of Denver a more volatile fuel is more efficient  .

Although  99% of late model vehicles are Mass Air Flow ( MAF ) controlled fuel delivery so they adjust to varying altitudes and temps because they are weighing the mass of air entering the engine . Max efficiency is at Stoichiometric ratio - or - 14.7 to 1 and is measured in pounds . There is a whole lot more that goes into the calculation , like throttle position , Engine Temp , load . etc which is all written into a 3D fuel map stored in the VCM .
I wont even start with adaptives like EWMA (Exponentially Weighted Moving Average)  Let's just say that most naturally aspirated late model vehicles can run on 85 octane Anywhere , and you'd never know the difference

Quoted: Octane is fuel retardant , the higher the number the slower it burns and the higher the flashpoint is . In the less dense air of Denver a more volatile fuel is more efficient  . Although  99% of late model vehicles are Mass Air Flow ( MAF ) controlled fuel delivery so they adjust to varying altitudes and temps because they are weighing the mass of air entering the engine . Max efficiency is at Stoichiometric ratio - or - 14.7 to 1 and is measured in pounds . There is a whole lot more that goes into the calculation , like throttle position , Engine Temp , load . etc which is all written into a 3D fuel map stored in the VCM . I wont even start with adaptives like EWMA (Exponentially Weighted Moving Average)  Let's just say that most naturally aspirated late model vehicles can run on 85 octane Anywhere , and you'd never know the difference

Yep, retarded timing if necessary. Thing is, I'm not sure if my Triton V-10 is up to it. And its definitely not something I would try if I was running a rice box at 20 PSI

Quoted: Yep, retarded timing if necessary. Thing is, I'm not sure if my Triton V-10 is up to it. And its definitely not something I would try if I was running a rice box at 20 PSI

Your Triton ( Please Dont Bring it to me for Plugs ) is COP ( Coil On Plug ) ignition , there is no way to adjust timing so in the past Ford added an octane shorting bar ( Plug Actually ) spacifically for this . I'm pretty sure they still include it on the IEDIS your truck uses  . Its there to retard timing 3-4° For when Ford sells those vehicles in 3rd world countries with high alcohol low octane fuels.

Quoted: Quoted: Yep, retarded timing if necessary. Thing is, I'm not sure if my Triton V-10 is up to it. And its definitely not something I would try if I was running a rice box at 20 PSI Your Triton ( Please Dont Bring it to me for Plugs ) is COP ( Coil On Plug ) ignition , there is no way to adjust timing so in the past Ford added an octane shorting bar ( Plug Actually ) spacifically for this . I'm pretty sure they still include it on the IEDIS your truck uses  . Its there to retard timing 3-4° For when Ford sells those vehicles in 3rd world countries with high alcohol low octane fuels.

Thanks. Damn, I am reminded why I love this site!

That put you in my neck of the woods.

I think I'm nearly the only arfkomer on the Western Slope. Or at least the only one who spends too much time here.

And what the other guys said about high altitude lowering the octane requirements.

and you'd never know the difference

We keep detailed records here at work on mileage driven and fuel bought, and in my experience, that's not true.  We have cheap Chevy station wagons, Ford & Chevy vans, and a few Ford pick-ups, and on every one of them, they got such worse gas mileage that it cost us more to use the cheap 85 octane gas than it did to buy the more expensive 87 octane.  A local company tried to sell us the 85 in bulk at 13% less than the price of 87, and it just wasn't worth it.  Also, the performance suffered terribly on both the Fords and Chevy's.  We carry a minimum of about a ton and a half of armor, shelves, lock boxes, and equipment in them, and the performance went from bad to worse.  I timed a couple of the Ford vans (in a privately owned parking lot where it was legal) from a stop to 40, and with 85 octane it was three seconds slower than with 89.  Retarding the timing hurts performance.  As any shade-tree mechanic.z

Quoted: Quoted: That put you in my neck of the woods. I think I'm nearly the only arfkomer on the Western Slope. Or at least the only one who spends too much time here. And what the other guys said about high altitude lowering the octane requirements. Well, I may be joining you. After my first year of living here in CO. I will be moving to a more "permanent" part of the state. I really like the Western slope of CO, so perhaps I'll buy my first house there.

Ok, the high altitude / lower octane makes sense.  It's real pretty there, I think I passed every famous ski area on I-70 on my way in from Denver.  If you're moving there, bring money.  A real estate office had a sold sign on a Victorian in Glenwood Springs for $320,000.  Oh, and every other sign I saw in Glenwood Springs was "Kerry / Edwards".  

Quoted: Quoted: Your Triton ( Please Dont Bring it to me for Plugs )   You know, I have always wondered why its so damn hard to change the plugs on a Ford? I have done it far too many times than I wish I had. Ford, while I think they make good trucks. Seems to not want anyone else but the dealer doing services.

The 4.6L is easy to change.

Want some real fun change them in a 350LT1

Quoted: Quoted: Quoted: That put you in my neck of the woods. I think I'm nearly the only arfkomer on the Western Slope. Or at least the only one who spends too much time here. And what the other guys said about high altitude lowering the octane requirements. Well, I may be joining you. After my first year of living here in CO. I will be moving to a more "permanent" part of the state. I really like the Western slope of CO, so perhaps I'll buy my first house there. Ok, the high altitude / lower octane makes sense.  It's real pretty there, I think I passed every famous ski area on I-70 on my way in from Denver.  If you're moving there, bring money.  A real estate office had a sold sign on a Victorian in Glenwood Springs for $320,000.  Oh, and every other sign I saw in Glenwood Springs was "Kerry / Edwards".

And it only gets worse the closer you get to Asspain.

Come on over M4.

I exchange e-mails with a guy on the Colo.AR15 board who lives in the Grand Jctn area, but I don't know if he does any more than an occasional lurk here.

Mahalibi lived in G.J. but he's gone AWOL lately. Don't know what happened to him.

Quoted: Octane is fuel retardant , the higher the number the slower it burns and the higher the flashpoint is . In the less dense air of Denver a more volatile fuel is more efficient  . Although  99% of late model vehicles are Mass Air Flow ( MAF ) controlled fuel delivery so they adjust to varying altitudes and temps because they are weighing the mass of air entering the engine . Max efficiency is at Stoichiometric ratio - or - 14.7 to 1 and is measured in pounds . There is a whole lot more that goes into the calculation , like throttle position , Engine Temp , load . etc which is all written into a 3D fuel map stored in the VCM . I wont even start with adaptives like EWMA (Exponentially Weighted Moving Average)  Let's just say that most naturally aspirated late model vehicles can run on 85 octane Anywhere , and you'd never know the difference

Uhhh, yeah, what he said! Karl.

I have a really stupid friend, a Democrat naturally, who buys the higher grade gas becasue he is worried that the 85 octane will void his warranty.
And he wonders why he never has any money.

At this altitude, I've always ran 85 in my '97 Nissan PF, '98 Honda VFR (782cc FI V4), and '89 CB-1 (carb).  No problems.

-z

Quoted: That put you in my neck of the woods. I think I'm nearly the only arfkomer on the Western Slope. Or at least the only one who spends too much time here. And what the other guys said about high altitude lowering the octane requirements.

Nahh, Bumblebee_Bob, there's at least one other - me, about 90 miles down I-70 from you.  I think I saw on another post that you live in Glenwood Springs...I'm in Grand Junction.

And I spend way too much time here, too.  

Quoted: At this altitude, I've always ran 85 in my '97 Nissan PF, '98 Honda VFR (782cc FI V4), and '89 CB-1 (carb).  No problems.

OK guys, I have a supercharged Xterra SE - manual says the supercharger works best with high-octane fuel, so I've always put 91 in it here in CO.  Should I downgrade to 87?  It runs great on 91, just wondering if it might get better mileage with 87 or something.

Dave

If it starts knocking, shut her down quick!

I think ECU computers will automatically adjust timing if knock is detected....  is this not true?

-z

I moved to CO in 96 with my 87 nissan 300zx turbo.  It ran fine on 87 octane 'regular' in VA, but knocked like hell up here at altitude on 85 octane.  I had to run it on 91 premium until I got rid of it.

Quoted: That put you in my neck of the woods. I think I'm nearly the only arfkomer on the Western Slope. Or at least the only one who spends too much time here. And what the other guys said about high altitude lowering the octane requirements.

I may not be on the west slope, but I am higher than all of you.

BTW, Do you know where Doc shot his last man?

SRM

I have an old 1984 Bronco full size with the 300 CID (4.9l) that I bought nearly new in 1985.  The only thing that it's ever seen is the 85 octane sold here (I live in Colorado Springs, about 6200 ft altitude).  So, it's either driven at 6200 ft or higher.

I've never had a problem with this fuel in this engine (pushing 185,000 miles on the engine).

85 octane is fine at altitude...

Quoted: Quoted: That put you in my neck of the woods. I think I'm nearly the only arfkomer on the Western Slope. Or at least the only one who spends too much time here. And what the other guys said about high altitude lowering the octane requirements. Nahh, Bumblebee_Bob, there's at least one other - me, about 90 miles down I-70 from you.  I think I saw on another post that you live in Glenwood Springs...I'm in Grand Junction. And I spend way too much time here, too.

Huh, he told me he lived in Rifle, CO.

Western slope (Palisade) here!

The higher the altitude the lower the cylinder pressure, so the lower the octane needed. Very general decsription put loosely in laymans terms for most people out there.

Ambient temperature also has a lot to do with this. Engines are more prone to 'ping' or 'knock' (detonate) at higher temperatures, mostly to do with combustion chamber design and what goes on inside when detonation (sometimes called preignition) takes place. For example, my late model high-performance vehicle (2000 Dakota R/T 5.9) will tolerate 85 octane in the dead middle of winter and 87 octane in the early spring and late fall. As soon as the ambient temperature gets above about 85*F, I must go to 91 octane fuel, or it pings like crazy on hills and under part throttle acceleration. And yes, I've checked its OBDII system thoroughly!

Most late model vehicles have knock sensors in their engine management systems to avoid damage when detonation or preignition occurs, but when the knock sensor sees this condition the first thing that it does is to retard the ignition timing to pull the engine out of trouble. This causes a lack of power and loss of fuel milage among other things. Not good. An extreme case of detonation will also cause the fuel management system to go to full rich condition and will basically put the system in a 'limp home' mode. Also not good.

There is no hard and fast rule for octane requirement at high (govt says over 4000ft) altitude driving. Internal combustion engines vary at least as much as our AR's do from one to the next. Two points of octane rating lower that what's recommended at sea level is a good rule of thumb for the uniniated to use, but that's not carved in stone. Use your brains. If your car is knocking on 85 go up a grade until it doesn't knock anymore. Never mind what the owners manual says. Remember the adage - YMMV!