85 Octane Gas in Colorado
Bill Bowen
never seen 85 sold anywhere else - is it an altitude issue? My owners
manual recommends 87 octane, but can I safely use 85 - I have the V8.
David Cooley
It's strictly due to altitude. Thinner air means less static
compression in the engine = less octane requirement.
Will be fine for your V8.
Clark Huffman
Perhaps you are trying to say that the engine has slightly lower pressure
at TDC of the compression stroke?
Anyway, for another reason, fill up with low altitude gas and then drive
in the mountains on a hot day. Be sure to bring a book and some water
because there is a fair chance of vapor locking so you may be setting
somewhere waiting for it to cool off.
Higher octane fuel usually has a higher vapor pressure so it tends to
be slightly more suseptable to problems at altitude. Of course Avgas
is formulated just a bit differently...
As for the question about using 85 or 87 octane, if it rattles with the
85, don't use it. The old 302 used to be fine with whatever gas was
handy (white gas anyone?) but with fuel injection and computer
controlled ignition, the current 302 may not be as tolerant.
Clark
David Cooley wrote in message <38DE5DEB...@bellsouth.net>...
David Cooley
Clark Huffman wrote:
>
> Ok, I'll bite, W.I.T.H. is "static compression"?
Cylinder pressure
>
> Perhaps you are trying to say that the engine has slightly lower pressure
> at TDC of the compression stroke?
>
That's what static compression is.
> Anyway, for another reason, fill up with low altitude gas and then drive
> in the mountains on a hot day. Be sure to bring a book and some water
> because there is a fair chance of vapor locking so you may be setting
> somewhere waiting for it to cool off.
>
Fuel injected vehicles do not vapor lock. Time to get with the 20th
century!
Clark Huffman
David Cooley wrote in message <38DEBAE6...@bellsouth.net>...
>
>
>Clark Huffman wrote:
>>
>> Ok, I'll bite, W.I.T.H. is "static compression"?
>
>Cylinder pressure
>
>>
>> Perhaps you are trying to say that the engine has slightly lower pressure
>> at TDC of the compression stroke?
>>
>
>That's what static compression is.
First you say static compression is "Cylinder pressure" now you
seem to agree with my description. Which definition do you
want to use? Hint - cylinder pressure is non-descriptive.
Another hint - static compression is non-descriptive.
Now, please consider the reduction in max observed cylinder pressure
because of altitude (static pressure in your terminology).
Lets keep it simple and assume ideal gas behavior (not because
we have to, but because the compressibility factors are very close to 1)
Assuming an engine with an 9:1 compression ratio and using the relationship
PV|1 = PV|2 (isothermal) or P2 = PV|1/V2 (note V1/V2 = 8) :
At sea level, P2 = 14.7 * 9 = 132 psia
At 5,000 ft, P2 = 12.26 * 9 = 110 psi
This is enough of a change (about 17%), so that gas may be formulated
differently. Now throw in the fact that lower octane fuel behaves better on
hot starts
and is cheaper to produce, and we get our lower octane fuels in Colorado.
As for the original question, I'll stand by my advise. Use the lower octane
fuel only if it doesn't rattle...
Yes, at this point I'm trolling - but Cooley deserves it in my
book. He posts a lot, frequently giving out gratuitus abuse.
Maybe the the abuse is his outlet, I dunno, but it is inappropriate
in this public forum.
>
>> Anyway, for another reason, fill up with low altitude gas and then drive
>> in the mountains on a hot day. Be sure to bring a book and some water
>> because there is a fair chance of vapor locking so you may be setting
>> somewhere waiting for it to cool off.
>>
>
>Fuel injected vehicles do not vapor lock. Time to get with the 20th
>century!
:-) 20th Century? Ok, no problem...
Hmm, what's that lump of aluminum setting on top of the intake
manifold on my '84 F-150? Looks a whole lot like a carb.
Now please describe the mechanism of vapor locking and why
many newer vehicles rarely vapor lock. Another hint - look at
fuel pump location and cooling.
Now, if you'd like to change your comment to vehicles with
fuel pumps located outside the engine compartment rarely
vapor lock, I'll agree whole-heartedly. (I'd even agree with
the rarity of vapor locking on any system with the fuel pump
not bolted to the block.)
Dr. Bob
Mechanical compression ratio is what most folks and car companies brag
about, the volume of the cylinder at BDC plus the chamber volume
divided by the volume of the cylinder at TDC plus the chamber volume.
Making the broad and foolish assumption that there is no leakage and
perfect pumping, one could calculate cylinder pressure if one knows
the air density. One of the major factors in air density is the
absolute pressure of the gas used to charge the cylinder, a factor
that changes fairly predictably with altitude when we are talking
about common air.
One can reasonably conclude that, assuming again that all other
factors are equal, the static compression pressure (or cylinder
pressure at TDC on the compression stroke) will be lower in a car at
5000 ft altitude than it will be at sea level.
Will the car run on 85 octane at 5000 ft? Try it! In cold weather,
you may find the car easier to start thanks to the lower vapor
pressure of the winter fuel. If it pings/knocks on the 85, switch up.
On Mon, 27 Mar 2000 07:52:36 -0700, "Clark Huffman" <c...@uswest.net>
wrote:
Clark Huffman
Dr. Bob wrote in message <38dff18e...@netnews.worldnet.att.net>...
>Is not static compression pressure the same as cylinder pressure?
Dunno, never heard those terms in my part of the world. I find the terms
non-descriptive of engine charateristics. Compression, in my
business, is a ratio with either a target outlet pressure or a source
pressure. Cylinder pressure can be just about anything and it varies
constantly.
Anyway, with respect to the original question, if someone needs
input on whether 85 or 87 octane is ok to use in a 5.0L, I sort of
doubted they had a handle on "static compression". Of course,
they may not know "tdc" either.
>
>
>Mechanical compression ratio is what most folks and car companies brag
>about, the volume of the cylinder at BDC plus the chamber volume
>divided by the volume of the cylinder at TDC plus the chamber volume.
>Making the broad and foolish assumption that there is no leakage and
>perfect pumping, one could calculate cylinder pressure if one knows
>the air density. One of the major factors in air density is the
>absolute pressure of the gas used to charge the cylinder, a factor
>that changes fairly predictably with altitude when we are talking
>about common air.
In general, I don't disagree with you at all. On a technical note, I
don't directly require air density to calculate the ideal pressure
at tdc on the compression stroke (as noted in my post) or static
pressure. Boyle's law and info on atmospheric pressure
is sufficient. As for the "broad and foolish assumption of no
leakage and perfect pumping", well, ok, guilty as charged with
just one reservation - how about equal leakage and inefficiency
in pumping? :-)
Of course, atmospheric pressure is function of density so knowledge
of density is sufficient to solve the problem.
>
>One can reasonably conclude that, assuming again that all other
>factors are equal, the static compression pressure (or cylinder
>pressure at TDC on the compression stroke) will be lower in a car at
>5000 ft altitude than it will be at sea level.
Ummm, I believe my previous post demonstrated the math on that one.
Not that I disagree with your conclusions one bit. Looks like I neglected to
account for the volume contribution of the combustion chamber. Oh well.
>
>
>Will the car run on 85 octane at 5000 ft? Try it! In cold weather,
>you may find the car easier to start thanks to the lower vapor
>pressure of the winter fuel. If it pings/knocks on the 85, switch up.
Yup, always consider the pragmatic approach...
Thanks for your contribution on the brake bleeder setup and other
topics Dr. Bob.
Clark
David Cooley
Clark Huffman wrote:
>
> >That's what static compression is.
>
> First you say static compression is "Cylinder pressure" now you
> seem to agree with my description. Which definition do you
> want to use? Hint - cylinder pressure is non-descriptive.
> Another hint - static compression is non-descriptive.
>
The term static compression means the cylinder pressure at TDC (In PSIG)
which you calculated in your math below.
> Now, please consider the reduction in max observed cylinder pressure
> because of altitude (static pressure in your terminology).
>
> Lets keep it simple and assume ideal gas behavior (not because
> we have to, but because the compressibility factors are very close to 1)
>
> Assuming an engine with an 9:1 compression ratio and using the relationship
> PV|1 = PV|2 (isothermal) or P2 = PV|1/V2 (note V1/V2 = 8) :
>
> At sea level, P2 = 14.7 * 9 = 132 psia
>
> At 5,000 ft, P2 = 12.26 * 9 = 110 psi
>
> This is enough of a change (about 17%), so that gas may be formulated
> differently. Now throw in the fact that lower octane fuel behaves better on
> hot starts
> and is cheaper to produce, and we get our lower octane fuels in Colorado.
>
> As for the original question, I'll stand by my advise. Use the lower octane
> fuel only if it doesn't rattle...
>
> Yes, at this point I'm trolling - but Cooley deserves it in my
> book. He posts a lot, frequently giving out gratuitus abuse.
> Maybe the the abuse is his outlet, I dunno, but it is inappropriate
> in this public forum.
>
Maybe if pompous assholes like you didn't poke, prod, and harass me for
giving a simple, to the point answer, maybe some of my posts wouldn't be
so abusive. You have a fucking problem with me then you email me and
we'll deal with it in private.
Otherwise, shut your fucking mouth. This is not a moderated group and
you don't fucking own it!
Got it asshole!
> >
> >> Anyway, for another reason, fill up with low altitude gas and then drive
> >> in the mountains on a hot day. Be sure to bring a book and some water
> >> because there is a fair chance of vapor locking so you may be setting
> >> somewhere waiting for it to cool off.
> >>
> >
> >Fuel injected vehicles do not vapor lock. Time to get with the 20th
> >century!
>
> :-) 20th Century? Ok, no problem...
>
> Hmm, what's that lump of aluminum setting on top of the intake
> manifold on my '84 F-150? Looks a whole lot like a carb.
>
> Now please describe the mechanism of vapor locking and why
> many newer vehicles rarely vapor lock. Another hint - look at
> fuel pump location and cooling.
>
> Now, if you'd like to change your comment to vehicles with
> fuel pumps located outside the engine compartment rarely
> vapor lock, I'll agree whole-heartedly. (I'd even agree with
> the rarity of vapor locking on any system with the fuel pump
> not bolted to the block.)
Vapor locking is the process where gas in the fuel line boils and causes
the fuel pump to lose it's prime.
On a fuel injected engine, the fuel pump is in the fuel tank, and the
fuel system is a continuous recirculating system (IE: fuel goes to a
pressure regulator that returns some to the tank to maintain it's set
pressure). Regardless whether you have TBI or PFI, you will never see
vapor lock on a fuel injected engine.
Now go grow a fucking brain!
Clark Huffman
David Cooley wrote in message <38E026D7...@bellsouth.net>...
>
>
>Maybe if pompous assholes like you didn't poke, prod, and harass me for
>giving a simple, to the point answer, maybe some of my posts wouldn't be
>so abusive. You have a fucking problem with me then you email me and
>we'll deal with it in private.
>Otherwise, shut your fucking mouth. This is not a moderated group and
>you don't fucking own it!
>Got it asshole!
>
Pompous, yes it was a demonstration, I plead guilty as charged.
Poke, prod, and harass, not in my opinion since I had a point.
Your "simple, to the point answer" did not include a warning on possible
damage due to detonation. Nor did you include a means to recognize
a potentially damaging situation. In short your advice was incomplete
and potentially harmful.
As for the rest of your comment, please take your own advise. You
may certainly suggest that I "shut my * mouth", but such advise is
in direct contradiction to your statement regarding the fact that this
is an unmoderated group.
Please clean up your language and present yourself in a reasonable
tone. And while you're at it, consider dropping the abuse since is serves
no purpose.
>
>
>Vapor locking is the process where gas in the fuel line boils and causes
>the fuel pump to lose it's prime.
>On a fuel injected engine, the fuel pump is in the fuel tank, and the
>fuel system is a continuous recirculating system (IE: fuel goes to a
>pressure regulator that returns some to the tank to maintain it's set
>pressure). Regardless whether you have TBI or PFI, you will never see
>vapor lock on a fuel injected engine.
>Now go grow a fucking brain!
Never is an extremely long time Mr. Cooley. I can think of a couple
situations where vapor lock will occur with fuel injection. One is
an overheated fuelpump, the other is called "out of gas" (insufficient
NPSH).
As for growing the brain, I learned to think a long time ago. I learned
to respect people after that. And then I learned to call a turd a turd when
that was apparently required. Please get it under control, Mr. Cooley.
Your intellectual abilities aren't exceptionally better than anyone elses
(and I suspect that they are no worse than anyone elses), but your
insistance on gratuitus abuse makes your contribution minimal in my book.
If I have offended you, then thats the breaks, what goes around
comes around.
Clark
Bill Bowen
blows! Thank you for your assistance, and I apologize for bringing up such
a controversial subject.
Bill Bowen <wbo...@ibm.net> wrote in message
news:wlrD4.14632$1g1.3...@den-news1.rmi.net...
Dr. Bob
wrote:
I think there's a bit of ego immaturity at work some days. All the
contestants gave the right answers for the most part, yet we stoop to
namecalling because one person's colloqial terminology doesn't line up
exactly with another's more scientific wording. I can blame this darn
keyboard for my speeellling errors, and nobody gets too excited about
that. But get to complex terms like cylinder pressure, and all hell
breaks loose!
In general, this newsgroup has been the most civilized of any I've
visited, and that' since it was founded way back in 1996. Every once
in a while, though, a roque response will set somebody else off and
away we go. It's almost like folks forget what e-mail is for! I
regularly display my ignorance, but try to limit the personal attacks
to e-mail... and I send that to NUL anyway.
Don't be afraid to post questions or comments. If you can filter
through the occasional flame, you'll almost always find a good answer
or two.
Best regards,
dr bob
David Cooley
Tony wrote:
>
> I would recommend you use 87 octane if the manufacturer requires 87.
>
What would you know, Spammer?
Tony
--
http://www.dsuper.net/~tonyg29/
Increase your Mileage by 20%
With the FuelMax Booster ®
Mark Barrett
: I would recommend you use 87 octane if the manufacturer requires 87.
I was thinking this also when I first got my Explorer. However the
thought of paying more for the higher grades was too much for me. I've
been using 85 octane in Colorado since my Explorer was new. I'm now at
133500 miles and counting with no noticeable problems with engine
performance.
Mark
bfu...@uswest.net
Your area qualifies as High Altitude (if it didn't, the 85 octane
wouldn't be available); there, 85 has the same anti-knock
characteristics as 87 for the rest of us. And, anti-knock is the
*only* reason for measuring octane.
On 5 Apr 2000 16:50:55 GMT, Mark Barrett <ma...@maverick.col.hp.com>
wrote:
Mark Barrett
: You *are* using the recommended octane gas.
: Your area qualifies as High Altitude (if it didn't, the 85 octane
: wouldn't be available); there, 85 has the same anti-knock
: characteristics as 87 for the rest of us. And, anti-knock is the
: *only* reason for measuring octane.
Thanks for making this clear.
Mark Barrett
Thomas Veik
> You *are* using the recommended octane gas.
> Your area qualifies as High Altitude (if it didn't, the 85 octane
> wouldn't be available); there, 85 has the same anti-knock
> characteristics as 87 for the rest of us. And, anti-knock is the
> *only* reason for measuring octane.
I've always wondered about that 85 octane thing too. Today I just
noticed the following in the 99 manual:
<quote>
Octane recommendations
Your vehicle is designed to use
"Regular" unleaded gasoline with an
(R+M)/2 octane rating of 87. We do
not recommend the use of gasolines
labeled as "Regular" that are sold
with octane ratings of 86 or lower
in high altitude areas.
</quote>
Tom