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  #1 (permalink)  
Old 27 Nov 2004, 10:03 pm
K-town
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Default Octane Overkill

Hello,

Not being an engine expert, I figured I'd throw this question out to
this NG. I have a 1990 Civic LX, 1.5L DPFI 5-speed, and usually I put
regular unleaded (87 octane) in it. Every once in awhile I'll put mid-grade
(89 octane) or premium (92 or 93 octane) in it because I heard that doing so
will keep your injectors clean. (Is that true?) Once I really splurged and
put 100 octane fuel in it (only 5 gallons) and it did run pretty good. One
thing I noticed, is that if I run premium (93) in it several tanks in a row,
it will actually not run quite as good. It's a very minuscule difference,
but I can tell there is a slight decrease in performance. If I drop it back
down to mid-grade or even back to regular on the next tank, it seems to go
back to running better. Is this all in my head, or is it possible to have
an "octane overkill" on such a small 4-cylinder engine?

Thanx in advance,

Jonathan


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  #2 (permalink)  
Old 28 Nov 2004, 06:39 am
Brian Smith
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Posts: n/a
Default Re: Octane Overkill


"K-town" <jdu52580@carolina.stopspam.rr.com> wrote in message
news6cqd.7794$Mu3.802926@twister.southeast.rr.co m...
> Hello,
>
> Not being an engine expert, I figured I'd throw this question out to
> this NG. I have a 1990 Civic LX, 1.5L DPFI 5-speed, and usually I put
> regular unleaded (87 octane) in it. Every once in awhile I'll put

mid-grade
> (89 octane) or premium (92 or 93 octane) in it because I heard that doing

so
> will keep your injectors clean. (Is that true?) Once I really splurged

and
> put 100 octane fuel in it (only 5 gallons) and it did run pretty good.

One
> thing I noticed, is that if I run premium (93) in it several tanks in a

row,
> it will actually not run quite as good. It's a very minuscule difference,
> but I can tell there is a slight decrease in performance. If I drop it

back
> down to mid-grade or even back to regular on the next tank, it seems to go
> back to running better. Is this all in my head, or is it possible to have
> an "octane overkill" on such a small 4-cylinder engine?


The vehicle was designed to run on regular fuel. Using any other grade is
just throwing your money away.

Brian


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  #3 (permalink)  
Old 28 Nov 2004, 07:09 am
Michael Pardee
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Default Re: Octane Overkill

"K-town" <jdu52580@carolina.stopspam.rr.com> wrote in message
news6cqd.7794$Mu3.802926@twister.southeast.rr.co m...
> Hello,
>
> Not being an engine expert, I figured I'd throw this question out to
> this NG. I have a 1990 Civic LX, 1.5L DPFI 5-speed, and usually I put
> regular unleaded (87 octane) in it. Every once in awhile I'll put
> mid-grade (89 octane) or premium (92 or 93 octane) in it because I heard
> that doing so will keep your injectors clean. (Is that true?) Once I
> really splurged and put 100 octane fuel in it (only 5 gallons) and it did
> run pretty good. One thing I noticed, is that if I run premium (93) in it
> several tanks in a row, it will actually not run quite as good. It's a
> very minuscule difference, but I can tell there is a slight decrease in
> performance. If I drop it back down to mid-grade or even back to regular
> on the next tank, it seems to go back to running better. Is this all in
> my head, or is it possible to have an "octane overkill" on such a small
> 4-cylinder engine?
>
> Thanx in advance,
>
> Jonathan
>

High octane fuel is for high compression engines, to prevent detonation
(ping). Your owner's manual will tell you what grade to use - probably 87
octane. Rather than going to a premium grade (which, it's true, often has
higher detergency), stick with the recommended octane. Some brands have more
detergents than others, and they advertise that. (I like Shell/Texaco and
Chevron.) I had a Nissan 300ZX that would get balky - the clutch would start
to feel grabby - if I ran 76 in it for a couple months but would straighten
right out about halfway through a tank of Texaco. My other cars never seem
to care.

We also have a Toyota Prius, and on the Prius newsgroup others have warned
me it won't run right and will even set the "check engine" light if premium
grades are used. (The Prius has what Toyota calls a "modified
Atkinson/Miller cycle" engine - it uses valve timing to tame the 13:1
expansion ratio to a variable compression ratio.)

Mike


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  #4 (permalink)  
Old 28 Nov 2004, 08:13 am
Elmo P. Shagnasty
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Posts: n/a
Default Re: Octane Overkill

In article <D6cqd.7794$Mu3.802926@twister.southeast.rr.com> ,
"K-town" <jdu52580@carolina.stopspam.rr.com> wrote:

> Not being an engine expert, I figured I'd throw this question out to
> this NG. I have a 1990 Civic LX, 1.5L DPFI 5-speed, and usually I put
> regular unleaded (87 octane) in it. Every once in awhile I'll put mid-grade
> (89 octane) or premium (92 or 93 octane) in it because I heard that doing so
> will keep your injectors clean. (Is that true?)


Prior to 1995, it may have been truer than not.

The oil companies used to put detergents into only their higher octane
fuels, as an incentive to get you to pay the price.

Around 1995, though, the feds defined a minimum level of detergency to
be put into ALL fuels. This dried up the oil companies' ability to
claim that "buy our expensive stuff, and your car will be cleaner and
run better".

Shell is back into that game now, though, with their V-Power. They
simply add MORE detergents to their 92 octane gas than is specified by
law.

This all being said, you can add a can of Chevron Techron to your fuel
every now and then and get the same results or better. And it's MUCH
cheaper than using Shell V-Power on an ongoing basis.



> Once I really splurged and
> put 100 octane fuel in it (only 5 gallons) and it did run pretty good.


Not as good as you think. You wasted your money, AND you wasted fuel on
top of that.



> One
> thing I noticed, is that if I run premium (93) in it several tanks in a row,
> it will actually not run quite as good. It's a very minuscule difference,
> but I can tell there is a slight decrease in performance.


That's right. The higher octane fuel won't give your engine as much
power as the lower octane fuel, believe it or not.

http://www.faqs.org/faqs/autos/gasoline-faq/part1/

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  #5 (permalink)  
Old 28 Nov 2004, 08:21 am
Elliot Richmond
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Posts: n/a
Default Re: Octane Overkill

On Sun, 28 Nov 2004 04:03:47 GMT, "K-town"
<jdu52580@carolina.stopspam.rr.com> wrote:

>Hello,
>
> Not being an engine expert, I figured I'd throw this question out to
>this NG.


What makes you think we are experts? We just have computers and
internet connections.

> I have a 1990 Civic LX, 1.5L DPFI 5-speed, and usually I put
>regular unleaded (87 octane) in it.


It is my understanding that using a higher octane than is called for
in the owner's manual is a waste of money. Modern engines are designed
to adjust the spark advance so as to avoid the "octane ping" that was
common with older engines.

On the other hand, it is true that some manufacturers claim the higher
octane gasoline ("premium grades") contains additives that may help
clean your injectors. You have to treat these claims the way you treat
all marketing claims.



Elliot Richmond
Freelance Science Writer and Editor
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  #6 (permalink)  
Old 28 Nov 2004, 10:08 am
Grumpy au Contraire
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Posts: n/a
Default Re: Octane Overkill



K-town wrote:
>
> Hello,
>
> Not being an engine expert, I figured I'd throw this question out to
> this NG. I have a 1990 Civic LX, 1.5L DPFI 5-speed, and usually I put
> regular unleaded (87 octane) in it. Every once in awhile I'll put mid-grade
> (89 octane) or premium (92 or 93 octane) in it because I heard that doing so
> will keep your injectors clean. (Is that true?) Once I really splurged and
> put 100 octane fuel in it (only 5 gallons) and it did run pretty good. One
> thing I noticed, is that if I run premium (93) in it several tanks in a row,
> it will actually not run quite as good. It's a very minuscule difference,
> but I can tell there is a slight decrease in performance. If I drop it back
> down to mid-grade or even back to regular on the next tank, it seems to go
> back to running better. Is this all in my head, or is it possible to have
> an "octane overkill" on such a small 4-cylinder engine?
>
> Thanx in advance,
>
> Jonathan




Waste of money. All modern gasolines regardless of grade have additives
to prevent injector problems...


--
JT

Just tooling through cyberspace in my ancient G4
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  #7 (permalink)  
Old 28 Nov 2004, 11:36 am
jim beam
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Posts: n/a
Default Re: Octane Overkill

K-town wrote:
> Hello,
>
> Not being an engine expert, I figured I'd throw this question out to
> this NG. I have a 1990 Civic LX, 1.5L DPFI 5-speed, and usually I put
> regular unleaded (87 octane) in it. Every once in awhile I'll put mid-grade
> (89 octane) or premium (92 or 93 octane) in it because I heard that doing so
> will keep your injectors clean. (Is that true?) Once I really splurged and
> put 100 octane fuel in it (only 5 gallons) and it did run pretty good. One
> thing I noticed, is that if I run premium (93) in it several tanks in a row,
> it will actually not run quite as good. It's a very minuscule difference,
> but I can tell there is a slight decrease in performance. If I drop it back
> down to mid-grade or even back to regular on the next tank, it seems to go
> back to running better. Is this all in my head, or is it possible to have
> an "octane overkill" on such a small 4-cylinder engine?
>
> Thanx in advance,
>
> Jonathan


increasing octane effectively = slower flame front propagation speed.
that reduces detonation in combustion chambers with poor flow/mixing
configurations, sharp angles & extended reach. good mechanical design
addresses these problems pretty much completely, therefore low octane
can be used without detonation and with ignition timing matched
accordingly. using a high octane fuel in a low octane timed engine puts
too much of the combustion energy out of the exhaust because it's still
burning on the down stroke, not expanding and providing push for the
pistons.

that said, you may notice a slight increase in power for a mid grade
fuel in that motor without a detonation sensor. partly because, in the
absense of a sensor, the engine timing used has to be a "compromise"
range designed to be safe and partly because of fuel chemistry.

here's an interesting post that touches on the subject:
http://www.digest.net/bmw/archive/v9/msg04942.html

it seems to assume that ignition timing is optimal for each different
combustion characteristic of the different blends described. you can be
assured that gas companies use all the cheap options for their lowest
grade of gas.

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  #8 (permalink)  
Old 28 Nov 2004, 11:37 pm
Edward Quinn
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Posts: n/a
Default Re: Octane Overkill

ive been using amoco ultimate in my 04 accord should i switch to regular??

"K-town" <jdu52580@carolina.stopspam.rr.com> wrote in message
news6cqd.7794$Mu3.802926@twister.southeast.rr.co m...
> Hello,
>
> Not being an engine expert, I figured I'd throw this question out to
> this NG. I have a 1990 Civic LX, 1.5L DPFI 5-speed, and usually I put
> regular unleaded (87 octane) in it. Every once in awhile I'll put
> mid-grade (89 octane) or premium (92 or 93 octane) in it because I heard
> that doing so will keep your injectors clean. (Is that true?) Once I
> really splurged and put 100 octane fuel in it (only 5 gallons) and it did
> run pretty good. One thing I noticed, is that if I run premium (93) in it
> several tanks in a row, it will actually not run quite as good. It's a
> very minuscule difference, but I can tell there is a slight decrease in
> performance. If I drop it back down to mid-grade or even back to regular
> on the next tank, it seems to go back to running better. Is this all in
> my head, or is it possible to have an "octane overkill" on such a small
> 4-cylinder engine?
>
> Thanx in advance,
>
> Jonathan
>



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  #9 (permalink)  
Old 29 Nov 2004, 05:07 am
Elmo P. Shagnasty
Guest
 
Posts: n/a
Default Re: Octane Overkill

In article <c_ydnWVcmJFbKDfcRVn-vw@comcast.com>,
"Edward Quinn" <edward-quinn@comcast.net> wrote:

> ive been using amoco ultimate in my 04 accord should i switch to regular??


Use the fuel that your owner's manual recommends.

In your case, 86 octane fuel is fine. Anything else, you're wasting
your money.

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  #10 (permalink)  
Old 29 Nov 2004, 02:27 pm
Michelle Vadeboncoeur
Guest
 
Posts: n/a
Default Re: Octane Overkill

"K-town" <jdu52580@carolina.stopspam.rr.com> wrote in message news:<D6cqd.7794$Mu3.802926@twister.southeast.rr.c om>...
> Hello,
>
> Not being an engine expert, I figured I'd throw this question out to
> this NG. I have a 1990 Civic LX, 1.5L DPFI 5-speed, and usually I put
> regular unleaded (87 octane) in it. Every once in awhile I'll put mid-grade
> (89 octane) or premium (92 or 93 octane) in it because I heard that doing so
> will keep your injectors clean. (Is that true?) Once I really splurged and
> put 100 octane fuel in it (only 5 gallons) and it did run pretty good. One
> thing I noticed, is that if I run premium (93) in it several tanks in a row,
> it will actually not run quite as good. It's a very minuscule difference,
> but I can tell there is a slight decrease in performance. If I drop it back
> down to mid-grade or even back to regular on the next tank, it seems to go
> back to running better. Is this all in my head, or is it possible to have
> an "octane overkill" on such a small 4-cylinder engine?


Unless your engine is knocking, there is no need to spend the extra
money for a higher octane fuel. Use what the owner's manual recommends.

I suggest reading:
http://www.ftc.gov/bcp/conline/pubs/autos/octane.htm
"The Low-Down on High Octane Gasoline"
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