A Cars forum. AutoBanter

If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below.

Go Back   Home » AutoBanter forum » Auto newsgroups » Technology
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

Long term octane test (>100k miles using the wrong octane rating)



 
 
Thread Tools Display Modes
  #1  
Old May 14th 05, 04:40 PM
dyno
external usenet poster
 
Posts: n/a
Default Long term octane test (>100k miles using the wrong octane rating)

James Robinson wrote:
> Thomas & Sons Cycle Shop wrote:

snip
> A second consideration is fuel efficiency, since the anti-knock sensors
> will retard the timing on an engine, when lower octane fuel is used in
> an engine designed for higher octane fuel. The side effect is that fuel
> efficiency will drop. That means that people might be thinking they are
> saving money by using lower cost fuel, when they really aren't.
> Further, the engine will lose horsepower, which is part of the reason it
> was designed for high compression in the first place.
>


Not necessarily. In fact usually not the case. The octane requirement
for spark ignition engines is a funcion of operating load. That is, as
load increases, octane requirement also increase. That's the load
effect. Then there is the speed effect. Generally, octane requirement
DECREASES as engine speed increases (for engines with standard valve
timing).

What this all means is that at highway or around town cruising speeds
engines are operating at fairly light loads. Here premium fuel octane is
not needed. Even the "premium recommended" engines will be able to run
optimal ignition timing.

Only only during heavy accels or WOT operation will the fuel octane
affect performance. But, since most people spend a low fraction of their
driving time at high loads the net effect on fuel economy will be very
small.
Ads
  #2  
Old May 14th 05, 08:56 PM
external usenet poster
 
Posts: n/a
Default

dyno wrote:
> There's the load effect (load up, octane requirement up)...
> Then there's the speed effect (speed up, octane requirement down) ...


There's also the altitude effect.
The higher you go, the lower the octane requirement.

O

  #4  
Old May 14th 05, 10:59 PM
Daniel J. Stern
external usenet poster
 
Posts: n/a
Default

On Sat, 14 May 2005, dyno wrote:

> True. There's also the inlet temperature effect; temp up octane
> requirment up.


Oops, no. Ambient temperature goes up, octane requirement goes DOWN, and
for the same reason that octane requirement decreases as altitude
increases: With both increasing altitude and increasing ambient
temperature, the intake air charge is less dense, therefore cylinder
pressure is lower, therefore tendency to ping is less.
  #5  
Old May 14th 05, 11:53 PM
Ashton Crusher
external usenet poster
 
Posts: n/a
Default

On Sat, 14 May 2005 17:59:01 -0400, "Daniel J. Stern"
> wrote:

>On Sat, 14 May 2005, dyno wrote:
>
>> True. There's also the inlet temperature effect; temp up octane
>> requirment up.

>
>Oops, no. Ambient temperature goes up, octane requirement goes DOWN, and
>for the same reason that octane requirement decreases as altitude
>increases: With both increasing altitude and increasing ambient
>temperature, the intake air charge is less dense, therefore cylinder
>pressure is lower, therefore tendency to ping is less.



You could be right, that it's not specifically intake air temp as the
cause, but in many years of driving in the hot desert, I've had
numerous cars and trucks that would run just fine on 87 octane in the
cool months but would ping like crazy at well below WOT unless I ran
91 octane in the hot summer months. All had proper thermostats so it
wasn't just a hotter engine.
--
New service to compete with paypal
Get $25 pre-registration bonus by
following this link
www.greenzap.com/25smackers4u
  #6  
Old May 16th 05, 06:06 AM
dyno
external usenet poster
 
Posts: n/a
Default

Daniel J. Stern wrote:
> On Sat, 14 May 2005, dyno wrote:
>
>
>>True. There's also the inlet temperature effect; temp up octane
>>requirment up.

>
>
> Oops, no. Ambient temperature goes up, octane requirement goes DOWN, and
> for the same reason that octane requirement decreases as altitude
> increases: With both increasing altitude and increasing ambient
> temperature, the intake air charge is less dense, therefore cylinder
> pressure is lower, therefore tendency to ping is less.


Wrong. The change in density goes with the change in absolute
temperature. But, the effect of inlet temperature is magnified during
compression. The compression effect dominates over the small change in
density.
  #7  
Old May 16th 05, 06:13 AM
dyno
external usenet poster
 
Posts: n/a
Default

Thomas & Sons Cycle Shop wrote:
> In article >, dyno
> > wrote:
>
>>>>As the load increases, the octane requirement increases .
>>>>As the speed increases, the octane requirement decreases
>>>
>>>As the altitude increases, the octane requirement decreases
>>>As ambient termperature increases, octane requirement decreases

>
>
> There's also the humidity effect.
> As the humidity goes down, the octane requirement decreases.
>

snip

No, I think you have it backwards. High humidity is good for knock
suppression, reducing octane requirement.
  #8  
Old May 16th 05, 07:21 AM
Napalm Heart
external usenet poster
 
Posts: n/a
Default


"dyno" > wrote in message
...
> Daniel J. Stern wrote:
> > On Sat, 14 May 2005, dyno wrote:
> >
> >
> >>True. There's also the inlet temperature effect; temp up octane
> >>requirment up.

> >
> >
> > Oops, no. Ambient temperature goes up, octane requirement goes

DOWN, and
> > for the same reason that octane requirement decreases as altitude
> > increases: With both increasing altitude and increasing ambient
> > temperature, the intake air charge is less dense, therefore

cylinder
> > pressure is lower, therefore tendency to ping is less.

>
> Wrong. The change in density goes with the change in absolute
> temperature. But, the effect of inlet temperature is magnified

during
> compression. The compression effect dominates over the small change

in
> density.


I had a Tempo that would run at the high end of the temp gauge when
using 87 in the summer. If I switched to 92 (or better) the temp came
back down into the normal range. In the winter I used 87 for easier
ignition.

Ken (MI)


 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Saturn horror stories- could (will) happen to you! [email protected] Saturn 3 June 22nd 05 12:49 AM
Long term parking near nyc [email protected] Driving 8 May 20th 05 08:39 PM
My new long term project is here Mike64Bug VW air cooled 5 February 16th 05 12:13 AM
Long term storage (3 months or more) xenman Ford Explorer 4 February 7th 05 12:46 AM
Stupid question (was Changing the oil filter only) Bill F Technology 20 January 18th 05 10:57 PM


All times are GMT +1. The time now is 01:28 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 AutoBanter.
The comments are property of their posters.