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Old 03-30-2007, 07:30 AM   #1
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Premium Fuel when "Recommended"

A discussion came up that someone was running 87-Octane in newer vehicle that is listed as "Premium Fuel Recommended".

Has anyone had any experience with using a lower Octane rating in such a situation, and did it effect FE?

This directly related to a possible experiment using the TSX:
  • Feasibility of Testing per this Thread
  • The "CarChip E/X Data Collection Device" would be used to collect/analyze engine operation parameters and emissions data
  • FE Data Collection as usual per fill-up
  • Subjective "Ping" and/or performance evaluation
  • A-B-A Testing Method Planned

If an experiment is warranted, a new thread will be started with expectations listed.

What do you think?

RH77
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Old 03-30-2007, 07:46 AM   #2
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I understand that modern cars that "recommend" higher octane also have knock sensors - making the use of lower octane fuels safe.

It's possible higher octane would help FE if the ECU to ran more timing advance as a result.
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Old 03-30-2007, 08:01 AM   #3
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from what I've read in owners manuals, lower grade gasoline doesn't harm the engine, but there clame is that you will not see clamed mpg without it.
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Old 03-30-2007, 09:32 AM   #4
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Originally Posted by MetroMPG View Post
I understand that modern cars that "recommend" higher octane also have knock sensors - making the use of lower octane fuels safe.

It's possible higher octane would help FE if the ECU to ran more timing advance as a result.
I've tried 91 premium in my Saturn and didn't see any change in spark timing, or FE for that matter. 87 to 91 octane, timing has always been +44 degrees give or take 1 @3000 PRM @ 70 MPH. I guess my car's engine is already running as best it can with 87 octane.
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Old 03-30-2007, 09:50 AM   #5
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If your car is designated for premium, it is likely it has a higher compression engine. By putting lower grade gas in, you are increasing the chances you will have pinging/detonation problems, which certainly can cause problems. Putting higher grade gas in a car not designed for it would probably do nothing for mpg. Like MetroMPG said, if you have advanced the timing, which could result in more detonation problems, it could help here, but I'm not sure if the mpg gains would offset the cost of the fuel.
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Old 03-30-2007, 12:02 PM   #6
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If your car is designated for premium, it is likely it has a higher compression engine. By putting lower grade gas in, you are increasing the chances you will have pinging/detonation problems, which certainly can cause problems. Putting higher grade gas in a car not designed for it would probably do nothing for mpg. Like MetroMPG said, if you have advanced the timing, which could result in more detonation problems, it could help here, but I'm not sure if the mpg gains would offset the cost of the fuel.
Advancing the timing, manually, yes, would require higher octane gasoline. I remember my brother tinkering with his Chevy Vega. He adjusted the timing (rotating the distributor left and right) by sound alone. No timing light to aim at the harmonic damper on the crankshaft pulley. And he wondered why his engine didn't last very long after that. He only used 87 octane. Now if he had properly tuned the timing, AND used premium gas, he may not have had that engine breakdown so much and ultimately die. And shame on me for loaning him the $1,500 to get the car he's never paid me back.
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Old 03-30-2007, 01:17 PM   #7
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I don't know tooo much more than other folks re. octane selecton.

I looked in the owners manual for my non-turbo Volvo. It says use 87 octane, and they recommend 91 for higher altitudes and hot weather/climate. For Volvos with turbo, from what I've seen, the spec is for 91 or 93 octane and they definitely need it.

I attempted to test whether mine gets better FE on higher octane. Looked like maybe it did best on 89 octane, but it's really tough to do a good test without a ScanGauge or similar, and my '89 car is too old for those.

Anyway, it does seem to run better on higher octane. Till early '07 I was using 91 or 93 octane, whatever was available. Now I'm using 89; I figure since I'm not a WOT guy any more I can prolly bring the octane down a bit to 89and not lose toooo much.

If gas goes back up above $3/gal. and the extra cost for 93 is only a dime a gallon, I might go back to it. At really high gas prices that dime is a smaller and smaller percentage of what you're paying so you don't need too much benefit from it to justify the cost. As hard as it can be to think about paying even a few pennies more per gallon.
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Old 03-30-2007, 01:41 PM   #8
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brucepick -

Quote:
Originally Posted by brucepick View Post
I don't know tooo much more than other folks re. octane selecton.

...

If gas goes back up above $3/gal. and the extra cost for 93 is only a dime a gallon, I might go back to it. At really high gas prices that dime is a smaller and smaller percentage of what you're paying so you don't need too much benefit from it to justify the cost. As hard as it can be to think about paying even a few pennies more per gallon.
I never heard it put that way but it makes sense to me.

I am using 91 right now because of my HAI, but I would use 89 or 87 otherwise.

RH77 -

I would think that if you put lower octane in your tank and it wasn't working, you could just put higher octane in to make it better. Just fill it to less than 1/2 tank or maybe only a 1/4 tank for awhile with the 87. If it's doesnt' work, then fill it up with 91. Does that make sense?

In LA there is a "racing car" gas station that offers even higher than 91. It's over in Brentwood, must be for the exoti-cars.

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Old 03-30-2007, 03:27 PM   #9
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Quote:
Originally Posted by rh77 View Post
A discussion came up that someone was running 87-Octane in newer vehicle that is listed as "Premium Fuel Recommended".

Has anyone had any experience with using a lower Octane rating in such a situation, and did it effect FE?

This directly related to a possible experiment using the TSX:
  • Feasibility of Testing per this Thread
  • The "CarChip E/X Data Collection Device" would be used to collect/analyze engine operation parameters and emissions data
  • FE Data Collection as usual per fill-up
  • Subjective "Ping" and/or performance evaluation
  • A-B-A Testing Method Planned

If an experiment is warranted, a new thread will be started with expectations listed.

What do you think?

RH77
Just a though for your testing. It would interesting to run 87 and a different blend of E-10, E15, E-20 and see if it can make up the difference in octane. It would be cheaper the more ethanol you could run without losing FE.
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Old 03-30-2007, 05:28 PM   #10
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Quote:
Originally Posted by davidjh72 View Post
I've tried 91 premium in my Saturn and didn't see any change in spark timing, or FE for that matter. 87 to 91 octane, timing has always been +44 degrees give or take 1 @3000 PRM @ 70 MPH. I guess my car's engine is already running as best it can with 87 octane.
some cars, particularly those with relatively lower compression ratios do not respond as well to timing that is advanced. there are plenty of exceptions and this definitely a generalization, but a lot of newer cars with higher compression ratios or forced induction can run on 87 octane but make a lot more power and become more efficient with 93+

it really varies from car to car. with my civic, it seemed to be that the cost of the higher octane was evenly balanced by the efficiency. but higher octane ran smoother so i just alternated tanks.
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