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Lower Octane Fuel,less Carbon Buildup?


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#1 ed850

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Posted 14 June 2004 - 09:00 PM

I have heard that 93 octain fuel causes more carbon build up in the engine than 89 or 87 particularly because cars with overdrive tend to keep the rpm's down and therefore do not burn the carbon off.So would it be better to run 89 if the engine does not knock. My independent Volvo mechanic said in his expierience Volvo engines are more prone to carbon build up than many other foreign cars he works on.Also when doing an Italian tuneup would it help to put a fuel system cleaner in like Volvoline supersynthetic that claims to remove carbon from the valves.
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#2 Ceenit

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Posted 14 June 2004 - 09:26 PM

I don't belive that higher octane fuel causes greater carbon buildup. In fact the reverse should be true as the higher octane fuels have a more predictive combustion temperature and thus typically burn cleaner.

The issue of overdrive keeping RPM's down is true and thus the threads on Italian tune-ups, but this seems unrelated to octane.

The engine management system will allow you to run lower octane and will advance the timing to retard knocking (to a point)...if you hear knocking then you have surpassed the tolerances built into the engine management system. I would not however depend on the engine management system to work at the lower end of the spectrum for long periods of time as it was not engineered as a long term fix to run lower octane fuels.

Running lower octane than recommended will impact performance (although running higher octane than recommended will NOT increase performance).
Chris
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#3 DEWFPO

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Posted 15 June 2004 - 01:06 AM

"The engine management system will allow you to run lower octane and will advance the timing to retard knocking (to a point)..."

The ECU will "retard" the timing so as to reduce ping/spark knock.

DEWFPO
1998 S90 071,245 1995 964 154,112

#4 ed850

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Posted 17 June 2004 - 12:01 PM

I was talking with service manager at the ford dealer service dept and he happened to mention that one of the bigger problems they have is engine carbon build up caused by people using 93 octain fuel.He said with the overdrive trans running at lower rpm and the egr the engines dont get hot enough to burn the carbon off.He said for some reason 93 oct causes more carbon build up than lower octain gas
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#5 Stormin Norman

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Posted 17 June 2004 - 01:16 PM

Aren't most Ford domestic products designed to run on regular? Hence the Service Manager's experience.

#6 DEWFPO

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Posted 17 June 2004 - 02:25 PM

With all due respect to the service manager, his statement is utter nonsense.

DEWFPO
1998 S90 071,245 1995 964 154,112

#7 DashingDaryl

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Posted 17 June 2004 - 04:35 PM

I just came back from Germany. I was kind of amazed that the minimum octane they sell is 91, with the maximum being 99. (At least that's what the pumps were marked)

The sucky part is that gas was $5 bucks a gallon
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#8 ziddey

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Posted 18 June 2004 - 03:04 AM

QUOTE(DashingDaryl @ Jun 17 2004, 10:35 AM)
I just came back from Germany. I was kind of amazed that the minimum octane they sell is 91, with the maximum being 99. (At least that's what the pumps were marked)

The sucky part is that gas was $5 bucks a gallon

was that ron, mon, or r+m/2?
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#9 ed850

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Posted 18 June 2004 - 12:00 PM

Seems to me there that someone had put a link to a site about octain ratings in a thread before the server problem a while back. The ford shoc v6 is an 87 octain engine.If it were true that octain and carbon were not related then 91 should not carbon the engines up. I seem to remember from the missing thread that the 91 octain is harder to ignite hence it may not burn as completly.
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#10 DashingDaryl

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Posted 18 June 2004 - 05:00 PM

QUOTE
QUOTE (DashingDaryl @ Jun 17 2004, 10:35 AM)
I just came back from Germany. I was kind of amazed that the minimum octane they sell is 91, with the maximum being 99. (At least that's what the pumps were marked)

The sucky part is that gas was $5 bucks a gallon 


was that ron, mon, or r+m/2?


Why yes it was...
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#11 KLS

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Posted 18 June 2004 - 09:22 PM

--quote--
Generally, [an engine] will not knock when operated on gasoline with the antiknock quality prescribed by the manufacturer. However, the engine's ONR (octane number requirement0 increases as combustion chamber deposits form during the first several thousand miles of operation (see Chapter 1, Gasoline and Driving Performance) and Figure 6-5). If the increase is large enough, the recommended gasoline AKI (antiknock index) may not prevent knocking or, if the vehicle is equipped with a knock sensor, the loss of power that accompanies knock suppression (see Chapter 5, Gasoline Engines).

Combustion chamber deposits increase ONR in two ways. They increase the combustion temperature both by transferring more heat to the incoming mixture and slowing the transfer of heat from the combustion gases (thermal insulation). They increase the compression ratio because their bulk volume reduces the volume of the combustion chamber at TDC (top dead center). The increase in compression ratio has a much smaller effect on ORI (octane requirement increase) than the heating effect.

Research has shown that precursors for combustion chamber deposits come from the fuel, some fuel additives and the engine oil, and that certain fuel and engine oil components form more deposits than others. So far, the only quick, effective means of removing these deposits is to treat the gasoline with an aftermarket deposit control additive concentrate based on polyether amine chemistry. The treat level is 10 to 20 times higher than that in service station gasolines. At this elevated concentration, one tankful of gasoline can decrease ORI 30 to 40 percent. Periodic treatment is required because the deposits re-form with additional driving and the ONR gradually returns to the previous equilibrium level.
--end quote--
http://www.chevron.c...bustion_chamber


Ken

#12 ed850

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Posted 19 June 2004 - 01:23 PM

That Chevron article was interesting.Sounds like an occasional Italian tune up and some fuel system/valve cleaner is the best course of action.
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