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Baza's Avatar
 
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Fact or Fiction

I have just been told by my spanner man.
That the reason I have been having problems with my mixture when warm starting is, that the fuel Iam running has an octain rating that is to high and is causeing it to start rich until the revs pick up. Iam currently running 98ron fuel and was advised to run a lower grade ie: 95ron. Is this fact or just some who thinks this problem is in the too hard basket?
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Old 08-03-2004, 08:21 PM
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I've never heard of running too high of an octane causing an engine to run too rich. But honestly, there's no performance advantage to running anything higher than what is reccomended. However, I have heard (I have no proof) that a higher octane fuel will help create better gas mileage.


btw-the US cars require 91 or higher octane (87 plus models). Not sure about you Ausie folks though.
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Old 08-03-2004, 08:41 PM
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well that is true on some extent...i run 93 octane (premium over here...87 is the cheapo stuff). The more octane gas has, the cooler it burns, which also means more hydrocarbons. This does tell the 02 sensor that you are running a tad rich, and gives that burning raw gas smell. On a low compression engine as some 8Vs are (9.5:1), 95 would work fine for your car (what is the lowest you have there?).

I shouldnt run 93 in my car (supposed to be 91) because it doesnt help performance (maybe if I had an S model 16V with 10.5:1 compression I would need to use it) and just causes nasty smells in the cabin when the windows are down. I had my friend drive behind me the other day and I took off from a light and in the upper rpm ranges the car blows some black smoke under hard acceleration (meaning its running rich). I put 91 in the car later that day and I didnt get it.

Also, there is an adjustment spot on the side of the DME where you can play with the timing and fuel settings within 3% (i dont know if your overseas cars have it, but we have it here to compensate for different altitudes and people who choose to run 87 in the car). Clark's Garage has a writeup on it..

Higher octane does decrease performance somewhat if the car is not tuned for it. My colt was tuned on pump gas for drag racing, and I wasted my time and money on a 5 gallon container of C16 leaded race gas (118 octane..smells very good ) because my car ran stupid rich (leaded gas burns a lot slower) and my 1/4 mile times actually were worse than before, because my car was not tuned for it (a few adjustments to timing later and cranked up the boost and the problem was resolved )
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Last edited by bluebullet; 08-03-2004 at 08:46 PM..
Old 08-03-2004, 08:41 PM
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The 914 guys were talking about this awhile ago... A 914 isn't a 944, but towards the end there's some interesting stuff.

High Octane?

I run 91 usually.

Any thoughts on the 89 - 90 octane with 10% ethanol? Out here they're trying to push ethanol pretty hard, and if it works then more power too 'em.
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Old 08-03-2004, 08:51 PM
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havent noticed a difference with the 10%....they have it at all pumps here (it was made a law in NY) but the ethanol is not supposed to affect performance...its supposed work in the emissions department and curb smog stuff...
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Old 08-03-2004, 09:00 PM
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well. if higher octane DECREASES performance, why do people run racing fuel when they are at the track?
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Old 08-03-2004, 09:04 PM
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My 944 seems to run like ***** with the ethy. I've heard that the ethanol will break particles in the fuel filter loose and they'll contribute to clogging injectures, but that could just be a rumor for all I know.
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Old 08-03-2004, 09:04 PM
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FYI Our (NZ and Aussie) 98 is your 93 over in the States
my lowly 931 and my old 924 n/a have a factory sticker in the engine bay saying to use 98 unleaded only
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Old 08-03-2004, 09:55 PM
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The motors are tuned for higher octane CJ.

I run 89 octane, 91 ron, with no problems. I wonder if the gas was diluted?

All kinds of different colored marbles enter the game with a euro 944.

Do you have a O2 sensor? Probably no. One good TPS cleaning might be all that is needed.
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Old 08-03-2004, 10:02 PM
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there was a tech question in EXCELLENCE this month asking about octane, and the answer was that if you mix racing fuel in your gasoline (actively increasing the octane) then you will get a performance increase.

What gives? Why the contradictions from the experts?
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Old 08-04-2004, 06:30 AM
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i think this question falls under the same catagory as "is it a motor or engine?" question. its something thats always going to be debated...
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Old 08-04-2004, 07:18 AM
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Running higher octane allows the timing to advance further, reducing pinging/knocking and allowing it to run a bit cooler, as well. Emissions are slightly different (more hydrocarbons as mentioned).

I run 91 (as reccommended) in mine and notice a significant difference between 87 and 91. But i have CIS, not EFI. So if i adjust my timing manually for 87 octane it wouldn't seem as different. But right now my timing is set for 91 Octane.

Also, you turbo guys should probably use the highest octane you can, with that boost and all.
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Old 08-04-2004, 01:37 PM
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