[MATTS92]

My 92 6sp. runs just as good on low test as on hi. there is no difference in performance that i can tell whatsoever, it this ok? I cant even get out of my driveway with my 66 Shelby with this stuff in my tank.

Just trying to save a few bucks. I drive my car just about every day 50 mi or so.

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[flash]

if you run low octane the system will retard the timing - below 90 ron+mon/2 is not recommended - detonation is likely, and expensive damage can result

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[MATTS92]

[quote name='flash' post='45880' date='Jan 17 2008, 10:32 AM']if you run low octane the system will retard the timing - below 90 ron+mon/2 is not recommended - detonation is likely, and expensive damage can result[/quote]

OK then, That settles that. Im going to top off with 93% .Thanx, Matt <img src="/forum/images/smilies/968/wink.gif" class="smilie" alt="" />

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[PorscheDude]

run 91 or better.

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[Renalicious]

I seem to notice a difference between 91 and 94. The car just doesn't have that pep, it's subtle, but I swear it's missing. I'd feel naughty if I filled up with anything lower than 91 hehe



On the subject of octanes, and I know this topic may have been done to death, but are there any positive experiences with octane boosters? Or are they a waste of time and money, especially for tanks our size?

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[moses]

here's the best octane booster test I'm aware of:

http://www.europeancarweb.com/tech/0503ec_...sted/index.html



I really wish cars had some indicator to tell when the ignition was being retarded and/or when the knock sensors "heard" something. THEN you could decide for yourself what octane rating you needed when. You can build such a gadget but who has the time to fool around when high test is available.



I put gas in the hybrid yesterday (first time since Nov., not bad for a 10 gallon tank) at a Sunoco station and noticed something peculiar. Every 2 point difference in octane cost 15 or 20 cents/gallon, but the jump from 91 to 93 was only 2 cents (or something like that). If I were more cheap or less rushed I would have mixed low test and 93.

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[Renalicious]

What I want to know if how do our cars actually deal with spark timing and knock? I mean, the distributor is driven by the exhaust cam, which is driven directly by the crank. In theory even if the vario-cam does its magic the distributor / spark plugs won't be affected. That just leaves the air fuel mixture, right?

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[968rz]

[quote name='Renalicious' post='46029' date='Jan 19 2008, 11:31 PM']What I want to know if how do our cars actually deal with spark timing and knock? I mean, the distributor is driven by the exhaust cam, which is driven directly by the crank. In theory even if the vario-cam does its magic the distributor / spark plugs won't be affected. That just leaves the air fuel mixture, right?[/quote]

The DME controls the spark by controlling the coil; when knock sensor detects a knock the DME triggers the coil to fire later thus retarding the timing.

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[flash]

the rule of thumb on octane is "a one point change in octane will affect the horsepower by 1%"



this presumes that you have the compression and ignition capabilities ot manage the change



this means that going from 91 to 93 will be about a 4.8 hp difference on a perfect engine - our engines were rated at 98 RON, which is 93 RON+MON/2 - more will likely not add much on a stock chip, but can on a good aftermarket chip - less will definitely have a power loss



remember too that compression is the key factor here - if your engine is brand new, you can take advantage of this - if it has miles on it (and a 75k engine is likely down 5-10%), then you can adjust starting numbers accordingly (that's as much as 25 hp) and it actually takes higher octane just to keep the sensors quiet, further complicating the power loss of age



altitude and heat also play into this, but that is another topic for another day

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[Gentleman Driver]

[quote name='flash' post='46041' date='Jan 20 2008, 11:21 AM']the rule of thumb on octane is "a one point change in octane will affect the horsepower by 1%"



this presumes that you have the compression and ignition capabilities ot manage the change



this means that going from 91 to 93 will be about a 4.8 hp difference on a perfect engine - our engines were rated at 98 RON, which is 93 RON+MON/2 - more will likely not add much on a stock chip, but can on a good aftermarket chip - less will definitely have a power loss



remember too that compression is the key factor here - if your engine is brand new, you can take advantage of this - if it has miles on it (and a 75k engine is likely down 5-10%), then you can adjust starting numbers accordingly (that's as much as 25 hp) and it actually takes higher octane just to keep the sensors quiet, further complicating the power loss of age



altitude and heat also play into this, but that is another topic for another day[/quote]



What if my previous owner only ran 87 in the tank??? I assumed the engine retarded the timing, but it appears there could be further damage done? The engine seems to run well from all indications and inspections...

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[Etnier]

Irving is a big source here in Maine. We have a nice local Irving gas/service station that I send as much work to as I can, but I don't buy gas from Irving stations, because it's rated 91 octane on the pump. They claim "all the high test in our area comes from the same sources" and that there's no practical difference between their 91 and the 93 octane I buy from Gulf.



Comments?





PS: wasn't that edited by tattletale supposed to have been removed months ago?

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[xrad]

I find that 91 works great...higher octane increase burn time (decreases preignition) and seems less powerful



Also, depends on your gas supplier. Apparently , there are only two tanbks under the pump. One 89 and one 93(or higher) you select 91 and it is a mix of the two. Altough supposed to be regulated, I find that BP or Shell or Mobil just makes my cars run better.

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[Cloud9...68]

Call me the resident skeptic, but I'm not sure I buy it. Provided the engine's controllers are working correctly, and they retard the spark enough to compensate for a lower octane fuel, I really doubt you're risking damage to your engine by running a lower octane. Yes, there is a horsepower penalty, but I bet if you did a double-blind test of fifty different cars (to average out car-to-car differences), filled half with, say, 89 octane, and the other half with, say 91, and assigned people to drive all of them in random order, I'd be shocked if there would be a statistically-significant number of people who could tell the difference.



Having said that, I've always used the highest available octane in mine, but if you're really tight on cash, and the difference in gas cost is a deciding factor over whether or not you drive the car, my bet is that you could use the lower octane fuel without worry.

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[Ryan]

Wish we could fit direct injection to our cars....



My wife drives an A6 with direct injection and it allows lower octane to be used without a seaming penalty. On her 03 A6 you could not run anything but priemo because the car would complain. The 06 car has the new system and it says to run priemo, but a person at the dealer told us you could run regular because of the DI now used. It works

great.



Sorry to wander off topic a little.

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[PorscheDude]

Anybody want to run out and try some 87?

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[Gentleman Driver]

[quote name='Cloud9...68' post='51432' date='Apr 24 2008, 06:45 PM']Call me the resident skeptic, but I'm not sure I buy it. Provided the engine's controllers are working correctly, and they retard the spark enough to compensate for a lower octane fuel, I really doubt you're risking damage to your engine by running a lower octane. Yes, there is a horsepower penalty, but I bet if you did a double-blind test of fifty different cars (to average out car-to-car differences), filled half with, say, 89 octane, and the other half with, say 91, and assigned people to drive all of them in random order, I'd be shocked if there would be a statistically-significant number of people who could tell the difference.



Having said that, I've always used the highest available octane in mine, but if you're really tight on cash, and the difference in gas cost is a deciding factor over whether or not you drive the car, my bet is that you could use the lower octane fuel without worry.[/quote]

This is the impression I was working under... I mean, I feel no discerable lack of power, and the engine runs smoothly with no pinging that I could tell, even before I filled up the first tank with 93.



Anyone hear of cars detonating or having pitted pistons on a 968???



Thanks!

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[porsche]

I run 100 octane & love it!!!

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[Cloud9...68]

[quote name='porsche' post='51471' date='Apr 25 2008, 04:05 PM']I run 100 octane & love it!!![/quote]

100 octane??!! Where do you find that, and for what cost? I doubt our engines' power would show any power increase by going above 93. Maybe if you slapped on a supercharger and cranked it to about 15 lbs boost...

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[porsche]

VP Racing Fuels sells 100 octane directly from the pump at their dedicated gas stations!



It's pricey at $7.99/gallon. But, WTF, local crappy grade 91 octane is $4.19/gallon. So for under "double" the price, I buy "race" quality 100 octane.



For those of you who "store" their cars, race quality 100 octane doesn't break down over time. However, regular pump grade gas begins degrading within a few short months.



Yeah, you can pour in some gas preservative such as "Stabil," but I prefer the race quality 100 octane route.



Difference?



My P-car "launches" like a rocket and idle quality is sublimely smoooooooth.



me likely lots!



Porsche

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[Cloud9...68]

That's interesting. I'd have to say, though, that to be able to tell the difference between 91 and 100 octane in a NA engine, even one with an 11:1 compression ratio (which isn't really all that high by today's standards), to me indicates something isn't quite right. I wonder if you have a lot of carbon desposits in your combustion chambers; maybe a Run-rite treatment would be a good investment. My engine has 101K miles on it, and idles very smoothly on 91 octane. Just a thought...

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