91 vs 87 octane, noticible difference in performance?
#1
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From: Albuquerque, New Mexico
91 vs 87 octane, noticible difference in performance?
I have used both 91 and 87 octance on my 944 s2. My car has 122k miles and burns about a quart of oil every 1000 miles (10-30W).
I think I get a few more mpg with premium (91 octane), but I don't really notice a performance difference (acceleration) or any "pinging" with regular (87 octane).
I know the manual says to use 93 octane but I can't find it around the Albuquerque area.
Maybe I don't notice the difference because my engine is high milage and burns oil (not running at peak performance).
Any thoughts?
Jon
I think I get a few more mpg with premium (91 octane), but I don't really notice a performance difference (acceleration) or any "pinging" with regular (87 octane).
I know the manual says to use 93 octane but I can't find it around the Albuquerque area.
Maybe I don't notice the difference because my engine is high milage and burns oil (not running at peak performance).
Any thoughts?
Jon
#2
Out in the MW 91 is high octane. On the east coast you can get 93 octane everywhere, and Sunco sells 94.
To notice a performance difference with high octane you'd have to advance your ign timing to take advantadge of the lower volatility of the premium fuel.
To notice a performance difference with high octane you'd have to advance your ign timing to take advantadge of the lower volatility of the premium fuel.
#3
Does Sunoco still have 94??? All the Sunocos dropped 94 in our area. I used to use it all the time. I used to get 94 octane for $1.81. That was cheaper than what i would have to pay for 93 !!!! I miss those days.
#5
Lower octane = pinging (and premature dentonation IIRC)
In my 89 NA, factory says 90 or higher. I have always run 91 (It's the only thing available in PHX). I think the reason why you have run 87 with few issues is the knock sensor on the S2's compensating for the lower octane fuel. You might be missing out on some HP, but since I don't have a S2 (soon I hope!!) I can only relate my own experiences.
1 QT of oil every 1,000 is a bit excessive for a water cooled Porsche. I know the manual says that is normal, but even with the KNOWN slow leak that I have, I am not going through oil that quickly.
Hmmmmmmmm
In my 89 NA, factory says 90 or higher. I have always run 91 (It's the only thing available in PHX). I think the reason why you have run 87 with few issues is the knock sensor on the S2's compensating for the lower octane fuel. You might be missing out on some HP, but since I don't have a S2 (soon I hope!!) I can only relate my own experiences.
1 QT of oil every 1,000 is a bit excessive for a water cooled Porsche. I know the manual says that is normal, but even with the KNOWN slow leak that I have, I am not going through oil that quickly.
Hmmmmmmmm
#6
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From: Albuquerque, New Mexico
89AZ944,
Yes I know I either have valve trouble or need rings. The car doesn't leak. The performance is adequate for its purpose as a daily driver (its faster than my old '78 911sc, which was tip top). Adding a quart of oil once in a while is cheaper (easier) than fixing it (valve job or re-ring). The only time I can see a hint of smoke is when I accelerate hard at night and will see some smoke against the car behind me's lights. I know the sound of the motor pinging, and it doesn't do it any more or less with 87 octane. Next time I change plugs I will do a compression check to really see where I am.
Yes I know I either have valve trouble or need rings. The car doesn't leak. The performance is adequate for its purpose as a daily driver (its faster than my old '78 911sc, which was tip top). Adding a quart of oil once in a while is cheaper (easier) than fixing it (valve job or re-ring). The only time I can see a hint of smoke is when I accelerate hard at night and will see some smoke against the car behind me's lights. I know the sound of the motor pinging, and it doesn't do it any more or less with 87 octane. Next time I change plugs I will do a compression check to really see where I am.
#7
A number of myths about octane have grown over the
years. There is a widespread perception that the greater the
octane the better the performance. However, once enough
octane is supplied to prevent engine knock, there is little,
any, performance improvement. One exception to this would
be in vehicles equipped with knock sensors. In these vehicles,
octane is insufficient, the computer will retard the timing
limit engine knock. If the vehicle is operating in the “knock
limiting” mode (retarded timing), using a higher octane fuel will
allow timing to be advanced, resulting in some level
performance increase. However, even in these vehicles,
tests have shown that there is no perceptible performance
improvement from using a fuel of higher octane than that
recommended by the vehicle manufacturer.
Another myth is that using a higher octane fuel will result
in improved fuel economy (increased miles per gallon). Octane
is nothing more than a measure of anti-knock quality.
Fuel economy is determined by a number of variables including
the energy content of the fuel. Some premium grades
fuel may contain components which increase energy content.
In those cases, fuel economy may improve slightly as a result
of higher energy content, but not as a result of the higher
octane. Two fuels of identical octane could have different
energy content due to compositional differences.
Consumers need only use a gasoline meeting the
vehicle manufacturer’s recommended octane levels. If engine
knocking occurs on such fuels and mechanical causes
have been eliminated, then the consumer should purchase
the next highest octane gasoline (above the manufacturer's
recommendation in the owners manual) that will provide
knock-free operation.
years. There is a widespread perception that the greater the
octane the better the performance. However, once enough
octane is supplied to prevent engine knock, there is little,
any, performance improvement. One exception to this would
be in vehicles equipped with knock sensors. In these vehicles,
octane is insufficient, the computer will retard the timing
limit engine knock. If the vehicle is operating in the “knock
limiting” mode (retarded timing), using a higher octane fuel will
allow timing to be advanced, resulting in some level
performance increase. However, even in these vehicles,
tests have shown that there is no perceptible performance
improvement from using a fuel of higher octane than that
recommended by the vehicle manufacturer.
Another myth is that using a higher octane fuel will result
in improved fuel economy (increased miles per gallon). Octane
is nothing more than a measure of anti-knock quality.
Fuel economy is determined by a number of variables including
the energy content of the fuel. Some premium grades
fuel may contain components which increase energy content.
In those cases, fuel economy may improve slightly as a result
of higher energy content, but not as a result of the higher
octane. Two fuels of identical octane could have different
energy content due to compositional differences.
Consumers need only use a gasoline meeting the
vehicle manufacturer’s recommended octane levels. If engine
knocking occurs on such fuels and mechanical causes
have been eliminated, then the consumer should purchase
the next highest octane gasoline (above the manufacturer's
recommendation in the owners manual) that will provide
knock-free operation.
well known and reputable source.
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#10
I think you might be getting your numbers mixed up. My 86 manual says 90 CLC or AKI is OK for the S and Turbo, I thing you are looking at the RON which is not used in the US. I run my turbo on 91 regularly, but I go to Sunoco for track time.
#12
Jebia-
Sorry to hear about your rings/valves. I understand holding off on the work completely. I am looking at an upper rebuild due to a small head gasket oil leak. (on a side note my car's P.O. purchased it in Albuquerque at Galles Motors)
Hope you get it fixed soon....
Sorry to hear about your rings/valves. I understand holding off on the work completely. I am looking at an upper rebuild due to a small head gasket oil leak. (on a side note my car's P.O. purchased it in Albuquerque at Galles Motors)
Hope you get it fixed soon....
#13
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From: A Quiet Little Lake In The Middle of Nowhere
I agree about the not so noticable difference. Runs cleaner/smoother/lack of ping...
I think for the most part a, stock car in good running condition will not notice it!
I think for the most part a, stock car in good running condition will not notice it!
#15
Originally Posted by bloodraven
I know that with forced induction, you need premium because the air being forced in is hot enough to detonate the gas before the spark plugs do...
The intake air charge is nowhere near the necessary temperature for autoignition of gasoline vapour, not even if you're running without an intercooler. However, because the intake charge is already compressed, the effective compression ratio of a forced induction car is much higher than that of a naturally aspirated car (this, even though the actual compression ratio, a mathematical calculation based upon the swept volume of the cylinder and the volume of the cylinder with the piston at TDC is almost always less than on a naturally aspirated vehicle). Since the intake charge is already compressed, the effective compression ratio of the engine increases, which means that when the intake charge is compressed _inside the cylinder_ it gets hotter which can lead to pre-ignition. Note that this is no different than what can happen when running 87 Octane in a high-compression N/A engine, it just happens at a lower mathematical compression ratio on a forced induction car because of the multiplication effect that the compressed intake charge has on the mathematical compression ratio.
In simpler terms, the temperature of the intake charge at the intake port is not sufficient to ignite even low octane fuel under boost, but since the intake charge is already compressed when it enteres the cylinder, it gets hotter under compression inside the cylinder of a forced-induction car than inside the cylinder of a N/A car.
Aaron