Minimum Octane
12-21-2003, 01:04 AM
#1
Racer
Thread Starter
Minimum Octane
Reading the GT3 owner's manual, I see the minimum octane fuel required for our cars is 95!!! Has PNA said anything about our CA 91 octane and its impact on performance? Or detonation?
Do these motors automatically increase timing when higher octane fuel (e.g. race gas) is used? And is there a max octane after which no further performance benefit is realized?
Following is a link to some home brew additive that has been used with some success by people I know. I'm not recommending this, but just putting this out FYI.
Thanks for any info on this subject.
John
http://www.team.net/sol/tech/octane_b.html
Do these motors automatically increase timing when higher octane fuel (e.g. race gas) is used? And is there a max octane after which no further performance benefit is realized?
Following is a link to some home brew additive that has been used with some success by people I know. I'm not recommending this, but just putting this out FYI.
Thanks for any info on this subject.
John
http://www.team.net/sol/tech/octane_b.html
12-21-2003, 01:08 AM
#2
Keeper of the Truth
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12-21-2003, 01:19 AM
#4
Racer
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I think I found an answer to one of my questions in the GT3 Manual. Max performance comes from 98 octane! I assume that means if you load up with 100, you get no further benefit than if you had mixed 100 with 91 to get 98.
12-21-2003, 03:40 AM
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John, 98 RON is equivalent to 93 AKI. AKI or pump octane equals the average of MON and RON. RON is typically 10 points higher than MON. So for the GT3, a blend of one quarter 100 AKI plus three quarters 91 AKI gives max performance.
Last edited by mds; 12-21-2003 at 12:01 PM.
12-21-2003, 11:41 AM
#6
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Re: Minimum Octane
[QUOTE]Originally posted by Johninrsf
[B]Reading the GT3 owner's manual
Owner's manual!!
You are lucky. We may have the RS in the UK but as far as I know our GT3 does not come with a manual? I can confirm that the RS definately does not have a manual.
[B]Reading the GT3 owner's manual
Owner's manual!!
You are lucky. We may have the RS in the UK but as far as I know our GT3 does not come with a manual? I can confirm that the RS definately does not have a manual.
12-21-2003, 12:24 PM
#7
Racer
Thread Starter
MDS,
You are correct! Thanks.
Have you ever used Toulene to increase octane?
Some more interesting info. on Toulene follows.
John
http://www.gnttype.org/techarea/misc...explained.html
You are correct! Thanks.
Have you ever used Toulene to increase octane?
Some more interesting info. on Toulene follows.
John
http://www.gnttype.org/techarea/misc...explained.html
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12-21-2003, 01:09 PM
#8
Rennlist Member
As stated above the GT3's DME engine management system is set for 93 = Research Octane + Motor Octane/2 for maximum performance. The engine management system, using the knock sensors, will retard the timing if lesser octane is used, probably at a reduction in cylinder pressure and horsepower.
How much horsepower? My friend and I noted that the European 964 Carrera RS's DME is also set for 93 octane, while the normal 964 C2 has a DME set for 90 R+M/2 octane. Porsche claimed a 10 DIN horsepower increase for this change in DME setting. If the logic can be carried forward to the GT3 engine (a big "IF" ?) and the comparison is made to 90 octane, the same percentage increase would result in something on the order of a 15 HP increase.
Going to http://www.76.com/products/76racing.asp and scrolling down to the mixing tables one finds that adding 5 gallons of unleaded 100 octane yields just over 93 octane in a GT3 with a US size 16.6 gallon fuel tank when mixed with 91 octane.
Armed with all this knowledge, my buddy and I did the study and filled his GT3's tank with a mix of racing and street gas to get 93 octane and, drumroll please:
The car *seems* to run better.
Placebo effect? 15 HP? Worth the time, money and energy? Who knows, lets just say it wasn't like a nitrous shot, but hey, it can't hurt to run 93.
How much horsepower? My friend and I noted that the European 964 Carrera RS's DME is also set for 93 octane, while the normal 964 C2 has a DME set for 90 R+M/2 octane. Porsche claimed a 10 DIN horsepower increase for this change in DME setting. If the logic can be carried forward to the GT3 engine (a big "IF" ?) and the comparison is made to 90 octane, the same percentage increase would result in something on the order of a 15 HP increase.
Going to http://www.76.com/products/76racing.asp and scrolling down to the mixing tables one finds that adding 5 gallons of unleaded 100 octane yields just over 93 octane in a GT3 with a US size 16.6 gallon fuel tank when mixed with 91 octane.
Armed with all this knowledge, my buddy and I did the study and filled his GT3's tank with a mix of racing and street gas to get 93 octane and, drumroll please:
The car *seems* to run better.
Placebo effect? 15 HP? Worth the time, money and energy? Who knows, lets just say it wasn't like a nitrous shot, but hey, it can't hurt to run 93.
Last edited by Cupcar; 12-21-2003 at 01:39 PM.
12-21-2003, 05:01 PM
#10
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Just re-hashed the issue with my friend, the extra "snap" ,which seems to be real, is probably not worth $30 at each fill given that in our area the gas is only available in 5 gallon cans at an out of the way depot.
If it were at my local pump, and I didn't have to go out of my way, I'd do it.
If it were at my local pump, and I didn't have to go out of my way, I'd do it.
12-21-2003, 11:48 PM
#12
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One thing that people forget is that the required octane is also altitude dependant. That doesn't help western costal dwellers, but those in mountainous areas probably don't need 93 AKI in their cars. This explains some of the places where they will see 92 or 91 AKI as the maximum available octane.
There are a number of places in Europe where it is impossible to get 98 RON (which is about 93 AKI). Most of Italy for example. I've had to run the car on tank after tank of 95 RON in these places. Honestly, in butt feel I can tell no difference. Maybe I can see a small difference in mileage (or how far I can go on a tank) but I'm not certain of this.
The price difference in Europe between 98 RON and 95 RON is usually quite small (a lot smaller than it is in the USA). Even so, many of my track friends will run 95 RON when they are cruising to and from the track and only put 98 RON in when they are on the track. The octane only makes a difference when you are using the engine in such a way that it might knock and thus retard the ignition. But if you are just cruising down the highway and the RPM and throttle setting are not at a point where the engine might knock, then why bother with the higher octane? There is no less energy in the lower octane fuel. It is simply formulated to avoid knocking. And with knock sensors in the engine we can be sure that the engine will not be damaged.
Stephen
There are a number of places in Europe where it is impossible to get 98 RON (which is about 93 AKI). Most of Italy for example. I've had to run the car on tank after tank of 95 RON in these places. Honestly, in butt feel I can tell no difference. Maybe I can see a small difference in mileage (or how far I can go on a tank) but I'm not certain of this.
The price difference in Europe between 98 RON and 95 RON is usually quite small (a lot smaller than it is in the USA). Even so, many of my track friends will run 95 RON when they are cruising to and from the track and only put 98 RON in when they are on the track. The octane only makes a difference when you are using the engine in such a way that it might knock and thus retard the ignition. But if you are just cruising down the highway and the RPM and throttle setting are not at a point where the engine might knock, then why bother with the higher octane? There is no less energy in the lower octane fuel. It is simply formulated to avoid knocking. And with knock sensors in the engine we can be sure that the engine will not be damaged.
Stephen
12-22-2003, 02:46 AM
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Move to NY - Every station sells 93 Octane.. Sunoco used to have 94, but they stopped making it because it cost to much and sales just werent there to support it. I assume using a good quality 93 Octane is fine for the car, no??
12-22-2003, 05:29 AM
#15
Nordschleife Master
Interesting...so would it make a difference in a 944 N/A? To be quite honest, I have not felt a difference between running 87 and 91 octane in my car; but then, I have not taken her on the track yet.
I would guess I'd feel a difference at 93, and I'm going to see if the 76 by me has that 100 octane, or at least 93.
But what I will tell you is that on the freeway, the power seems the same on the 87 and 91, but then our cars have to be de-powered by about 10%, as compared to other states, to meet Smog tests (had to do that to my first 944 that I brought in from out of state).
So I feel that for a street car in California, maybe that would be why I don't see the difference. But then my current '83 944 could use an overhaul, for good measure. Maybe then I would see the difference on a 20 year old Porsche.
- Julie
I would guess I'd feel a difference at 93, and I'm going to see if the 76 by me has that 100 octane, or at least 93.
But what I will tell you is that on the freeway, the power seems the same on the 87 and 91, but then our cars have to be de-powered by about 10%, as compared to other states, to meet Smog tests (had to do that to my first 944 that I brought in from out of state).
So I feel that for a street car in California, maybe that would be why I don't see the difference. But then my current '83 944 could use an overhaul, for good measure. Maybe then I would see the difference on a 20 year old Porsche.
- Julie
