Aviation fuel OK?

[sailmotion]

OK - so I'm retarded. Now that we've gotten that out of the way-

Does anybody know if it's ok to use AvGas

(aviation fuel) - 100 octane in a 911? If so, any performance advantages? Any danger mechanically?

[whs]

OK - so I'm retarded. Now that we've gotten that out of the way-

Does anybody know if it's ok to use AvGas

(aviation fuel) - 100 octane in a 911? If so, any performance advantages? Any danger mechanically?

Don't think so. If I am correct, av fuel is a "leaded" fuel. Not a good idea even if it is cheaper (not to mention it's illegal to run leaded fuel in a street car). Leaded fuel will damage the oxy sensor and catalytic converter at a minimum.

Will

[PAULSPEED]

Hi,

The price of avgas 100 and racing gas is very close. You

can buy leaded or unleaded racing gas at the track. All

Avgas has lead in it to prevent pinging. Sugest you run

101 unleaded racing gas.

Paul

[seafeye]

Hi,

The price of avgas 100 and racing gas is very close. You

can buy leaded or unleaded racing gas at the track. All

Avgas has lead in it to prevent pinging. Sugest you run

101 unleaded racing gas.

Paul

Down in Miami a while back and at Signature FBO they were charging $4/gallon for avgas.

The owner of a navajo i was flying was considering parking it because of the high prices.

On a different note...If you were to put avgas in your car i bet you wouldn't get to burn the

whole tank down...your engine will be toast. That avgas burns HOT. I used to know the temp

that it burnt at but not now.....i switched to JET A.

[RF5BPilot]

Aviation fuel is 100LL (100 octane "Low Lead")....which is somewhat of a misnomer as it actually contains fairly high quantities of lead. So much so, that aviation piston engines have a continuing problem of having the plugs lead-fouled and other areas of the piston/valve assemblies coated with the stuff.

Higher octane means that a fuel is actually harder to burn. That's needed so you don't get spontaneous combustion in engines with unusually high compression. So, to some extent, car manufacturers try to run the lowest octane they can that does not allow detonation. Going to higher octane for no reason will simply decrease your fuel efficiency.

The lead in standard aviation fuel will trash your emission systems and foul the engine. When possible, many airplane owners get special permits to run unleaded autofuel. A few aviation engines specifically permit it. So, aviation fuel is not an advantage....nor is unnecessarily higher octane. It has nothing to do with "higher power" in the fuel, it just permits higher compression in your engine. If you haven't modified your engine to get unusually high compression, just use standard fuels and get a better fuel burn.

[sailmotion]

I believe you're right WHS, avgas is leaded - bad thing for the catalytic converter. Thank you Paulspeed for the suggestion of unleaded racing fuel. I don't live too far from Limerock Racetrack in Connecticut. I'll look into the possibility of getting a tank of 101 unleaded there. Has anyone used 101 unleaded? Does it make a noticable difference? Thanks eveyone for replying.

[KevinMac]

No do not use AV gas, it's classified as low lead, not no lead!

[JonesnSince78]

I don't live too far from Limerock Racetrack in Connecticut. I'll look into the possibility of getting a tank of 101 unleaded there.

Not sure if it's still true, but there was a convenience store/gas station at the corner of Routes 4 and 43 just East of Cornwall that sold 100 racing fuel. We stopped there often for snacks going to ski at Mohawk. Also don't remember if it was leaded or not, but if they're along the roadside, I guess it would have to be lead-free? If that's not too far, you might try that spot, too. Always thought it was an odd place for racing fuel, but I guess they were catering to the crowd from Torrington headed to Lime Rock...

[KevinMac]

Not so sure anything above 93 is going to benefit you anyway, since the maps are written to 93. It may be just a matter of more expense and no more output switching to 100. Sometimes going too much can hurt performance.

[wross996TT]

Not so sure anything above 93 is going to benefit you anyway, since the maps are written to 93. It may be just a matter of more expense and no more output switching to 100. Sometimes going too much can hurt performance.

My car specifically calls out 96 (R+M)/2...in any case I have heard the argument that higher octanes may hurt performance, but never seen any data to support it. The car usually states the minimum Octane not the maximum. The ECU will adjust for pre-mature detonation to some extent if you use lower octanes...I wonder if higher octanes don't allow the ECU to allow for better detonantion? In any case I run VP100 in my car (granted it is modified). It does not have a high octane ECU map. It runs great...do not think performance is hurt at all.

[KevinMac]

The manual specifically states that the recommended octane is 93, but 91 can be used and performance will be lost since the knock sensor will come into play.

Maps usually provide a curve based on the max amount of perfomence and driveability under stock conditions and available octanes. Now if 100 was readily available and the maps were written to it, then you probably would get more performance.

Porsche would capitalize on every thing available to increase output with less cost.

[Joe90mmm]

Higher octane does NOT improve horsepower.

To increase the horsepower of an engine you need to increase its compression ratio or supercharge air-fuel in the cylinder.

The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine.

So your engine is build with a compresion so high the 87 octane will auto ignite, 93 octane will support this compression. The power of gasoline is measure in btu,(british thermal unit),all fuel at the pump have the same BTU, only the octane change.

Racing fuel are oxygenated fuel that will produce a bit more horsepower because they have a better vaporisation, and they have also higher octane rating to accept higher compression engine, you buy those fuel usualy in barrel of 5 15 or 45 gallons.

Very expensive.

Edited September 28, 2007 by Joe90mmm

[wross996TT]

The manual specifically states that the recommended octane is 93, but 91 can be used and performance will be lost since the knock sensor will come into play.

uh...I'm driving a turbo.....recommended octane is 96 FYI.

[Westcoaster]

Not so sure anything above 93 is going to benefit you anyway, since the maps are written to 93. It may be just a matter of more expense and no more output switching to 100. Sometimes going too much can hurt performance.

My car specifically calls out 96 (R+M)/2...in any case I have heard the argument that higher octanes may hurt performance, but never seen any data to support it. The car usually states the minimum Octane not the maximum. The ECU will adjust for pre-mature detonation to some extent if you use lower octanes...I wonder if higher octanes don't allow the ECU to allow for better detonantion? In any case I run VP100 in my car (granted it is modified). It does not have a high octane ECU map. It runs great...do not think performance is hurt at all.

I am not questioning that your car specifically calls for 96 octane, but as was correctly said by an earlier poster, this would not really be the mimimum, but rather the recommended octane. The manual should state the acceptable range.

The ECU and sensors work to adjust the engine parameters to compensate when the combustion conditions reflect this. You can run higher octane (assuming there are no harmful additives present), it is just that the ECU may not be able to adjust engine parameters for an octane above which it was designed for.

Having said all of this, In Canada I have never seen higher then 94 octane at a regular station (I'm not saying it doesn't exist), but what is an owner expected to do, carry octane boost to add at each fill-up?

Edited October 2, 2007 by Westcoaster

[Team996]

Not so sure anything above 93 is going to benefit you anyway, since the maps are written to 93. It may be just a matter of more expense and no more output switching to 100. Sometimes going too much can hurt performance.

Can someone tell me why I'm paying $0.20 more per gallon for 91 than I would for 87? Right now, it feels like a gas-company propagated superstition and I feel like a sheep by not really knowing the empirical difference.

[JonesnSince78]

Can someone tell me why I'm paying $0.20 more per gallon for 91 than I would for 87? Right now, it feels like a gas-company propagated superstition and I feel like a sheep by not really knowing the empirical difference.

Read Joe90mmm's post, three posts above yours. I think it explains the issues quite succinctly.

[mxdave74]

It's worth noting that in many circumstances higher octane fuel does indeed provide greater performance by allowing our engines to avert retarding the ignition. Porsche uses knock sensors to tell the engine when to reign things in. On hot days at the track for instance, you might be surprised how often engine ignition is being retarded to save itself. In any of these scenarios, there is a measurable and felt difference by running 100+ octane fuel, so while many of you are correct in saying that higher octane fuel does not provide greater horsepower in and of itself, there are indeed many circumstances where it does allow the engine to use the fuel/air to its greatest potential and ultimately generate more horsepower in those conditions.

Higher octane does NOT improve horsepower.

To increase the horsepower of an engine you need to increase its compression ratio or supercharge air-fuel in the cylinder.

The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine.

So your engine is build with a compresion so high the 87 octane will auto ignite, 93 octane will support this compression. The power of gasoline is measure in btu,(british thermal unit),all fuel at the pump have the same BTU, only the octane change.

Racing fuel are oxygenated fuel that will produce a bit more horsepower because they have a better vaporisation, and they have also higher octane rating to accept higher compression engine, you buy those fuel usualy in barrel of 5 15 or 45 gallons.

Very expensive.

[Izzy]

Please use avaition fuel and /or the highest octane you can find for all your everyday driving. And don't forget to use your VISA card when purchasing, the Amercan economy thanks you for your support.

[KevinMac]

Mxdave - you seem to be forgetting that the fuel and advance curves are already mapped, they are not open ended, so even if environmental conditions would allow as you say more advance etc the map will restrict, regardless if there is a knock sensor or not. Hence the reason for rechip or tune via a dyno and remap. So stock ECU with factory fuel and advance maps, it is very safe to say 100 octane will buy you nothing. You are limited by the predetermined map. Maps are not open ended there is a limit.

[mxdave74]

Kevin, I'm no expert and you may be... I wasn't assuming some unlimited boundaries on ECU mapping, but I and several others I've run with can attest to higher octane fuel making a noticeable difference on days at Thunderhill with ambient temps over 85 degrees. Question?.... if the ECU capabilities are limited (effectively not cognizant of the difference between 87 and 93 octane), that would mean our ECU has no way of countering differences in fuel quality? Seems odd.

Mxdave - you seem to be forgetting that the fuel and advance curves are already mapped, they are not open ended, so even if environmental conditions would allow as you say more advance etc the map will restrict, regardless if there is a knock sensor or not. Hence the reason for rechip or tune via a dyno and remap. So stock ECU with factory fuel and advance maps, it is very safe to say 100 octane will buy you nothing. You are limited by the predetermined map. Maps are not open ended there is a limit.

[KevinMac]

MX - going from 87 to 93 there would be a difference, since 87 is too low in a 11:1 compression ratio causing preignition with fuel lower then 91. Porsche specifically says to use 93 but 91 can be used, since this is in the lower parameter for the knock sensor to adjust accordingly. This is the reason Porsche has a recommended octane and a mnimul octane listed. There is only so much advance and fuel adjustment based on the maps written for 93 octane. Once again, these maps can be tailored by using a chip or map upgrade to take advantage of higher octane. The only true way to know if performance is different is to actually use a dyno, since driving can effect performance. I'm in 90 plus heat and running anything more than 93 octane has no increase in performance.

It is true that combustion temp is a factor in the determination of octane, as is pressure. So as you go to a higher altitude you could litteraly use lower octane since the available air is thinner and in essence lower compression. BTW octane measurement uses temperature as a an input to determine octane. So running at 85 degrees a sea level, should provide max performance as specified by the manufacturer.