Fuel suggestions

[HenneGT05]

Can someone tell me the best fuel for my 05 GT? Thx Aaron

 

[fjpikul]

Minimum 91 octane. If you want something fancy, you will need to alter the tune.

 

[Specracer]

Welcome to the forum (your 1st post).

I go to a brand name gas station.

 

[RPM217]

I use 93 octane, name brand.....Sunoco, BP, Mobil, etc

 

[dreimer]

I use 93 octane, brand name (Sunoco or Mobil where I am in FL). 93 is the general highest premium in FL at all stations. I have the somewhat normal pulley/tune modification and it is tuned for 93. When at the rally in Arizona this fall 91 octane was the highest I could get at the random stations I stopped at. I had absolutely no problems, not even at the track day, but if given the choice, I would use the fuel it was tuned for.

 

[2112]

92 is our high octane. For me, Chevron only.

 

[fjpikul]

If you really want all the knowledge about it, look for a lengthy post by Chip Beck about fuels. More than 10 years ago.

 

[PeteK]

In many western states, the octane is a couple points lower for each grade. “Regular” is usually 85 or 86 octane rating (R+M)/2. The rationale is that you are at higher elevation, so the air is thinner, so the engine doesn’t need as much octane because you won’t get as high absolute manifold pressure, and thereby less tendency to detonate.

However, that practice was implemented many decades ago, for naturally aspirated engines. It does not take into account the needs of boosted engines, which more and more cars use today. Boosted engines can compensate for changes in air density with altitude, to maintain the same absolute manifold pressure and the same power.

Both our old and new GTs are boosted, so you should try to get the correct octane regardless of operating altitude. If your car didn’t detonate on 91 octane, you probably don’t need higher than that, but I would ask, how do you KNOW you weren’t getting detonation?

You can usually hear the pinging at low RPM and high load, but as the engine reaches to higher RPM, where it’s making a lot more noise and the combustion events are much closer together, you often can’t hear the detonation. You need a sensor to detect it. Most cars have knock sensors of some type, and when detonation is detected, the engine management system retards the timing to stop detonation. So, you can use lower octane fuel and the engine will compensate for it. Unfortunately, the 2005-06 GT ECU does not use this sensor. Be careful if you use lower than the recommended octane level. The New GT has a much more sophisticated ECU, which uses two (I think) knock sensors, so you can stomp the pedal with any gas in the tank and it will compensate for low octane by retarding timing and reducing boost.

I will often use lower octane (and cheaper) fuel if I am driving cross country at pretty much highway speed. I just keep an eye on the boost gauge and don’t exceed about 3/4 of the maximum boost if I put my foot down.

 

[HighHP]

I have considered using regular, in my high octane cars/trucks, on cross country trips as PeteK mentioned above. However, at that instant for some reason that I really feel the need for full power, I am afraid that at that split second, I will forget about the low octane and romp on it. The cost of repairs might greatly exceed my savings. So I am afraid to do it.

 

[HighHP]

Regarding fuel. I used to work with the local fuel delivery system, mainly by pipeline. There are two tank farms in town. All brands of gas deliver fuel to their stations from the same storage tanks. They add the ethanol, brand name cleaners and other additives while the delivery truck loads. So all brands use the same base fuel from the same tank. Just the additives differ.
Fuel is a an open market commodity and can be traded many times between refining and delivery. Chevron in Washington might take delivery from a competitor refinery in Washington and at the same time, on an exchange, deliver an equal amount of fuel from a Chevron refinery in California to a third or fourth company. Fuel exchanges/swaps save $$$$. So you never really know whose fuel you get.

 

[2112]

The additives are why I go Chevron.

 

[HighHP]

Yeah. I think Chevron Techron cleaner is better. Not sure why I think that, but I do.

 

[twobjshelbys]

In many western states, the octane is a couple points lower for each grade. “Regular” is usually 85 or 86 octane rating (R+M)/2. The rationale is that you are at higher elevation, so the air is thinner, so the engine doesn’t need as much octane because you won’t get as high absolute manifold pressure, and thereby less tendency to detonate.

However, that practice was implemented many decades ago, for naturally aspirated engines. It does not take into account the needs of boosted engines, which more and more cars use today. Boosted engines can compensate for changes in air density with altitude, to maintain the same absolute manifold pressure and the same power.

Both our old and new GTs are boosted, so you should try to get the correct octane regardless of operating altitude. If your car didn’t detonate on 91 octane, you probably don’t need higher than that, but I would ask, how do you KNOW you weren’t getting detonation?

You can usually hear the pinging at low RPM and high load, but as the engine reaches to higher RPM, where it’s making a lot more noise and the combustion events are much closer together, you often can’t hear the detonation. You need a sensor to detect it. Most cars have knock sensors of some type, and when detonation is detected, the engine management system retards the timing to stop detonation. So, you can use lower octane fuel and the engine will compensate for it. Unfortunately, the 2005-06 GT ECU does not use this sensor. Be careful if you use lower than the recommended octane level. The New GT has a much more sophisticated ECU, which uses two (I think) knock sensors, so you can stomp the pedal with any gas in the tank and it will compensate for low octane by retarding timing and reducing boost.

I will often use lower octane (and cheaper) fuel if I am driving cross country at pretty much highway speed. I just keep an eye on the boost gauge and don’t exceed about 3/4 of the maximum boost if I put my foot down.

Octane in higher altitudes is usually 2 points lower so 85 in Denver is equivalent to 87 lower. 89 would be 91. But most stations also had 91 so mostly my car ran 93 equivalent. A few times I had to use 89 because that's all they had and it ran fine.

 

[PeteK]

Ed, I expect that in Spokane, you don’t have special regional fuel formulation requirements. California and many other locations in other states do have those requirements, so you can’t easily re-direct fuel formulated for one area to another area. Chip explains those in detail in his posting about different fuel some years ago.

 

[Tomcat]

Welcome to the forum (your 1st post).

I go to a brand name gas station.

And don't go to a gas station where the tanker is filling up the inground tanks...I understand it sturs up sludge.

 

[HighHP]

Ed, I expect that in Spokane, you don’t have special regional fuel formulation requirements. California and many other locations in other states do have those requirements, so you can’t easily re-direct fuel formulated for one area to another area. Chip explains those in detail in his posting about different fuel some years ago.

Yes. And in my theoretical example the fuel stayed in the region that it was refined. Only the ownership got swapped around. All I am saying is that fuel like any open traded commodity can get sold and resold blended and mixed many times from manufacture to end use. Of course they only mix within the allowed specification. If you list all the brands of fuel of sold in the NW, I am sure it will exceed the number of refinery owners in the NW.