GT pinging on 87 octain

This exact same argument has been argued a million times in the mod4.6 forums. The conclusion is always the same, people argue that premium is better than regular, or plus is the best or that premium will hurt the engine. The majority of the guys with 99-mid 01 cars that are N/A are running 87-89 octane. The guys with mid 01-04 cars that are N/A are generally running 89 octane fuel. Why the higher octane in the later SN95's? Because compression was raised slightly on those models and a slight ping is noticed with 87 octane. Seems as though this is what is happening with the 05's as well. If 89 fixed the problem, I would suggest running 89 on a stock tune.

Not sure if you have an automatic or a manual.

If you have a manual & are lugging the engine, say trying to accelerate from a slow speed in a high gear, you may get pinging.

I'm not going to go into the whole debate about gasoline. I think it's been covered on the scientific side of things so many times that let people believe what they believe and be happy. Away from the scientific straight-forward method all cars are different. Even if in the lab they can reproduce the same results when you get your car, it may be just different. You should also note that most of the upper states, well at least North-east for me, are using ethanol as 10% of the gasoline. In you case go with what makes your car happy. If it needs 89 stick with it. I would wait till the summer months when the ethanol isn't used and try 87 again. Premium will not burn better then 89. It will guarantee that you will never get pinging, but the 89 may do the same since its still tuned for 87. When i ran my 01 GT i used 87 from day one and never heard it ping once.

I've got a question or two for those NOT in the midwest. What is your 89 octane gas like? I live in Iowa, so we're pushing ethanol pretty hard. Almost every pump in the state has 89 octane only as an ethanol blend, and cheaper than 87 octane. I'm curious if most other states also have 89 octane with ethanol blend (guessing probably not)?
I've heard that the ethanol blend isn't as good for performance in the 2V motor despite the higher octane, so I've been staying away from it for that reason (and haven't had any trouble with 87 octane either). Curious if anyone else knows more about this or if it may be a factor for the 3V motor? Thanks.

fellamansteve said:

I've got a question or two for those NOT in the midwest. What is your 89 octane gas like? I live in Iowa, so we're pushing ethanol pretty hard. Almost every pump in the state has 89 octane only as an ethanol blend, and cheaper than 87 octane. I'm curious if most other states also have 89 octane with ethanol blend (guessing probably not)?
I've heard that the ethanol blend isn't as good for performance in the 2V motor despite the higher octane, so I've been staying away from it for that reason (and haven't had any trouble with 87 octane either). Curious if anyone else knows more about this or if it may be a factor for the 3V motor? Thanks.

Click to expand...

Ethanol contains less energy per gallon than gasoline. Since your car isn't adjusting for that in any fashion, that means you will get lower HP from gasahol than gasoline all other variables held constant.

BUT, if you have a car that can be tuned to take advantage of higher octane, then you can get some of that performance back.

The new E85 fuel (85% ethanol) is so high on the ethanol content that you should not run it in a gas vehicle. But some cars are FFV (flexible fuel vehicles), which can detect the percentage of ethanol and change their fuel rates and AF ratio to match. Since E85 is about 104 octane equivalent, you could, in theory, build an FFV with a very high compression ratio that would perform GREAT.

But we digress. Your 10% gasahol is slightly lower on energy than straight gasoline, and you will have modestly lower HP ratings on it (probably measureable but only slightly noticeable, if at all, in daily driving).

Sounds like something is wrong with your tune in the PCM or maybe a bad knock sensor isn't adjusting the timing correctly. You shouldn't have any pinging whatsoever.

Take it in ASAP.