Am i using the right gas?

Jagerbeast · Apr 9, 2010

I recently bought my 98 GT from a buddy of mine and he was telling me to just use 87 octane. Ive been going back and forth every tank between 87 and 89, which seems to be working out fine so far.

My real question is this:

I just ordered a diablo predator tuner from American Muscle, and to my understanding it has a tune for 93 octane, would it be in my best intrest to use that tune and start putting the higher grade gasoline in my car?

Does anyone know if theres a tune for mid range gas?

sneaky98gt · Apr 9, 2010

You need to put in whatever gas the tune is programmed for. What the tune does is advance the spark timing a bit. If it does that, and the octane isn't high enough, pre-detonation will start happening, and very, very bad things will follow if that happens much. The higher octane tunes will advance the timing more (which gives you more power, maybe 10-15 hp worth), but you need to have the gas to match.

I can't speak for the Diablo, by my SCT had tunes for 87, 91, and 93 octane. I would think the Diablo would be similar.

And off topic, but why the Diablo and not the SCT? I don't know about the Diablo, but AM is doing free Bama Chips tunes for life on the SCT programmers, which is pretty awesome.

Jagerbeast · Apr 9, 2010

Thanks for the response.

I went with the diablo one because some people from work gave it some good feedback. Now that you mention it, i did see that i can get custom tunes via email and such ... but im not sure if i will have to pay for them, probly something i should look into. Hopefully they will let me exchange if so.

ChillPhatCat · Apr 9, 2010

I believe that these cars are tuned to take advantage of higher octane from the get go, if it senses detonation it retards the timing... not saying it gives you much of a boost, but putting in higher octane keeps it away from the threshold of detonation, I guess you could say higher octane helps prevent power loss as opposed to improving power. At the very least I'd run 89, but I usually just put whatever is the highest available in... 92/93 octane.

Jagerbeast · Apr 10, 2010

i did a search before i posted this thread.... and it looks as though using a higher octane than is actually needed would do more harm than good to the car.

But i guess if you have a tuner that will make your car run better/faster off of the higher octane then using it is preferred which is the part that had me confused.

ChillPhatCat · Apr 10, 2010

Jagerbeast said:
i did a search before i posted this thread.... and it looks as though using a higher octane than is actually needed would do more harm than good to the car.

I don't believe that one bit. The only thing you'll do is maybe waste some money paying for a higher grade than you need. If you run too low, it will lead to detonation eventually, whether it happens on the dragstrip at full throttle or climbing a steep hill, eventually you'll get detonation. And THAT is not beneficial to your car. Occasional detonation will not really hurt the car, but it will hurt power because of the computer's retardation of advance. So don't take this as me saying that it is harmful to the car to run 87 in a modern performance engine, but at some point it is going to hamper you if just by a few horsepower.

I know the NPI 4.6 is not quite the same as my motor, but I could have swore in my driver's manual I read that Ford recommend at 91 octane or higher.

RedDaemon · Apr 10, 2010

Jagerbeast said:
But i guess if you have a tuner that will make your car run better/faster off of the higher octane then using it is preferred

thats the thing though. if you have a tune that is for '93 octane' then 93 octane is REQUIRED. you put in anything less youre looking for trouble

trinity_gt · Apr 10, 2010

ChillPhatCat said:
I believe that these cars are tuned to take advantage of higher octane from the get go, if it senses detonation it retards the timing...

The 2V mod motor doesn't have knock sensors and so the factory tune was fairly conservative to ensure the cars would run on 87 without detonation issues.

The general sentiment is correct though: If you're stock, 87 is fine and more octane won't do anything other than drain the wallet. If you have a Diablo or SCT (etc) tuner, the fuel grade you need to run will be dictated in large part by the tune loaded. If you go F/I you should run the best street gas you can find no matter what.

Jagerbeast · Apr 10, 2010

I cant seem to find the thread that was talking about this for the life of me. I believe (if i can remember correctly) it stated that using 93 octane in a car that really only neeeds 87 would cause the 93 to not burn 100% and leave some residue of sorts? Damn i wish i could find that thread

ChillPhatCat · Apr 10, 2010

trinity_gt said:
The 2V mod motor doesn't have knock sensors and so the factory tune was fairly conservative to ensure the cars would run on 87 without detonation issues.

Huh... oh well, I sure thought I read that they did.

trinity_gt · Apr 10, 2010

Jagerbeast said:
I cant seem to find the thread that was talking about this for the life of me. I believe (if i can remember correctly) it stated that using 93 octane in a car that really only neeeds 87 would cause the 93 to not burn 100% and leave some residue of sorts? Damn i wish i could find that thread

Octane is only a measure of a fuel's resistance to auto-ignition (more commonly termed "detonation.") Increases in octane is typically achieved by specific blending the component parts of the fuels and by additives like MMT.

It's the additives like MMT that can cause deposits and fouling of parts like spark plugs and O2 sensors. Likewise, aside from the environmental and health concerns of tetraethyl lead, the fouling of catalytic converters was a major driving force of getting the stuff out of motor fuel. MMT is raising the same sort of concerns. Not all higher octane fuels use such additives or they do so in varying quantities.

trinity_gt · Apr 10, 2010

ChillPhatCat said:
Huh... oh well, I sure thought I read that they did.

The 4V has them

Ateup · Apr 10, 2010

http://www.stangnet.com/mustang-forums/799655-who-uses-premium-gas-their-2v-4-6-a.html

sneaky98gt · Apr 10, 2010

Jagerbeast said:
I cant seem to find the thread that was talking about this for the life of me. I believe (if i can remember correctly) it stated that using 93 octane in a car that really only neeeds 87 would cause the 93 to not burn 100% and leave some residue of sorts? Damn i wish i could find that thread

Yup. I've heard the same thing. Put whatever gas in it the tune calls for.

trombonedemon · Apr 11, 2010

trinity_gt said:
The 2V mod motor doesn't have knock sensors and so the factory tune was fairly conservative to ensure the cars would run on 87 without detonation issues.

The general sentiment is correct though: If you're stock, 87 is fine and more octane won't do anything other than drain the wallet. If you have a Diablo or SCT (etc) tuner, the fuel grade you need to run will be dictated in large part by the tune loaded. If you go F/I you should run the best street gas you can find no matter what.

Dosn't the the Crankshaft positioning sensor do the same thing? I'm positive that the Cam shaft and the Crankshaft act the same, Piezoelectric same as a knock sensor. If there is was a repeated knock wouldn't that throw off the timing and the crankshaft a bit.
Also, the computer advances and decreases timing based on the driving habits and the MAF sensor. We are talking about pretty advanced computers that can and will sense what gas your using. If this was like say early 90s then yes I wouldn't use a higher octane gas than what the manual says.

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