Gas

What kind of Gas do you guys put into your GTs?
My GT is stock...for now

87 octane is all you need.

Is 91 octane bad for the car?
What about after I get the exhaust and gears done. Should be done tomorrow.
Still use 87?

You shouldnt need anything higher than 87 until you start messing with compression, timing, ect.

My GT runs on 89 for now, my coupe runs 87 for now.

If your still foggy on the whole octane thing, then freshen up with this.

Unfortunately, many people assume that higher octane fuel is better for all engines, no matter what. This, as I'm sure you know, is absolutely false. Ultimately, the best octane for any vehicle is the lowest one you can run without detonation (pinging) occuring.

Running too high of an octane will ultimately make it necessary to continue using that octane.

Just to clarify, it's not the fuel that increases the performance, it's the fact that the timing has been advanced. The higher octane permits this to happen. Basically, the way it works is something like this:

Octane represents a fuel's stability. When you compress an air fuel mixture, it becomes quite unstable, and explosive. In fact, this is why diesel engines don't require spark plugs. They commonly have compression ratios of 22:1 (as opposed to a stock Mustang with 9:1), which makes the air/fuel mixture so explosively unstable that it ignites itself when the piston reaches TDC.

Octane, for all intents and purposes, is used to slow down, or control the burn rate. Modifications that increase performance, such as increased compression, or advanced ignition timing, will cause the mixture to become too unstable, and pre-ignition (aka: detonation, pinging) will occur. This is when the mixture fires on it's own, at the wrong time. Severe damage will occur if left untreated. Anyway, the only way to perform the mods that increase the power is to further slow down and control the burn rate of the air/fuel mixture, and the method used to do this is increased octane.

People often think of high octane fuel as being more flammable, and easier to explode, whereas that is actually the opposite of the truth. 110 octane race gas is much tougher to light than low grade 87 octane. BUT, because of that fact, it is the use of 110 octane fuel that permits the compression to be increased to 12:1 without melting the pistons.

On a side note, nitrous oxide works on a very similar principal. With nitrous, the power comes from the added oxygen. The problem has always been trying to find a way to add oxygen safely. As I'm sure you know, oxygen is EXTREMELY flammable, and if you were to try and add it straight to your engine, you would likely die, and not even be able to explain to people why it was you died. It was discovered that the nitrogen in the nitrous oxide was just enough to keep the oxygen from burning uncontrollably, thus permitting it to be used in a gasoline engine. In other words, the nitrogen is to nitrous oxide what the octane is to gasoline, except for the fact that octane is a calculation, and nitrogen is an actual element, but you get the idea.

Okay, back to the story...

Use of a fuel that has a higher octane than is required by the engine and the way it has been tuned will result in unburned deposits being created and left behind in the combustion chamber, and on top of the piston. Often referred to as carbon deposits, these cause the combustion chamber to become very unstable, for several reasons, all of which will ultimately require you to use a higher octane fuel to restore stability. Among the reasons, are increased compression (the deposits take up space, and actually increase the compression enough to make it unstable), retained heat (deposits retain heat at times when those surfaces shouldn't, increasing the likelyhood of pre-ignition), and the development of sharp edges (like sand under the waves, carbon deposits can be "shaped" by their environment, and can develop sharp edges, which act to the compressing mixture like a hat pin would to a balloon.

Hiflow Are you a tech?

Well, I'm not certified if that's what you mean. I was planning on taking a mechanics class at the local community college, but applied too late for the program. Now I have to wait another year before I can get into it because it's only offered every other year.

As far as that octane post, I cannot take credit for that as much as I would like too. It came from a guy named Chris over at the www.ricerhatersclub.com (http://www.ricerhatersclub.com). That info is also very detailed, and saves me the time of actually writing eveything out.

lol, Well you would still make a good tech. I work with a lot of them and most don't know half of what you seem to know.

Thank you!

I give credit where credit is due and it is definatly due to you.

And thanks for all the help you provide for us!

definitely

Is that a turd smudge on the front of the T-Bird?
Just Kidding.
I had often wondered myself if you where a tech.

wow, i learned a ton during this thread.
at the pump, i once read a sign that said the highest octane rating was "better for the environment, cleaner burning, better acceleration"

i now understand why this 'can' be the case, but in most cases it is a trap.

I guess its back to 87 for me...thanks for the info

wow, yeah, thanks for explaining. my friend told me not to put mid-grade gas in my car, which i was considering cause i thought it would be better for my engine, he explained why but all i heard was "low compression...bad..."

i wished i would have known that a few months ago, i've been putting 93 octane in my stock 5.0, i just rebuilt the thing too, i guess i'm gonna have to check everything out....again, thanks for the info