Fuel, regular or extra?

[Sailor Bob]

Went to the community gas station today to fill up and they were out of regular (which is the only fuel I use for the most part) so it was extra or walk, so I filled up with the high test type. Pretty disappointed with the cost - seemed like a waste of money. After all it's only gas.

After a 10 minute spin I thought the car was pulling a little better, so I gave her a run on the crosstown and it seemed to be significantly stronger. Got me wodering if it was me or was I missing something from day one.

I'm not going to say anymore on the matter for now, tommorow I'll try again:D.

Anyone else have this experience?

[mbc]

Well, I can say this. Talking octane is like talking politics: everyone will speak their mind and most likely not listen to anyone else. Dogma runs deep on this subject.

I always run the highest octane I can get. New car, or old Z, I even use premium in my Tundra work truck. I just feel better about doing so. I am well aware of the technical aspects of octane and its effects on combustion, as well as computer controlled ignition timing, etc.

If you notice a change for the better, then the solution is obvious. If not, there will be plenty of low octane gas to suit your needs.

CLICK HERE FOR INFO ON OCTANE

[MikeW]

I know octane has been discussed here a lot. I buy most of my gas at a chain of stations called QuikTrip. Just the other day I went to their web site and was quite surprised to find the following:

http://www.quiktrip.com/gasoline/myth.asp

[red_dog007]

My Haynes manual says to run 98 octane. I am thinking that it is just the RON measurement, so it would be 93 octane here in the US. I just go a head and use 91 octane, highest there is in Cali. Once it gets out here it will run on 93 octane. It may not need it, but I don't care. Usually only motors with 10.0:1 compression need it or super/turbo charged motors need higher then 87 and if I am not mistaken, and L24 runs at 9.0:1.

Though each motor its own. My girlfriend drives a Ford Escort 2.0L SOHC 110hp. The motor was sounding a little rough when we first got it, running on 87 octane. On our trip to Huntsville, I decided to put in 89 octane just to see if anything happens. The motor doesn't run rough anymore and there is a noticeable increase in power due to cylinders not pre-igniting under hard acceleration. I am sure that it would even run better and smoother with 93 octane.

Though in my dad's Honda Accord, going from 87 to 93 was not noticeable.

[beandip]

We here in Oregon have three grades of fuel. Regular, Plus and Premium. I am only running 9.5 to 1 so I use the plus. I have never noticed any detonation but I haven't tried the regular. I saw a interesting thing at the local Dyno that was holding a ''dyno day'' . There was a 280 on the Dyno and I don't know what any mods were made on this car . But he made two pulls with the premium fuel and then they took the car off the Dyno and drained what was in the tank. They then loaded some lower octane gas and put it back on the Dyno and the Z made more power than before. Nothing had been done to the car other than the change of fuel. Now it wasn't a great difference in HP but it did increase. I don't remember the figures now it was 5 years ago , and I didn't know the owner of the car. I must say it did surprise me , I had heard of this but this was the first time I actually saw it proven. My Wife always used Plus in her Camry and a couple of years ago we drove down to Palm Springs to visit friends . On the way down I watched the mileage and we were using the plus. on the way back we ran regular. It is a 1000 miles each way and we got the same 29.5 MPG going each way. No difference. So the information that if you are not running high compression the higher octane gas has no advantage. Now with a turbo or blower this raises the compression because of the boost and it is a different matter. Gary

[Walter Moore]

On some newer cars with computer controlled ignition and knock sensors premium fuel MAY improve performance. This is due to the computer retarding the ignition when it detects engine knock, normally before the driver notices. Typically cars that require premium will say so in the owners manual.

On cars the age of most original Z cars, premium fuel is only required if you notice one of the following symptoms:

1. Knocking or pinging under heavy acceleration.

2. Engine run-on. (only happens on cars with carbs...)

At one time I had a Chevy with the dreaded "electronic quadrajet". That car would NOT shut off when the engine was hot unless we used premium gas. The stupid thing would actually idle (sort of) in DRIVE for several minutes with the ignition off if the tank contained either regular or plus octane fuel.

Short answer, if you need premium in an older car, it will be obvious.

[jmortensen]

On some newer cars with computer controlled ignition and knock sensors premium fuel MAY improve performance. This is due to the computer retarding the ignition when it detects engine knock, normally before the driver notices. Typically cars that require premium will say so in the owners manual.

On cars the age of most original Z cars, premium fuel is only required if you notice one of the following symptoms:

1. Knocking or pinging under heavy acceleration.

2. Engine run-on. (only happens on cars with carbs...)

At one time I had a Chevy with the dreaded "electronic quadrajet". That car would NOT shut off when the engine was hot unless we used premium gas. The stupid thing would actually idle (sort of) in DRIVE for several minutes with the ignition off if the tank contained either regular or plus octane fuel.

Short answer, if you need premium in an older car, it will be obvious.

This is the right answer. Cars make the most power on the lowest octane gas that they can run optimal timing on. A stock L28 running 8.3:1 should be running 87 octane.

[red_dog007]

Octane is just a detonation term. Higher the number, harder it is for the fuel to combust. In that one motor that was combusting with regular and plus, it needed the premium. As you shut your motor off it is still in motion. If the fuel sucks, it will keep going and combusting. It sort of turns into a diesel. No spark, but the high compression is what makes the power. High compression with sh/t fuel it will keep going.

If your car only needs 87, it will not hurt to put in 93. All it is is a waste of money. The fuel is getting ignited well before the fuels ignition threshold.

The thing about dynoing, is you can do 10 pulls and have a 20hp difference from the lowest pull to the highest pull. Happens all the time. That is why people do several pulls with no changes.

Now with some vehicles like an SRT4, Cobalt SS with stage kits, almost anything turbo/supercharged with a bunch of PSI, going from 93 to 100 octane can actually give you a nice 20hp increase or so just from the octane boost, though it is also probably has a higher carbon-carbon ration also. Also, like the Cobalt SS, if you run 93 you get the most of the motor, but if you chose to run on 87 you can, the computer will just sense the decrease in the fuels igniting threshold and decrease the amount of psi that the supercharger pushes through the intake.

[Mckrack]

I use premium and have no run on and no pinging. I am concerned about the valve stems. I have heard that unleaded fuel of any octane damages valve stems because I believ in our early Z cars the stems were not hardened like new cars.

We just bought a new 2007 Jeep wrangler with Chrysler's new 3.0 liter engine and it calls for regular unleaded which I thought was odd.

[red_dog007]

We just bought a new 2007 Jeep wrangler with Chrysler's new 3.0 liter engine and it calls for regular unleaded which I thought was odd.

If I recall correctly it is a 3.8L and the motor isn't new at all. That motor was originally only in their minivans from 1991, and they have moved it over to the Pacifica and Wrangler since 07.

Why would it be odd to see it use regular?

[janaka]

I run premium (we only have 91 or 94 available) for daily flogging and track use.when i drove the car home from florida all highway I just ran 87 or regular and i had no issues, but that was consistant speeds and nothing hard on the car.

cheap piece of mind for me with the slightly higher CR (flat tops) and the large cam in the car.

[jmortensen]

The thing about dynoing, is you can do 10 pulls and have a 20hp difference from the lowest pull to the highest pull. Happens all the time. That is why people do several pulls with no changes.

That doesn't change the fact that a car will make more power on the lowest octane that it can run at optimal timing. Dan Baldwin even posted his dyno sheets here where he lost power on race gas, and then lost more power when he tried to add timing to get the power back.

It is true that a newer car with 11:1 compression or even better a turbo and a much more advanced FI system with knock sensor and all that will make more power on higher octane, but that is because the computer will adjust to take full advantage of the extra detonation resistance.

On a mid 70's L28 with 8.5:1 compression 87 octane will make more power than 92, and even if you installed some high $$$ FI system, it isn't going to be able to produce more power with the higher octane, because in a stock Z there is no need for the higher octane.

I use premium and have no run on and no pinging. I am concerned about the valve stems. I have heard that unleaded fuel of any octane damages valve stems because I believ in our early Z cars the stems were not hardened like new cars.

That's the valve SEATS that you're referring to. You are correct that it doesn't matter what octane you have, the lead lubicates and cushions the valve seats and not having lead is what makes the difference. I think the hardened seats were installed in 76 and later cars. I could be wrong there, but that's when they started getting catalytic converters in CA so they COULDN'T run leaded. If yours is later you have nothing to worry about. If it's earlier then when your engine needs a valve job you just need to have the machine shop install the hardened seats. No biggee.