I do not have the owners manual for my 1985 Corvette and would like to know what fuel is reccomended. :confused:

 

From the mouth of Gordon Killebrew:

The L98 was designed to run on regular... if it pings, go to midgrade.

 

:iagree: :yesnod:

 

Thanks for the help

 

The owners manual for my 89 C4 says; "your engine is designed to operate on premium grade unleaded fuel. However, with the electronic spark control system, you may use either middle or regular grade unleaded fuel at slightly reduced acceleration performance".


[Modified by GKK, 9:25 PM 4/14/2004]

 

The 1984 and 1985 share the same long block. They have 9.0:1 (nominal) compression and forged pistons. Don't ask! I run mine on 85 octane with the base timing set at 14* btdc. I haven't had the nerve to try kerosene, yet.

RACE ON!!!

 

quote:
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From the mouth of Gordon Killebrew:
The L98 was designed to run on regular... if it pings, go to midgrade.


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:iagree: I run midgrade in my 86 because it would ping a little bit. Bone stock as far as I know.

 

You guys are killing me! :crazy: We're talking about 10 cents a gallon difference between midgrade and premium. That's $2 difference per tankfull! Your driving a VETTE, isn't worth it?

When I was in high school (1984), we had a big break on gas one month. It went from $1.02 to .98 per gallon.My best friends dad had us fill up both cars and the lawnmower gas can.When we got done I said "Wow, we just saved 80 cents". It was so true, people act like that $2 per fill up will make them or brake them! :troll

 

You dont need more than 87 octane on the 85 or 86.

At most I run midgrade.

 

You're absolutely correct, the cost difference isn't that much. HOWEVER, running a higher octane fuel than your motor demands actually costs you performance AND fuel economy. So by "buying the best" you are likely spending more money for lower performance. That's just plain foolish.

Gas stations however follow my thought that "It is immoral to let a fool keep his money." So of course they're gonna try to sell you premium because they know that ultimately they'll sell you more of it at a higher price.

 

OK Nathan, you just lost me. :confused: If your motor doesn't demand premium I can see how you will not benifit from it, but how do you lose power from running it. :confused:

 

Premium fuel is less prone to detonation in higher compression engines. This means that it's harder to detonate period. This is kinda hard to explain, others can explain it better I'm sure. Don't yell at me if it isn't 100% correct, it's close enough to get the point across.

Higher octane fuels burn slower, in a more controlled manner. In a high compression engine you get the benefit of the higher compression and are greeted with a powerful explosion that is perfectly timed and makes peak power. The higher compression ratio more than compensates for the slower burn rate and you make more power.

Just for an example, if your engine is running perfectly on 87 octane, meaning it isn't detonating and you've got full spark advance, you'll cost yourself power. How? Well at full spark advance the fuel mixture will be ignited so as create peak cylinder pressure at the optimal point, and drive the piston downward with the maximum amount of force. Now insert a slower burning fuel and see what happens. The fuel is still ignited at the same point, but it burns slower. This means that your cylinder pressures are going to be lower. When the combustion process reaches the point at which peak pressure occurs, it's going to be late. The piston will be further down in the bore, where it is already moving away from the burning gases. This means that the combustion will have to fill a larger volume before it can even begin to press down on the piston.

This results in less power for any given volume of gasoline. The poor fuel economy comes into play because you will actually give it more throttle to get the same power level. This burns more fuel and thus costs you more money in the long run.

If you don't believe me take something with REALLY low compression, something like an american 4-cyl out of the early 90's or late 80's. My 91 Cutlass Calais was a perfect example, it only make 8.3:1 compression. Fill said car with 87, keep doing so for a little while until you're sure that you've got pure 87 octane in the tank. Let the car sit overnight and start it cold in the morning. Time how long it takes for the engine to start. Ideally the car is running correctly and it'll fire up immediately, you probably won't even be able to time it. Do this for a while until you get a good feel for how long it takes the car to start. When you've got a good idea run that tank out as far as you can without having to push it into the gas station. Fill it with the highest octane you can find. Drive it back home and park the car. The next morning start the car. I promise you it will take 3 or 4 times as long for the car to start. Why? Because the completely cold low comrpession engine has a hard time igniting the high octane mixture.

Now how much difference does this make in performance? Hard to tell really. I kept VERY close records of gas mileage with that car until the day I sold it. There was never a measureable difference in mileage between regular and high octane. Performance? Other than the hard starting you couldn't tell. What's the differernce really between 82 horsepower and 85 horsepower? Now remember this was on a fuel efficient 4-cyl that made very little power. You've got twice the cylinders and it makes quite a bit more power. Any difference in performance and economy will be amplified.

You asked why not spend the extra $ per tank? Well because in my case if I ran regular in my car over the past 3 years I would have saved enough money to buy those tires that I'm needing. Sure a couple of hundred over 3 years doesn't seem like a big difference, but every little bit counts.

BTW, yes you heard me right, I run premium in my car. It's also running over 10.5:1 compression and a very aggressive timing curve. It may well run fine on lower octane, I just haven't got the chance to data log and test that yet. In the mean time I'll play it safe. For a stock application though, you can run lower grade fuel and you won't have any trouble. :cheers:

 

Nathan, you hit it right on the head. Exactly correct. My Dad used to race 1/4 mile motorcycles and he would always use the lower octane fuel, becaue it "burnt hotter" producing more power. Of course, something built to run the 1/4 mile isn't necessarilly reliable on the street for everyday driving, but it's the same principle. And of course, once in a while, they'd sneak in some alcohol when nobody was looking, because it burnt "even hotter". So, your explaination gets my vote. :smash:

 

That theory works but with the slower burning higher octane fuel you can run more advance on your timing and make more power. :smash:

 

LT4 = 10.8: = Premium for Kevin

...thank god im a spoiled brat whos father owns a gas station so i get gas for free :skep: :leaving:

 

Thats fine, but youre not getting anything extra. Your engine wont perform any miraculous leaps by putting in octane booster and running 14* of timing.

 

Every little bit helps. A little more timing, a little more air, a little more fuel, a little cooler thermostat for a cooler head and cooler intake temps= more horsepower. Also most high octane gas has more additives to keep your injectors and cylinders cleaner. :auto:

 

:iagree: with Chriswtx.

[Yoda]Octane leads to spark advance, spark advance leads to higher cylinder pressures, and higher cylinder pressures lead to power.[/Yoda]

 

That's all well and good, except that there's a point of maximum timing advance. Beyond that you'll give up performance. If you're running full spark advance on 87 with no detonation there is nothing to be gained from going with a higher octane.

 

How do you know your not getting detonation? If the computer is doing its job right and your having detonation it will pull timing for you, and you will never know it unless you have a dataloger. Thats my point when the computer heres detonation it retards timing and you will never know it.