Premium gas

[Ryan]

It's the only gas I use

 

[ISAslot]

I remember when i fed my car 87 octane.

When I would shut the car off, it would stay going for a bit, and make a lot of racket.

It's a bit scary when your gas car 'diesels', cause your like, um, how do I shut this thing off now?

 

[Mean MrMustard]

I have been told on numerous occasions that premium or 93 octane gas was made for 8 (or more) cylinder engines. 4 and 6 cylinder engines run best with regular 87 octane. I don't know a car that doesn't "recommend" premium gas.

 

[Jerboy]

<< I have been told on numerous occasions that premium or 93 octane gas was made for 8 (or more) cylinder engines. 4 and 6 cylinder engines run best with regular 87 octane. >>



Flat head or big head American V8 are the last things to use premium fuel. Premium fuel is the fuel of choice on many sports European and Japanese sedan with high compression engines, especially on forced aspiration type. Some cars recommend regular, some recommend premium and some require premium such as certain model of Toyota Celica.




<< I don't know a car that doesn't "recommend" premium gas. >>



Most boring cars recommend regular fuel.

 

[Kadarin]

The higher the octane rating, the slower the burn rate of the air/fuel mixture. This means that with higher octane fuel, you can run higher compression and/or advance the ignition timing, both of which can result in more power (depending on the motor). Typical generic low compression engines will typically not benefit from higher octane unless there are significant carbon deposits inside the combustion chamber (which will have the effect of increasing the compression). Turbo/supercharged engines typically need higher octane fuel due to the increased cylinder pressure resulting from forced induction.

 

[gooseman]

I have a 2001 Jeep Cherokee Sport 4x4 and the owners manual specifically says to NOT use premium gas!!! I never saw that before I bought this vehicle!

 

[Eli]

<< The higher the octane rating, the slower the burn rate of the air/fuel mixture. This means that with higher octane fuel, you can run higher compression and/or advance the ignition timing, both of which can result in more power (depending on the motor). >>



That is incorrect.

The Octane rating has nothing to do with how fast the fuel burns. It has everything to do with how much pressure(compression) it can stand before it spontaneously ignites.

The more you compress the fuel/air mixture, the more force is exerted on the top of the piston when its "lit". That's where the real performance gain comes from.

If your lawnmower had a compression ratio of 10.5:1, you would have to put premium in it, too... lol.. But it doesen't. You could probably run 70 or 75 octane fuel in most small engines without fear of pinging, as their compression ratio can be anywhere from 5:1 - 8:1

 

[Kilgor]

<< Flat head or big head American V8 are the last things to use premium fuel. Premium fuel is the fuel of choice on many sports European and Japanese sedan with high compression engines, especially on forced aspiration type. >>



Where did you here that? Most High performance V-8s from the mid sixties to 1974 can?t even run on the gas sold at stations today because the compression ratios where so high. I can run 87 octane in my caprice because the computer retards the timing but it still will knock sometimes when under high stress unless I use midgrade.

 

[Tominator]

<< The Octane rating has nothing to do with how fast the fuel burns. It has everything to do with how much pressure(compression) it can stand before it spontaneously ignites. >>



False! Burn rate is the exact difference in octane ratings. If the engine were designed to spontaneously ignite the fuel it would be a diesel!

 

[MadRat]

Our local news did a story on the differences between gasolines. It turned out that premium and regular unleaded are nearly identical except for measurable water content in the gas. The premium gasoline can actually be the same as the regular unleaded if the premium is not fresh or stored properly. Otherwise the gasoline in the midwest all comes from the same supply chain. Ethanol is mixed at the distribution point. Special blends are mixed on the delivery truck.

 

[Stifko]

It's the only gas I use

Me2, I notice sluggishness & a rattling noise w/lower octane fuel. I have an 87 VW w/a lil 4 banger, BTW.

 

[Ladies Man]

5.0 is fine with 87 octane till the hot summer hits...
then i have to start shelling out the $$ for premium

 

[tm37]

<< Those 3 hoses at the gas pump all go into 1 big tank. It's all the same gas. Any difference is all in your mind. >>



No it not some staions do mix to get the midgrade.

Midgrade was brought in to replace LEADED gas when that was taken out. (rather than have the tnak sit empty)

Most places Have seperate tanks.

 

[Sundog]

<< The Octane rating has nothing to do with how fast the fuel burns. It has everything to do with how much pressure(compression) it can stand before it spontaneously ignites. >>


Correct

 

[Triumph]

<< False! Burn rate is the exact difference in octane ratings. If the engine were designed to spontaneously ignite the fuel it would be a diesel! >>


Eli is right.



<< Where did you here that? Most High performance V-8s from the mid sixties to 1974 can?t even run on the gas sold at stations today because the compression ratios where so high. >>


This is because most of these engines used leaded fuel to reduce the engine knock at high compression ratios. Lead was the cheapest way of increasing the octane rating before it was banned in the mid 70's.

 

[yakko]

Use what the manufacturer recommends.

 

[Tominator]

<< If your lawnmower had a compression ratio of 10.5:1, you would have to put premium in it, too... lol.. >>



Go to a lawmower race....ask what fuel they use....come back and admit you are incorrect...

 

[Eli]

<< << If your lawnmower had a compression ratio of 10.5:1, you would have to put premium in it, too... lol.. >>



Go to a lawmower race....ask what fuel they use....come back and admit you are incorrect... >>



Huh? Is that not a true statement? If your lawnmower engine had a CR of 10.5:1, you would have to put higher octane fuel in it.

Again, the Octane rating is a measure of how much pressure and therefor heat the fuel can withstand before it spontaneously ignites. It has nothing to do with how fast the flame front moves. It is more complicated than this now, due to additives and such.. But basically:

Octane has an Octane rating of 100.
Heptane has an Octane rating of 0.

87 octane gasoline is a mixture of 87% Octane and 13% Heptane.

Why do you think some high performance engines use alcohol? The alcohol has less energy stored in it than gasoline does, but because it has an Octane rating of ~110, you can raise the compression ratio to perhaps 12:1. The resulting increase in efficency outweighs the loss in specific heat. Sure, you could run alcohol in a normal, 8:1 engine. But you would lose power, not gain it..

The cheapest and easiest way to make your engine more powerful is to lap, or grind the engine head. By removing metal from the gasket surface, you decrease the volume in the combustion chamber and raise the CR.

You could do this to your lawnmower yourself. Buy a 1'x1' piece of plate glass, and some coarse and fine valve grinding compound. Smear some onto the glass, and start working your head around in a figure eight motion. Make sure to keep pressure as even as possible. Don't go too far, or you'll have to have it machined for valve clearance. Even if you didn't have to put higher octane fuel in your tank at this point, you would notice a difference in engine behavior and power.

 

[Daniel]

<< I have a 2001 Jeep Cherokee Sport 4x4 and the owners manual specifically says to NOT use premium gas!!! I never saw that before I bought this vehicle! >>



I have a Wrangler, I just use regular, I think I could pour a case of dr. pepper in there and it would still keep running.

 

[Eli]

<< << I have a 2001 Jeep Cherokee Sport 4x4 and the owners manual specifically says to NOT use premium gas!!! I never saw that before I bought this vehicle! >>



I have a Wrangler, I just use regular, I think I could pour a case of dr. pepper in there and it would still keep running. >>



I wouldn't try.

 

[Tominator]

<< The cheapest and easiest way to make your engine more powerful is to lap, >>



That is not true all the time...valve timing and duration is the most effective way..

There are a lot of mistatements made on this subject by everyone including myself. Octane and the need for higher ratings have a lot more to do than just the compression ratio. Flame propagation is a science all it's own and there are lots of modern motors running 9 to 1 compression and greater that run fine on less than premimum gas. Compression ratio is just one element in determining if high octane fuel is required. I had an Oldsmobile 394 with 10.25:1 compression that ran quite well on regular gas.

Valve lift and duration, timing, engine load, combustion chamber design, valve area, designed rpm limitations, all are taken into account as well as compression ratio are taken into account before a certain motor meets the need for premimum fuel. The method of fuel delivery and it's timing as well as the timing and duration of the ignition spark all have effects on the need for certain octane. Engine age and maintanence or lack thereof need to be included as well.

There is no one element in judgeing what fuel you should use. I always try and abide by the owner's manual.

 

[Eli]

<< << The cheapest and easiest way to make your engine more powerful is to lap, >>



That is not true all the time...valve timing and duration is the most effective way..

There are a lot of mistatements made on this subject by everyone including myself. Octane and the need for higher ratings have a lot more to do than just the compression ratio. Flame propagation is a science all it's own and there are lots of modern motors running 9 to 1 compression and greater that run fine on less than premimum gas. Compression ratio is just one element in determining if high octane fuel is required. I had an Oldsmobile 394 with 10.25:1 compression that ran quite well on regular gas.

Valve lift and duration, timing, engine load, combustion chamber design, valve area, designed rpm limitations, all are taken into account as well as compression ratio are taken into account before a certain motor meets the need for premimum fuel. The method of fuel delivery and it's timing as well as the timing and duration of the ignition spark all have effects on the need for certain octane. Engine age and maintanence or lack thereof need to be included as well.

There is no one element in judgeing what fuel you should use. I always try and abide by the owner's manual. >>



Yeah, you're right. I shouldn't have said it like that. It is still one of the easiest ways to increase raw power though.. along with camshaft modification/swaps.

Still, though.. At its base, the Octane rating is how much pressure/heat the fuel can withstand before it ignites itself. All those other variables will determine what fuel you want to use in your engine

You want to put the fuel in that will account for all driving conditions. My dads Chevy truck with modified 350 will drive all day on Regular, around town. It's when you start going up hills that the pinging starts. He uses midrange 89 octane, and his engine has a CR of 10:1.

If you don't know about the specific needs of your engine, just use whatever your manual says.

 

[Pacfanweb]

<< False! Burn rate is the exact difference in octane ratings. If the engine were designed to spontaneously ignite the fuel it would be a diesel! >>
(Tominator)

<<Eli is right. >>(Triumph)

No, Eli is not right. Higher octane gas burns SLOWER than low octane. Tominator is right.


<< Where did you here that? Most High performance V-8s from the mid sixties to 1974 can?t even run on the gas sold at stations today because the compression ratios where so high. >>(Tominator)
Correct.

<<This is because most of these engines used leaded fuel to reduce the engine knock at high compression ratios. Lead was the cheapest way of increasing the octane rating before it was banned in the mid 70's. >>
Wrong.

The reason older engines with less compression than newer ones detonate is mainly due to cam timing. Lead has nothing to do with it. There was low octane leaded gas, too.
Plus, they didn't quit selling leaded gas at the pumps until the late 80's or early 90's.
I've seen buildups on old small block engines that had 11-1 compression and would run on unleaded premium gas, due to the way it was cammed.

Look here to see the facts

 

[Tominator]

Yes but it is the slower rate of burn that does prevent preignition...so to say>

<< The Octane rating has nothing to do with how fast the fuel burns. It has everything to do with how much pressure(compression) it can stand before it spontaneously ignites. >>

>the first part is false, but the second part is true because it is that slow reaction to pressure, or call it slow to burn, that is a result of the higher octane. In other words it is because the fuel is slow to burn that prevents the spontaneous ignition.

The main reason older, pre 1973, cars had problems with newer fuels was the lead being excluded. The lead acted as a lubricant for the valve seats and prevented premature wear. By now most all those old engines have ben overhauled and new hardened valves and/or seats have been installed. Timing was an issue as well.

The older motors were assembled without the close tolerances possible with todays technology. They had more ring blowby and less efficient fuel delivery. The oils were not as good either. All these lead to more carbon in the combustion chamber. That effectively raised the compression ratio and as a result using higher octane was a neccessity as there were not the sophiscated ignition and fuel delivery we now have today.

 

[killmeplease]

<< Yes but it is the slower rate of burn that does prevent preignition...so to say>

<< The Octane rating has nothing to do with how fast the fuel burns. It has everything to do with how much pressure(compression) it can stand before it spontaneously ignites. >>

>the first part is false, but the second part is true because it is that slow reaction to pressure, or call it slow to burn, that is a result of the higher octane. In other words it is because the fuel is slow to burn that prevents the spontaneous ignition.

The main reason older, pre 1973, cars had problems with newer fuels was the lead being excluded. The lead acted as a lubricant for the valve seats and prevented premature wear. By now most all those old engines have ben overhauled and new hardened valves and/or seats have been installed. Timing was an issue as well.

The older motors were assembled without the close tolerances possible with todays technology. They had more ring blowby and less efficient fuel delivery. The oils were not as good either. All these lead to more carbon in the combustion chamber. That effectively raised the compression ratio and as a result using higher octane was a neccessity as there were not the sophiscated ignition and fuel delivery we now have today. >>



The first part was true too.