Just wondering if anyone has noticed much difference in mpg or anything else with the different types of fuel? Is it worth it to pay more for premium? And why doesn't dsl come in reg/premium? Just curious.

 

Using a higher octane than is recommended by the manufacturer for a stock engine won't usually show any increase in performance or mileage. In most cases, the additional cost of the higher octane gas is a waste of money.

 

Use only what the manufacturer tells you to use and nothing else.
Use premiun with a chip.

 

For low compression gasoline engines, there's not much difference other than some premiums have more detergents in them. In higher compression performance engines, it makes a difference. Most modern fuel injected engines are equipped with knock sensors. Knock sensors detect the onset of engine knock and signal the PCM to retard the ignition timing to eliminate it. While retarding the timing may eliminate knock, it also reduces engine performance. In a high performance engine, the higher the compression, the more horsepower that is generated.
One thing that I've been wondering about lately is what effect blended high octane gasoline has on performance. I would think that replacing 10-15 % of the gas with ethanol would decrease the amount of energy generated per pound of fuel consumed. I would expect it to reduce fuel economy AND performance.

With diesels, it's a different ballgame from that described above. I'll leave it to a diesel guy to answer that part of the question.

 

I use 89 octane ethanol blend in my pickup, because it is a few cents cheaper than regular 87. I think that it might be more efficient and produce slightly more power than the regular 87 does. It is hard to say, because I also use 87 octane once in a while. Ethanol is good for the fuel system in an engine, because it cleans it out. But, the contaninats that the ethanol cleans out can clog up fuel filters and such, so it must initially be used with caution.

 

If the vehicle is recommended for 87 and you put in 93 it won't really do anything if the motor is running correctly. If you advance the timing, it will require a higher octane fuel. The higher octane fuel resists pinging and detonation which will destroy a motor. The higher the compression and the more advanced the timing, the higher the octane needs to be. They have race fuel thats 104 and even 110 octane. Basically if the compression is too high or the timing is advanced, more than one explosion can occur in the combustion chamber and cause the explosions to crash into eachother. This is very violant and will destroy a motor quickly. The higher octane resists this, I believe it has to do with flash points in the fuel. Diesel engines have much higher compression ratios, in the 18-20 area vs 8-9ish on a normal gas motor. On a diesel motor, 1 drop of fuel will cover a 4" piston (thats how high the compression is). Like the other guy said it's a totally different ballgame. I believe diesel is already high in octane so it's not needed, but I could be incorrect. I believe diesel is more difficult to ignite so its more difficult for it to ping or detonate.

 

Yees diesel has alot higher detonation, hence the reason for glowplugs and the high compression, even with a turbocahrger. A sparkplug wiil not ignite under those high compression, high temp conditions. This is also the reason that diesels produce so much torque.

 

I don't know about the newer motors but in my '73 Mark IV, 460, it does boost the MPG.
Ten on regular and close to 13 on premium. It's only got 38,000 miles on it so I guess it would do better if it was broke in . :~)

 

Here's the word on Octane.

Put the octane rated fuel that your owner's manual states to use,anything else is a waste of money.

 

In my last truck I had a 300six that was on its last legs. The higher the octane i'd put the fewer mpg's I'd get.

 

I run a high compression, very well built 302 in my bronco. I have found that the two times I did not run high octane the motor did a bit of diesling and pinged. Same thing with my wife's, uh, non-ford.

 

Yup...timing and compression. Dennis was right, run whatever the manual says and make sure the timing is correct if it's not running well.

 

Since octane is basically a measurement of a fuel ability to NOT detonate at high temps, diesel would be LOW in octane. But diesel isn't even measured that way. They use a measurement called cetane. Cetane is a measure of the fuel's ability to combust. Cetane or CN is a hydrocarbon molecule that ignites very easily under compression, it is assigned a rating of 100.

Diesel at the pump can be found in two CN ranges: 40-46 for regular diesel, and 45-50 for premium diesel.

Diesels "ping" all day long. That is why they sound like they do. They detonate thier fuel.

Not exactly sure of what you're sayin' but diesel have a lot of torque because they have an extremely long stroke. The longer stroke is needed to compress enough air (high compression ratio) to raise its temperature enough to cause the diesel to ignite when it is introduced.

Glowplugs preheat the combustion chamber to help get the compressed air hot enough to ignite the fuel. Obviously they are only needed when it is very cold.

Sparkplugs can ignite fuel under high compression. It's just you cannot control the detonation in gas at such high compression ratios. Sparkplugs don't have really anything to do with it.

Back to subject...

If your vehicle requires (or asks) for higher octane fuels, running lower ones will usually result in a very minimal performance decrease. If your vehicle doesn't require it and is a proper state of tune, higher octane fuel does nothing. And in some cases may even hurt performance and/or engine parts.

MotorTrend just asked that very question and wrote a really nice article about it all. If I can find it, I'll post a link.

 

Here's one... kinda hollow.

The other report musta been from a different rag. It was much more indepth.

http://www.motortrend.com/features/n...41/index3.html

 

I read the article. It appears to only be talking about new car and manufacturer's recommendations. GM didn't build my Z28's engine and I doubt they'd warranty it on 87 octane at 11.5:1 compression if they did.
In fact, come to think of it, they recommend premium for it in its original ~10:1 compression configuration.