Special gas for special cars

[Fardor]

Today I was pretending I was about 10 years older than I am, with money to spend on a new car (yet to have my own car still).

Anyways, you guys know that a car like a MazdaSpeed3 is supposed to be filled with special gas. I'm sure the special gas must be more expensive than normal gas. So would a MazdaSpeed3 owner have to buy the special gas, or would it be fine to sacrifice a little performance and use normal gas? How much more expensive is 91 Octane than regular?

 

[Jumpem]

With my Forester XT and STi I would only put 91 or 93 in them. I would never put regular gas in a turbocharged vehicle.

 

[shabby]

Why would you want to sacrifice performance... in a performance oriented car? You paid 5k more for it to get that 260hp, now you want to skimp on premium fuel?
Its going to cost you a couple dollars more at the pump for premium fuel, you're not going to go broke because of that. But if you do then you shouldn't of bought the car.

 

[Throckmorton]

Using lower octane fuel in a high compression car is hard on the engine and hurts gas mileage. You won't see any benefit, especially considering that with gas at $4 the extra cost of the 93 octane is a smaller percentage. If you can't afford the extra 10 cents, how can you afford the massive cost of a new car when you factor in interest etc?

 

[Uhtrinity]

The Insights get the best mileage with regular unleaded. In fact mileage can go down slightly with higher octane.

 

[ElFenix]

Originally posted by: Throckmorton
Using lower octane fuel in a high compression car is hard on the engine and hurts gas mileage. You won't see any benefit, especially considering that with gas at $4 the extra cost of the 93 octane is a smaller percentage. If you can't afford the extra 10 cents, how can you afford the massive cost of a new car when you factor in interest etc?

premiuim is only a 10 cent premium where you are?


but yes, mileage will likely suffer so much that you won't get any monetary benefit using cheaper gas in a car like a speed3.

Originally posted by: Uhtrinity
The Insights get the best mileage with regular unleaded. In fact mileage can go down slightly with higher octane.

that makes sense, the insight was designed for regular and regular actually has more energy per gallon than premium.

 

[mooseracing]

Originally posted by: Throckmorton
Using lower octane fuel in a high compression car is hard on the engine and hurts gas mileage.

On older cars yes, but there is no damgae on new computer controlled timing, fuel, boost cars. The engine can tell where it is igniting at in the cyliders and whether there is premature detonation.

On my carb'ed car I use to adjust the timing jsut about everyday depending on how I wanted to drive, what gas I was running, and whether I wanted to have fun.

 

[AstroManLuca]

My parents have an older car that, a couple years ago, started to suffer from valve knock unless they put mid-grade gas in. Normally it only required regular unleaded.

I would not use a lower grade gas than what is recommended for the vehicle, and it pains me to think of all the clueless performance car owners out there who, despite owning an expensive car, will still go out and wreck their wonderful cars by putting slightly cheaper gas in them.

 

[Throckmorton]

Originally posted by: mooseracing

Originally posted by: Throckmorton
Using lower octane fuel in a high compression car is hard on the engine and hurts gas mileage.

On older cars yes, but there is no damgae on new computer controlled timing, fuel, boost cars. The engine can tell where it is igniting at in the cyliders and whether there is premature detonation.

On my carb'ed car I use to adjust the timing jsut about everyday depending on how I wanted to drive, what gas I was running, and whether I wanted to have fun.

Hmm, I thought that the ECU started ignition earlier to beat the detonation, but I don't think that's what happens because I found this http://www.faqs.org/faqs/autos...q/part3/section-1.html

It starts ignition later. How does that stop detonation?

 

[Bignate603]

Originally posted by: AstroManLuca
My parents have an older car that, a couple years ago, started to suffer from valve knock unless they put mid-grade gas in. Normally it only required regular unleaded.

I would not use a lower grade gas than what is recommended for the vehicle, and it pains me to think of all the clueless performance car owners out there who, despite owning an expensive car, will still go out and wreck their wonderful cars by putting slightly cheaper gas in them.

If your modern car was correctly designed cheaper gas will have no ill effects. The computer will detune the engine so it's not running as aggressively so it can run safely with the lower octane gas. You'll lose some horsepower but the engine will be fine.

 

[Throckmorton]

Originally posted by: Bignate603

Originally posted by: AstroManLuca
My parents have an older car that, a couple years ago, started to suffer from valve knock unless they put mid-grade gas in. Normally it only required regular unleaded.

I would not use a lower grade gas than what is recommended for the vehicle, and it pains me to think of all the clueless performance car owners out there who, despite owning an expensive car, will still go out and wreck their wonderful cars by putting slightly cheaper gas in them.

If your modern car was correctly designed cheaper gas will have no ill effects. The computer will detune the engine so it's not running as aggressively so it can run safely with the lower octane gas. You'll lose some horsepower but the engine will be fine.

It's IMPOSSIBLE to reduce the compression ratio though. I still don't get what timing retardation does, but it's not the same as having a lower compression engine to begin with.

 

[Bignate603]

Originally posted by: Throckmorton

Originally posted by: Bignate603

Originally posted by: AstroManLuca
My parents have an older car that, a couple years ago, started to suffer from valve knock unless they put mid-grade gas in. Normally it only required regular unleaded.

I would not use a lower grade gas than what is recommended for the vehicle, and it pains me to think of all the clueless performance car owners out there who, despite owning an expensive car, will still go out and wreck their wonderful cars by putting slightly cheaper gas in them.

If your modern car was correctly designed cheaper gas will have no ill effects. The computer will detune the engine so it's not running as aggressively so it can run safely with the lower octane gas. You'll lose some horsepower but the engine will be fine.

It's IMPOSSIBLE to reduce the compression ratio though. I still don't get what timing retardation does, but it's not the same as having a lower compression engine to begin with.

Yes, but most cars aren't so high of compression that they'll detonate on compression alone. I would assume that there are vehicles that would have issues, but I highly doubt the OP is thinking about running cheap gas in his Ferrari. Turbocharged cars that can control the boost also will bring down the pressure too.

 

[Bignate603]

Originally posted by: Throckmorton

Originally posted by: Bignate603

Originally posted by: AstroManLuca
My parents have an older car that, a couple years ago, started to suffer from valve knock unless they put mid-grade gas in. Normally it only required regular unleaded.

I would not use a lower grade gas than what is recommended for the vehicle, and it pains me to think of all the clueless performance car owners out there who, despite owning an expensive car, will still go out and wreck their wonderful cars by putting slightly cheaper gas in them.

If your modern car was correctly designed cheaper gas will have no ill effects. The computer will detune the engine so it's not running as aggressively so it can run safely with the lower octane gas. You'll lose some horsepower but the engine will be fine.

It's IMPOSSIBLE to reduce the compression ratio though. I still don't get what timing retardation does, but it's not the same as having a lower compression engine to begin with.

Modern cars will actually have the spark slightly before TDC. If the cheaper gas is used it will burn faster, and reaches maximum pressure before the piston hits top dead center, causing detonation, severe power loss, and possible engine damage. Retarding the timing will counteract this, causing the maximum pressure to be reached after TDC.

Here's a better explanation from Wikipedia...

"Timing advance" refers to the number of degrees before top dead center (BTDC) that the spark will ignite the air-fuel mixture in the combustion chamber during the compression stroke. "Timing retard" refers to the number of degrees that ignition is delayed after top dead center. In a classic ignition system with breaker points, the basic timing can be set statically using a test light or dynamically using a timing light.

Timing advance is required because it takes time to burn the air-fuel mixture. Igniting the mixture before the piston reaches top dead center (TDC) will allow the mixture to fully burn soon after the piston reaches TDC. If the air-fuel mixture is ignited at the correct time, maximum pressure in the cylinder will occur sometime after the piston reaches TDC allowing the ignited mixture to push the piston down the cylinder with the greatest force. Ideally, the time at which the mixture should be fully burnt is about 20 degrees ATDC. This will utilize the engine's power producing potential. If the ignition spark occurs at a position that is too advanced relative to piston position, the rapidly expanding air-fuel mixture can actually push against the piston causing detonation and lost power. If the spark occurs too retarded relative to the piston position, maximum cylinder pressure will occur after the piston is already traveling too far down the cylinder. This results in lost power, high emissions, and unburned fuel.

 

[Throckmorton]

Oh ok, so it's the burning fuel that detonates?

 

[Bignate603]

Originally posted by: Throckmorton
Oh ok, so it's the burning fuel that detonates?

Yup. You don't want your gas to explode, you want it to burn quickly but smoothly. With the cheaper gas the compression and the heat from the small amount of burning from over advanced timing will cause the gas to detonate and explode rather than burn normally, and do it before TDC. This means that the piston is trying to push the wrong way.

 

[dsity]

so what about using 93 or 91 for a 89 vehicle

 

[Bignate603]

Originally posted by: dsity
so what about using 93 or 91 for a 89 vehicle

It won't help you at all. Some cars as they age will knock a bit and this can be helped by using higher octane gas.

 

[potato28]

Normal being 87, yea most cars up here use that as normal. 93 is easy to find too, but nothing higher than that.

 

[Fardor]

Originally posted by: shabby
Why would you want to sacrifice performance... in a performance oriented car? You paid 5k more for it to get that 260hp, now you want to skimp on premium fuel?
Its going to cost you a couple dollars more at the pump for premium fuel, you're not going to go broke because of that. But if you do then you shouldn't of bought the car.

That's a good question... lol

Anyways, I was just wondering. Don't really know anything about cars.

 

[Xyclone]

Your future self bought a mazdaSPEED3 to save a few bucks on a fillup and sacrifice performance and fuel economy?

 

[Zenmervolt]

Originally posted by: Uhtrinity
The Insights get the best mileage with regular unleaded. In fact mileage can go down slightly with higher octane.

And they are designed for regular unleaded. That's not a valid comparison and bringing it up in this thread only serves to cloud the issue for the OP.

The bottom line is that for the best mileage, you should use the type of fuel recommended by the owner's manual.

ZV

 

[SuperSix]

If it says "Premium Fuel Only" on the dash, and/or the car is supercharged/turbocharged, yes - you have to use premium fuel, octane 91 or higher. I have 2 cars - both require premium fuel. One is turbocharged (Buick Turbo), and one has a high-compression engine (10:1, 1992 Cadillac Eldorado) Both run like crap, knock/ping/etc on anything less than 91.

 

[lurk3r]

I will not even run 87 octane in a car that's recommended for 87 (Michigan gas at least, Canadian 87 is not as horrible). My last 4 cars ALWAYS have had issues if I mistakenly fill up with 87, noticeable power loss, stalling when backing out of parking spaces, and considerably worse mileage.

This can probably vary from car to car, but my history was 06 Altima, 02 Suby Impreza TS, 98 Avenger V6, 95 Avenger 2.0l

 

[JJ650]

Originally posted by: SuperSix
If it says "Premium Fuel Only" on the dash, and/or the car is supercharged/turbocharged, yes - you have to use premium fuel, octane 91 or higher. I have 2 cars - both require premium fuel. One is turbocharged (Buick Turbo), and one has a high-compression engine (10:1, 1992 Cadillac Eldorado) Both run like crap, knock/ping/etc on anything less than 91.

QFT.


DO NOT use a low octane fuel in a turbo/super charged engine. Using it in a pinch is fine but it WILL not be good for everyday use. You'll greatly reduce the life span of the engine.

In N/A (natually aspirated) engines low octane isn't much of a problem (depending on engine age, driving conditions, etc). Turbos/supers force feed air into the cylinders to charge the mix with more oxygen to generate more power per cylinder/per burn.
'Boosted' engines have higher pressures associated with the charging and will raise temps in the cylinder prior to ignition (It's thermodynamics. Cramming a lot of something in a defined space and then compressing the material will raise the temperature). With higher temps due to the high compression you will want a fuel that is detonation resistant like the 91 or 93 octane fuels.
Using a fuel with low resistnace to detonation in an enviroment that is being subjected to higher pressures and temperatures is asking for it to have detonation issues.
Intercoolers won't help the siutation either since the intercooler allows the incoming air to be cooled. Cooler air is denser than warm air. Intercooled engines allow even MORE air per volume raising pressures even higher.

 

[Zenmervolt]

Originally posted by: JJ650

Originally posted by: SuperSix
If it says "Premium Fuel Only" on the dash, and/or the car is supercharged/turbocharged, yes - you have to use premium fuel, octane 91 or higher. I have 2 cars - both require premium fuel. One is turbocharged (Buick Turbo), and one has a high-compression engine (10:1, 1992 Cadillac Eldorado) Both run like crap, knock/ping/etc on anything less than 91.

QFT.


DO NOT use a low octane fuel in a turbo/super charged engine. Using it in a pinch is fine but it WILL not be good for everyday use. You'll greatly reduce the life span of the engine.

In N/A (natually aspirated) engines low octane isn't much of a problem (depending on engine age, driving conditions, etc). Turbos/supers force feed air into the cylinders to charge the mix with more oxygen to generate more power per cylinder/per burn.
'Boosted' engines have higher pressures associated with the charging and will raise temps in the cylinder prior to ignition (It's thermodynamics. Cramming a lot of something in a defined space and then compressing the material will raise the temperature). With higher temps due to the high compression you will want a fuel that is detonation resistant like the 91 or 93 octane fuels.
Using a fuel with low resistnace to detonation in an enviroment that is being subjected to higher pressures and temperatures is asking for it to have detonation issues.
Intercoolers won't help the siutation either since the intercooler allows the incoming air to be cooled. Cooler air is denser than warm air. Intercooled engines allow even MORE air per volume raising pressures even higher.

Modern forced induction systems have electronic boost control and will reduce or eliminate boost if low-grade gasoline is used. Granted this will greatly decrease power, but it will not damage the engine.

ZV