What does GM mean by "Premium Gas Recommended" on the 2.4L I4?

[gmsickofan]

The HHR's new I4 says "recommends premium but accepts regular" or something to that extent.

Is it exactly the same as putting regular in a 2.2L? With NO possibility of damage to the engine or other problems down the road from excessive knocking and pinging?

Can I trust the computer to figure out what grade I've filled the tank with and run with it?

20 cents per gallon is pretty big, especially over time. If gas prices go up again I want the option of using regular, perhaps for months at a time, is this going to be a problem if I choose the 2.4L engine?

TIA!

[bgfpt]

If you drive 12,000 miles a year and get a modest 20 MPG, you will only spend $120/year extra for premium (at $.20/gal. extra).

Go with the premium

[Canyonaro]

Usually if it recommends it, you would get better gas mileage with it anyway. Compromise and use mid grade then.

[gmsickofan]

Originally Posted by bgfpt

If you drive 12,000 miles a year and get a modest 20 MPG, you will only spend $120/year extra for premium (at $.20/gal. extra).

Go with the premium

Actually I drive about 30K a year, so it's almost the cost of one month's car payment!

That's a lot of moola for something that may or may not be necessary.

But seriously, does anyone know if damage would or could occur with regular use in the 2.4L?

[73ChevelleSS]

Originally Posted by gmsickofan

The HHR's new I4 says "recommends premium but accepts regular" or something to that extent.

Is it exactly the same as putting regular in a 2.2L? With NO possibility of damage to the engine or other problems down the road from excessive knocking and pinging?

Can I trust the computer to figure out what grade I've filled the tank with and run with it?

20 cents per gallon is pretty big, especially over time. If gas prices go up again I want the option of using regular, perhaps for months at a time, is this going to be a problem if I choose the 2.4L engine?

TIA!

First off the computer will not know what octane fuel you are running.Both of the 4 cyl's available in the HHR have the same compression ratio 10:1.The reason the 2.4 requires 91 or higher is because the PCM calibration is more agressive.Meaning it adds more timing,fuel curve is different etc.

[DuSpinnst]

The Car should have a knock sensor, especially with VVT and electric controlled cams, that allow it to adjust to the octane level.

[327]

Yep, engines adjust to the octane level. it wont do damage at all if you run a lower octane, like 89 instead of 91. 89 octane is cheaper than 87 and 91 anyway!

[01cavalier]

You should be just fine running regular in the 2.4. Them saying its recommended is just that you may lose a small amount of power with regular. Modern engines typically have sensors to make adjustments if there are any issues with the fuel causing knocking.

[73ChevelleSS]

Originally Posted by 327

Yep, the engines adjust to the octane level, it wont do damage at all, if you run a lower octane, like 89 instead of 91. 89 octane is cheaper than 87 and 89 anyway!

Really why don't you explain to the class how the PCM will know the difference between 87 octane and 91 or 93 octane?So what you are saying is the PCM will recognize a lower octane fuel and adjust the timing etc. based on the octane?I really would like to hear this answer.The only thing the PCM will do is retard timing if it hears spark knock.Which i doubt would happen if you run 87 instead of premium in this engine.

[327]

Originally Posted by lynch mob

Really why don't you explain to the class how the PCM will know the difference between 87 octane and 91 or 93 octane?So what you are saying is the PCM will recognize a lower octane fuel and adjust the timing etc. based on the octane?I really would like to hear this answer.

no I didnt say anything like that.I dont know how it works Im not a GM tech, But ive been told by plenty of them that it has a knock sensor, just like Dupinnst said. And it adjusts spark and fuel.

Ive never EVER had a problem running any octane. Unless I actually had a engine problem. Like when the EGR went bad on my truck. It would run a lot better with 91, and fuel injector cleaner or octane boost. until I put in a new one


Why dont you do a little story telling of your own? Im pretty sure you dont gain or lose HP by using the wrong octane of fuel

[DuSpinnst]

Originally Posted by lynch mob

Really why don't you explain to the class how the PCM will know the difference between 87 octane and 91 or 93 octane?So what you are saying is the PCM will recognize a lower octane fuel and adjust the timing etc. based on the octane?I really would like to hear this answer.The only thing the PCM will do is retard timing if it hears spark knock.Which i doubt would happen if you run 87 instead of premium in this engine.

The PCM when it gets a message from the knock sensor it adjusts the spark timing. Octane is actually a knock resistant measurement. When you use higher Octane your engine is less likely to knock. On old cars that don't have knock sensors need to be switched to premium fuel later on to prevent them from knocking. Now a days the knock sensor adjusts the octane level, but only in the direction down. So any car that says it requires or recommends 91 octane will run on 87 but a SIGNIFICANT performance reduction. Running 91 in an car that requires 89 doesn't allow the engine to run faster though.

[73ChevelleSS]

Originally Posted by DuSpinnst

The PCM when it gets a message from the knock sensor it adjusts the spark timing. Octane is actually a knock resistant measurement. When you use higher Octane your engine is less likely to knock. On old cars that don't have knock sensors need to be switched to premium fuel later on to prevent them from knocking. Now a days the knock sensor adjusts the octane level, but only in the direction down. So any car that says it requires or recommends 91 octane will run on 87 but a SIGNIFICANT performance reduction. Running 91 in an car that requires 89 doesn't allow the engine to run faster though.

Exactly.It is not like there is a magical octane sensor that adjusts the timing etc.This is why if your vehicle only requires 87 octane it is a waste to run premium.But if the manufactor suggest premium you should always use it.

[bgfpt]

This is a good explanation of octane.
No, it won't hurt your car to run less than premium. As many others have stated, the PCM will retard timing if the knock sensor detects the potential for knocking and there will be a slight loss of performance.

The higher compression engine (10:1 vs. 8:1) will have a greater potential for pre-ignition using a lower octane fuel.


Octane
from the website how stuff works

If you've read How Car Engines Work, you know that almost all cars use four-stroke gasoline engines. One of the strokes is the compression stroke, where the engine compresses a cylinder-full of air and gas into a much smaller volume before igniting it with a spark plug. The amount of compression is called the compression ratio of the engine. A typical engine might have a compression ratio of 8-to-1. (See How Car Engines Work for details.)

The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine. Knocking can damage an engine, so it is not something you want to have happening. Lower-octane gas (like "regular" 87-octane gasoline) can handle the least amount of compression before igniting.

The compression ratio of your engine determines the octane rating of the gas you must use in the car. One way to increase the horsepower of an engine of a given displacement is to increase its compression ratio. So a "high-performance engine" has a higher compression ratio and requires higher-octane fuel. The advantage of a high compression ratio is that it gives your engine a higher horsepower rating for a given engine weight -- that is what makes the engine "high performance." The disadvantage is that the gasoline for your engine costs more.

The name "octane" comes from the following fact: When you take crude oil and "crack" it in a refinery, you end up getting hydrocarbon chains of different lengths. These different chain lengths can then be separated from each other and blended to form different fuels. For example, you may have heard of methane, propane and butane. All three of them are hydrocarbons. Methane has just a single carbon atom. Propane has three carbon atoms chained together. Butane has four carbon atoms chained together. Pentane has five, hexane has six, heptane has seven and octane has eight carbons chained together.

It turns out that heptane handles compression very poorly. Compress it just a little and it ignites spontaneously. Octane handles compression very well -- you can compress it a lot and nothing happens. Eighty-seven-octane gasoline is gasoline that contains 87-percent octane and 13-percent heptane (or some other combination of fuels that has the same performance of the 87/13 combination of octane/heptane). It spontaneously ignites at a given compression level, and can only be used in engines that do not exceed that compression ratio.

During WWI, it was discovered that you can add a chemical called tetraethyl lead (TEL) to gasoline and significantly improve its octane rating above the octane/heptane combination. Cheaper grades of gasoline could be made usable by adding TEL. This led to the widespread use of "ethyl" or "leaded" gasoline. Unfortunately, the side effects of adding lead to gasoline are:

Lead clogs a catalytic converter and renders it inoperable within minutes.
The Earth became covered in a thin layer of lead, and lead is toxic to many living things (including humans).
When lead was banned, gasoline got more expensive because refineries could not boost the octane ratings of cheaper grades any more. Airplanes are still allowed to use leaded gasoline (known as AvGas), and octane ratings of 100 or more are commonly used in super-high-performance piston airplane engines. In the case of AvGas, 100 is the gasoline's performance rating, not the percentage of actual octane in the gas. The addition of TEL boosts the compression level of the gasoline -- it doesn't add more octane.
__________________
Tim (formally Classic66vair)
2007 Sky
Chili Pepper Red
Permium package
Tan Leather seats
AM-FM Mp3 Monsoon sound system

[1BadPig]

Premium means you get all the advertised ponies... regular you only get most of them!

[73ChevelleSS]

Originally Posted by bgfpt

This is a good explanation of octane.
No, it won't hurt your car to run less than premium. As many others have stated, the PCM will retard timing if the knock sensor detects the potential for knocking and there will be a slight loss of performance.

The higher compression engine (10:1 vs. 8:1) will have a greater potential for pre-ignition using a lower octane fuel.


Octane
from the website how stuff works

If you've read How Car Engines Work, you know that almost all cars use four-stroke gasoline engines. One of the strokes is the compression stroke, where the engine compresses a cylinder-full of air and gas into a much smaller volume before igniting it with a spark plug. The amount of compression is called the compression ratio of the engine. A typical engine might have a compression ratio of 8-to-1. (See How Car Engines Work for details.)

The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine. Knocking can damage an engine, so it is not something you want to have happening. Lower-octane gas (like "regular" 87-octane gasoline) can handle the least amount of compression before igniting.

The compression ratio of your engine determines the octane rating of the gas you must use in the car. One way to increase the horsepower of an engine of a given displacement is to increase its compression ratio. So a "high-performance engine" has a higher compression ratio and requires higher-octane fuel. The advantage of a high compression ratio is that it gives your engine a higher horsepower rating for a given engine weight -- that is what makes the engine "high performance." The disadvantage is that the gasoline for your engine costs more.

The name "octane" comes from the following fact: When you take crude oil and "crack" it in a refinery, you end up getting hydrocarbon chains of different lengths. These different chain lengths can then be separated from each other and blended to form different fuels. For example, you may have heard of methane, propane and butane. All three of them are hydrocarbons. Methane has just a single carbon atom. Propane has three carbon atoms chained together. Butane has four carbon atoms chained together. Pentane has five, hexane has six, heptane has seven and octane has eight carbons chained together.

It turns out that heptane handles compression very poorly. Compress it just a little and it ignites spontaneously. Octane handles compression very well -- you can compress it a lot and nothing happens. Eighty-seven-octane gasoline is gasoline that contains 87-percent octane and 13-percent heptane (or some other combination of fuels that has the same performance of the 87/13 combination of octane/heptane). It spontaneously ignites at a given compression level, and can only be used in engines that do not exceed that compression ratio.

During WWI, it was discovered that you can add a chemical called tetraethyl lead (TEL) to gasoline and significantly improve its octane rating above the octane/heptane combination. Cheaper grades of gasoline could be made usable by adding TEL. This led to the widespread use of "ethyl" or "leaded" gasoline. Unfortunately, the side effects of adding lead to gasoline are:

Lead clogs a catalytic converter and renders it inoperable within minutes.
The Earth became covered in a thin layer of lead, and lead is toxic to many living things (including humans).
When lead was banned, gasoline got more expensive because refineries could not boost the octane ratings of cheaper grades any more. Airplanes are still allowed to use leaded gasoline (known as AvGas), and octane ratings of 100 or more are commonly used in super-high-performance piston airplane engines. In the case of AvGas, 100 is the gasoline's performance rating, not the percentage of actual octane in the gas. The addition of TEL boosts the compression level of the gasoline -- it doesn't add more octane.
__________________
Tim (formally Classic66vair)
2007 Sky
Chili Pepper Red
Permium package
Tan Leather seats
AM-FM Mp3 Monsoon sound system

Just to let you know but both of the available engines for the HHR have the same compression ratio which is 10:1.The 2.2 L61 vin code "F" and the 2.4 LE5 vin code"B" both have 10:1 compression.