Gasoline. Regular or premium? That 'tis the question.

[smockers83]

Every once in awhile a member inquires about what other members are using in terms of gasoline. Do you guys use regular or premium? What are pros and cons of running one over the other? What happens to the car, will it blow up? But the manual says…

To put it straight with the G35/G37, it may really depend on your very own driving style to determine which gas you should use. We will now jump into the world of gasoline to discover the answers to these questions.

I believe that, after observing many of these threads over the last couple of years, it is safe to say that the majority of people on this forum use premium. I personally use premium as well for a few reasons. First, because the manual says so and secondly, because of my driving habits, but that is not to say that I am a rabid driver. There are many on this forum that seem to drive much more aggressive than I do.

So, what are the pros and cons to premium versus regular? To get into this, a little research is needed to understand why there are regular, mid-grade, and premium grade fuels, which are given the respective names to easily convey to the consumer the octane grade of the fuels. Many people use premium gasoline in the belief that it's better for engines than regular. They think that doing so gives them more power and their engine will run better. The only truth behind that train of thought is, “It depends.”

Octane grades don't represent a “good, better, best” choice; they simply measure the resistance of fuel to knocking or pinging, a condition in which gasoline burns uncontrollably in the engine's combustion chambers. Knocking and pinging can damage an engine. While high-octane formulations resist knocking better than lower octanes, most engines are designed to take regular gas. Engines requiring premium gas are typically the more powerful ones found in sports and luxury vehicles. Those engines use a very high compression ratio, making them more vulnerable to knocking, so recommended fuels have octane ratings of 91 or higher. Using premium gas in an engine designed to run on regular doesn't improve performance.[1]

So, the compression ratio of your engine should determine the octane level of the gasoline that you should use. However, this is only strictly true when your engine doesn’t have an engine management system. The ECU, the Engine Control Unit, monitors all aspects of the engine, including the burning of fuel. If it detects engine knock, it will retard the timing of ignition relative to the position of the piston in order to promote the optimal burn of fuel. When an engine experiences knocking, the fuel is burning uncontrollably, meaning it is self-combusting and not burning. The temperature and pressure build up too quickly in the combustion chamber and before the piston can reach the top of its travel, the mixture explodes. This explosion tries to counteract the advancing piston and puts an enormous amount of stress on the piston, the cylinder walls and the connecting rod.[2] With an engine management system, the computer can change the timing in order to prevent self-combustion.

So you know that a fuel-air mixture, under the right conditions, can spontaneously combust. In order to control this property, all gasolines have chemicals mixed in with them to control how quickly the fuel burns. This is known as the octane rating of the fuel. The higher the rating, the slower and more controlled the fuel burns. Here are a couple of charts that show octane ratings relative to compression ratios and how octane ratings change with elevation.

Compression ratio = Octane 5:1 =72 6:1 =81 7:1=87 8:1=92 9:1=96 10:1=100 11:1=104 12:1=108



The table of compression ratios and octane levels is based on compression ratios with no engine management system. With an engine management system, the octane levels drop 5-7 points. [3]

Onto the pros and cons of using premium or regular with your G.

The pros of using premium are that you don’t have to worry about engine knock, it says so in your manual, and you’ll have no issues with warranty claims if need be. If you drive aggressively all the time or even just on occasion when you need to let loose and have the engine in high RPMs, using premium would be the best choice. Another pro is that you maximize the engine’s potential to make maximum power and potentially maximize engine efficiency, or gas mileage. The cons are that it is more expensive than regular and may be unnecessary if you don’t drive aggressively and have it high up in the RPMs.

The pros of using regular are that it is cheaper than premium and is useable. You can use regular if you don’t drive aggressively and/or have the engine under high loads and RPMs. If you drive like a chauffer who drives politely and doesn’t use all the power available, you can just allow the ECU to retard the timing to allow the use of regular. The cons to using regular are that you lose out on the potential to make maximum power and the possibility of a loss in engine efficiency. Some here may report no loss in efficiency, but the possibility is always there as you are changing the timing of the engine and therefore the optimal performance level. Sometimes the difference in efficiency isn’t noticeable and sometimes it can be quite large.

Using regular won’t necessarily cause your engine to blow up. If you use regular and have the engine under high loads such as quick acceleration, you may damage your engine over time. So if you decide that you want to utilize all of your G, go with the premium. If not, bump down to the mid-grade or regular.

1. Consumer Reports2. The Car Bibles

[G_whizz]

Awesome job Eric!!!!



I wish I could give you a second Custome Title or something!!

We'll get this articlized!!

Was there a pic you tried to put in? I'm seeing a red X

Again, thanks for taking the time!

[Poyzinous]

dude I would give you the 3 dollars extra for filling up on premium just so you can try it. The truth is, your car will improve on both power and economy. I get about 20 miles more per tank on premium. and Its been dyno proven that 87 octane takes away 8 to 10hp.

[smockers83]

Awesome job Eric!!!!



I wish I could give you a second Custome Title or something!!

We'll get this articlized!!

Was there a pic you tried to put in? I'm seeing a red X

Again, thanks for taking the time!

There is a pic. It shows up in my browser...anybody else have issues? You should see a 3D graph.

But you're welcome.

As for the 2nd title, could you just add on to mine? Something to the effect of NICO Chief Economist or just Chief Economist as I am also working on a whole series on various economic topics over in Politics. If so, just separate them with a & or a /, yeah?

[smockers83]

I'm thinking about trying a tankful of premium next week to see if I can detect an increase in MPG?

I hope my G doesn't explode

You are going to try premium? I hope that not only does your G not explode, but the rest of the world!

What's next, the liquidation of your 401(k)? Oh, there goes Mars, too.

In all seriousness though, try it for a couple of tanks so your ECU relearns. Or better yet, reset your ECU. Then see what kind of results you get. I'd be interested to hear back on this. If you do that and report your MPG findings with premium and you give me the last two tanks' MPG ratings with regular, I'll do the math for you to figure out which one is more economical over the course of a year.

[pfarmer]

You are going to try premium? I hope that not only does your G not explode, but the rest of the world!

What's next, the liquidation of your 401(k)? Oh, there goes Mars, too.

In all seriousness though, try it for a couple of tanks so your ECU relearns. Or better yet, reset your ECU. Then see what kind of results you get. I'd be interested to hear back on this. If you do that and report your MPG findings with premium and you give me the last two tanks' MPG ratings with regular, I'll do the math for you to figure out which one is more economical over the course of a year.

Should he not reset the ECU for both tests, with and without premium?Also I think this should be controlled such as using the vehicle on exactly the same routes at the same speeds. That may be hard to maintain the test standards.

Perry

[zozoka1212]

Smokey nice article. You deserve another title or it should at least have a X2 behind your title. LOL

Nice post

I'm thinking about trying a tankful of premium next week Telcoman

Telco you should stop going to the political forum. Lately you do things I never thought I would see from you. LOL

Should he not reset the ECU for both tests, with and without premium?Also I think this should be controlled such as using the vehicle on exactly the same routes at the same speeds. That may be hard to maintain the test standards.

Perry

He knows what he is doing. He probably can drive his G to work blindfolded. He knows what rpm he is using on hwy all the time. LOL

3krpm for him on hwy.

[SVTCOBRA]

Nicely put smockers!!! remember to wear your body armor in the politics....

[joe603]

I'm not seeing the graph either....

Excellent article

[smockers83]

Sean or Joe, if you guys go to the carbible link, can you see the graph on that website?

I'm going to try re-inserting it into my post.

*edit* I re-inserted it and then cleared my cache. I wonder if copying the location saved it in my cache so therefore it displayed for me? So now let me ask if NICO supports gif files.

[smockers83]

Should he not reset the ECU for both tests, with and without premium?Also I think this should be controlled such as using the vehicle on exactly the same routes at the same speeds. That may be hard to maintain the test standards.

Perry

No, I don't think that he should reset it for both regular and premium. He's used regular ever since he got it and he has all the data. Resetting the ECU when he switches to premium I figured would achieve the best results quicker as the ECU doesn't have to relearn everything, it can just start from scratch. Technically he should drive the same route but that is asking a little much but I don't think he will vary too much with his routes or where he goes.

Nicely put smockers!!! remember to wear your body armor in the politics....

Haha, thanks. I just get involved with stuff that I know a thing or two about and can support my argument. I don't get involved with the partisan bickering. I can take a beating though...I've resisted a few onslaughts of my knowledge and integrity only to be the last one standing.

If anything, you guys could check out and just read the series that I'm writing, some people may learn a lot. It's been pretty popular and people have liked it except for one person. The series is in it's 3rd stage right now.

[pfarmer]

No, I don't think that he should reset it for both regular and premium. He's used regular ever since he got it and he has all the data. Resetting the ECU when he switches to premium I figured would achieve the best results quicker as the ECU doesn't have to relearn everything, it can just start from scratch. Technically he should drive the same route but that is asking a little much but I don't think he will vary too much with his routes or where he goes.

Having done a lot of NDT I believe that in order to have a valid test, everything needs to be operating off the same baseline.

Perry

[smockers83]

The graph is reappearing for me now, is it for you guys?

[G_whizz]

Nope...still not there for me and yes, GIF's are ok...

[smockers83]

If you can't see it, I don't know why. It's a GIF file and I can see it, Howie saw it before. I can't find a similar graph.

[pfarmer]

The graph is reappearing for me now, is it for you guys?

Nope still not seeing it. Now if I right click it and then paste it into the address bar it will take me to the picture.

Perry

[smockers83]

Could someone do me a favor and right click what is supposed to be the graph, paste the location into their address bar, save the picture, open it in a photo program like Photoshop it and resave it as a JPEG, and then email it to me? Maybe that'll work; I just don't have any photo editing software on my computer at the moment.

[pfarmer]

Could someone do me a favor and right click what is supposed to be the graph, paste the location into their address bar, save the picture, open it in a photo program like Photoshop it and resave it as a JPEG, and then email it to me? Maybe that'll work; I just don't have any photo editing software on my computer at the moment.

Other GIFs are on this site. Haven't looked at other links, does it have anything to do with it not having a size listed when you right click it, or the dimensions. A first look and the img link format seems correct.

Perry

[G_whizz]

I fixed it. Well I can see it at least..so that's the important thing..

[pfarmer]

I fixed it. Well I can see it at least..so that's the important thing..

I see it now.

Perry

[smockers83]

I fixed it. Well I can see it at least..so that's the important thing..

Sneaky bastards, you mods are.

[joe603]

Telco, thanks for doing this! We will trust your results...I'm curious to see if you could have been saving money all along...that could have went into your 401k!! lol!

[smockers83]

If he does do it and he gives me the data, I'll do some calculations and graphs in Excel and convert it to a PDF if I can find a website to host it or if NICO will host it to go along with my article. And Howie can add his story of his findings as well.

[pfarmer]

This came out much better in Excel

How does one copy a spreadsheet into a post?

Telcoman

If you want a simple way (there are ways of making this into tables for html formatting) simply enlarge the section of spreadsheet you want to show, hit print screen (copies the screen into the clipboard), open a paint program, then paste it into the paint program. Save the picture in format desired, and post.

Perry

[G_whizz]

If you want a simple way (there are ways of making this into tables for html formatting) simply enlarge the section of spreadsheet you want to show, hit print screen (copies the screen into the clipboard), open a paint program, then paste it into the paint program. Save the picture in format desired, and post.

Perry

BTW Telco, I thought you would be doing 91 not 93. I only occasionally put in 93. But ALWAYS 91

Thanks for doing this!

[joe603]

I wonder if having a JWT intake/z-tube would increase gas mileage too?

[uprev]

Just to be clear, I'm not trying to throw a monkey wrench into the whole deal.

Fact of the matter is the way the Nissan and Infiniti ECU works is that it measures parameters and adjusts itself based on data it gets from sensors. There are very few static settings in the ECU. Most of the data it runs its routines on are look up tables and the way it calculates its outputs are based on numerous tables from different points of input.

You have some tables that are target guidelines and some that are corrections. No single adjustment is made without referencing a number of different tables. The ECU learns by way of adjusting to hit its given targets. If it cannot reach those targets, it is often because of another table that limits the corrections allowed.

Timing and fuel corrections in the ECU that would be directly affected by changing your Octane rating may also need to reference a given load, calculated or predetermined and it may not be able to adjust because from the factory it was designed to use a certain octane level and Nissan limits those references for safety purposes.

On the G/Z cars the ECU is set (in north american markets) for 91 Octane fuel. The trucks are all set for 87 Octane. Using 91 Octane in the G/Z will obviously cause the ECU to adjust itself, and it will try its best to cope with it. The primary means it has is the high det ref table. If you add load to the motor while running lower octane fuel, you will come up against detonation. The ECU will compensate quickly for this by using the high det table timing references and it will lower the timing to a more safe setting temporarily. It however will not change it for the rest of the time you own the car, it is very temporary. This does not change drastically over time, contrary to what people think, it is not learned. It happens very quickly and hopefully that reference table on your particular car works well enough to cause it to stop detonating. You lose power and economy when this happens.

Now that said if you never go up a hill, or carry 4 people in your car, or accelerate quickly, you might just be safe. The only way to change this is to get a tune designed for your car with low octane. That way those reference tables are changed and you don't have issues with load.

Realize that timing is done based on fuel burn rates, and peak cylinder pressures. If you don't use the recommended octane, the fuel burn rates change, and the ECU doesn't change to match that. So your timing will be off no matter what argument you wish to make about it. This is part of the code running on every ECU.

The same goes for the Truck owners that want to run premium fuel. It is better for the motor (the higher octane helps keep the cylinders cooler and less chance of detonation under load), but you really won't see any power gains unless you adjust the tune for the higher octane.

[GAU-8]

Sorry for necro-posting. Good info here, but I have a question. Wouldn't the ECU carry fuel tables for both low and high octane maps?

[fiveliterbeater]

Every once in awhile a member inquires about what other members are using in terms of gasoline. Do you guys use regular or premium? Compression ratio = Octane 5:1 =72 6:1 =81 7:1=87 8:1=92 9:1=96 10:1=100 11:1=104 12:1=108

nice info bud!! so according to your table, our cars can run 100 octane safely without a tune correct? i always figured that but wanted confirmation : )

[fiveliterbeater]

Sorry for necro-posting. Good info here, but I have a question. Wouldn't the ECU carry fuel tables for both low and high octane maps?

i'm not an expert but i know 3rd and 4th gen camaros do. my old LS1 camaro was a pretty advanced littlE machine. . the ECU would receive data from all vital sensors and then mapps out the adequate fuel curve and timing. i don't see why the new G (or M for the matter) would'nt have fuel tables already mapped out.
Modified by fiveliterbeater at 12:37 PM 10/1/2009