Premium gas? Facts & Myths

[Scottwax]

My Mazda's owner's manual recommended 91 octane (only can get 87/89/93 here so I used 93 octane) and when I used regular, the throttle response was noticably less sharp and mileage dropped about 1 mpg city. Didn't ping though. Went back to premium after that.

[Masta Z]

use what is recommended.

the only "cleanliness" aspect might be given by Shell's V-power, but that is about it

[Poisoned Pony]

use what's recommended. My tuner and the maker of the cams I'm running in my Mustang say 93, so that's what I'm running.

[lawrencea]

Originally Posted by Masta Z

use what is recommended.

the only "cleanliness" aspect might be given by Shell's V-power, but that is about it

The regular Shell has a lot of cleaners in it also.

[01TrublUGT]

Originally Posted by grease

Paragraph's illegal in your neck of the woods? JAYSUS!

While all these arguments are valid, what you are forgetting is that alot of newer computers can adjust well beyond what you are saying they can. Lots of the newer Cadillacs can run 87 and lower, not just in safe mode, but as normal operations, tho the suggested is 91. Others can as well. I know my car can basically run perfectly fine on 83 octane (mathematically theoretical). It will also run normally on 87, and further adjust timing on 93. Most newer up level cars will allow a spread of over 15 pts octane, 10 degrees timing...The biggest reason for this is that lots of areas only supply 87...I know some gas in my own area has been tested less then 87.

I know someone who's been running 87 octane in an SLK32 for over 2 years now, and engine is as good as new, dealer certified.

LOL paragraphs are not illegal if you look back in my original post all of the "\r\n\r\n" were where I tried to skip lines and start a new paragraph, but for whatever reason it did not show up.....Hopefully it won't do it this time too.

While some would think that the computer can adjust more than I stated believe me it can't. There is NO WAY for the cars computer to tell what octane fuel you are using. The ONLY side effect of using a lower grade octane fuel than what the factory specified is pinging/detonation. So if that is the only side effect then the only way the computer will know what is going on is by the knock sensor input. Most all modern computers can "Learn" to a degree, so if you take a car that was programmed to run premium fuel and start feeding it a diet of 87 after a while it will learn what is going on and make corrections to compensate. While most people take that as the cars ability to adjust for different fuel grades it isn't and that is not what it was intended to do. While your computer is not running in safe mode per se, it is backing off timming to prevent any damage. Backing off the timming from factory specs will both hurt performance and MPG.


As for the Caddy, most of them are programed to run on 87, IIRC the only Caddy that states Premium fuel is the XLR. As for the SLK32 while it may check out with the dealer, it is getting just that...checked out. They are not testing the fuel in any way as there is no reeason to. Now if something were to happen and it went in for warranty work on the motor they would hook up the computer and see that the knock sensors were pulling timming enough for the computer to permanently re-adjust its fuel maps, from there they would take a sample of fuel from the tank, have it tested, and when it came back under 91octane your friend would get the apologetic phone call saying that the cost of a new motor would not be covered.

I will do you one better here. My car runs 10.1:1 compression and from the factory it states premium fuel only. I had my car tuned on a dyno with 93 and it was putting down 330rwhp, at that I was getting about 23mpg on the freeway. I had to drive my car from La to Tx so in an effort to save cash I brought it back to the tuner and had the tune adjusted to run on 87. The end result of that tune took my 330rwhp down to 293rwhp, no pinging and the car ran fine the whole trip. Once I got home I totaled up the miles and the fuel I used, my MPG dropped from the 23 I was getting running 93 to about 17-18MPG running 87. While I saved money at the pump, I spent more in the end needing more fuel to get the same distance.

While it would seem that running 87 would save you money over running 91, IF the car in question came from the factory tuned for the 91, it won't. You will be giving up the motors efficency to spend less at the pump so while you are leaving the gas station thinking you just saved $4.00, you will be making a return visit to the pump sooner as the less efficient a motor is the less MPG it will get.

I realize that gas is not getting any cheaper but if you spend $25,000.00+ on a car that suggests you run premium fuel, why would you not in an effort to save maybe $250.00 a year?? Look at the amount of time and money we spend keeping the outside of our cars looking like they are brand new, then skimp on the things that keep that car running the way it was designed. If you are going to buy a car and either can't afford to or don't want to do what the maker suggests maybe you should look for another car that does not need the premium fuel.

[kaval]

Originally Posted by 01TrublUGT

LOL paragraphs are not illegal if you look back in my original post all of the "\r\n\r\n" were where I tried to skip lines and start a new paragraph, but for whatever reason it did not show up.....Hopefully it won't do it this time too.

While some would think that the computer can adjust more than I stated believe me it can't. There is NO WAY for the cars computer to tell what octane fuel you are using. The ONLY side effect of using a lower grade octane fuel than what the factory specified is pinging/detonation. So if that is the only side effect then the only way the computer will know what is going on is by the knock sensor input. Most all modern computers can "Learn" to a degree, so if you take a car that was programmed to run premium fuel and start feeding it a diet of 87 after a while it will learn what is going on and make corrections to compensate. While most people take that as the cars ability to adjust for different fuel grades it isn't and that is not what it was intended to do. While your computer is not running in safe mode per se, it is backing off timming to prevent any damage. Backing off the timming from factory specs will both hurt performance and MPG.


As for the Caddy, most of them are programed to run on 87, IIRC the only Caddy that states Premium fuel is the XLR. As for the SLK32 while it may check out with the dealer, it is getting just that...checked out. They are not testing the fuel in any way as there is no reeason to. Now if something were to happen and it went in for warranty work on the motor they would hook up the computer and see that the knock sensors were pulling timming enough for the computer to permanently re-adjust its fuel maps, from there they would take a sample of fuel from the tank, have it tested, and when it came back under 91octane your friend would get the apologetic phone call saying that the cost of a new motor would not be covered.

I will do you one better here. My car runs 10.1:1 compression and from the factory it states premium fuel only. I had my car tuned on a dyno with 93 and it was putting down 330rwhp, at that I was getting about 23mpg on the freeway. I had to drive my car from La to Tx so in an effort to save cash I brought it back to the tuner and had the tune adjusted to run on 87. The end result of that tune took my 330rwhp down to 293rwhp, no pinging and the car ran fine the whole trip. Once I got home I totaled up the miles and the fuel I used, my MPG dropped from the 23 I was getting running 93 to about 17-18MPG running 87. While I saved money at the pump, I spent more in the end needing more fuel to get the same distance.

While it would seem that running 87 would save you money over running 91, IF the car in question came from the factory tuned for the 91, it won't. You will be giving up the motors efficency to spend less at the pump so while you are leaving the gas station thinking you just saved $4.00, you will be making a return visit to the pump sooner as the less efficient a motor is the less MPG it will get.

I realize that gas is not getting any cheaper but if you spend $25,000.00+ on a car that suggests you run premium fuel, why would you not in an effort to save maybe $250.00 a year?? Look at the amount of time and money we spend keeping the outside of our cars looking like they are brand new, then skimp on the things that keep that car running the way it was designed. If you are going to buy a car and either can't afford to or don't want to do what the maker suggests maybe you should look for another car that does not need the premium fuel.

Finally compression ratios are brought up.

What is the compression ratio on your friend's car?

[itb76]

Quite a while back someone did dyno runs on a GTI very similar to mine, and found 10 whp difference between regular and premium. This is only a 172 (crank) hp car. To me that's significant.

I hooked up my laptop running VAG-com to see if the computer was retarding the timing with regular in the tank...at WOT it was. Ran the test again with premium and it did not cut the timing. I'm running premium.

That said, if all you need is the cleaning, run some Techron through it once in a while.

[74 thing]

Yep techrolene concentrate, gumout regane and seafoam are all good at getting rid of the carbon build up.

Higher octane burns slower that is why it is recomended on higher compression engines. New state of the art systems do have so many sensors that the computer will retard the timing to compensate for the lower octane gas but performance will suffer. There are other systems like safegard which is a knock sensor and adjusts each cylinders timing to fire just before detonation so you get the most performance out of your engine.

I would recommend using what your owners manual suggests for a daily driver.

Another unkown is that the mid grade is mixed at the pump/nozzle since gas stations only have tanks for regular and premium.

[TigerMike]

I don't have facts or figures or anything, but in my G35 (which I consider a fairly high performance engine w/ 260HP), I have used mostly regular during the car's life without much fuss. Now that the car is getting older and with 70K+ miles, it is running much better on premium and very noticable for this engine. With regular, I hear all kinds of ungodly knocking and pinging sounds and throttle response isn't too good. With 93 octane, there is significantly less pinging/knocking, and I've noticed that "instant" throttle response is *much* better than with 87 octane. For instance, I notice this most often when at highway speeds. With 87, if I floor it to pass, the car is just kinda sluggish and doesn't want to rocket forward. When I run 93, the car responds much quicker and power seems to be greater, i.e. seems to have greater pull and seat of the pants feel. Hard to explain, but after comparing the two, it was very noticable, and I don't think it is all in my head. I can hear that the engine is performing better with 93 and I can feel it too. So, my conclusion is that if your car is designed for premium, run it!! It's not gonna kill anyone to spend the extra $3-4 per fillup for the premium vs regular, and your car will thank you too!

[Masta Z]

if your car is tuned for premium, you will get premature detonation by using lower levels

[32VDOHC]

I would guess that the only cars that really needed Premium fuel would be the some of the high compression big block American V8 engines.
From my personal experience the difference is in how you drive.
If you never put the engine under any pressure, regular is OK, however if you are going for performance, Premium does make a difference.
Cars that require premium will accelerate faster, run smoother and quieter with premium fuel.
Pre ignition which is the cause of the knocking sound in a engine under a strain, does not happen while using premium fuel. This pre ignition reduces power and fuel mileage.
If the car does not call for it, consider yourself lucky.

[BigJimZ28]

Originally Posted by 32VDOHC

I would guess that the only cars that really needed Premium fuel would be the some of the high compression big block American V8 engines.

WOW that's just wrong
how about a 3.2L V6 from a SHO?
I can tell you first hand that it needed 91+