i always use premium grade gas but prices are killing me. anyone made the switch to midgrade to save a bit of cash? or even switch back and forth?

 

I used the middle stuff 89 I think, and the car ran great for over a year. I never put premium in it. Now that I'm chipped I put 93, but am thinking about going back to 89 when I install my second program in a few months.

 

You have to run atleast 91 so your car doesn't get bottled up.I run 91 or 93 if thats all they have so I don't have high repair costs for clogged up intake and such.How much more is it a week to run 91 $3.00 bucks for better performance.I know gas prices suck but its only money!

 

i heard USA 93 is = to overseas 87

 

You've got the right idea but wrong reason.

Due the the mass air flow sensor being before the intake manifold, the fuel never touches it. We have fuel injection so the fuel is put directly into the intake manifold right before the valves to each cylinder. The mass air flow sensor gets dirty simply from impurities that get past the air filter.

Also, the quality of fuel doesn't have anything to do with the octane rating. The rating is there as a measure of how explosive the fuel is. The higher the rating, the slower the burn (less explosive)....in this order as an example....87, then 89, 91, 93...lastly diesel.(this is why a diesel engine will self destruct if you put gas in it rather than diesel fuel.) Therefore, if you use the higher octane rating...you timing will advance more meaning better gas mileage and better performance (automatic timing advance and retard on our cars). If you put the lower octane gas in, the timing will automatically retard and therefore worse performance and worse gas mileage. As always, there is a limit. Don't go putting in 100 octane thinking your car will turn into a rocket ship.

That said you can only put so low of an octane rating in before the timing cannot retard enough to save the engine from damage. This is not a danger with our cars because the compression ration ratio is not terribly high. However, if you have a turbo or supercharged engine, you do not want to put in low octane gas as the compression is raised so much by the forced air. This especially goes for those of us with chipped forced air engines. That chip in most cases raises the pressure of air allowed to the cylinders (psi or boost) and therefore the compression. IF YOU GET YOUR TURBO CAR CHIPPED DO NOT RUN 87 OCTANE FUEL!!! I would not even run 89 octane fuel in that case. Ask the installer or shop about it. They have a minimum octane for a reason.


This idea does not work with older cars (about 95 and older). Those cars had fixed timing. This means that they were designed for only one grade of fuel. If you put low octane gas into an old high compression engine then the engine would start to ping upon an applied load. This can bend connecting rods (very very bad!) and burn holes in valves and piston heads.

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Lastly, if you want to treat your car right and not harm the injectors, lines or regulators then simply don't buy gas at the cheap stations. They add alchohol to their fuel to lower costs. This can harm you seals and rubber (minimaly though...not any real danger on cars after 1996). The more costly stations don't add as much alchohol and they also add some cleaners to their fuel that help to keep your injectors and lines clean.



Hmmmm.........................I wonder if anyone will read this explanation????????

 

I had bad experience with lower grade 89...poor gas mileage and performance (more engine noise) Stick with 91 or 93...few extra bucks is worth it and will go long way. You save few dollars now but will end up paying more on your car.

 

The car is designed for 93 or better. To spend $60K on a car and then try to save a few bucks on cheaper gas is just silly.

 

Yeah I never put anything besides 93. Also never anything besides BP Ultimate or Shell V-Power. These are premium cars designed for premium fuel. Its a proven fact that your car runs better on higher octane and either way you'll get a couple MPG's higher so it all equals out. Like Kevin said, these are $60k cars and trying to save a Lincoln ($5) at a fill-up its not worth it.

Frankinstyn: yeah I did read all of it and I agree to it all but I thought higher octane grades were also a bit less polluted? Maybe I was misinformed.

 

I'll stick my neck out and get bashed again. I've run midrange gas (89-91 octane) every since I owned the car, from 37k to 115k. I tried a few tanks of premium last summer and found no difference in gas mileage. So I went back to midrange. According to the manual, the 2.7T has less compression than the 3.0 or 4.2l engines. So it may tolerate better. I do avoid 10% ethanol as it does return poorer gas mileage.

Did it hurt the engine? I was supposed to have spark plugs changed at 80k and when my indie pulled a couple, they were clean/good. We ended up changing them at 107k because I just felt it was time. The gas mileage did not change with the new plugs.

Now, if I was accelerating hard I might notice some ping or lack of performance. But I generally accelerate conservatively and just drive fast.

PS - And in anticipation of the sarcasm, I do NOT drink Starbucks (I'm perfectly content with Speedway coffee) but I do drink premium craft brew beer.

 

I think you are correct regardingcompression. I understand that the cross-over betweenbeing able to use regular gas and needing to use premium is determined by whether or not the car has a compression ratio of under or over about 10:1. If it is under 10:1 then you can use regular, if it is over 10:1 then you need to use premium.Since your 2.7T has a compression of 9.3:1 itcan run fine on regular or mid-range. However, in 05 the 4.2 hada compression of 11.0:1, and by 07 the 4.2 was up to 12.5:1, these cars require premium.