Is Premium gas a must for Turbos ?

volvoaddict007 · Post by **volvoaddict007** » 26 Aug 2007, 10:56

TRIPLE THREAD ALERT !!!

The author of this thread is totally confused as to where to place this discussion. Yet he feels it is without a doubt, THE SINGLE MOST IMPORTANT QUESTION EVER ASKED in the history of Matthewsvolvosite... and perhaps the history of all forumns, everywhere in the World.

So he has placed it here as well as the 850 and 740 sections: .

On my last trip back to K.C. I had to get gas at a station that sold only regular.

I never heard a single ping and I DO have excellent hearing so I 've been using it ever since in both cars. With my license in jeopardy at the moment, I keep the car under 80 and am usually around 65.

Another thread mentioned something about Cats not doing well. That thread also mentioned running low on gas was hard on a Cat?

I'm pretty easy on both of them but have my moments at the lower speeds under 80.

Is anyone able to set the record straight.

Opinions as well, are always treated w/ kindness, speaking for myself.

va007

Post by **MadeInJapan** » 26 Aug 2007, 12:03

Octane rating for turbo cars is relative. The manual recommends the higher octane rating as the car performs more efficiently. Some who have tried regular vs. premium claim that the mpg is better with premium, off-setting the cost. Modern computers in these cars will retard the timing to compensate so you don't have the "pinging" or knocking that is associated with low quality gas....it will not harm anything.

Hope this helps.

volvoaddict007 · Post by **volvoaddict007** » 26 Aug 2007, 17:49

Thanks MIJ,

And thanks Matt, I was kind o' hoping you were going to lock those down. I was planning on running around and pasting the replys to the different sections.

I would like to get people's experiences with gas mileage and performance( relating to octane ratings )

I am obsessed with watching gas mileage and trying to improve it. It's really a challenge for me to drive easy through a whole tank of gas. Are the digital gas mileage meters accurate on the 850s?

I personally have never noticed a difference in gas mileage but I believe I may drive a bit harder than the average driver. ( uhh... right, just a bit )

I heard many years ago that on the average, a steady 38mph would achieve optimum gas mileage.

I do seem to notice a slight difference in performance w/ premium but I'm never sure if it's psychological.

--------------------------------------------------------

Engine knocking

From Wikipedia, the free encyclopedia

Knocking (also called pinking or pinging)

Post by **MadeInJapan** » 26 Aug 2007, 19:03

I don't know the nitty gritty either, but maybe someone does and they can post. I'm also not sure how the mpg on the computer is determined but what I've found is that when I watch the instantaneous read-out of the mpg and try to increase it (lifting up on the gas) is when my mileage is best. Of course, that can be no fun. I just put premium in my T5 and drive it like I enjoy it and don't worry to much anymore about mpg.

zenmervolt · Post by **zenmervolt** » 27 Aug 2007, 08:57

I can shed a little more light on the functional details.

The knock sensor is really a simple vibration sensor that is attuned to the vibrations that are caused by knock. The knock sensor is much, much more sensitive than the human ear and the "knock" that it detects is well below the levels that can be heard or felt by a human. When the sensor detects knock, it signals the ECU to retard the spark. In turbocharged cars, the ECU may also decrease the available boost.

Retarding the timing of an engine reduces efficiency and power, as does reducing boost.

Now, a knock sensor does not simply work once and set the car's adjustment at a fixed point. Modern ECUs will constantly re-calibrate as you drive due to changing conditions. The ECU will use an iterative process to gradually add back boost and spark advance until pinging starts again, then it will back off again, then add again, in a continuous cycle meant to run as close to the "normal" map as possible. So on a cool day without much load in the car and on level ground, there may not be much difference in power output because the conditions are favorable and knock is overall less likely to occur. However, on a hot day with a heavy load, the ECU is very likely to need to take some fairly extensive measures to prevent knock and there will be a definite and noticeable power loss.

A better explanation of what knock is can be found here: http://www.stanford.edu/~bmoses/knock.html

volvoaddict007 · Post by **volvoaddict007** » 30 Aug 2007, 00:25

Very informative. And a great link.

Thanks zenmervolt

va007

kurt robinson · Post by **kurt robinson** » 02 Nov 2007, 06:49

the stoichiometric ideal ratio comes to mind....15:1. The knock sensor is one of the policemen that keep it around there, including the MAF and O2 sensor. if you aren't running higher compression than 10:1 I wouldn't worry about premium....we just did a lab where using premium gas in an 8:1 compression ratio actually had adverse effects on the efficiency due to incorrect ignition location....the only difference between a turbo and a n/a engine is the turbo increases the volumetric efficiency of the available area.....gets it closer to ideal by force feeding air in.

don't fund terrorism anymore than you have to...stick to 87. Your volvo is modern enough to cope w/ it.

volvoaddict007 · Post by **volvoaddict007** » 03 Nov 2007, 05:37

Thanks kurt,

Since posting this write up I have switched back to premium and again it SEEMS to give a little better performance as I got bored and slightly insane putzing around everywhere and have been driving more 'spirited' lately...

I also switched from economy to sport which seems to have made a difference. Armed with this new info I think I will try going back to the 87 ( minimum requirement as per manual )

Sure wish someone would run some 1/4 mile time trials and post the results. Just don't think I could do it accurately myself...

Post by **MadeInJapan** » 03 Nov 2007, 05:53

volvoaddict007 wrote: Sure wish someone would run some 1/4 mile time trials and post the results. Just don't think I could do it accurately myself...

Well, without actually doing that, I have noticed that in EVERYWAY my '98 S70 T5 (high pressure turbo with modified ECU) runs better and is faster (and better MPG on trips) with the premium gas. My wife's '04 V70 2.5T (low pressure turbo) which does not have a modified ECU does well on mid-grade gas and probably would on regular was well, as we notice absolutely no difference between mid-grade and premium gas in her car. However, we fill her car up with premium Chevron for long trips where highway miles are sustained for the main purpose of cleaning the injectors.

c70_lindsay · Post by **c70_lindsay** » 02 May 2011, 19:43

I just returned from a 1400km+ road trim in my 2000 c70 hpt. On my way there I used premium gas and averaged 8.1 litres/100km with an average speed of 105km/hr. On the way back I used regular and averaged 7.6litres/100km with an average speed of 99km/hr. (Also on the way back I had a passenger @ 270lbs lol) Without any noticeable loss of performance. This was calculated with the trip computer which I have found to be pretty accurate. As a side note I can get 800km on a tank of gas.