Mid Grade Gas in Turbo?

C@lvin · Post by **C@lvin** » 14 May 2010, 07:25

I see that using regular in a Turbo can lead to internal engine component issues. What about mid grade fuel? Is there a recommended lowersafe limit of octane?

Post by **FlyingVolvo** » 14 May 2010, 07:33

Depends on the turbo. The light pressure turbo like in my 2000 V70XC had been using mostly regular for about 120K of its life, no issues. Since I got it, I've been using premium. There is a bit of a difference noticeable when I really push it and I am at sea level.

Now if you have a high pressure turbo, then you definitely want to run the higher octane. But for general use, any gas should do you fine. Your knock sensors will retard the timing a little bit to avoid knocking on lower octane fuel, so no damage will occur.

I'd say mid grade is a good compromise for people who don't want to spend more on premium, but want a bit more octane.

Post by **jblackburn** » 14 May 2010, 07:40

I run 89 in mine most of the time. It gets angry and really slow if I use 87 (made that mistake only once), but 89 seems to run pretty good. I can tell a small bit of difference stepping up to 93, but nothing huge.

C@lvin · Post by **C@lvin** » 14 May 2010, 07:42

Thanks to you both for responding. I am specifically asking about the 2.3L High Pressure Turbo. I am looking at a 94 163K Turbo for my daughter and I need to let her know that if she gets the car it will require (the expense of) Premium fuel if using mid grade or regular will damage the internals. I had read a post by Ozark Lee that indicated regular fuel can lead to problems/damage (can't remember for sure the specific problems he mentioned). If using lower grade fuel is just a trade off of performance under load (regulated by the knock sensor) that's one thing but if it leads to damage, then of course that is something else entirely.

Post by **jblackburn** » 14 May 2010, 07:54

Regular has been seen to cause burnt valves in them. During the summer, under heavy load and running A/C, I think it causes that to happen.

One of the big differences, I think, is where you get the gas from. In my old Accord, I could tell a big difference between filling it up with cheap, 7-11 gas and somewhere like Shell.

Mine's a 2.3, and hasn't blown up yet anyway. The P.O. told me they used mid-grade in it, so that's what I kept using.

C@lvin · Post by **C@lvin** » 14 May 2010, 08:42

OK.....so to follow your logic a little further, if the ambient temperature is under, say, 80 degrees and you are not pushing the moto,( basically heavy acceleration/turbo usage or extended high speed driving (over 75-80MPH)) then you should be able to run 87 Octane with no ill effects for the valves?

I know this is nit picking, but if she ends up with this car she needs to know the operating parameters and I'll need to make it as black and white as possible for her. Of course you could say that if she is that cost sensitive she shouldn't own a turbo (or for that matter even a Volvo) and I've also heard it argued that running high test gas maximizes MPG and so balances out the fuel cost savings but decreased MPG of running regular.

Post by **jblackburn** » 14 May 2010, 10:55

I would tell her to run the mid-grade just to be safe.

a) better gas mileage
b) better for the engine in the long run
c) only 10 cents/gallon more expensive.

Really, I think it about evens out paying more for the more expensive gas in these cars.

Post by **charlyW** » 14 May 2010, 11:03

What about UK/EU models ? We have 95, 97-98 or 99 Shell V power. Then the supermarket brands which will give different mileage to the premium brands ie Shell, BP, ESSO

Post by **jblackburn** » 14 May 2010, 11:12

The European octane ratings are based on a different system that I don't fully understand. They rate it using some different aspect of the fuel than we do here. As I understand, Charlotte, you want to get quite a bit of power out of your car from all the modifications you've been doing, so you'll want to use the highest octane you can put in it, or else that power goes to waste as soon as the added compression from the turbo kicks in and the engine has to cut back because it starts knocking/pinging.

RON: (Research Octane Number). Most common fuel used in Europe, Australia and some other Countries. It is determined with measurements of fuel behavior in a variable compression engine. Results are compared with other iso-octane fuels, wish means, compared with other fuel types with equal number of similar octane molecules present, but not the of the same organic compound.

MON: (Motor Octane Number). Determined also with a variable compression engine, but with the fuel already preheated, variable ignition timing and higher RPMs than the RON method. This method is more precise on determining fuel behavior on an loaded engine.

PON or AKI: (Pump Octane Rating or Anti-Knock Index): This is the method used in USA and Canada, expressed as [R+M]/2, wish means RON number plus MON number, divided by 2. In other words, it is the average between both methods above.

And here's the equivalency chart (USA->European):
87 -> 91
89 -> 93
91 -> 95
93 -> 98

And to give credit where credit is due:
http://ezinearticles.com/?What-is-an-Oc ... id=3618239

Post by **charlyW** » 14 May 2010, 11:19

it's bizarre that there's no set in stone spec for fuel as to speak. My T-5 get Shell V power thats 99-100 RON [uk spec] then once I'm happy with it I will be fitting water/methanol injection system to bring the octane higher