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AHUNTER
07-13-2005, 11:39 AM
I have a '90 Tristar - what octane fuel should I be running it?

east tx skier
07-13-2005, 11:43 AM
As early as 1991 (according to my manual), 89 octane was recommended. They were still using the same engines as on your 90 tristar in 1991 for the Prostars. So I'll wager 89 octane is the answer.

WilliamsFamLV
07-13-2005, 12:14 PM
I just received a copy of 90 Maristar manual from MC and it says 89. I guessed right for once! :D

BrianM
07-13-2005, 12:22 PM
Same motor as you in my '88. I run and the manuel calls for 89.

east tx skier
07-13-2005, 12:28 PM
So, since we've got that cleared up, can someone, once again, clear up for me whether 89 can truly be a 2 parts 87 octane to 1 part 93 octane mixture, which averages 89 octane? Or is that just a myth. I've never found any definitive evidence that this works.

Workin' 4 Toys
07-13-2005, 12:41 PM
So, since we've got that cleared up, can someone, once again, clear up for me whether 89 can truly be a 2 parts 87 octane to 1 part 93 octane mixture, which averages 89 octane? Or is that just a myth. I've never found any definitive evidence that this works.
Unless you have the equipment to test the ACTUAL octane level of the fuel at the exact station you fill up at, you will never know. The fuel stops are supposed to maintain the posted rating, but are they really testing it? And who is checking it.
As I understand, the rating of the fuel is only acceptable for a certain amount of time, a shelf life we'll call it. At the prices they are getting for fuel these days, most people have stopped using 92, 91, and 89. The less consumed, the more that sits in the tanks, and for longer periods therefore decreasing the accuracy of the rating, and diminishing the value of the octane, and decreasing the shelf life. Sort of why they recommend and fuel stabilizer before storing anything. Same goes for stations. But how do we know they are using the correct amount for the unsold portion the station sells, the world may never know.

Workin' 4 Toys
07-13-2005, 12:47 PM
So, since we've got that cleared up, can someone, once again, clear up for me whether 89 can truly be a 2 parts 87 octane to 1 part 93 octane mixture, which averages 89 octane? Or is that just a myth. I've never found any definitive evidence that this works.
Sorry east tx, I sort of went on a rant there and did not get to the point. As I have been told yes it works, but depending on the unknown octane level, you very well could decrease the rating. If you were ultimately concerned about running a higher octane, the additives in the aftermarket will do a much better job than trying to "figure out" the consistancy of the fuel you use. Some manufacturers of additives go to great lengths to provide the best fuel possible so you continue to use their products.

east tx skier
07-13-2005, 12:50 PM
If you were ultimately concerned about running a higher octane, the additives in the aftermarket will do a much better job than trying to "figure out" the consistancy of the fuel you use. Some manufacturers of additives go to great lengths to provide the best fuel possible so you continue to use their products.

Can you give me some examples as to what you're talking about?

BrianM
07-13-2005, 03:09 PM
I blended gas myself last time I filled up. The gas station that is closest to the lake pump's were messed up so they didn't have any 89. I put in 14 gallons of regular 87 and about 8 of premium 93. I found a site a while back and posted it somewhere on this board that says yes many stations do mix on site.

wakesport
07-13-2005, 03:55 PM
So, since we've got that cleared up, can someone, once again, clear up for me whether 89 can truly be a 2 parts 87 octane to 1 part 93 octane mixture, which averages 89 octane? Or is that just a myth. I've never found any definitive evidence that this works.

Yes this is correct. When they determine the octane they test the fuel on a special engine to see when it knocks. They compare this to a known octane that knocks the same amount. Years ago when I was racing there was a couple of different brands of gasoline that you could blend together and get a higher octane due to the different additives that they put into their fuels (Shell and Amoco). We used to go to both stations so that we could make high octane fuel when we could not get 107 from Unocal. But, if you go to the same station and mix two different octanes together you can just calculate the new level by the proportions you mixed them in (Gallons of Fuel A * Octane of Fuel A + Gallons of Fuel B * Octane of Fuel B)/(Gallons of Fuel A + Gallons of Fuel B).