Fuel Choices?

p5_jeff

Member
:
2002 P5
I have a question that may seen stupid but I need a solid answer. I have an 02 P5 with Mazdaspeed Cams, UR underdrive pulley, CAI, Header-back exhaust, and other un-related mods. Should I be using 91 octane fuel or will a lower grade fuel work just fine. Any thoughts or suggestions are appreciated.
 
You are fine. The main reason you would need to upgrade your fuel would be if you were running turbo applications, etc.

I see you have nothing that would change your engine management or need (in my opinion) higher octane fuel.

One could possibly argue by putting in 91 octane you could be doing more harm than good. I know that before I had went turbo in my P5, I was using 87 octane.

Hope this helps, though I am sure some of the more technically advanced gurus will chime in and make their own arguments for or against.
 
You should be just fine with 87.

If you had higher compression, advanced timing, or turbo then 91 would be more appropriate.
 
The MP3 required higher octane more for the ignition timing. And the Mazdaspeed required higher octane to handle the boost. Since you don't have the MP3 ECU, you probably don't have the more aggressive timing curves. Other than the cams, none of the mods you listed will affect your octane requirements. Cam timing can affect your dynamic compression ratio. However, I don't think the cams would change your dynamic compression ratio enough to justify premium fuel. Do you have the FS-DE cams (j-spec cams purchased from Mazdaspeed) or cams from an MP3 or MSP? If the latter, than they're the same specs as the P5. Consequently, there will be no difference in your dynamic compression ratio.

Regular will do. Looks like I'm voting with the census.
 
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im curious too...I use nothing but 91 for the sake ive heard it is just overall better for your engine and such and im pretty much down for anything to preserve the life of my P5, anyone heard of better gas mileage, ect.?
 
I used to run 87 in my MP3 and my EGR blew out and I thinks thats why it did. Now I'm using 93 cuz 91 is extremely hard to find here. I filled up on 87 a month ago to drive out to school (40 miles each way) and I got worse gas mileage on 87 than I do on 93, I dont think it should matter but apparently my car just sucks down 87 more than 93? Oh well I dont mind spending the money because well my car needs it and I feel a slight boost in response when I've switched from 87 to 93.
 
My car runs like crap on premium, I get much better milage on regular (89 octane, I think)
 
if you do that math, you'll find that it's cheaper in the long run to use premium in some applications. my fuel economy drops significantly if i use 87 octane vs. 93. i acctualy save money and have to get gas les often using premium. i don't know if anyone else's car is like that.
 

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