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87 vs 89?

RichSNJ

Well-known member
So I have a V8 GCL on the way and I've read that while Jeep "recommends" 89 octane, 87 is "perfectly acceptable". Since it's 40 cents more a gallon, or about 9 bucks a tank, I don't plan on using 89 unless there is a significant reason to. Anybody out there use 87 or 89 in their 5.7 Hemi and have experiences either way? What about octane booster products? I have a v8 Mustang that I've never put anything other than 87 in and have never had an issue.
 

SweetAndLow

Well-known member
So I have a V8 GCL on the way and I've read that while Jeep "recommends" 89 octane, 87 is "perfectly acceptable". Since it's 40 cents more a gallon, or about 9 bucks a tank, I don't plan on using 89 unless there is a significant reason to. Anybody out there use 87 or 89 in their 5.7 Hemi and have experiences either way? What about octane booster products? I have a v8 Mustang that I've never put anything other than 87 in and have never had an issue.
Octane boosters are stupid don't bother.

And like the manual says either will work. It will have more power and probably better has mileage with 89 though. It all depends on what the engine is tuned for, your mustang was probably tuned for 87 so using 89 or 92 wouldn't make a difference.
 

tjw68

Active member
So I have a V8 GCL on the way and I've read that while Jeep "recommends" 89 octane, 87 is "perfectly acceptable". Since it's 40 cents more a gallon, or about 9 bucks a tank, I don't plan on using 89 unless there is a significant reason to. Anybody out there use 87 or 89 in their 5.7 Hemi and have experiences either way? What about octane booster products? I have a v8 Mustang that I've never put anything other than 87 in and have never had an issue.
I ran 91 for the 1st 2600 miles (Costco, so cheaper than midgrade anywhere else). I then tried 87 to see how it affected my gas mileage. It went up, no idea why. I've run on 87 ever since. I've now got 38,000 miles on my GCL and the average gas mileage is 17.96 mpg.
 
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