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TyBauz 03-04-2013 03:20 PM

Best fuel for 87 Tune? 87 pure or 89 w/ ethanol - Jeep Hemi
I have a 2005 Jeep Grand Cherokee with a 5.7L Hemi with MDS. I have a cold air intake and a Flowmaster muffler. The manual recommends 89 octane. I have the Superchips 87 tune installed.

I am trying to decide what fuel to use. I am pretty sure the 91 octane won't provide any benefit with this tune. I am mostly considering 89 w/ 10% ethanol or 87 with no ethanol. The only pure gas (non-ethanol) I can easily get is 87.

With the Superchips 87 tune installed I am wondering which fuel would provide the best power and fuel economy between these options:

87 w/ 10% Ethanol
87 w/ NO Ethanol (pure gas)
89 w/ 10% Ethanol

Any ideas or feedback would be appreciated.

jeepgcoman 03-04-2013 05:09 PM

Re: Best fuel for 87 Tune? 87 pure or 89 w/ ethanol - Jeep Hemi
Generally, the ethanol blends will get you up to ~20% less fuel economy than the "straight gasoline". Also, I have found, with the SC 91 tune (running 91 straight gasoline), that I get some knock retard at WOT. Don't know if that would be true with the 87 tune or not, since I have never tried it.

IMO, the best thing to do is try them all, making sure to run several tanks of each through the system (and hand calculate results) before you make your final decision. Remember, all fuels are not created equal. Different brands of the same octane may deliver better or worse fuel economy. If your ride is basically stock, running 91 won't do a thing for you with the 87 tune. It might actually deliver less FE than the 87/89 would. Again, give it a try though Also, if you're at altitude (above ~2000 ft.) you may be able to get away with using lower octane....i.e. with my mods., if I am at altitudes above ~4000 I can run 87 without issue. Where I live (~3000 ft.) I can
"get away with" running alternate tanks of 87/91 (non-ethanol) in the winter, but I must run all 91 in the summer. No matter what, with any of the fuels, at any time of the year, I still get a little KR with the SC tuner. With the Diablosport tuner, running the 93 tune (using the same fuels) I don't get any KR. The DS tuner also delivers slightly better FE, but doesn't allow for complete adjustment of the transmission which is, IMO, essential.

SvenskaJeepGuy 03-04-2013 05:31 PM

Re: Best fuel for 87 Tune? 87 pure or 89 w/ ethanol - Jeep Hemi
if you have no ethanol fuel available in your area then go for it, i dont have that option

Lucas J 03-04-2013 05:39 PM

In my experience with a similar setup. I get the best MPG with the 91 tune running 93 octane. Then the 87 tune running 89 octane.

TyBauz 03-04-2013 06:05 PM

Re: Best fuel for 87 Tune? 87 pure or 89 w/ ethanol - Jeep Hemi
Thanks for the detailed reply. I really appreciate it. I tried the 91 tune with 91/ethanol but my MPG decreased when compared to the 87 tune. The performance may have only been slightly better, but the MDS would surge and that was annoying. The surging and poorer fuel economy is the only reason I am running the 87 tune now. I am at 2700 Ft in Boise, ID so maybe the 87 octane pure gas will work better than the 89 with ethanol. Like you said though, I think I will have to give both a try and see what works best. I hope I can find some 89 and 91 octane gas without ethanol some day. It's sad that they add ethanol to our gas now.

jeepgcoman 03-04-2013 09:16 PM

Re: Best fuel for 87 Tune? 87 pure or 89 w/ ethanol - Jeep Hemi
I don't think you'll have any problem finding non-ethanol fuel where you live. Try the Baird Oil (CFN) place on Chinden. They have both 87 and 91 non-ethanol fuel. It's a card lock system, so you'll have to sign up with them first.

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