Ever swap injectors?(4.7)

[lekmedm]

I will say my mechanic recommended running premium in the 4.7 or some cleaner in a lower grade gas- so just a heads up to those with the motor. Looks like I'll be throwing the 91 tune back on her next tank.

I could never understand this thinking. Octane has absolutely nothing to do with the additives a petroleum company gives to its fuels. Fuels are of different octanes to work with the compression of a particular engine. This is directly related to the fuel's volatility. On the compression stroke, you increase pressure on the fuel, and, therefore, increase its temperature. In a high compression engine, this could lead to pre-ignition of the fuel (catches fire before complete piston compression and firing of spark plug). That results in "engine knock." This is why there are higher octane fuels, because they are less volatile and resist pre-ignition (detonation).

Save your money on the 91 octane, and just buy a couple of cans of fuel system cleaner for a couple of tanks. I've always heard great things about Techron, but try whatever you think is best. I've tried various cleaners and can't say I feel any difference between them, but maybe I've just never had a fuel system issue for the additives to make any difference.

Good luck.

[Matt]

Is the mechanic on the "older" side?

This was before my time as i'm a relative youngin... so someone else who lived through this era please correct me if the following is wrong....(Edit: yes this is 2nd hand information that I have not personally verified.)

My understanding from talking to some of the more seasoned engineers at work is that gasoline companies used to "up-sell" their premium grades by putting special additive packages in it, and not including those additives in the lower grade fuels. So at one point there was some logic behind running premium in your engine to help "clean" things out.

Since then however, regulations have been passed that require a minimum amount of additives be included in every fuel grade (i'd have to google to figure out what regulation). So you're still getting the additives now and there's no reason to run premium for this feature anymore.

With that said... some companies still try to up-sell their premium fuels saying they have more or newer additives. Considering how money hungry oil companies are, I'm skeptical that ANY grade of fuel has anything more than the minimum additives required.

[lekmedm]

Considering how money hungry oil companies are, I'm skeptical that ANY grade of fuel has anything more than the minimum additives required.

I agree with the youngin'!

[07JeepXK]

My 4.7 liter seems to run better on the 91 octane especially with the 91 octane tune on the flashpaq. If I don't run that tune the transmission shifts weird due to the fat meats I'm Rollin on

[paroxysym]

My 4.7 liter seems to run better on the 91 octane especially with the 91 octane tune on the flashpaq. If I don't run that tune the transmission shifts weird due to the fat meats I'm Rollin on

same here... she shifts so much crisper and runs so much smoother on the 91 tune with 91 in the tank.

yes my mechanic is a bit on the older side.

[lekmedm]

Running a higher octane with a tune and feeling a difference in performance is different from running high octane to "clean out" your fuel system.

Just make your choices based on the right reasons.

[07JeepXK]

That is true.

[06JeepXKHEMI]

I would have to agree with most of this but I think age of the also plays into it. My 240s run better, better mpgs and smoother idles with premium fuels, especially from racetrac. The HEMI XK was also sensitive to the fuel brand I ran in it, Sunoco was best I tried. I would have to believe this is based on what/how much additives are being used. I've never heard of using higher octane to "clean" the system but have heard of using name brand fuels rather than your eco fuels. I'm also I big fan of Techron, my family has used it in all their vehicles

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