Mine knocks under full throttle when i run 87. I run 91 normally and the difference is huge. As for the what to run at the track question: race fuel of course[sm=gears.gif]

 

I think it's the best thing to do, but you know your truck better than me. I can see a difference in the mileage as well as feel one in the performance. Maybe with the ultra-low gearset, it's not as eveident for you.

 

I have run several consecutive tanks of 89 then switched back to 87. I could tell no noticable difference between the two and there was no difference in my MPG.

Mine doesn't ping on 87 even when towing 4000lbs. So in my case, 87 runs great my needs. I don't care if 89 could possibly give me an extra .1 in the 1/4 since I don't race and would not be embarassed if a Titan passes me.

 

I use premium Racing Fuel 116 octane

 

So, Your using Sunoco Purple, Why ? I hope you removed your converter first. Two much lead, three grams per gallon. How do I know this ? I used to make the stuff before retiring.

 

The real answer is both simple and complicated (kind of like life). The only reason to increase the Octane rating is to prevent detonation and preignition (pinging, knocking and rattling of the piston in the cylinders).

If every engine were made to EXACT specifications and tested to perform with the EXACT same compression in each cylinder and engine (will never happen) THEN an exact Octane would work the same for all engines at the same altitude, humidity, temperature and throttle. Did you catch the number of variables involved?

If you do not have any detonation or preignition with 87 Octane then 89, 91, 100 or 119 is a waste of money and absolutely will not enhance HP. HOWEVER, you may not be able to detect minor detonation in your engine with CAI screaming and the Flowmaster hollering. So use your best judgement. If you not towing, or racing, or over heating and your engine sounds sweet using 87 Octane - use it. It sure wont hurt to try a tank of it for yourself.

Except for the 1st tack I've been using 87 Octane in Phoenix over two years and 51,000 mile without issues. Change your oil often and keep your ears open for different sounds from your engine. (Drive without the stereo on once in a while.)

By the way 119 is actually referred to as a Performance Number since pure Octane fuel can only be 100. All else has Heptane. Unless your driving at an altitude of 20,000 feet or so with a super charged engine, 119 Performance Rated fuel is like checking your oil using a $100 bill for an oil rag - waste of your resources.

 

i have had my hemi for over 2 months, there has never been anything in it becides 91, i am running on 38inch tires and 22in rims with 11inch lift, i am geting around 300-320 a tank still, so i guess 91 makes a little difference.

 

How do you know it makes any difference if "there has never been anything in it becides 91"?

 

That is a very good question. Also, 300-320 miles per tank is a fairly good number for having an 11" lift and 38" tires. Maybe he has the larger tank (32 gal.?), because according to my calculations that would equate to about 11.5 to 12.3 MPG with the smaller tank. Seems high for the mods. The MPG would be about 9.4 to 10 MPG with the larger tank. Incidentally, I've run both 87 and 89 octane. The owners manual suggests 89 octane and states that 87 octane is acceptable, but does not recommend the use of Premium or high octane.

 

That's not right. The computers are able to vary the ignition timing enough to prevent spark knock. That's the whole purpose of the knock sensor. By retarding the timing, to compensate for the spark knock induced by the lower octane fuel, you lose HP and torque.

But hey, it's your truck. If you weren't concerned about having the power, then why waste the extra money on the Hemi and required transmission?