Thanks for all the posts,

the info is appreciated.

 

I have always run 89 since it was new, just kinda cheap insurance.

 

Yeah because it runs hotter on the 87 octane than the 91 octane,more octane = cooler combustion temperature,and your compression in that bike obviously does'nt warrant running 91 octane.Unless
you have at least 10.5 -11.0 compression you dont need 91.

 

OK, this opens a question for me. I use the mid grade in my 2006; I am unsure what the octane number is for that.

Someone define "knock" for me please. I have noticed that at times I wil get a momentary shudder from the engine as if it didn't fire. Not a gentle loss of power, but noticable "kick". If it were a jet engine I would call it the infamous un-start (except by that standard it is very mild).

I guess for the next tank I will try premium and see if the problem goes away.

GJ

 

Regular - 87 octane
Mid-Grade - 89 octane
Premium - 91 to 94 octane

Assuming the engine temperature does not exceed the standard operating temperature (just below the center line on the temp gauge), then 87 octane gas should work just fine.

When hauling heavy loads or racing, the temperature could rise above the standard operating temperature, resulting in engine knock because of pre-detonation. This is why the manual says that 87 is acceptable, but 89 is recommended... in case of possible excessive engine heat.

Engine knock occurs during the compression stroke of an engine cycle, where the piston is compressing the gas-air mixture. This compression causes the gas-air mixture to heat, in addition to the ambient temperature (engine temp), and if this mixture gets too hot it is possible to ignite before the spark plug fires. If the mixture ignites before the compression stroke is complete, then the "explosion" is working against the piston causing power loss, possible engine damage, and an audible "knock" that nobody ever likes to hear.

 

It says in the owner manual to use premium or plus rather. I use supreme in mine because I set my hemi up with the Hypertech Programmer III part# 50013. On the Hypertech, you can set up your program for stock, 87 octane or 93 octane. I get 19-23 MPG driving 1 MPH to 55 MPH. When I climb to 65 it still gets 17 MPG, but when I go to 70 plus it only get a range from 14-15.5 MPG. Soon I'm going to set up the program with 87 octane but I'll use plus grade fuel and see what happens with the mileage. I'll keep you posted.

 

Dude just use 87 octane, your fine. Unless you have a crap load of miles, your hemi doesn't need that expensive gas. It's a truck! It will be fine, if you feel better about yourself putting 89 or more then go ahead. Oh yeah, you do not need to put synthetic! If you're pulling a lot or red lining your truck, then yeah put synthetic, other than that your truck will be just fine. Your Hemi is pulling 1/2 a ton, that isn't crap. If you had a small block or V-6, then yeah do all of the above. For more advise, just go to your local auto parts store. Oh yeah, you have a 1/2 ton Hemi, your fine.

 

The higher the octane, the slower the fuel ignites and the slower the flame front travels across the atomized gasoline in the combustion chamber, giving a more controled and gradual pressure rise in the cylinder. With lower octane fuel, the fuel ignites more quickly, giving a faster rise in pressure in the cylinder. Under heavy load conditions, more fuel goes into the cylinder, and the resultant pressure from the extra fuel igniting goes higher. Too high, and the pinging noise occurs, which is detonation.

If you're running a stock-configuration Hemi, as I am, anything above 89 octane only wastes your hard-earned money and doesn't "treat" your engine as many people think. Here's what it says under fuel requirements for the 5.7L in the 2004 Ram owners manual on page 256: "The use of premium gasoline will provide no benefit over regular and mid-grade gasolines, and in some circumstances may result in poorer performance."

The 87 octane should work just fine in your Hemi, as it does in mine. Just plan ahead if you're going to be towing or hauling and then use 89.

 

Ram04Rules Writes:

I'm glad to see someone post this as it seems that it is needed in this thread.

Using premium fuel in an engine that does not require it is one of the most common errors that is made. There's just something about running premium fuel that causes some people to think that they are getting better performance or are doing their engine a favor. I compare it to some people taking a placebo pill and suddenly think that they are feeling better.

Always consult your vehicle operation manual and stick with the manufacturer's recommendations on this and other subjects. You will have much less chance of either wasting your money or, worse, harming your vehicle.