What gas octane???

Octane requirement is determined by the engine's compression ratio. Higher octane gas resists 'knocking' better in higher compression engines (the higher compression, the more energy you get out of the gasoline when you burn it). Truck engines are notoriously low compression to avoid 'knocking' (too-fast combustion that has the combustion chamber flame-front striking the piston face before it has begun it's downward travel making the distinctive noise) when pulling a heavy load. Higher octane gas contains no more 'power' than lower octane and only helps when you have an engine with higher compression to match (which can be achieved by adding turbo or supercharging). All RV engines do just fine on low octane gas. Anti knock sensor are installed to minimize detonation when the engine is heating up from heavy use.

Interesting::: still thinking of going from 7.3 diesel to gasser (perhaps ram 6.4.... thanks for replies..

pastorbillv wrote:
Basically, they get what's leftover after the refinery puts out its trucks for the day.

Pastor or not, you just don't understand how gasoline distribution works in most of the US.

The gas ALL comes out of the same tanks at the end of the pipeline.

Some brands add extra additives and some don't......but there are no "left overs".

ScottG wrote:

Dennis12 wrote:
Use what the manufacturer recommends.

X2.
Some will tell you to use the cheap stuff but the effects of doing so will add up.

Add up to what exactly ? A significant savings on gas over time ??

Your X2 doesn't quite match the next comment......as I suspect most WILL say to "use the cheap stuff".

At altitude, you can safely substitute 85 octane fuel if your engine is designed for 87 at sea level, unless of course you're running a supercharger, turbo charger, or have an exotic variable compression engine of some sort. Less dense air on input results in lower absolute pressure in cylinder and hence, lower octane requirement as you won't reach detonation pressure in a fixed compression cylinder chamber. Keep in mind the result most noticeable to the driver will be a loss of approximately 3 percent of power for every 1000 feet of elevation gain on a modern engine that compensates as much as possible to the change. Power loss on an older manual carburetor type engine is even more unless you get out periodically adjust the carburetor for optimal air fuel mix.

Targa wrote:

jimbow2 wrote:
Users of the big gassers: Dodge 6.4, GM 6.0, Ford 6.4....... Can the lower octane be used or do you need the higher octanes????? Colorado we have either 85, 87, or I think 91..

Word on the street is that due to our altitude in Colorado 85 octane is equivalent to 87.

Last year 80% of the gas sold in Colorado was 85 octane and only 9% was the mid grade 87. I've been driving here at altitude for almost 50 years with assorted vehicles and have never had any issues using the 85 octane. Now if Costco sold the 87 octane (only 85 and 91) I might be convinced to switch.

http://www.denverpost.com/2006/10/16/some-knock-states-lower-octane-levels/

jimbow2 wrote:
Users of the big gassers: Dodge 6.4, GM 6.0, Ford 6.4....... Can the lower octane be used or do you need the higher octanes????? Colorado we have either 85, 87, or I think 91..

Word on the street is that do to our altitude in Colorado 85 octane is equivalent to 87.
As for me? I stick with manufacturer recommendation to keep it simple.

My manual says 87. I use 87 or the next higher when available. I would only use 85 if that was all there was.

I suppose it depends on your purpose. I've played around some with tuning of my Mustang that has custom tunes. 91 tune is more powerful, but I don't get much of a mpg payoff. So, I generally run the 87 tune.

I agree that the minimum should be what the mfg recommends, but add that if you can buy gasoline outside of the large cities with less ethanol you'll be better off as well.

ScottG wrote:

Dennis12 wrote:
Use what the manufacturer recommends.

X2.
Some will tell you to use the cheap stuff but the effects of doing so will add up.

X3, If you rig is OEM why ask for opinions when the manual tells you the MFG recommendations.

BTW 6.x engines are not large. They are low end of the v8's