89 octane is recommended for 6.4 truck engine, 87 is allowable. Must be an algorithm to advance ignition timing with 89 octane, thereby gaining more power. Your choice, but I always gas with 89 octane when I tow.

btw - don't fall for the extra ethanol crap fuel - it increases octane but burns too lean.

 

Thank you. I agree the extra octane will make zero difference. I search the thread but did not come up with anything concrete but the algorithm program makes perfect sense. I assumed it had to do specifically the way the engine is tuned.

 

It's not exactly the SAME engine.
Maybe the same basic engine, but more compression, hotter cam timing and higher performance tuning is why the 392 in the Challenger needs higher octane.

 

As per the above post, I doubt they are the same engine, definitely different tune but there are more differences guaranteed! Higher comp pistons (if it requires higher octane fuel) probably different cams, maybe different heads, pistons, headers, intake, etc...
On octane subject: it's not octane number that matters in ethanol mix fuels, it's the ethanol itself. Ethanol has way less energy (BTU) than gas (and for comparison sake, even lesser than diesel fuel). Engines designed and tuned specifically for ethanol fuel will take advantage of it but all this "Flex fuel" is BS and a waste of money.

 

I agree it all makes sense that the cam and other components would be different.

 

This will help you understand the Truck 6.4 Hemi better, it is not the same engine as the 6.4 Hemi used in the cars, there are many differences.

6.4 liter Hemi truck engines for Ram pickups and chassis...

6.4 liter Hemi truck engines for Ram pickups and chassis cabs Launched in the 2014 model-year, the 6.4 liter "truck Hemi" V8 was specially created for heavy duty Ram trucks. Despite having the same displacement, this engine was quite unlike the 6.4 liter SRT Hemis (also used in certain...

www.allpar.com