The 6.4 tows better, more about the TQ than the HP, a 5.7 downshifts a lot without a trailer, my 6.4 (not exactly stock) pulls way better than a 5.7. I actually buy 5.7 trucks with bad engines and stick 6.4s in with a simple upgrade recipe that is much better than even a stock 6.4.
If your willing to build a truck up the best combo seems to me to use a 6.4 truck short block, 6.4 SRT8 injectors with 5.7 heads, intake cam... as the 5.7s make more TQ per CID than the 6.4. This also gives you more compression than a regular 6.4 truck and is a beast for towing, I currently have this exact combo in my 2011 4x4 4 door long bed and towed an identicle configuration truck on a heavy 20ft tilt-deck trailer and even going up a couple big mountain grades only un-locked the TQ converter and did not downshift. I got 11.5 MPG towing that truck. It pulls even better than an actual stock 6.4 truck and cost about 1/2 what one of those trucks would cost. The real 6.4 trucks use EGR witch I hate, the 5.7s don't have it.
I did one with a 6.4 SRT8 engine and it pulled even better but it liked to run much higher RPM also, this current one is much more satisfying when pulling.
That is good info HRD. Appreciate you sharing it. I have driven several 5.7 trucks and did not care for them because of the high rpm needed to get them to move anc constantly hunting gears. Your recipe seems like it might be the answer to nice driving cheaper truck- and I am all about cheap.
Will the 5.7 computer and electronics run this setup without any aftermarket stuff? Did you get a tune done on it? Are you running the eagle 5.7 heads or will the older ones work?
