I have a 4.8 with a 5.3 crankshaft, 5.3 rods and what I'm wondering is what will I gain. If I use the 4.8 flattop to gain more compression what does that do. will I gain more torque or HP. Or do I gain both, thanks guys

 

Both as it's a displacement increase, though probably more torque.

 

Horsepower = RPM X Torque X conversion constant. Change one, you change the other.

 

Not necessarily - if you increase the torque, but it occurs at a lower rpm, horsepower can remain the same or even decrease.

 

There are too many factors to say that much but you will gain both. You are basically doing an 05+ 5.3 with (possibly) crappier heads. The 4.8 is really a turd.

 

He means that a torque increase at a specific rpm will result in a horsepower increase. So going from 200-215 ft/lbs even at 1500 rpm will cause the HP to increase at that rpm.

 

Compare OEM outputs. The 4.8l and 5.3l seem to have used the same heads/cam/intake for a given year and aren't the aluminum block HO versions flat top with a slightly larger cam. Not exactly what you are looking for but should give you some idea.