Hello,

I am currently looking at buying either the dynomax part # 39450 or dynomax Part # 19387. I am confused however, the 39450 says its a 2.5" system and the 19387 says its a 3" system. Both say they fit the 06 FX4 F150. I do not know what the size of the straight pipe is that goes in to the muffler inlet. I am currently deployed to Iraq so i cannot go out and measure it. Does anyone know the correct size or do both the si/so si/do mufflers have the same inlet size?

Thanks

 

your stock size is 2.5". You can upgrade to 3" for a tad more low end tq, but nothing really noticeable. 3" will mainly be louder and deeper than your stock 2.5" size.

 

Going to 3" will NOT boost your low end. If anything, 3" will loose a little bit of your low end torque, but it will perform better while in the higher RPM range.

 

3" won't hurt low end that badly, maybe only noticeable if pulling 6000lbs of load from a stop. Otherwise its a much healthier size for gas flow, Super Dutys all have full 3" for that reason.

 

I believe the 39450 is a dual system and the 19387 is a single outlet system.