How much louder?

[Redneckintraining]

I am thinking of making a 4" downpipe for my truck that would feed into the factory tubing where the first clamp is.so the 4" will just be the couple of 90*s and a slight bend.I am just wondering how much louder it will make the truck? Have an hx35,muffler delete,piston lift pump,slightly tweaked pump,BHAF.Right now the truck is fine but it bellows pretty good loaded up a hill.Im wondering if I should start looking into a muffler?

also my thinking on the exhaust: for the power levels I am aiming for a 4" downpipe is fine then the stock 3" will flow fine enough for my needs.I was thinking about remaking the factory section by the transfer case in 3", but with smooth bends not the dented/crushed factory tubing...I was wondering if you guys had any ideas on the best way to do that?

Im thinking that the biggest restriction in the exhaust until about 400 HP is the small downpipe and that dented/crushed section by the transfer case.So then 4" after the DP serves no purpose other than sound.

[lectro_static]

I have 4" from the turbo back, it isnt too loud but it is noticeable, mine is a DD and the only time I even really hear it is when the passenger window is down and Im in a tunnel or againt a wall or barricade.

[Ptothej]

I found more 3" factory pipe I replaced with 4" (no muffler) the louder it got