i might be getting a 05 cummins, and usually the best mod you can do is a straight pipe, relatively cheap, and makes a world of a difference, but i have heard several common rails and some of them dont have the deep cummins sound, is that because of the cat, or does the intake silencer make that much of a difference. thanks

 

they do have a different sound than the 2nd gens but they are actually louder. when my 2nd gen buddy with stacks rides with me he cant get over how loud it is
http://www.youtube.com/watch?v=9z0f_t3Dxxc

 

really, does adding fuel make a big difference on loudness, tone

 

Straight piped mine was just flat out annoying. And when I pulled a boat, cattle trailer, equipment trailer it just got worse. I put on an aeroturbine 4040, but it didn't quiet it at all, so i added a 30" MBRP straight thru muffler. Now I like the sound, a nice deeper rumble when I want it, and just a bit louder at idle.

 

i love my strait pipe. if its too loud your too old!!!

 

There really isnt much benefit by straight piping it. I dont know who told you that... my truck feels the same.

You will see a benifit on a 500hp truck though but dont expect anything except a really loud truck.

Since my 03 didnt have a cat it is really loud at WOT...alot louder then my other 2nd gens that were also straight pipes but I let the resonator on thoes.

 

I didn't particularly like mine straight piped. Wasn't too loud for me, just didn't sound good. Loved my 02 straight piped and my 03 sounds similar under 1800 or so rpm. Heard a newer one the other day(04.5 and up) and it sounded good, I think it still had the cat because it wasn't super loud, no muffler though. The only thing I miss about the straight pipe is the whistle.

 

The stock 3rd gens sound like crap straight piped. The best straight piped sound is from a 12-valve (IMO).

That being said, when I installed the cam it changed the engine note to more deeper instead of sounding like a bee or nasal-sounding. This was with a 4" straight through muffler.

Then when I installed twins, it was way too quiet with the muffler so now it's straight piped. It sounds now like a jet turbine, but even deeper tone than the straight through muffler yet still has the same noise level as with the straight through muffler.

 

Dans right, you won't see a power increase unless you are way overfueled, and you drop EGTs enought to burn more fuel...

You will find a lot that agree with you, including me