trying to find out what performance gains if any are to be had by removing the muffler and replacing with a straight pipe 4" ?? I plan on keeping the Cat on but cant find any info on gains with just a straight pipe - i.e., quicker spool up, lower egts, better throttle response ??

I replaced the stock muffler with a straight pipe. The sound is quiet. Didnt really notice any gains with throttle response or spool up. I didn't have a way to measure before and after egt reading so I can't answer that. Just a little info for you.

I REMOVED MY MUFFLER AND FOUND NO GAINS, A SLIGHT LOUDER EXHAUST NOTE AT IDLE. REMOVING THE CAT AND PUTTING IN A LB7 DOWN PIPE HELP A LOT. IN PERFORMANCE AND EXHAUST NOTE, AND N CEL.

This is just an unscientific observation of course, But here is my thought...


It seems like the Catalytic converter would be as much, or more restriction than the stock muffler would be. Since the Muffler is after the cat. I wonder, Why would it help much at all to replace or remove Just the muffler and leave the greater restriction (The Cat) still in place?


Sounds like a waste of money and time to do the muffler, unless you remove the cat as well.


Just one mans humble oppinion...http://www.dieselplace.com/forum/smileys/smiley2.gif

I agree , the kitty needs the boot .http://www.dieselplace.com/forum/smileys/smiley18.gif

I have a Q for you LLY guys with a straight pipe


When you first start the truck the note is deep like an lb7 for a few secs then it changes (im assuming this is the vanes in the turbo changing) but it then sounds more like a jet and diesel. The Q is is that really the turbo vanes constricting when the sound is like a jet (just a bunch of tubine/fan noise no exhaust tone from the motor) and when it is deep (like the lb7) is that when the turbo vanes are open all the way??

good question - i always wondered the same thing as well, you cant miss the noise it makes, but from what ??

i have a 04.5 lb extended cab lly. yesterday i removed the cat and the muffler and installed a 3.5 inch straight pipe. the turo seems to spool up faster, and the noise is bitchin. on my cousins lb7 i also noticed that when we straight piped his the egt went down also. i am putting the edge on tonight so i dont know exactly what the egts are now. my question is this - about 10 miles after the straight pipe was installed i got check engine light. i scanned it with my tech2 and it had an egr low flow code, and an egr insufficent flow code. i cleared the code and it came back about 10 miles later. has anybody had egr codes set after the exhaust swap? i assume it is due to the lack of back pressure. whe you install the egr sick and block off plate does the check engine light come on? would that keep codes from setting?Edited by: ytmotorsports

Egr codes appear when you remove the cat. Basically not enough back pressure for the EGR to work properly. The question is, Is that such a bad thing?

i dont think that the egr codes will send the truck into limp home mode. so all i have to deal with is the light, have you tried the finger stick?

I been there soon as you take off the cat they will throw codes. Contact fingers and get a fingers stick and you will be golden. good luck John

ytmotorsports.



Results with the Finger stick and block off plate look very favorable
right now. Search for EGR defeat circuit and you will have what
you need to make one. Fingers was talking about doing another
small run if there was enough interest, too.



Dennis

thanks. i am on the list for his next run.

ytmotorsports
So does the dmax sound pretty good with the straight pipe? good as a dodge and ford?

I straight piped mine and LOVE IT. Sounds great, turbo spools way faster feels more like my old lb7 used to for power. Haven't had any codes set. And it is quieter than my lb7 was with a 4" flow master. Ill never keep a muffler or cat on a diesel again. http://dieselplace.com/forum/smileys/hihi.gif

i cant figure it out, some people say their dmaxs are really loud straight piped and others say its not much louder than stock?