Is it safe to remove the cat and muffler and run a straight 4" pipe on a 2004.5 lly duramax. I have a hypertech already installed. what kind of results can I expect as far as power, sound and fuel mileage. Will this throw any codes or hurt the motor or other components? Any feedback will be appreciated.

LarryJewell,


You might or might not get an engine light related to the EGR system. Some truck sget it some don't. The other thing is you might not like the sound volume or tone, the straight piped D-max's are a little "droney" for most owners. Our MBRp system is pretty good at no drone, and for those that want it super quiet we have a special resonator that can be installed as well.


Mark @ DPPI

Does that erg light mean anything as far as hurting the motor or is it just a nuicense. I like a load and deep exhaust, is this what you mean by a droan sound? My main concern is that I dont hurt the motor with the straight pipe without the cat and muffler.

You would like the sound of the straight pipe. I'm removed my cat and muffler and replaced with a straight pipe, and love it. It is deeper sounding at slower throttle, and when you get on it, it sounds like a jet taking off. I can really hear my turbo whistle now too. Edited by: codythom

ya but how much louder is it? is it like stupid loud? or just a nice rumple. is it street legal is what i am saying?

You can not remove or modify pollution controls.


What do you have against clean air and water?

In cab sounds the same eccept when you get on it then it rappes real nice. As for hurting the motor, I highly dout it would hurt anything. In my case the engine runnes cooler, turbo spools faster, allaround performance is uphttp://dieselplace.com/forum/smileys/hihi.gif I couldnt be happier unless i had the banks chip.

The engine light. When I get in my truck start and split, the light comes on. If I wait a minute or so the light does not come on. I believe the EGR is testing itself when the truck first starts, with big pipe and no cat if you split wile the egr is testing the egr wont get enough flow, however it gets enough at idle. Just a theory.

It got cold right after i straight piped it, so I let it warm up with high idle all the time. But I have taken off a few times without warm up and had no problems. I think it is mostly cally trucks with the check engine problem.

It's not near as loud as the LB7 with a straight pipe. It is not too loud at all though. Perfect! When it's time to take the truck in for inspection, I'll just bolt the cat back on, so yes it is legal as far as they know.http://www.dieselplace.com/forum/smileys/hihi.gif

I just have installed the MPBR 4" downpipie with cat delete an
single 4" all the way out with muff, in which yuo can se all the
way through .. On my 05 Max so far no light with the cat off I
hope it stays that way .. I also installed the diablo tuner with a
Stage 2 AFE intake.. Im happy with everything an its not really
loud @ all. Kinda sounds like a UPS truck now.. I think the LB7
motors were louder for some weird reason... I like the power the
diablo makes only went as far as 65 HP thus far.. But it stinks
how the Allison has to learn to accept the power increase I
mean @ first it would flare up in every gear an I could not get
on it @ all. I was like %$#%^$#^& but now i've settled down an
the tranny is getting better , guess its learning.

ya they do need to learn. How do you like the intake would you say it was worth it? I am trying to decide if I should get one. Is the turbo louder? Any comments welcome.

It got cold right after i straight piped it, so I let it warm up with high idle all the time. But I have taken off a few times without warm up and had no problems. I think it is mostly cally trucks with the check engine problem.





I believe that all the trucks will set a code saying insufficient flow, but the cali trucks have that code set to some special settign that cause the light to come on. I think I heard that some were on this second generation forum...?