WhozNxtLS1

Hey guys. Buddy of mine has a 2005 quad cab short bed just like mine. He welded a piece of 3.5" pipe and deleted the cat and muffler and turned a 5" tip out the side in front of the pass rear tire.

Now the truck sounds amazing, but is going from factory 4" to a 3.5" bad for the truck? It drives great and everything seems to run smoothly.

Just wondering

Thanks

Chris

rustyshakelford

well itll create higher egts, more back pressure...not sure why anyone would want to weld on a smaller diamater than stock piece of pipe, but to each his own...i was even giving away my old exhaust, the 4" wouldve been perfect for that

brett

WhozNxtLS1

Anyone else with any advise on this. Is it a bad thing to do? I mean would it really create more back pressure? In theory there is less restriction on the exhaust side I would figure due to the dropping of the cat and muffler so wouldn't the loss of .5" balance that out? I mean I'm not saying that I would do this, just looking out for him on his bahalf. He can be a bit stubborn sometimes.

RD TRCTR

Any decrease in diameter will cause pressure to increase and velocity to decrease, hence causing higher egt's as brett mentioned above. Cummins/ Dodge made our trucks with 4 inch exhausts for a reason. Yes, the removal of the cat (for offroad use only) and muffler will decrease back pressure and theoretically lower egt's. With 4 inch pipe and nothing in the way, the amount of back pressure is the least. With all factory installed equipment it is the most back pressure that can be achieved. So, by removing the cat (for offroad use only) and the muffler but adding a piece of 3.5 inch exhaust the back pressure exisiting is between the two examples mentioned above. Anything in a flow path causes back pressure. Elbows, turns, changing diameter, changing shape, everything in a flow path causes back pressure, so it's best to minimize all of it to obtain the best system for performance.

fordkiller43

Like everyone else has said it will not harm youre truck but will run higher egt's and increase backpressure. He should think about trying to find someone selling or giving away a 4 inch muffler delete system. Thats just my opinion though.

WhozNxtLS1

Well for my truck I will probably be looking into a 4 inch delete system, maybe even a 5". I just really wanted to know if it was going to harm his truck and see if he was going to have problems. As for EGT's, what does this harm when these increase. I myself am pretty darn new to the game of diesels, but thus far loving every minute to it. I want to do everything right, and hit all my bases

fordkiller43

EGT's can cause thermal meltdown when not monitored and run too high. Unless youre buddy has lots of mods he should be fine. EGT's are a very important thing to monitor tho in our diesels. Before getting a box/module myself and many others would recommend getting some gauges Good luck!

tcr

He will be fine, look at all the crap he took out of the system, plus it's a much shorter exhaust system. EGT's will still be lower than what they were. I don't know why he didn't just use 4" though