2nd Gen Non-Engine/Transmission Why replace stock 3" exhaust pipe with 4" .

[WLehman]

I was wondering why Dodge used the 3" exhaust pipe instead of something bigger? Do you think that was a Dodge decision or a Cummins reccomendation? I was wondering if a Cummins engineer would say the 3" is a comprimise, for what ever reason, and they really suggest a bigger size is better. I need to replace mine one of these days and I don't want to put on a 4" if I'm not making the engine burn fuel more efficiently.



Wayne

 

[Wyomingcowboy]

FWIW - I switched to 4" along with my cam (that was supposed to lower egt's) and I have not noticed much less egt's. I also got bigger injectors at the same time, but I am disappointed with the overall egt reduction. The fit-up of my exhaust was also terrible and consequently i am rubbing on spare tire and shock absorber. I'm actually considering going back just to see the difference... ...

 

[MChrist]

I've always wondered that too... when the size of the exhaust turbine in our turbos is only about 1 1/2 - 2 inches across, why do we need a pipe to be so big. It seems that 3" should be fine. I have the stock 4" pipe on mine with the catalytic converter still in place. I am running twin turbos, and Smarty on SW#7, and my egt's never go above 1200.
Dunno...

 

[Gary - K7GLD]

The super-heated exhaust gasses expand substantially as they exit the turbo housing - a far more pertinent question would be, WHY install a 4 inch exhaust section AFTER leaving the existing 3 inch down tube ahead of it?



A chain is STILL no stronger than it's weakest link - and the still-existing 3 inch down pipe, in this case, would SEEM to be the weakest part of the exhaust chain!



Providing the added expansion capacity directly after the turbo, would SEEM to provide both faster spooling of the turbo AND reduced EGT - valuable in all driving situations, but especially in heavy hauling or towing.



I also had larger injectors (1. 6's) installed in my truck, along with a complete turbo-back 4 inch exhaust - those, and the Edge Comp got me to the power level seen in my sig, rapid turbo response, EGT that stays well below 1200 degrees in the vast majority of heavy towing situations, and power to clear just about any mountain pass while towing at 100 MPH, if courage and road conditions permit - I have NO regrets at insisting on a 4 inch down pipe on my exhaust system!

 

[GAmes]

When Joe D was building "Sickly" he found that a larger exhaust wasn't needed until he went over 400hp.

 

[Wyomingcowboy]

My 4" (exhaust) starts right at the turbo. I wonder how much of the problem might be my crappy Quadzilla gauges? I'm hoping!!! Thise dumb things haven't worked right from the get-go and given that they replaced 2 units right up front, the sending unit for the fuel pressure is on unit #4, and now the boost gauge is all over the place puts the whole dang thing into question. I guess until I get a real set of gauges and compare I can't get too busy blaming... ... just wondering "what if"... ... ... .....

 

[Gary - K7GLD]

My 4" (exhaust) starts right at the turbo. I wonder how much of the problem might be my crappy Quadzilla gauges? I'm hoping!!! Thise dumb things haven't worked right from the get-go and given that they replaced 2 units right up front, the sending unit for the fuel pressure is on unit #4, and now the boost gauge is all over the place puts the whole dang thing into question. I guess until I get a real set of gauges and compare I can't get too busy blaming... ... just wondering "what if"... ... ... .....

This power-modding path is often a game of inches, rather than yards or miles - many aftermarket 4 inch setups for our trucks retain the OEM down-pipe, which was the basis of my original post in this thread - and even on mine, it was suggested that I also leave the OEM in place - I didn't, and have no reason to regret my choice. I have no illusions as to any vast power gains, but in RV towing, and combined with my other mods, am pretty sure the full 4 inch setup DOES contribute in various speed/power demanding situation - just as my pretty DTT stainless intake tube - mostly for looks, but probably worth at least a few HP and reduced EGT in some situations.



Like I said, sometimes it's a game of inches! :-laf

 

[WLehman]

I appreciate all of your responses to my question. If I'm understanding what members are saying is, I will at the least see lower egt's with a 4 inch exhaust. If the gases are exiting faster should I have a higher flowing system to introduce air faster? I have never weighed my camper when it's loaded but it weighs (14,750 lbs. empty). I keep my rpm's within the suggested range in all gears. I have no additional gauges and am running the original fuel pump. I bought the truck new in 2000 and have 42,000 miles on it. According to the temperature gauge, it runs about 195 degrees all the time. I've never been in mountainous regions of the country but my truck hums along all day and it is dream to drive in midwest area. Thanks again for your responses.

 

[Gary - K7GLD]

WELL, the 4 inch exhaust system is only part of my mods - but I gotta say, driving loaded or empty is all grins, both in the flatlands, and especially in the steep mountain grades - this Cummins/NV5600 combo just never meets a challenge it can't easily master - in SPADES! Oo.



Pretty easy to take at the fuel pumps too!:-laf

 

[Allnew2Me]

My modifications are very much as Gary's and I did the exhaust last. I installed the F1. 6 injectors, the PDR35 turbo and have the Edge Comp. I removed the stock exhaust (muffler,resonator, and 3' pipe) and installed a Jardine 4" turbo-back with a 30' straight-through muffler. I felt a very noticable difference. Turbo spool was quicker, egts lower and overall response better.

Keep in mind I had the stock restrictive exhaust, I would bet that going from 3' straight to 4' straight would be less of a difference.

The fit of the Jardine system was perfect, no rubbing, touching or mods needed. All the angles were as they should be and the tailpipe came out in the stock location.

As far as why Dodge used what they did, I'm sure it as a matter of cost or emissions or noise issues.

 

[BHaden]

Until a couple months ago I had a 2006 MegaCab G56 combo. It already has a 4 inch all the way from turbo to tip. All I did was install a Rocktek Muffler(straight through) and got a noticably better turbo spool and drivability. I did not have an EGT gauge at the time so can't give before and after temps but they almost HAD to be lower. Go for the 4" and whatever muffler suites you. The engine will like it.

 

[HCannon]

I will go with BHaden, your engine will like it. I couldnt tell you who builds the best but I do know that there is a lot of difference in them. The last one I put on was head and shoulders above the first two that I put on. It fit like it should without touching anything. Sorry, I cant tell you who made but I could find out. A friend got it for me and this is what he was tell me, and he was right. If you are going to have to replace it any way I wouldnt thank the cost would be that much more.



Harvey

 

[QWaller]

My EGT's went down approx 50-100 degrees with the placement of a 4 inch turbo back MBRP exhaust. Fitment could not have been better either. I can't say why but this is what I can see on the gauges. Power is a little better as well. My clutch now slips quicker than it did before. Saving for an SBC

 

[JMcCoy]

X2 on MBRP 4". Perfect fit, cooler, faster spool up, and will outlast stock aluminuized exhaust.