4" exhaust...is it REALLY helpful???

[EagleEye]

I am looking at 4" exhaust systems, but a couple of points keep bugging me...



If I do NOT plan on changing my turbo to a monster, or duals, the exit port is only SO big... if you have a 4" exhaust, it still necks down at the turbo, and will still restrict, so how does it help if I am already 3" straightpiped?



I remember awhile back Banks did not recommend the larger exhausts because the gains were minimal. They apparently backed it up with some testing (water column flows and dyno). NOW they offer bigger exhaust! I know, some people like Banks, others don't. I am wondering if it is a marketing ploy (they finally got the tools to do larger exhaust). I had faith in Banks awhile back when I did my 97, and their system was SERIOUS fun. I wasn't impressed with what they did with the 24 valve engines, so I passed. Are they just jumping on the bandwagon?



I also don't need any more noise. What I have is fine, and can still scare old ladies, small children and wildlife while having an intelligent conversation with the better half. My stock exhaust is not rusty or damaged. Stainless is awful expensive.



With a couple of interesting mods, EGT's can climb when loaded down with the camper and boat while taking Grapevine style grades at insanity speeds.



Bottom line... will the drop in EGT's be significant, or is it just wishful thinking? The exhaust side of the turbo is only SO BIG!!!



What are your thoughts??? Input good and bad always welcome.

 

[rweis]

There was another thread I read tonight that said that to get a clean 4" flow through you would have to go to a HX40 size or larger turbo.



I don't know, not an expert, but my KSB1B is a full 4" output though.



I am after superior air flow both into and out of the "air pump" then limiting the fuel flow to what I need (not to what is possible) so the fuel burns as completely as possible.



FWIW,



Bob Weis

 

[Sticks]

There is a member here that reported an increase in EGT's with his 4" system, on an auto, 275's and FMS.



Have you gone to a cone style aftermarket air filter of some sort (BHAF, AFE)? Air moving fast and easy in, fast and easy out = cooler EGT's.

 

[WadePatton]

Ask a vendor like DD, who isn't selling exhausts--or at least don't push them, what limits they see with straight 3".



Big Joe has chimed in a couple of times and said that 4" is good for up to about 570 RWHP.



So I got 5". Oo.



If I really had to bet, I'd say that an ATS manifold would help your EGT's as much as a 4".



I'm in it for the sound. My system has a 3" turbo, 4" down, and 5" all the way out, plus a gutted 10x51 muffler. Turbo soon to be upgraded to 4".

 

[Mark Craig]

4 Inch Exhaust

Eagle Eye,



We see EGT reductions as well as HP and torque gains on stock and modified trucks. Some folks call us back and claim they got more MPG too, we don't promote that very strongly, but it does happen with some customers etc.



While 4 inch will support more HP than anyone really needs, some folks go for 5 inch as well. Don't be fooled, marketing does enter into the "we sell so and so beacuse it's the best" picture, always has always will, especially for those companies that just want to sell something/anything.



Talk with the members here and you will get the real skinny on exhaust performance and who makes what you need and who doesn't. If you want to call us and we'll explain our designs and product benefits etc etc.



Mark @ DPPI

 

[GMocanu]

I've got a simular question in my mind about this topic. I'm looking to upgrade my exhaust also. I don't intend to change the turbo and I don't want a straight piped system. I have been thinking about a muffler elmination kit but I see some problems with that also.



With the stock turbo you will always have a 3" restriction no matter how large the exhaust is. I just went out and looked at my stock system. The down pipe is one continuous run to the resognator (sp?). It does make a 90 (almost) but it is a long sweep type 90 that looks to provide good airflow. The problem that I do see with a 3" straight pipe or mufflerless system is that the bends in the 3" tailpipe make for a lot of restriction. I think that if I leave the resognator and pipe it 4" from there that I will get most of the benefit of a complete 4" system without having to purchase the whole system. Now I am going on the assumption that the stock res is simular to an aftermarket res in it's restriction of the airflow.



My point is that by taking out the stock muffler and increasing the tailpipe size I should come close to the airflow of a 4" system with a res on it. It should at least be a major improvement over the stock system. The reason that I'm not concerned about the first section of 3" is because the gasses are hotter and hot gas flows more easily then gas that is cooling off plus the first section only has one bend.



Does this make sense to anyone or am I missing something? A 4" tailpipe, a short piece of 4" pipe and a couple of clamps should be much cheaper than a full 4" system.

 

[Deezul1]

Several people on these Forums who know their stuff have done a lot of testing on dynos and street and generally agree that until you reach pretty close to 500 HP a 4" system sounds better but doesnt help much otherwise.

 

[athompson]

When I put a 4" exhaust on my truck, the only "performance" mod so far, I didn't do it to increase power or fuel economy. I did it to decrease the turbo lag and increase the exhaust volume so I could actually hear it. While I didn't get any increase in economy or power (as I expected), the turbo lag is almost gone (even more than I expected), but the exhaust volume is just loud enough to hear at the tail pipe (quieter than I expected).



Did I "need" a 4" exhaust? No. Would I do it again? Yes. What else matters?

 

[CRSmith]

As for if we need a 4" on the dodge, I don't have any testing to support it. But, I'll get one when the time comes because I've heard enough testimonials on here to convince me it reduces egts.



Your question was, will the 4" do any good because there is a 3" neck down at the outlet of the turbo. The answer is yes, theoretically. Restrictions such as bends and small pipe are cumulative. The neck down you mentioned will give you x amount of pressure head. Then you add y, z, a, b, c amounts of pressure head from bends and wall friction. If you can reduce the cumulative effects of the exhaust system, it should help performance.

 

[krs]

On our '97 the tailpipe, which evidently had been changed before I bought the truck was rusted through over the axle. I had to do something and even though I was convinced that a 4" system wouldn't help the power those mailorder systems were cheap. So I put one in with an Allied muffler from Rip. I was pleasantly surprised to find that it does lower EGTs between 50 - 100 degrees in all driving. It cools down to 250 also and never got below 300 before. I don't notice any performance increase at all but I don't treat that truck as a performance vehicle even though I did put in a fueling plate. It hauls our camper and is auto so my wife and I can share driving. We go slow with 3500 lbs. in the bed - sometimes a 4000 lb boat behind.



So even though there's no logic to it I guess the 4" pipe was a good change.

 

[Joseph Donnelly]

low restriction 3" is fine to about 330-350 hp, the point where you should go to HX40 turbo which should use 4". I saw a gain of only 7 hp at 380 going from 3" with Walker 21468 to 4" with no muffler, both using HX35 and 16 or 18. 5 cm2 housing. See TDR Issue #23 or 41 (it'l be out soon!) for more.

 

[JBlock]

2003 have larger exhaust

Rather Dodge is to marketing or not, No one Knows, but the 305 hP HO have a 3-1/2 down to 4 inch exhaust, and even the std so have 3-1/2 I believe.



So they maybe some benfits at the 250hp mark.



Expensive those $350-$400 for alumized steel.



JB