Can your exhaust be too big?

[RussW1911]

I am getting ready to upgrade exhausts. I heard somewhere that if you go to a 5 inch and don't have oodles of power that it can actually be detrimental to your performance. I want to run a 4 inch downpipe either straight or through an aeroturbine muffler. Then from there go to a 5" for the rest of the way. I would put the muffler at the bottom of the downpipe, or have toyed with the idea of putting it on the downpipe after it was mentioned to me. Don't know if there is clearence though.

Anyway, can it be TOO big.



Russ Wallis

 

[Riflesmith]

I'm sure others will chime in, but here's my slightly educated opinion. I am a steam turbine guy by trade, but I'm sure the comparison is still valid. Steam turbines exhaust into as perfect a vacuum as possible. This extremely low backpressure environment allows us to extract the maximum possible energy from the steam before it is condensed back into water. The turbine on our turbochargers is no different. The greater we can make the differential pressure from the turbine inlet to outlet, the more work will be extracted.



Go with as large an exhaust system as you want. It can't hurt a thing, especially performance or economy.

 

[Chipstien]

Like Riflesmith said, go with as big as you want. On naturally aspirated motors it does hurt if you get too big but when turbos are involved "the bigger the better".

 

[Sticks]

The only time Too Big comes up is in appearance. Saw a kid with 2 7" stacks in the bed of his truck. Functional but reeeeaaaaly stupid looking. I would imagine the same for a 7" system and tip sticking out the back.

 

[CEpp]

5" isnt really benifitial until your at about 550 hp, 4" will do just fine on a street driven truck, 5" will lower your egt's and will give you a unbelievable sound, my opinion, if u like the 5" then do it, but 4" will do just as well.

 

[RussW1911]

Like what I am hearing.....

Well from what you are telling me... .....

I think I am just going to go to the 5 and not have to redo it later. If it can't hurt anything no reason to go with the 4 and wish I put on the 5, right?



Besides I can get a heck of a deal on the setup. Will cost me about 240 but then I add another 125 for the aero-tubine muffler to put that on. Will let ya'll know what I decide.



Some guys are asking me to post any increases and decreases on the turbine muffler so I will be sure to get that on here. Thank again. Russ WallisOo.

 

[CEpp]

i dont know what truck model u have, but here's a link to the co. i bought mine from, and he's really knows exhaust. its nice stuff and clean install, check it out.



for 2nd gen:

http://www.mufflerandperformance.co...=PROD&Product_Code=DSD2-5&Category_Code=Dodge



for 3rd gen:

http://www.mufflerandperformance.co...=PROD&Product_Code=DSD1-5&Category_Code=Dodge

 

[Hammer]

Can your exhaust be too big?

NO !!!!

 

[CEpp]

lol @ hammer

 

[Bill Lins]

You can neither be too big nor too rich!

 

[DOUGMartin]

Russ where are you getting a 5" for 240?

 

[RussW1911]

240 or so

We have a place here in Salt Lake called NPS. I lucked into a few pieces of 4" and 5" for 10 bucks a length. So with a guy here at the exhaust shop and some horse trading... . I will be in it about that or less. The only cost on top of that is the aero-turbine muffler I want that will be another 125.

 

[GiesJ]

Kevin Arts mentioned that at our altitude (Rocky Mountains) he saw some laggy-ness. I'll do a search tonight and see if I can find those posts. What Altitude are you at in UT?

Jason

 

[GiesJ]

Here you go - not trying to muddy the water, just some things I remember reading:

https://www.turbodieselregister.com/forums/showthread.php?threadid=54186&highlight=exhaust



https://www.turbodieselregister.com/forums/showthread.php?threadid=37233&highlight=exhaust



the second one is quite interesting. Good luck,

jason

 

[RussW1911]

Which side of the fence?

GiesJ,



Those are some interesting posts. You get to see both sides of the fence. My problem is that they all just go back and forth.



I am at 4906 in elevation on my GPS. Give or take 10 feet I should be able to go with a 4" down pipe and a 5" tale end. Atleast that is what I am hoping. When I get the whole thing done I will post on here to let ya know what I find. I am trying to do my truck a peice at a time so I can see where I get performance and mileage gains..... besides its easier on the wallet and the ears (i. e. my wife) to take it a bit at a time. Thanks again GiesJ

 

[Hohn]

Theoretically, your exhaust can never be too big.



But you have to keep in mind that flowing air does NOT like change. So if you run a big pipe, you have to transition to that diameter slowly. If someone slaps a 5" downpipe on a stock turbo, you can totally expect to lose spoolup and power. The rapid expansion causes a restriction. The gases cool and slow down, making them tougher to move and this causes restriction.



Now if you upgrade that turbo and the outlet is larger, then a larger exhaust will benefit you more.



Ideally, the downpipe and the turbine outlet would be the exact same diameter for a bit, then transition slowly to larger pipe.



I would say to think of a Meg's exhaust tip for how you want your transition to look like-- a nice gradual cone.



Look closely at the Magnaflow systems. Magnaflow is one of the most highly respected names in exhaust engineering. Their system uses a smaller downpipe, THEN transitions to full 4". There is definitely a reason for this.



While all the guys spouting compressor theory are correct about the delta enthalpy, you have to remember that we don't have a turbine engine!



We have a PISTON engine with a turbo attached. As such, you can't disregard NA flow theory completely. The Pulsed nature of the flow in the exhaust (while less than an NA engine) is STILL there, albeit reduced by the turbine.



Also, keep in mind that a certain "IDEAL" exhaust is a compromise. Want the best spoolup? Be prepared to sacrifice peak EGT. Want EGT control? Understand your spoolup will be reduced. Sound familiar (turbine housings)?



Also, understand that as machines constantly in transition (fueling, timing, load, airflow) our engines determine that ANY and ALL exhaust systems are only "ideal" for a very limited range of conditions-- all else is a gross compromise.



Justin

 

[Forrest Nearing]

actually a drastic change in size directly after the turbine HELPS to break up the swirling down the downpipe... this is also why you often see a tight 90* bend right after the turbo on many cars, even when one is not necessary...



lots of times you'll see cars with a 3" downpipe and 2. 5" exhaust... right after the turbo, the gas is swirling around the outside of the pipe (think of water going down a drain) and it can get backed up. an instant jump in diameter helps to break up that swirling effect and increases flow and shortens spool up time.



Forrest