2 down pipe Q's

[bioniccruiser]

the search function here is terrible! so sorry if this has been asked recently-

what is the ID of the stock down pipe?

for those that did 4" and 5" down pipes and exhaust, does it increase the cabin noise at all? if so, how much?

my old 7.3 w/ 4"DP was loud as hell. could barely carry a conversation at highway speeds. this engine is quieter already, but I'm curious.
trying to decide if I should go 4" or 5". I'm going full exhaust the same size when I do it (w/ deletes of course).
thanks.

Shawn

[08stroker250]

Stock is a dual walled 4" pipe that has an interior diameter of 3". So even though the factory downpipe may look like plenty, when you cut it open....you are VERY surprised to see how little space their is for air flow.

4" is the biggest that will fit, and is all that is really necessary in my opinion. I don't think we could really benefit much from a 5". No increase in cabin noise on my truck. If the downpipe fits properly (no rubbing), you should not hear any excess noise.

[bioniccruiser]

sweet, thanks! I'll likely go with a 4" all the way back then.

I have heard that by the exhaust opening up to a bigger diameter from a smaller one (like 4"DP to 5" exhaust) doesn't really help much because of the air swirls it causes along the sides increases friction/resistance, negating the benefit. or something like that. anyone else heard that? it makes a little sense. I know the concept of larger diameter makes for less friction since I am a firefighter and deal with these concepts in hoses with water, but we are usually going from larger to smaller and calculating the friction loss that way.

[08stroker250]

I have a 4" downpipe in to a 5" downpipe back exhaust. It's all for sound really. Beyond the 4" downpipe, there really is no performance gain.

[powerstroker67]

I've tried my F450 a few different ways and Jeff's right, anything larger than the 4" downpipe offers no performance gains. I think the best sounding setup I've run was one of our 4" downpipes connected to a 5" CAT/DPF delete pipe(one piece delete pipe) and that attached to a Magnaflow 5" DPF back exhaust kit WITH the supplied Magnaflow muffler. It had a very nice deep tone, not much change inside the cab for noise if the windows get up, and the muffler knocks back the turbo/hairdryer sound. Rubbing exhaust is the biggest issue for exhaust noise in the cab, and downpipes are the worst! Our downpipe fits like a glove, you won't be disappointed! As a note the 5" setup does have a deeper and IMO better sound than the same stuff in all 4". Let Aaron or I know if we can help you.

Sean

[bioniccruiser]

thanks for all the good info! I will be shopping shortly and will look at and/or call several of you guys that are vendors here. I will be looking at a full package most likely of turbo back exhaust, intake, tuner, intercooler elbow. I am still studying EGR delete stuff too and will probably include that stuff as well.

[Vettester]

What Jeff said about the double walled stock downpipe is the key. His setup 4" into 5" would be the optimal for a tuned engine.

[Redram99]

Originally Posted by 08stroker250

Stock is a dual walled 4" pipe that has an interior diameter of 3". So even though the factory downpipe may look like plenty, when you cut it open....you are VERY surprised to see how little space their is for air flow.

4" is the biggest that will fit, and is all that is really necessary in my opinion. I don't think we could really benefit much from a 5". No increase in cabin noise on my truck. If the downpipe fits properly (no rubbing), you should not hear any excess noise.

I always wondered why anyone would change out the stock downpipe.... looked like a 4" pipe to me but now I know its not truely 4"!!

they must have double walled it for noise reduction.

[bioniccruiser]

I would think heat first and noise second. I had seen a post about the F450's being double wall, 3" ID, but wasn't sure if the 250/350's were too. hence the question. glad it helped someone else too.

[powerstroker67]

Originally Posted by bioniccruiser

thanks for all the good info! I will be shopping shortly and will look at and/or call several of you guys that are vendors here. I will be looking at a full package most likely of turbo back exhaust, intake, tuner, intercooler elbow. I am still studying EGR delete stuff too and will probably include that stuff as well.

We have a EGR delete kit that just removes the coolers and doesn't include a wastegate. This is a great option of trucks not pushing the hp levels thats would require back pressure or drive pressure control. The kit installs without major work or cab removal. The short version to the install would be remove both EGR coolers, install plates(one at inlet to the first horizonal cooler and other at throttle/EGR housing in the engine bay. Then it's a matter of installing two coolant plugs(supplied in kit). All gaskets and orings are supplied for install. The great thing is by blocking the exhaust inlet down at the first cooler inlet you not having to work in the area behind the turbos and under the cowl or windshield. Give us a call when your ready.

Sean