4" or 5" exhaust? 3.5" or 4" downpipe? - Diesel Truck Forum - TheDieselGarage.com
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post #1 of 21 (permalink) Old 09-19-2005, 03:24 AM Thread Starter
 
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4" or 5" exhaust? 3.5" or 4" downpipe?

Hi all. Nice site you have here. I mostly lurk and try and learn from all of you.
Okay, here goes. My truck is an '05 for starters and totally stock for now. For my first mod I'd like to do the exhaust and then a module or programmer in the future. I'm not looking for extreme hp gains as I want to avoid puking as much as possible. Thinking about the Quad XZT module but if the dealer I'm going to tomorrow doesn't mind mods I might get a programmer instead.
Now that thats out of the way! What size exhaust is going to show the most power gains? Would a 5" system be overkill and not produce anymore power than a 4" system with a moderate program? And of course, noise is a concern. Too loud and the wife might get mad!

:thanks:
Sydwaiz
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post #2 of 21 (permalink) Old 09-19-2005, 03:40 AM
 
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Programmer is a much better solution since it has complete control over the trans. No matter what power level you choose the trans should be controlled. Letting the pcm compensate for the extra power is no where near as good as mofifying the trans control tables in the computer. 5" system is overkill and is also not made in stainless steel. Aluminized steel readily radiates heat from it, so using that pipe in a turbo diesel application will allow it to cook anything near by. Stainless steel keeps alot more of the heat inside the pipe where it belongs. A 3.5" downpipe is fine since the outlet of the turbo is only 3.5 inches. Going to a 4" downpipe will result in a slight loss since the factory programming looks at exhaust backpressure and adjusts the Variable geometry turbo. When is doesn't see backpressure it opens the vanes and will cost you some low end, but this can be compensated for with an SCT. A magnaflow system isn't too loud until you get on it and then it makes a mean growl thats not over powerful.
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post #3 of 21 (permalink) Old 09-19-2005, 05:07 AM
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Here's my $.02 and its what I've learned from this site and others........so I don't have first hand knowledge of a 5" exhaust.

If you're not going crazy with hp, a 4" exhaust will suit you just fine. The sound of a 5" is certainly different and a lot of people like it. I haven't heard one yet, so I dunno.

3.5" or 4" downpipe? I just put a 3.5" in my 05 and it was a TIGHT fit. If you want a 4" dp, there's a 90% chance you're going to have to mod your firewall to make clearance. To me, it wasn't worth the time/effort to make clearance for the 4" dp and my understanding is that the gains will be minimal. Gains being better flow and lower EGT's.

About your noise and keeping your wife happy---I'd recommend checking out MBRP exhausts. They give you the option of deleting your cat and your muffler. The pipes are $40-$50 and if its too loud, you can swap your cat, your muffler, or both back in.......in about 30 min with hand tools. I'm running the cat delete (MBRP calls it a "cat test" pipe) and the muffler delete and have been very happy with the way my truck sounds. Not too loud at idle, some nice turbo whistle, but if you get on it, it really rumbles.

--Snake
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post #4 of 21 (permalink) Old 09-19-2005, 05:21 AM
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I have a 4" system now with a 3.5" DP...It sounds awesome....but I love the massiveness of a 5" system...I'll be picking mine up tomorrow.
I figure I'll lose a bit down low.....but I also figure I can afford to lose a little....so no worries.
If it sounds as good as it looks I'll be extremely happy.
I think I'll be keeping my 3.5" DP though....and welding it into the 5" system myself....I don't feel like messing with a 4" DP.
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post #5 of 21 (permalink) Old 09-19-2005, 09:35 AM
 
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I'm running a 5" exhuast and wouldn't have it any other way. Not exactly sure if it is a 4" dp or 3.5". I also have no cat and no muffler and I like the sound more. There will be pics in my garage shortly. The SCT will not only control the trans, but also, they seem to be very good at controlling cylinder pressure and reducing puking. Check the vendors on this site. They are all helpful and will get you pointed in the right direction.
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post #6 of 21 (permalink) Old 09-19-2005, 06:25 PM
 
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Quote:
Originally Posted by Snake
Here's my $.02 and its what I've learned from this site and others........so I don't have first hand knowledge of a 5" exhaust.

If you're not going crazy with hp, a 4" exhaust will suit you just fine. The sound of a 5" is certainly different and a lot of people like it. I haven't heard one yet, so I dunno.

3.5" or 4" downpipe? I just put a 3.5" in my 05 and it was a TIGHT fit. If you want a 4" dp, there's a 90% chance you're going to have to mod your firewall to make clearance. To me, it wasn't worth the time/effort to make clearance for the 4" dp and my understanding is that the gains will be minimal. Gains being better flow and lower EGT's.

About your noise and keeping your wife happy---I'd recommend checking out MBRP exhausts. They give you the option of deleting your cat and your muffler. The pipes are $40-$50 and if its too loud, you can swap your cat, your muffler, or both back in.......in about 30 min with hand tools. I'm running the cat delete (MBRP calls it a "cat test" pipe) and the muffler delete and have been very happy with the way my truck sounds. Not too loud at idle, some nice turbo whistle, but if you get on it, it really rumbles.

--Snake
Im kind off wondering why people would go to the trouble of putting in a 3.5 in. downpipe when that is what they come with from the factory, Im not being a smart a-- I would like to know your thoughts...
j.schall
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post #7 of 21 (permalink) Old 09-19-2005, 07:19 PM
 
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It's 3 inch from the factory.
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post #8 of 21 (permalink) Old 09-19-2005, 07:26 PM
 
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I must be doing the math wrong my old oem dp out in the barn has a 9.75 inch circumfrence... I need to look up the formula again perhaps i used the wrong one..Psd your a walking treasure chest of info...Thank you..
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post #9 of 21 (permalink) Old 09-19-2005, 07:33 PM
 
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9.75 divided by PI. The math symbol not the pilot injection. 9.75/3.14 is 3.1 inches. But since we know the outlet is 3.5 and you see the pipe neck down just after the V-clamp i call it 3 inches but who knows maybe its all Metric. Maybe its a oh dear god 76mm pipe.
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post #10 of 21 (permalink) Old 09-19-2005, 07:39 PM
 
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Yep found it C=2pieR comes to 3.1 but does that .4 gained worth the trouble, I have the 4in. magnaflow system and love it and I did not have too alter my firewall to get her in and it does not touch either..
my 2 cents..
j.schall
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