Switched downpipes

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Oct 9, 2007 | 11:51 AM

bartender

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Joined: Aug 2003

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From: West End NC

Switched downpipes

I switched to a 4'' dp from a 3.5'' dp. I mainly wanted a little better cooling. I went with the 3.5'' dp because on this forum, many years ago, I read that a 3.5 '' gave a little better low end power on a lightly modified engine. From the seat of the pants dyno, I would say that this is a true. It feels like I have lost just a bit of low end grunt, but not enough to worry about. On the other hand, it seems to spool up a little faster and I know it has to be cooling better. I have to tap the manifold for the egt probe this weekend. I was lazy before and just used the one on the dp before. The only other negative that I have seen so far, is there seems to be a little more exhaust drone than before. The mods I have are: Micro-tuner, 4'' exhaust, ais intake, and the zoo-dad mod. I have tried a Jody chip, however, it did not work for me. My hpop may be a bit on the weak side. I have just over 100k on my 03', cc, long bed, 4x4. Has anyone else switched dp before? I would be interested in hearing about their results. Later, Jonathan

Oct 9, 2007 | 12:03 PM

Izzy351

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Joined: Feb 2007

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From: Dallas-Ft. Worth

From what I understand, smaller downpipes = HIGHER EGTs, not lower. Maybe I'm wrong here, but more restriction at the turbo outlet will get it spooled faster (hence the idea behind the wastegate!!), but I have never hear of it going the other way. And I'm a little confused -- usually I hear about losing a little on low-end with a bigger exhaust, unless I'm misunderstanding what you're getting at by "losing low end grunt" vs. "better low end power" (you stated both). Without a pyro, you really can't know that it's cooling better, so it might be worth trying both pipes again after you get it in.

I hate to put it like this because it sounds bad, but almost everything I know is the opposite of what you posted, even about Jody's chip. I'd like to know what didn't work out for you though, just for curiosity sake.

Joe

Oct 9, 2007 | 12:57 PM

7.3L DID TD

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From: Cincinnati, Ohio

I too have a 4" down pipe and a lot of drone, and I actually don't like it, but oh well, I just turn up the radio and the cars next to me roll up their windows.

Oct 9, 2007 | 01:27 PM

DieselCamper01

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Joined: Mar 2007

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From: BLT, MN

If I read this correctly Bartender, you switched from a 4" to a 3.5" back to a 4"?
After going back to 4" the low end power seems less but spools better since switching
from 3.5"?

Oct 9, 2007 | 01:30 PM

F250_

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Joined: Nov 2006

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From: North of Greenville

Hey, Joe... re-read his post. I think your confusing his observations with the 3.5" DP in comparison to what he's now getting with his new 4" DP. I had to read it twice myself to get it straight, but I believe his observations are consistent with your explanation... he just sort of did a "reverse" comparison.