Difference between 3.5" & 4" down pipe??
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Postmaster
Joined: Jul 2006
Posts: 3,754
Likes: 1
From: Indianapolis
Difference between 3.5" & 4" down pipe??
I am currently running a Magnaflow 3.5" downpipe to a 4" straight pipe. My question is, being I have an early 99, is it even worth it to put a 4" down pipe on for about $100 or so? Will I gain a decent loss in EGT's, or my wallet??
Post Fiend
Joined: Feb 2006
Posts: 11,892
Likes: 2
From: Middle Tennessee
I'm not sure Danny. Does your current 3.5 DP neck down from the flange to meet the 3.5 pipe you have now? IOW, what size flange is on the turbo? If it is a 4" you ought to benefit some. I say bigger is better. Even 1/2 inch right there allows the gas to expand that much more right after the turbo. Expanding gas=cooler, compressing gases heat up. Blah Blah. Not sure what the benefit to $ value is though.
Last edited by Tenn01PSD350; Apr 17, 2007 at 01:28 AM.
Senior User
Joined: Jul 2003
Posts: 491
Likes: 2
From: Spicewood, TX.
Some people say you will lower your EGT's, I believe the turbo housing matches with the 3.5" better then a 4".. I also believe you will push your max torque figure further up the RPM scale..I have had both on my 7.3 and I only do/use the 3.5" unless someone has an EGT problem, or is over 400HP..
If you need the EGT's lowered then you might consider it. The exhaust system you have is one of the best and I wouldn't mess with it, you have better things to spend your $100+ dollars on..
If you need the EGT's lowered then you might consider it. The exhaust system you have is one of the best and I wouldn't mess with it, you have better things to spend your $100+ dollars on..
Hotshot
Joined: Nov 2006
Posts: 11,286
Likes: 263
From: North of Greenville
Just a technical detail for hte back of everyone's mind.
The 4-inch pipe, in comparison to the 3.5-inch pipe, will provide a 31% increase in "area", which also translates into a 31% decrease in gas velocity. The lower velocity provides a small amount of time for additional cooling, but the amount of improvement is proportional to the length of pipe. Therefore, even if there are no EGT problems, there will still be the same "percentage" gain in cooling, but because the EGT values are already not a concern, the real benefit may be very small. On the other hand, if EGT's are very high, they will be reduced by the same percentage, but the actual change in absolute temperature will be more noticable because it is a ratio of a higher value to begin with.
The 4-inch pipe, in comparison to the 3.5-inch pipe, will provide a 31% increase in "area", which also translates into a 31% decrease in gas velocity. The lower velocity provides a small amount of time for additional cooling, but the amount of improvement is proportional to the length of pipe. Therefore, even if there are no EGT problems, there will still be the same "percentage" gain in cooling, but because the EGT values are already not a concern, the real benefit may be very small. On the other hand, if EGT's are very high, they will be reduced by the same percentage, but the actual change in absolute temperature will be more noticable because it is a ratio of a higher value to begin with.
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Elder User
Joined: May 2002
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From: Robbinsville NJ
Originally Posted by greagin
how much louder is your truck without the muffler? just curious.
www.milchman.us/nomuffler.wav
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Postmaster
Joined: Nov 2003
Posts: 3,595
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From: Utah County, UT
If it works why mess with it. If I was ordering again, went with MBRP 4" turbo back, I'd probably order the 3.5" DP as it would be just a little easier to instal for clearance. I have also heard that 3.5" doesn't move the torque curve as much. But when you click to the 140 setting, who needs torque down low anyway?
Senior User
Joined: Mar 2007
Posts: 491
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From: Kingsland, GA
You will not see a 31% decrease in temperature. The laws of thermodynamic will tell you that. What is not factored in is the heat transfer curve of the metal and ambient temperature of the environment, heat transfer of the turbo. Just the make-up of the exhaust gas as far as difference of the air changes the heat transfer rate. Anyway, even after studying thermodynamics, I can tell you how much percentage you could lose. BTW I'm not trying to get in a pissing contest.