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Discussion Starter #1
I've got a question on puting straight pipe on our DMAX's, I was talkin with a guy yesterday who owns his own "Performance Diesel" shop here in "Titletown,WI" about straight piping my exhaust. He strongly recommended me not too. He said he would recommend leaving the exhaust stock before using straight pipe! He made the comment about using straight pipe the exhaust is too free flowing and that the engine needs to have some back pressure, and wanted to sell me a system for a mere $695.00. Now the system he wanted to sell me was a 4" with a straight thru muffler. Wouldn't that system flow just as much exhaust as a straight pipe exhaust?
So now I'm feeling kinda
about the whole exhaust thing!! He also mentioned that using straight pipe could cause the turbo to cavitate!! Now I'm no diesel mechanic, but I'm no dumdie either. Sooo is any of this true or is this guy blowin smoke up my A$$? I know several of you guys are running straight pipe and I'd appreciate any help/info on this matter. Also some have had ?? on where to find pipe to do this, and what I have found is if you go to a "Big Truck" dealer Kenworth,Peterbilt,Mack, etc...I found the Packer City International dealership very helpful here. they have 3 1/2" stainless flex pipe (which we get 500,000 miles out of on a Big Truck ) for around $14.00 ' and band clamps also. So I can get all needed parts but don't know what to do!!
Thanks for any info in advance!!
 

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Find a new exhaust guy. He was blowing smoke up your butt and it wasn't diesel fumes.





Straight pipe it if you want, no problem if you like the sound.
 

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More free flow is more mo jo!
 

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Diesels do not need backpressure. More flow more power, cooler egts.
 

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The engine doesn't need any back pressure from the exhaust, the turbo makes plenty. The turbo wants as little back pressure as possible so it can spool up quick and the gasses move away quicker keeping the heat from building up as much (lower EGTs). I drove Mavs truck a while back, and let me tell ya the straight pipe doesn't hurt it! I suggest that you go for a ride in a strait piped truck first to make sure you like it. If that's not an option, cut the muffler out in a way that you can get it back in, or a performance muffler in there. I think Tomac posted what all is involved with a flowmaster on the page.

Hope to help,

Ox Edited by: BlueOx03
 

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Discussion Starter #6
Thanks much for the info!
I'm goin to check out "Jegs" to see if they carry any Race mufflers that have 3 1/2' in/out nipples, I had a 92 GMC w/ a 6.2 diesel and ran straight pipe for about 6 months...It sounded great but at 75 mph the dreaded droaning sound in the cab about drove me nuts!! So then I had true dual exhaust put on w/ glass packs and it sound real good also!!.... So I think it's time to play w/ my exhaust, Thanks alot for your help!!
-Jammer
 

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Why not start with a straight pipe and add a muffler if you don't like it. A piece of pipe to replace the existing muffler will be cheaper than a replacement muffler and since your not increasing the exhaust system size you might not want to add any extra restriction.
 

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Discussion Starter #8
Thats true, Good way to start, I just got off the "Jegs" web site and they carry race mufflers w/ 3 1/2" in/out for only $35.00 which would flow as well as a diesel flowmaster or anything of the sort. so if the straight pipe is too loud I'd have an easy fix.
without a flowmaster price tag, I've had Dynomax mufflers B4 and I would recommend them to anyone.
 
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