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-   -   Straight pipe exhaust (http://www.jeepgarage.org/f222/straight-pipe-exhaust-73683.html)

Evolv0 04-04-2014 05:18 PM

Straight pipe exhaust
 
Has anyone done this yet on their Diesel? I know some people have put the magnaflow on and there was no sounds difference. So why not go all out and put a straight pip on her right after the DEF/CAT ... I really wanna hear what these trucks sounds like with some roar!

ExcursionDiesel 04-05-2014 01:55 PM

Re: Straight pipe exhaust
 
Quote:

Originally Posted by Evolv0 (Post 1003617)
Has anyone done this yet on their Diesel? I know some people have put the magnaflow on and there was no sounds difference. So why not go all out and put a straight pip on her right after the DEF/CAT ... I really wanna hear what these trucks sounds like with some roar!

Someone has done this and reported very little difference. The DPF is restrictive enough that any improvement downstream is of little value. The MagnaFlow Cat-Back system was also reported to make very little difference in sound or performance.

Deleting the DPF, which requires the ECU to be reprogrammed, hasn't been done by anyone yet. That is the first step to higher performance IMHO.

racer-xerols 04-06-2014 01:53 AM

Re: Straight pipe exhaust
 
I've played with turbo (gassers) for years, and will say that eliminating the DPF/cat is NOT the "first step".

I have run an '89 Shelby CSX with a Garrett VNT25 turbocharger - the FIRST production VNT turbo like is used in the VM motor - since 1991 or so. I've run them stock. I've raced them. I've blown them up and rebuilt them. One thing I've learned over the years? DO NOT remove the cat, it acts as a backpressure-stabilizer. Removing the cat will remove ALL backpressure, and the VNT will lose the ability to control boost levels. My boost values are all over the map without a cat, no matter what I do to the programming.

The best performance I get out of any of my 2.2/2.5 turbo cars - wastegated or VNT - is a 2.5" mandrel single system, no muffler, WITH cat. But fact of the matter is...it's turbocharged. The turbo acts as a "muffler" itself - it's going to purr, not roar. That's the nature of the beast. Want something loud? Go buy a thirsty Hemi. Want performance? Diesels are efficient by nature...if you want to get more grunt, you have to change the whole SYSTEM - fuel, timing, breathing (intake/exhaust). I put a 4" Banks exhaust with power elbow on my '01 Cummins last year, not for "performance" but to lower my EGT's. And...it did. But it didn't turn it into a rocket - it's still a big honkin' diesel, and until I throw more fuel at it and change the boost curve it's not going to do burnouts. Which is fine with me - because even at 230k miles, it starts every time I turn the key and will pull anything I hook to it, and gets me 24mpg (once we get off crap winter-blend diesel!).

ExcursionDiesel 04-07-2014 01:07 AM

Re: Straight pipe exhaust
 
IMO needing back pressure on a turbo, especially a diesel, is a myth. However, maintaining proper boost on a gasser is important since the fuel mixture ratio must be right to avoid damage. Proper tuning with the least back pressure yields the best results but may be challenging on closed loop systems designed with cats. Gassers are way more difficult to tune with forced induction.

On diesels, air/fuel ratio isn't critical to engine health in the same way...especially in turns of lean burn. The best performance is always achieved with the least back pressure and the DPF is very restrictive. I run a 5" straight pipe with no mufflers on my big truck. Its not very loud under normal operation.

DPF removal as a first step is only in reference to exhaust improvements. A better intake might actually be better at this point since no tuning and method is available to defeat the ECU's regen process. Maybe we'll see some options soon with more VM3.0 vehicles on the road with the release of the Diesel Ram.

crabman 04-17-2014 10:11 AM

Re: Straight pipe exhaust
 
Hmmm, well I'm pretty sure that if you run stacked boxes, hone the injectors, install twins, 5" off the turbo all the way with no muffler, up rate the fuel system because you will get to zero fuel pressure if you don't, you will in fact exceed the sound volume of a jet taking off when on the dyno as measured with a decibel meter. :) Yes I'm evil and did those things. Also since I was leading the charge and among the very first I tested the limit of a stock clutch, lunched a transmission, blew the rail, head gaskets, lots of stuff. That part was less happy...

Anyhow I was down to Rips at one point and we installed a series of mufflers varying in size from small to massive 3 foot long suckers and also straight piped it both in 4 and 5" in each case and took decibel measurements along the way. Racer was right about that at least as it applied to a 3G Cummins, going from stock to straight pipe surely upped the ante but it was not nearly so much as expected. That was on a truck with no cat, no DPF. I'm thinking that as you gents surmised it wont be easy to get much volume on this car unless surgery is performed on the upstream exhaust along with the aid of burning more fuel.

I'm not going to mod this car since I share it with my wife and I'm not so old as I don't want to see her naked again but I'm a performance guy and I'll be curious to see what comes up now that the engine is hitting the trucks which I'm guessing will be a much more fertile market for performance mods.


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