Weekend project: M931A2 straight pipe

[MO MV man]

After reading all the posts about straight pipes, hearing the faint whistle of the turbo in my truck (and vivid memories of my old whistler turbo deuce....) and knowing the "cork" the stock muffler undoubtedly is in the exhaust, I dug around the garage, found a couple old 4" mandrel bends from projects years ago and a friend had a piece of 4" straight for free.
About 4 hours of work on Sunday in the driveway and I've totally changed the personality of the truck.
My original muffler had a leaking rust crack about 1.5" long at the bottom (could smell it in the cab, undoubtedly where moisture has sat) and it was VERY rusty.
What better excuse to ditch that thing and get to the straight pipe!
I was able to salvage the lower V-Band clamp arrangement from the muffler and welded it to the bends and straight that then connect to the original stack (I like the original look). The original stack/upper V-band clamp was beyond saving, rusted away.
Wanting to preserve the original look as much as possible, I maintained the muffler heat shield and painted the whole pipe with flat black heat paint on the bottom and camo black on the top.

Folks, I can't say enough how it's changed the entire personality of the truck.
Yes, it's louder than stock, definitely in the cab. But FAR from LOUD and stock is almost silent, after all!
The first person who'd be all over the noise like flies on stink would be my better half if it was too loud.
So I laid into the throttle a little on it's maiden voyage as I left the house and asked her how it sounded when I returned.
"Sounded good! Nope, no problem". Sweet!
A lot of the noise could be redirected with a change in upper stack configuration; maybe pointing straight up (with a flapper?), or up with a bologna cut or.....

It feels SO much smoother getting up to speed now. Not "laboring" whatsoever.
The biggest tell-tale was how it seems to go through the gears at such a faster rate and pulls and pulls.......

I can only imagine what a few turns of the fuel screw would do in addition to the stack. Whew!

I love this truck.

 

[machinist75]

I put a straight pipe on my nhc 250 powered 923 and boy was it loud. I ended up putting a small off road muffler to tone it down just a tad.

 

[MO MV man]

Turbo's are a "muffler" of sorts on their own.
Without a turbo between the exhaust port and the outlet of the stack on your NHC, I bet it was loud!

Speaking of turbo......the whistle of the 8.3 in my truck is incredible with the straight pipe.

If I want to change the noise in the cab, it's just a matter of rearranging the stack outlet to direct the noise upward.
Right now? I'm basking in it.

I put a straight pipe on my nhc 250 powered 923 and boy was it loud. I ended up putting a small off road muffler to tone it down just a tad.

 

[DIndFab]

Has anyone ever run the 8.3 cummins with a hood stack? I think a large dia. 24" high flat black would look nice on an m939 series.

 

[61sleepercab]

You would be surprised what a difference a dirt tract race car header muffler makes on a loud open header car. They are straight through and various lengths and diameters.

 

[redneck20]

I put a straight pipe on my nhc 250 powered 923 and boy was it loud. I ended up putting a small off road muffler to tone it down just a tad.

I love the straight pipe on my Nhc 250, I ran a full 5" exhuast, I wanted to match the size of the intake for looks.
It really isn't too loud. I can tolerate it around town without ear protection it wear it on the freeway

 

[MO MV man]

I think I left enough straight in my design to splice in a straight-through, small bodied muffler if need be.
On my old deuce, I used a Donaldson industrial muffler.

You would be surprised what a difference a dirt tract race car header muffler makes on a loud open header car. They are straight through and various lengths and diameters.

 

[MO MV man]

Update:
I talked to a few folks in town over the past two days that I drove past or stopped in to visit while I had the truck out the other day for it's stack "maiden voyage" about how loud the truck is and their opinions. None of them had anything bad to say.
The reason I contacted them is because since it is louder in the cab, I wanted to make sure the locals wouldn't throw a fit and have the local deputy waiting for me some day.
Success!

 

[74M35A2]

Wanting both, I just ordered a 4" electric cutout and stainless Y pipe from DMH performance today for my M925A2. Valve will go below passenger door, with a short piece of stainless pipe to route the diverted outlet to the edge of the door. Stay tuned....literally.

 

[MtnSnow]

I'll be watching for your update on the E-cutout!

 

[DIndFab]

Electric cutout will be awesome!

I know that some companies make manual cable actuated cut outs as well.

 

[MO MV man]

Looking at another post by 74M35A2 on another thread, he may be building an eighth-mile drag racing capable 5 ton!

Open that cutout and leave anyone in the lane next to you in a smoke screen!

 

[NJDEUCE]

I just fabbed up a straight pipe yesterday. I cut the flanges off the muffler and re-welded them onto my new pipe. The new stack is the same length and offset as the muffler, so it still will look stock. Does anyone know where to find the 4" U-bolts that hold the stack up? Mine were rusted, so I torched them off.

 

[jarhead1086]

I have been wanting to go straight pipe to the rear so when I start it in the garage it blows out the open door as well as for the reduced restriction. I am hearing rumors of mandatory emissions and having mufflers required on diesels for Northern Utah guys like us Mntsnow. I would hate to buy all that stainless and get nailed on inspection. I have the 250 so going to the rear exhaust without a muffler will be obnoxious to the people on my 6 until I could get to the dirt where I belong.

 

[MO MV man]

Mine were in fine shape so I reused them.

But as I during my build process, the clamps looked like very "standard issue" 4" exhaust clamps that I'd THINK you could pick up locally, if not from mail order for sure.

Here's an example: http://www.summitracing.com/parts/wlk-35752/overview/

I just fabbed up a straight pipe yesterday. I cut the flanges off the muffler and re-welded them onto my new pipe. The new stack is the same length and offset as the muffler, so it still will look stock. Does anyone know where to find the 4" U-bolts that hold the stack up? Mine were rusted, so I torched them off. View attachment 487585View attachment 487584

 

[NJDEUCE]

Yeah I did end up finding them at my local big truck parts store. I just bought the only two clamp kits they had. Man the truck sounds mean now, not like the deuce, but much closer.

 

[MO MV man]

Glad you got the clamps!

Speaking of sound.....my brother said mine sounded a LOT like my old whistler deuce used to.
Glad to hear that!

I didn't want something obnoxious and OH how I loved the sound of that whistler.

 

[NJDEUCE]

It's nice getting more of the turbo sound. Amazingly, I think the truck is almost as quite at idle as it was before, but accelerating is a different story!

 

[MO MV man]

Yessir, you hit the nail on the head with that statement!