Straight pipe straight dope?

[Jones]

Hey guys,
Well I'm thinking about a straight pipe for this Ramcharger of mine, but I've got a little problem. The absolute largest pipe I can get past my NP205/frame rail/cross-member pinch point is 3" which means 3" all the way out still sounds a little nasal and higher pitched than I'd like. 4" or bigger is only possible from the cross-member back and where do I find some body who can mandrel bend 4" in the sacramento area?
And won't cost me an arm and a leg. Any thoughts/suggestions would really be appreciated.
Jones

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Jones
'84 Ramcharger w/CTD, non-gated 12, torqflite, NP205, Dana 60 and 70 w/ 3. 07s. Looks more or less stock, definately doesn't sound stock.

 

[Cooker]

The shops around here don't actually bend the pipe they just weld up elbows and straight pieces of pipe. Maybe you can locate some pipe and elbows and have the shop weld it up for you. Also check at some big rig shops (Kenworth), they might be able to help you.

 

[R.E. Miller]

How about a single zoomie through the hood #ad
, blue flame and all #ad
?

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1992 W-350 Club Cab Dually 3. 5" straight pipe(thanks jardine!)
W-350 8' contractors dump with 3. 5"BD exhaust, 16cm^2 housing, DI pyro&boost
Russell

 

[DJP]

I use to have my exhaust straight piped, but now have a performance muffler installed instead. Flowmaster muffler claims better exhaust scavenging with their muffler installed, than straightpiped (no muffler).
I recently installed a muffler very similar to the Flowmaster, but at a fraction of the cost. I can honestly tell you I now have better mid range performance with this muffler than when it was straight piped. I also don't get the dirty looks from the neighbors anymore!

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89 D-250 LE 5 speed 3. 55 Limited slip, Banks Intercooler, K&N, Full Boar Muffler, 3" exhaust, Diesel Dynamics Stage 1 kit, Boost/Pyro. & 16cm2 215K miles.

 

[ScottB]

Please explain to me how a muffler with weird little plates and baffles in it can "scavage" exhaust. I to have heard this but would love to have it explaned.

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93 W350 5spd White 3. 54 gears 4" stack Powerwagon Injectors. Headache rack with lights. Cummins Mudflaps. 2" lift on seat. Goosneck ball Beefed up reciever. Fog lamps, Back up lights. CB 98 Factory sound system

 

[Jones]

Yeah Scott, I know what you mean about it not making sense. It has to do with getting
the exhaust gases cooled/slowed down and close to atmospheric again. Less differential, less noise. Supposedly at some point you can actually create a vaccuum like with a venturi. If this could be repeatedly done you could actually get the exhaust gases to "pull themselves out by their own boot-straps" but there's a lot of variables that tamper with the equation. at least that's what I picked up from all those "Watch Mr. Wizard" shows I watched as a kid.
Jones

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Jones
'84 Ramcharger w/CTD, non-gated 12, torqflite, NP205, Dana 60 and 70 w/ 3. 07s. Looks more or less stock.

 

[DJP]

I looked at the muffler before it was installed, and I could see straight through it. The muffler inlet and outlet are offset about 4" from each other, but other than that, there was really nothing to restrict flow. I don't know how a muffler can scavenge exhaust either, but all I can say is this muffler works better for me than a straight pipe. I still get the deep throaty diesel sound, but without the tinny, ratty noise.

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89 D-250 LE 5 speed 3. 55 Limited slip, Banks Intercooler, K&N, Full Boar Muffler, 3" exhaust, Diesel Dynamics Stage 1 kit, Boost/Pyro. & 16cm2 215K miles.

 

[unclebilly]

Ok, Ok so if the gas cools, it becomes more dense, concequently more viscous and harder to push through the pipes. For 2 cycle diesels and gas engines, back pressure is desired but for a turbo charged diesel, you want as little back pressure as possible. I think my stacks actually help the exhaust out because the system is bigger at the cold end of the system and allows the hot gasses to rise - thus "creating a vacuum" - somewhat.



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91. 5 CTD 4X4, 5" Stacks, Tweaked Pump, 33" Boots (in the summer), Unlimited Slip,
<P><B><A Big, Bad Dodge

 

[R.E. Miller]

Now I feel green, I just straight piped my truck with a jardine kit and a leftover piece of pipe from my BD exhaust. The muffler that came with there kit looks sweet it is straight thru, and I mean straight thru! Now I knew that this fact of more power was available with a muffler, but you guys just had to start up on this days after I completed this job #ad
. Oh weeeelll, still have it maybe later.

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1992 W-350 Club Cab Dually 3. 5" straight pipe(thanks jardine!)
W-350 8' contractors dump with 3. 5"BD exhaust, 16cm^2 housing, DI pyro&boost
Russell

 

[Jones]

Well yeah but, in addition to getting denser the gases get "smaller" if you shrink something then the space it used to occupy becomes the partial vacuum that the hotter gases upstream try to rush in and fill. You're right though Uncle Billy, like I said there's a lot of variables that like to get in and mess with the "perfect equation".
I think I read that in "The dynamics and thermo-dynamics compressible fluids" about a jillion years ago.
Jones

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Jones
'84 Ramcharger w/CTD, non-gated 12, torqflite, NP205, Dana 60 and 70 w/ 3. 07s. Looks more or less stock.

 

[PHaller]

Wait a minute, did I miss somthing? I thought that exhaust gasses are compressed and hot as they exit the cylinder. Remember 17-1 compression? They then cool as they travel down through the turbo and down pipe and expand. They don't get smaller and more dense as they cool!
-Paul R. Haller-

 

[R.E. Miller]

Gases that are heated expand, the atoms move and bounce around faster. Cooling gases slows down the atoms and the gas takes-up less space. The case maybe that the gases do cool as the exit the exhaust manifold and the gases now fill a larger space, but I do not think that they expand #ad
feel free to correct me if I'm an idoit #ad
.

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1992 W-350 Club Cab Dually 3. 5" straight pipe(thanks jardine!)
W-350 8' contractors dump with 3. 5"BD exhaust, 16cm^2 housing, DI pyro&boost
Russell

 

[unclebilly]

Jones and Mr Miller are right, I don't want to get into perfect gas law here but basically pv=nRT

pressure X volume = number of moles X universal gas constant X temperature (in Kelvin, the gist is as the gas cools, under constant pressure (like in an exhaust system assuming a low flow rate (flowrate<<Mach number of gas)) it takes up less room.

1 more thing must be considered...

bernouli's equation: p1a1v1=p2a2v2

this states that pressure, area, and volume at one point in the system must equal pressure, area, and volume at another point. Assuming once again, constant pressure for a straight pipe system, your gas velocity will be purely a function of cross sectional pipe area. With a stacked truck, the hot gasses expanding out of the top (to a lower environmental pressure -this gets somewhat more favorable with height) will tend to increase the velocity of exhaust in the exhaust and create a slight amount of suction. This is evedent when my truck is not running on a cold day, the hot gasses and vapour continue to come out of the stacks for 5 or so minutes after I shut it off as the exhaust system cools.

I didn't want to get into a lecture but...

Scott.

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91. 5 CTD 4X4, 5" Stacks, Tweaked Pump, 33" Boots (in the summer), Unlimited Slip,
&lt;P&gt;&lt;B&gt;&lt;A Big, Bad Dodge

 

[Racer Brown]

Hummmmm! Let's see. Mufflers=performance? And how many racing applications, diesel or otherwise, run mufflers? Sonny Leonard doesn't use them on his Mountain Motor Pro Stock engines. Gene Fulton doesn't use mufflers on his Pro Modified engines. In the Pikes Peak diesel truck race, I didn't see any mufflers on those trucks. Stacks yes, (but not on all of them), mufflers no! In all the racing applications that I know of, with the exception of the required mufflers that NHRA has on Super Gas and down because of noise problems at it's tracks, there aren't any mufflers used! And as one of the other posters said, "you can correct me if I'm wrong on this"!
I've run tests with my car, (URL in the signature), and found that even a racing muffler like the Super Trapps that I run (and they are "tunable") will slow the car down! So, having said all this, I don't see how mufflers can make more flat out power. ANY INTERNAL COMBUSTION ENGINE IS NOTHING MORE THAN AN AIR PUMP! Air in, air out,=power! MORE AIR IN AND OUT = MORE POWER! It's simple physics. Racer

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Ken-1993 W350, Cummins TD, 5 Speed, 4X4, Club Cab, LE, K&N, Straight Pipe. http://users. lynchburg.net/ken0069

[This message has been edited by Racer Brown (edited 02-27-2001). ]

 

[Jones]

Sounds like I really started something out there and from the replies I think I'm running with some pretty edi-cated people. All I'd like to say is thanks for all the great input and I WAS the one who said I was considering straight-piping this thing to begin with. You guys just confirmed my thinking.
Jones

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Jones
'84 Ramcharger w/CTD, non-gated 12, torqflite, NP205, Dana 60 and 70 w/ 3. 07s. Looks more or less stock.

 

[CrewCabDiesel]

You guys got me all confused with this high brow tech talk. All I know for sure that without a muffler on a 3" exhaust that
1. I am getting 26 lbs of boost with no trailer and mostly stock settings/timing.
2. my truck sounds great going down the road.
3. I have fun setting off car alarms #ad
.
Kyle

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1985 DODGE 1 ton Crew Cab(imported from California with no rust) W/8' box converted to 4X4 in 1999. Converted to a non-intercooled 1991 Cummins Turbo diesel & rebuilt 5 speed Getrag in 2001(wife can't drive a stick . Freshly rebuilt and Balanced Cummins, Rebuilt NP205, Rebuilt Injector pump and tweaked, Matched Injectors, 3" New Mandrel Bent Exhaust,no muffler, Borgeson Steering Shaft, K&N Air Filter, 4:10 gears, limited slip rear end, 16" Goodyear GSA Wranglers, 16K Reese 5th Wheel Hitch,and LE Package and a Sony CD Stereo. Next add-on some “Banks” toys ! If you want to know why I did all of this, 2 kids, one on the way and I can't stand F**d and Ch**y. Kyle Hoover ,Fruitport, MI.

 

[R.E. Miller]

Ha ha ha I'm right there with you CrewCabDiesel, minus the boost #ad
It is hard for me to want to try out the muffler, when it sounds so good!

 

[drives mopars]

i found a new use for my MUFFLER!!!!!!!

its in the box it came in(banks) may make
good mouse tunnel!!!!

ive even thought about tape recording the
noise from exaust pipe and playing it as i drive. this way when cold i dont have to roll
down the windows. and with head phones
the wife willnot get mad. or want to take her punny grand prix

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1993 w350 ex cab, banks,nv 4500 in
open exaust, pw Injectors are in. Big rig flaps,tach in,. Its loud and goes ok, for a 93,Ham radio Call KK6dm
has ability to communicate any where in the world. Headliner shelf
5 antenna's