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Tube size dual exhaust? |
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Gelalthedamned
AMC Nut Joined: Nov/28/2014 Location: Athens ga Status: Offline Points: 376 |
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Posted: Apr/08/2018 at 10:26pm |
So my 258 has had dual headers for 20 years, they’ve mostly spent that time “y”ed into a single 2”.
Had glasspacks under the doors the only time it’s ran duals, but that was very very loud. Presently I have a dual inlet/outlet muffler that’s 2.25 I’m gonna cram up in there. So, the question I have is pipe diameters? Keep 2.25 duals, get 2.0 cause there’s 2 of them? And, what’s this about stepping down a size at the exits, old wives tale? |
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Calamity - 73 Gremlin X zombie rod (daily driver)
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tached_out
AMC Nut Joined: Feb/08/2008 Location: Vancouver, BC Status: Offline Points: 328 |
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If the muffler mixes the two inlets inside, it should sound sweet.
I'd run 2'' tubing. Just expand it into the inlets and outlets. You can run a smaller outlet because the gasses have cooled by the time they get there, so they don't have the same volume. A lot of the sixes had a 1 7/8'' head pipe and a 1 3/4'' tail pipe or 2'' head pipes and 1 7/8'' tail pipes. But if you're thinking performance I'd size it the same all the way.
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farna
Supporter of TheAMCForum Moderator Lost Dealership Project Joined: Jul/08/2007 Location: South Carolina Status: Offline Points: 19610 |
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I wouldn't go too big -- because there's two now. For a street engine you need some back pressure at low speeds. Real big exhaust pipes only help at WOT. I'd run 1-7/8" or 1-3/4" duals on a six, but 2" pipe is going to be easier to get and get mufflers for. That dual in/out muffler sounds like a great idea. I'd probably run 2" in and out with it. The mixing will work like a X pipe or crossover -- will equalize pressure.
I suppose you know what that muffler came out of? If it's a Camaro muffler it's a cross flow, and has an entrance and exit on each end! I don't think that would work well with both ins on one end... don't know how those are made inside... |
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Frank Swygert
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Gelalthedamned
AMC Nut Joined: Nov/28/2014 Location: Athens ga Status: Offline Points: 376 |
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Yeah, it came out of a box. http://gibsonperformance.com/i-22731397-cft-superflow-dual-dual-oval-muffler-stainless-55105s.html There are 2 muffler shops in this town, I called one to set an appointment... after a lot of minutes of telling them what I need for my set up...they told me to just bring my car and they’ll get to it when they can. I’m against that. I’m not leaving my car anywhere and no one operates it but me, that’s that. Surely I’m not the only person like this..paranoid or overly protective...call it what you want. |
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Calamity - 73 Gremlin X zombie rod (daily driver)
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tyrodtom
AMC Addicted Joined: Sep/14/2007 Location: Virginia Status: Offline Points: 6199 |
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I've worked on cars over 40 years, if a customer doesn't trust me enough to work on his car without his supervision, or overview, then I don't work on it.
I'm not going to let his paranoia become my problem.
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66 American SW, 66 American 2dr, 82 J10, 70 Hornet, Pound, Va.
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billd
Moderator Group Forum Administrator Joined: Jun/27/2007 Location: Iowa Status: Offline Points: 30894 |
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Not an old wive's tale - proven at the track. A fellow did a real test, real car, it's out on the internet somewhere, where he actually track-tested the idea of smaller outlets.
Gasses have cooled and condensed - |
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Lyle
AMC Addicted Joined: Jul/17/2014 Location: None Status: Offline Points: 772 |
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As Build states, larger on engine exit to clear the cylinder, balance the pressure waves of ignition to the point were they equalize, and then gasses have cooled, so you need a smaller diameter to increase velocity to continue evacuation.
You can design this for street and track, but specific to CI, number of cylinders, cam, RPM range wanting to achieve. Engineering science all of it's own and like most engineering - based on trial and error. If your only interested in WOT then as large as you can muster straight out.
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bob401
AMC Nut Joined: Sep/23/2009 Status: Offline Points: 263 |
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here's a nice propaganda article..
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billd
Moderator Group Forum Administrator Joined: Jun/27/2007 Location: Iowa Status: Offline Points: 30894 |
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Exhaust tuning is a science. The tube you are tuning actually starts at the carburetor air-horn and ends at the tip of the tail pipe.
It's been likened to an acoustic guitar by some.... waves travel and actually much like a time domain reflectometer works on a cable (for example, Ethernet), waves travel through the air - exhaust - and are reflected at the end.
You want things timed to aid scavenging and not impede it. |
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Gelalthedamned
AMC Nut Joined: Nov/28/2014 Location: Athens ga Status: Offline Points: 376 |
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I need 3 exit pipes to get a power chord, but with a dual I can get exits 1/3 the length of the other and get a perfect 5th. (I got all weird and researched tube organs, cause hertz values are a thing) I was wanting a Dflat... but the math on the head work and compression says I can hit a C4th at best. |
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Calamity - 73 Gremlin X zombie rod (daily driver)
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