TheAMCForum.com Homepage
Forum Home Forum Home > The Garage > AMC 6 Cylinder Engine Repair and Modifications
  New Posts New Posts RSS Feed - Tube size dual exhaust?
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

Click for TheAMCForum Rules / Click for PDF version of Forum Rules
Your donations help keep this valuable resource free and growing. Thank you.

Tube size dual exhaust?

 Post Reply Post Reply Page  123>
Author
Message
Gelalthedamned View Drop Down
AMC Nut
AMC Nut
Avatar

Joined: Nov/28/2014
Location: Athens ga
Status: Offline
Points: 376
Post Options Post Options   Thanks (0) Thanks(0)   Quote Gelalthedamned Quote  Post ReplyReply Direct Link To This Post Topic: Tube size dual exhaust?
    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?
Calamity - 73 Gremlin X zombie rod (daily driver)
Back to Top
tached_out View Drop Down
AMC Nut
AMC Nut


Joined: Feb/08/2008
Location: Vancouver, BC
Status: Offline
Points: 328
Post Options Post Options   Thanks (1) Thanks(1)   Quote tached_out Quote  Post ReplyReply Direct Link To This Post Posted: Apr/11/2018 at 12:41am
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.
Back to Top
farna View Drop Down
Supporter of TheAMCForum
Supporter of TheAMCForum
Avatar
Moderator Lost Dealership Project

Joined: Jul/08/2007
Location: South Carolina
Status: Offline
Points: 19610
Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: Apr/11/2018 at 6:35am
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...
Frank Swygert
Back to Top
Gelalthedamned View Drop Down
AMC Nut
AMC Nut
Avatar

Joined: Nov/28/2014
Location: Athens ga
Status: Offline
Points: 376
Post Options Post Options   Thanks (0) Thanks(0)   Quote Gelalthedamned Quote  Post ReplyReply Direct Link To This Post Posted: Apr/11/2018 at 8:27pm
Originally posted by farna farna wrote:

I suppose you know what that muffler came out of?

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.
Calamity - 73 Gremlin X zombie rod (daily driver)
Back to Top
tyrodtom View Drop Down
AMC Addicted
AMC Addicted


Joined: Sep/14/2007
Location: Virginia
Status: Offline
Points: 6199
Post Options Post Options   Thanks (0) Thanks(0)   Quote tyrodtom Quote  Post ReplyReply Direct Link To This Post Posted: Apr/11/2018 at 8:44pm
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.
66 American SW, 66 American 2dr, 82 J10, 70 Hornet, Pound, Va.
Back to Top
billd View Drop Down
Moderator Group
Moderator Group

Forum Administrator

Joined: Jun/27/2007
Location: Iowa
Status: Offline
Points: 30894
Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: Apr/11/2018 at 8:53pm
Originally posted by Gelalthedamned Gelalthedamned wrote:


And, what’s this about stepping down a size at the exits, old wives tale?

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 - 
Back to Top
Lyle View Drop Down
AMC Addicted
AMC Addicted
Avatar

Joined: Jul/17/2014
Location: None
Status: Offline
Points: 772
Post Options Post Options   Thanks (0) Thanks(0)   Quote Lyle Quote  Post ReplyReply Direct Link To This Post Posted: Apr/11/2018 at 9:42pm
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.
Back to Top
bob401 View Drop Down
AMC Nut
AMC Nut
Avatar

Joined: Sep/23/2009
Status: Offline
Points: 263
Post Options Post Options   Thanks (0) Thanks(0)   Quote bob401 Quote  Post ReplyReply Direct Link To This Post Posted: Apr/11/2018 at 10:03pm
here's a nice propaganda article..   

Back to Top
billd View Drop Down
Moderator Group
Moderator Group

Forum Administrator

Joined: Jun/27/2007
Location: Iowa
Status: Offline
Points: 30894
Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: Apr/11/2018 at 10:06pm
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. 
Back to Top
Gelalthedamned View Drop Down
AMC Nut
AMC Nut
Avatar

Joined: Nov/28/2014
Location: Athens ga
Status: Offline
Points: 376
Post Options Post Options   Thanks (1) Thanks(1)   Quote Gelalthedamned Quote  Post ReplyReply Direct Link To This Post Posted: Apr/11/2018 at 10:22pm
Originally posted by billd billd wrote:

Exhaust tuning is a science. It's been likened to an acoustic guitar by some. 

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.
Calamity - 73 Gremlin X zombie rod (daily driver)
Back to Top
 Post Reply Post Reply Page  123>
  Share Topic   

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 12.03
Copyright ©2001-2019 Web Wiz Ltd.

This page was generated in 0.156 seconds.
All content of this site Copyright © 2018 TheAMCForum unless otherwise noted, all rights reserved.
PROBLEMS LOGGING IN or REGISTERING:
If you have problems logging in or registering, then please contact a Moderator or