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Tube size dual exhaust?

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Dave Z View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dave Z Quote  Post ReplyReply Direct Link To This Post Posted: Jul/08/2018 at 7:20pm
Here's some thoughts on the need for back pressure.

If cam timing is engineered to compensate for a restrictive exhaust system and then the restriction is eliminated, the cam profile may no longer be optimum for the application.
If restriction is necessary, shouldn't it vary with throttle opening? For instance, at 1,000 rpm 2" dual exhaust is probably the same as open manifolds. But at 5,500 rpm it would be restrictive.
I don't believe anyone has addressed length. A Gremlin dumping the exhaust in front of the wheels is a lot shorter than an Ambassador out the rear of the car.
Why do X pipes help? They can only reduce back pressure, therefore a lot of people are going to a lot of extra trouble to make things worse.

Dave Z
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6768rogues View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 6768rogues Quote  Post ReplyReply Direct Link To This Post Posted: Jul/08/2018 at 7:27pm
For every gallon of gas you burn, a gallon of water goes as water vapor out of the exhaust. If you go too big, it condenses in the pipes and rusts them from the inside out.
Content intended for mature audiences. If you experience nausea or diarrhea, stop reading and seek medical attention.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote one bad rambler Quote  Post ReplyReply Direct Link To This Post Posted: Jul/08/2018 at 8:28pm
Dual 2 inch is more than fine...1 3/4 would also be fine....Too big and it will sound like a boat...
68 AMX 390 4 Speed,68 American,64 American 2 Door Wagon Altered Wheelbase,78 Concord Build 360,727,8.8
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farna View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: Jul/09/2018 at 5:26am
2" is hardly any restriction at all with duals. You're only running half the V-8 through each -- so you have a 2" exhaust on a 200 inch (3.2L) four cylinder with a 401, 180 inches (3.0L) with a 360. Most 3.0L V-6s only run a 1.5-1.75" single exhaust from the factory, with some performance models like the Nissan Zs running duals that size, but they turn a lot more rpm (more rpm = more exhaust volume).  Unless you're running a drag car or really high power (over 500) 2" duals should be sufficient, 2.25" or 2.50" tops. If you run the one in two out muffler a 2.0-2.5" in and 1.75-2.0" out would be great -- the muffler itself will be the biggest restriction. I think mine is 2" in and dual 2" out, factory Toyota in (4.7L).
Frank Swygert
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Post Options Post Options   Thanks (0) Thanks(0)   Quote one bad rambler Quote  Post ReplyReply Direct Link To This Post Posted: Jul/09/2018 at 9:17pm
Originally posted by farna farna wrote:

2" is hardly any restriction at all with duals. You're only running half the V-8 through each -- so you have a 2" exhaust on a 200 inch (3.2L) four cylinder with a 401, 180 inches (3.0L) with a 360. Most 3.0L V-6s only run a 1.5-1.75" single exhaust from the factory, with some performance models like the Nissan Zs running duals that size, but they turn a lot more rpm (more rpm = more exhaust volume).  Unless you're running a drag car or really high power (over 500) 2" duals should be sufficient, 2.25" or 2.50" tops. If you run the one in two out muffler a 2.0-2.5" in and 1.75-2.0" out would be great -- the muffler itself will be the biggest restriction. I think mine is 2" in and dual 2" out, factory Toyota in (4.7L).
The problem with the Tundra isn`t the pipe size it`s the poor design of the exhaust manifolds...especially before 2007..I will say the 4.7 has proved to be stout and reliable...So are the 4.6 and 5.7...My son and i talked about a 5.7 in concord..but whats the fun of having a classic car if it`s never going to break down..lol
68 AMX 390 4 Speed,68 American,64 American 2 Door Wagon Altered Wheelbase,78 Concord Build 360,727,8.8
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farna View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: Jul/10/2018 at 6:18am
I have thoughts of building a Wagoneer to pull my camper. Needs to be able to tow 7000 pounds as max load like my 2003 Tundra. Stock Grand Wagoneer with tow package (360, 727, 3.31 gears) is only rated for 5K. I'd want at least a four speed auto trans and something like 3.90 gears... like my Tundra. I have thought about finding a Tundra and using the drivetrain... maybe even a 4x4. But I could keep it RWD only by cutting axle ends off the front and using a straight tube. Fitting the Tundra IFS might be an issue, but could shorten frame for the Jeep body I suppose. May as well go with the bigger motor though and get a bit more than 7K towing capacity. Could keep the Jeep axles... another option. 

I've pretty much decided it would all be too much work though. I sort of like the old GW, but not enough to put $20K+ in one.
Frank Swygert
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tached_out Quote  Post ReplyReply Direct Link To This Post Posted: Aug/04/2018 at 12:01am
One of the sweetest sounding cars you'll ever hear is a Jaguar XKE. They had two engine sizes 3.8 litre and 4.2 litre same as AMC.

Those cars had a dual 3 into 1 manifolds. They ran fully separated 2'' pipes. There was a straight through muffler in each pipe under the cockpit and resonators could be seen side by side under the rear valance.

Check out You Tube for some sweet sounds.
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