Replacing XR7-G dual exhaust - 390GT

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propayne
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Replacing XR7-G dual exhaust - 390GT

Post by propayne » 31 Dec 2016, 07:06

I've had the 390 for my G rebuilt, along with the C6, radiator, etc. and I need to replace my entire exhaust system.

I have a few questions and I would appreciate some feedback -

Since this is a G it all will end up dumping out of the factory style "pipe within a pipe" chrome exhaust tips - so I assume I would need to stick with the factory 2" exhaust?

I would like to improve the exhaust if I can. I was thinking of getting everything that is included in the OEM setup except for the mufflers and substituting a better performance muffler, like a Magnaflow, etc. Is that doable?

And I assume that since the G's exhaust goes straight out the notched rear valence, my exhaust shop will need to cut off the "down turns" and weld on my chrome tips?

Again, any and all advice is much appreciated :beerchug:

- Phillip
Last edited by propayne on 31 Dec 2016, 08:19, edited 1 time in total.

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Re: Replacing XR7-G dual exhaust - 390GT

Post by catlover » 31 Dec 2016, 07:56

Phillip, Sounds like you have a plan, should not be a problem for a custom exhaust shop.
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Re: Replacing XR7-G dual exhaust - 390GT

Post by Royce » 31 Dec 2016, 10:21

The 390GT manifolds and H pipe are the worst part of the system.

Summit Racing sells a nice set of mandrel bent 2 1/4" pipes for 68 Cougar. Change to 428CJ manifolds and then the H pipe will also be 2 1/4". You can use aftermarket mufflers by welding bolts to the rear face of each muffler. That way the aftermarket muffler can bolt to the factory hangers.

The reproduction tips can be necked up to 2 1/4". The larger pipe for the entire run will help performance considerably.
1968 GT-E XR-7 W code 427 Augusta Green / Saddle
1968 XR-7 R code 428CJ Ram Air Red / Black
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Re: Replacing XR7-G dual exhaust - 390GT

Post by propayne » 01 Jan 2017, 12:16

Thanks guys -

Guess I should have mentioned that I decided to stick with my original 390GT manifolds and the engine is already back-in-the-hole, so whatever I do will have to include those.

So, the larger 2 1/4" pipes wouldn't work with 390GT manifolds?

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Re: Replacing XR7-G dual exhaust - 390GT

Post by Royce » 02 Jan 2017, 11:09

The pipes from Summit start at the back side of the mufflers so they will be fine. The 390GT H pipe is 2" diameter. I suppose that you could have one made in bigger pipe but it would still have to be reduced to 2" right where it comes out of the manifolds.
propayne wrote:Thanks guys -

Guess I should have mentioned that I decided to stick with my original 390GT manifolds and the engine is already back-in-the-hole, so whatever I do will have to include those.

So, the larger 2 1/4" pipes wouldn't work with 390GT manifolds?
1968 GT-E XR-7 W code 427 Augusta Green / Saddle
1968 XR-7 R code 428CJ Ram Air Red / Black
1910 Model T Ford Touring Red / Black
1914 Model T Touring Maroon / Black
1915 Model T Ford Touring Black / Black
1917 Model T Ford Torpedo Runabout Green / Black
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Re: Replacing XR7-G dual exhaust - 390GT

Post by propayne » 02 Jan 2017, 11:36

Thanks a lot Royce, I appreciate the information.

Could you elaborate a little more on what you mean by "The reproduction tips can by necked up to 2 1/4"?

How exactly is that done?

- Phillip

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Re: Replacing XR7-G dual exhaust - 390GT

Post by 1969XR7Vert » 02 Jan 2017, 12:01

propayne wrote:Thanks a lot Royce, I appreciate the information.

Could you elaborate a little more on what you mean by "The reproduction tips can by necked up to 2 1/4"?

How exactly is that done?

- Phillip
Not to speak for Royce but he probably means a good exhaust shop can "swage" (stretch) the tip ends up to the required size.
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Re: Replacing XR7-G dual exhaust - 390GT

Post by ClawIt » 03 Jan 2017, 07:25

Phillip,
I was in your situation years ago. I ran the 2" H-pipe and intermediates into Flowmaster 40s that had the same in/out orientation and were within an inch of the same length as the original mufflers. Summit has 2.25" tailpipes that fit Cougars without the turn down, so 2" in 2.25" out on the mufflers. I would hesitate welding the tips on because after 5+ years of use the outside edges started rusting or you got a dent in the edge. Royce's answer about the mounting works, I didn't have a welder so made a sheet metal half circle and used that with the muffler clamp at the back of the muffler to the hanger. Stretching the tips can be done by inserting a pipe expander (borrow from auto parts), but the tailpipe metal will expand easier then the tip steel. I just needed about 16th " on the tailpipe then slid the tips into the pipe and clamped. The flowmasters have a great rumble at idle and high speed pull was way better.
Jim

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Re: Replacing XR7-G dual exhaust - 390GT

Post by propayne » 03 Jan 2017, 09:53

Very helpful stuff - thanks Jim!

- Phillip

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Re: Replacing XR7-G dual exhaust - 390GT

Post by Royce » 03 Jan 2017, 13:35

I've done the weld - a - bolt - to - the - muffler thing several times without owning a welder. I put marks on the mufflers where I wanted the bolts, and handed the mufflers and the bolts to the muffler shop guy. He's got a welder.
1968 GT-E XR-7 W code 427 Augusta Green / Saddle
1968 XR-7 R code 428CJ Ram Air Red / Black
1910 Model T Ford Touring Red / Black
1914 Model T Touring Maroon / Black
1915 Model T Ford Touring Black / Black
1917 Model T Ford Torpedo Runabout Green / Black
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