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Unread 04-29-2013, 04:09 PM   #1
Keith_b00ne
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AMC 304 Manifold to Headers

I am interesting in getting some personal opinions from those that switched from a stock exhaust manifold to headers on a AMC 304. In particular: Did they fit well? What did you think of the power improvement? Any brands you would steer away from? Any durability issues? Any comments are welcome.

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Unread 04-29-2013, 05:04 PM   #2
Jamesromeos
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Im going back to manifolds, they have leaked since a month after I installed them, prob. because they were summit brand....my fault for being cheap.
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Unread 04-29-2013, 07:25 PM   #3
RDH
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Crappy gaskets can cause leakage as well.
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Unread 04-29-2013, 09:27 PM   #4
pman
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Keith-
I've been debating the same issue recently, and after combing through numerous threads, decided to keep the stock manifolds. From what I've read (whether it's true or not I'm not sure) the "dog leg exhaust ports" on the AMC motors provide good breathing, so the header gains aren't as significant. I too, read many comments about people fighting leaky headers. I stole a page from Matts1981CJ7 and cleaned mine in Ospho, wire brushed them and repainted in POR Intake Manifold Gray paint (in hindsight I wish I had gone with the VHT silver color that Matt used). I literally dropped it off at a buddies shop to have the dual exhaust put on this morning. I'll let you know how it turns out.


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Unread 04-29-2013, 09:42 PM   #5
Alex77cj7
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Quote:
Originally Posted by Keith_b00ne
I am interesting in getting some personal opinions from those that switched from a stock exhaust manifold to headers on a AMC 304. In particular: Did they fit well? What did you think of the power improvement? Any brands you would steer away from? Any durability issues? Any comments are welcome.
Well I just finished putting fenderwell headers with 2.5" pipe and thrush welded mufflers exiting before the rear tires. Sound is incredible and the performance gain was out of this world! Definitely noticeable! Also my gas mileage went from about 10-11 to 15-17. I used summit brand and they fit great, came with all the hardware, and seemed like they were very great quality. Had them on for a couple of weeks now.
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Unread 04-30-2013, 05:52 AM   #6
Matt1981CJ7
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Keith,

I'd be more inclined to trust advice given by people who have run both manifolds and headers for longer than a "couple of weeks".

FYI, when I was making the same decision, every piece of advice, from sources I trust, said that stock manifolds flow just as well as headers and they are less prone to leaks.

Matt
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Unread 04-30-2013, 06:50 AM   #7
Alex77cj7
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Quote:
Originally Posted by Matt1981CJ7
Keith,

I'd be more inclined to trust advice given by people who have run both manifolds and headers for longer than a "couple of weeks".

FYI, when I was making the same decision, every piece of advice, from sources I trust, said that stock manifolds flow just as well as headers and they are less prone to leaks.

Matt
I ran manifolds for atleast a year and the headers have been on for a few weeks. I'm pretty sure that's long enough to notice a difference in power and gas mileage. I noticed it on my first drive after I put them on. It's been a couple of weeks and I still don't have any leaks. For the questions he asked a couple of weeks is enough time.
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Unread 04-30-2013, 07:15 AM   #8
swatson454
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Quote:
Originally Posted by Alex77cj7 View Post
Well I just finished putting fenderwell headers with 2.5" pipe and thrush welded mufflers exiting before the rear tires. Sound is incredible and the performance gain was out of this world! Definitely noticeable! Also my gas mileage went from about 10-11 to 15-17. I used summit brand and they fit great, came with all the hardware, and seemed like they were very great quality. Had them on for a couple of weeks now.
Yep. Good deal.

I keep saying, flow is secondary to the main benefit of headers.


Shawn

Edit and disclaimer: Alex has an aftermarket cam; which will show greater improvements than headers on a stocker. Gains are still there, though.
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Unread 04-30-2013, 11:24 AM   #9
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Quote:
Originally Posted by swatson454

Yep. Good deal.

I keep saying, flow is secondary to the main benefit of headers.

Shawn

Edit and disclaimer: Alex has an aftermarket cam; which will show greater improvements than headers on a stocker. Gains are still there, though.
If flow is secondary what it primary?? That doesn't make sence.
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Unread 04-30-2013, 11:41 AM   #10
swatson454
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Originally Posted by CjHouch View Post
If flow is secondary what it primary?? That doesn't make sence.
Giving the exhaust from each cylinder a clear path out so it's not fighting another one for access to the dump or pressurizing the manifold during another cylinder's overlap period and equally, if not more importantly, wave tuning.

Get those done correctly and even a pipe that's too small will outflow the exhaust port.


Shawn
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Unread 04-30-2013, 11:42 AM   #11
Alex77cj7
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Quote:
Originally Posted by swatson454

Yep. Good deal.

I keep saying, flow is secondary to the main benefit of headers.

Shawn

Edit and disclaimer: Alex has an aftermarket cam; which will show greater improvements than headers on a stocker. Gains are still there, though.
Yup forgot the mention the cam, crank, pistons and rods, bore, and intake manifold with a 4-bbl Holley truck avenger. The science of headers makes a lot of since and it makes since that they would flow better than stock cast iron manifolds. Plus the flow must be better to get improvements right?
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Unread 04-30-2013, 01:23 PM   #12
ADDZ71
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pman,

Are those manifolds off your CJ? The reason I ask is the driver's side manifold is a rear dump which if I understand correctly will not work in a CJ due to interference with the clutch linkage. The CJ's had a special Driver side dump that is in the center of the bank. Look at Matt's thread on this and you will see the difference.
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Unread 04-30-2013, 01:41 PM   #13
ASteve
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Kieth,

If you go with headers make sure your flange is thick, primary tubes are 1 5/8" and reduce down to 2.5" collectors. Also, use Percy's gaskets they do not leak once installed correctly.

I went with Doug's and couldn't be more happier. Although if I were to do it again, I might consider in frame headers...

http://www.summitracing.com/parts/do...view/make/jeep
dougs-headers-close-up.jpg   borgeson-steering-shaft.jpg  
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Unread 04-30-2013, 02:29 PM   #14
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Thanks for the engine p0rn, Steve!


Shawn
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Unread 04-30-2013, 02:40 PM   #15
Davis77Cj
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