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I would appreciate your opinion! I am putting a 390GT motor back in my '69 Mach 1 (orig. S code - 390GT) and can't decide on the 390GT stock cast manifolds vs. headers. Is the increased restriction of stock (street use only) with less headaches better than the added HP/sound of headers with exhaust leaks? Thanks.
 
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The stock GT manifolds from what I've read on forums don't flow very well for high rpm's. If you put headers on it it's supposed to improve performance quite a bit. If headers are a problem you could put 428 manifolds on it which flow better than the GT ones but not quite as good as headers. You may need to drill one bolt hole into the drivers side head to put these on also. There is a lot of information about performance on the big block forums on network54 and fomoco.com.

Adrien.

65 GT Coupe, dismantled waiting for resto.
67 Restomod Coupe, in assy.
69 Mach 1, SWMBO say don't take it apart!
91 5.0 LX HB, driver.
http://albums.photopoint.com/j/View?u=1594363&a=12146434&p=44060413.jpg
 
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Properly installed quality headers don't leak.I have Hooker's on my 69 428cj for 10yrs now and they have never leaked.
I would look into a set of Sanderson headers for yours they are of high quality and they make them with the correct port match for your heads

Greg B
 

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For headers to be the most effective you have to address the whole system with big enough exhaust pipes, an x-pipe and good flowing mufflers. You should also stay with a good quality set like Hooker or Hedman. If you start out with some econo headers they won't fit quite right, the flanges are made cheaply and thats where a lot of the leak problems are.

I have had the same set of headers on my car for 10 years now. I check the snug on my header bolts from time to time but they don't leak. About once every year or so based on how they look I take them off, clean them up and re-spray them with black stove paint and put new gaskets on. Thats about it.

The only big downside with headers is that they allow more heat to escape into the engine area. It can actually make your floor panels hotter. I've been told that the new ceramic coatings help this a lot but those are a bit more expensive.


You can see my 65 fastback at: http://hottarod.stangnet.com/
http://members.aol.com/macstang/Gifs/macstang3.jpg
 

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If you're going for oringinality, stick with the stock manifolds. If you want performance, headers are the only way to go. Do as Hottarod suggested, though, and do the whole exhaust system.

A good set of headers with a set of Stage 8 bolts, will not leak. I haven't touched my JBA's in almost 2 years now with no leaks (and it's a daily driver).

If you always do what you've always done,
You'll always get what you've always got

http://www.classic-mustang.net/johnpro
 
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