Lets talk headers

[Jroch]

I am kinda in a bind with the current exhaust manifolds, got a couple of leaks on them and are going to be a challange to fix. So my thought is to maybe put some headers on it and just string up a new exhaust with some glass packs?

My question is this:

How closely do headers match the path of the original manifolds? Looking at the engine bay of my Jeep it's pretty tight between the frame rails, I am also concerned about how they angle out, meaning will they drop low enough to clear the fire wall. So in short what I am asking is will they terminate in the same area as the manifolds do?

Second Part to the above question:

Would it be better to order the headers specific to the car "AMX"? or would it be better to order them by the motor. Looking at the headers on Summitt there seems to be a significant difference between the two?

Motor: is a 343 out a 69 AMX, which is what exhaust manifolds are on it now.

Thanks in advance

Justin

 

[Petescj]

You'll need to order headers for an 8 cyl. Jeep. Not the Amx. If you order by the Amx thats what you'll get , headers that fit the engine compartment of a Amx not a Jeep. Where the headers terminate depend on what style your getting. In frame headers are just that , theyll drop down inside the frame rail and Transmission with the collector ending up a little behind the starter. Outside the frame headers come through the wheelwell and end somewhere around the front of the tub. Then you weld the collector on after you get your mufflers in the correct position.


Usually the outside the rail ones are used for clearance issues like Automatic transmissions and such wich take up more room. I prefer inside the rail cause you dont have the muffler right where the nerf bars would be on yours.

 

[Jroch]

You'll need to order headers for an 8 cyl. Jeep. Not the Amx. If you order by the Amx thats what you'll get , headers that fit the engine compartment of a Amx not a Jeep. Where the headers terminate depend on what style your getting. In frame headers are just that , theyll drop down inside the frame rail and Transmission with the collector ending up a little behind the starter. Outside the frame headers come through the wheelwell and end somewhere around the front of the tub. Then you weld the collector on after you get your mufflers in the correct position.


Usually the outside the rail ones are used for clearance issues like Automatic transmissions and such wich take up more room. I prefer inside the rail cause you dont have the muffler right where the nerf bars would be on yours.

Pete, Thanks for your reply, all I am seeing is full length headers nothing that says differently how do I tell the difference? The other thing I am noticing while doing the header search is they keep showing the AMC 304 motor in the same application list, I am wondering if these two motors share the same exhaust manifolds?

I did a search using a jeep with a AMC 304 and this is the results that came back, which was a lot different then the 343 searches I was doing. If the 343 and the AMC 304 share the same exhaust/head platform then this may be a lot easier then I was thinking I did the search using a 73 Jeep as I was unsure up to what year they continued to offer the AMC 304 , My Jeep is an 85, but the application list for the listed headers was showing the CJ7

Exhaust - CJ6 - JEEP - 1973 - SummitRacing.com

Thanks again

Justin

 

[Petescj]

One type is called in frame headers the other are fenderwell headers. All the headers I see are sold as V-8 headers AMC 304 -401. So as far as that goes Id say their all the same exhaust manifold. Im going by 4wd hardware and Quadratec.

 

[Petescj]

Their probably only showing the AMC 304 cause thats the only Amc V-8 that came stock in a Jeep. I have a 360 in my CJ5 and used the same part # as a AMC 304 for my headers.

 

[CJ]

AMC 343 is a GEN II engine, the AMC 304 - 401 headers you see for Jeeps are for GEN III engines - they have dogleg exhaust ports...

Good reference here -->> http://en.wikipedia.org/wiki/AMC_V8_engine#343

 

[Petescj]

I wonder why they dont exclude the 343 then in their advertisment.

AMC 343 is a GEN II engine, the AMC 304 - 401 headers you see for Jeeps are for GEN III engines - they have dogleg exhaust ports...

Good reference here -->> AMC V8 engine - Wikipedia, the free encyclopedia

 

[CJ]

I wonder why they dont exclude the 343 then in their advertisment.

Guess they (header) have some wrong info huh?

Here is the info on 70 and up GEN III

In 1970, all three blocks grew in deck height and gained a new head design. These changes made this the third generation of AMC V-8, hence it is sometimes referred to as the GEN-3 AMC V-8. The stroke and deck height on the 290 and 343 was increased by 0.16 in (~5/32 in), becoming the AMC 304 and 360, respectively. The 1970 AMX 390 remained at the same displacement by using a special rod and piston for this year only. It is believed that AMC kept the 390 this last year due to the reputation it had garnered in the two seater AMX, which was discontinued after 1970. In 1971 the 390 was stroked by 0.16 in to become the 401.
The other change in 1970 was the switch to the dog-leg heads. These heads flow ~20% better on the exhaust side than the 1966-69 rectangle port heads and are thus the best for performance. There are two reasons for the flow increase: First, the area of the port is larger, due to the dog leg. Second, the shape of the port floor was changed from a concave to a convex curve. The concave floor tended to bend the exhaust flow upwards which caused turbulence when the flow was forced to go down into the exhaust manifolds. By switching to a convex floor the curvature of the flow starts in the head and proceeds much more smoothly into the exhaust manifold resulting in less turbulence and better flow.
The center two intake bolts on each head were relocated to prevent accidental mix-ups of GEN-2 and GEN-3 intakes. The intakes can be interchanged by slotting the bolt holes, but the added deck height of the GEN-3 engine means that sealing and port match will be compromised. GEN-3 intakes can be machined to fit GEN-2 engines by surface grinding the intake flanges (by a machine shop) and slotting the center holes.
There is a persistent myth about 1970-mid 1971 "319" or "291" AMC heads. These heads have the dog-leg exhaust ports and 50-52 cc combustion chambers. They are commonly identified by the first three (319) or last three (291 for the 360-401 heads; AMC 304 used a different casting) digits of the casting number. There was a U.S. auto industry-wide shift to lower compression ratios in mid 1971, so AMC increased combustion chamber size to 58-59 cc. The first three digits of the casting number on the large chamber heads are 321, 322, or 323 depending on year. The ONLY difference between small and large chamber GEN-3 heads is the combustion chamber size. The early heads are not "the best" AMC heads as many have come to believe. They will raise compression on a later engine with no other changes, but if building an engine get the proper pistons for the desired ratio. There is no reason to search out these relatively hard to find, and more expensive when found, heads for performance.

 

[Petescj]

Thats some good info there. Thanx for correcting me on that. So I guess he should be looking for replacement exhaust manifolds instead ?

 

[Jroch]

WOW!!!! Thanks for the info, but once again I have ran into a road block LMAO seems to be the trend with my Jeep.

When I do the search for the 343 they also bring up the AMC 304 application very perplexing, Headers - SummitRacing.com
Now I am back to square one on this, it would almost seem that the best route would be to go with a pair of shorty's, unless I missing something, I am just concerned of ordering some and not having them fit and having to go through the hole return thing which ussually leads to a hassle. Any ideas on which direction I should turn?

As always thanks for the help

 

[Jroch]

Guess they (header) have some wrong info huh?

Here is the info on 70 and up GEN III

In 1970, all three blocks grew in deck height and gained a new head design. These changes made this the third generation of AMC V-8, hence it is sometimes referred to as the GEN-3 AMC V-8. The stroke and deck height on the 290 and 343 was increased by 0.16 in (~5/32 in), becoming the AMC 304 and 360, respectively. The 1970 AMX 390 remained at the same displacement by using a special rod and piston for this year only. It is believed that AMC kept the 390 this last year due to the reputation it had garnered in the two seater AMX, which was discontinued after 1970. In 1971 the 390 was stroked by 0.16 in to become the 401.
The other change in 1970 was the switch to the dog-leg heads. These heads flow ~20% better on the exhaust side than the 1966-69 rectangle port heads and are thus the best for performance. There are two reasons for the flow increase: First, the area of the port is larger, due to the dog leg. Second, the shape of the port floor was changed from a concave to a convex curve. The concave floor tended to bend the exhaust flow upwards which caused turbulence when the flow was forced to go down into the exhaust manifolds. By switching to a convex floor the curvature of the flow starts in the head and proceeds much more smoothly into the exhaust manifold resulting in less turbulence and better flow.
The center two intake bolts on each head were relocated to prevent accidental mix-ups of GEN-2 and GEN-3 intakes. The intakes can be interchanged by slotting the bolt holes, but the added deck height of the GEN-3 engine means that sealing and port match will be compromised. GEN-3 intakes can be machined to fit GEN-2 engines by surface grinding the intake flanges (by a machine shop) and slotting the center holes.
There is a persistent myth about 1970-mid 1971 "319" or "291" AMC heads. These heads have the dog-leg exhaust ports and 50-52 cc combustion chambers. They are commonly identified by the first three (319) or last three (291 for the 360-401 heads; AMC 304 used a different casting) digits of the casting number. There was a U.S. auto industry-wide shift to lower compression ratios in mid 1971, so AMC increased combustion chamber size to 58-59 cc. The first three digits of the casting number on the large chamber heads are 321, 322, or 323 depending on year. The ONLY difference between small and large chamber GEN-3 heads is the combustion chamber size. The early heads are not "the best" AMC heads as many have come to believe. They will raise compression on a later engine with no other changes, but if building an engine get the proper pistons for the desired ratio. There is no reason to search out these relatively hard to find, and more expensive when found, heads for performance.

I was rereading the artical you linked and one thing popped out at me during the reread "The 343 and AMX 390 used the same larger valve heads, 2.025 in (51.4 mm) intake and 1.625 in (41.3 mm) exhaust." It almost sounds like the 390 has the same heads?

 

[LongHorn]

I was rereading the artical you linked and one thing popped out at me during the reread "The 343 and AMX 390 used the same larger valve heads, 2.025 in (51.4 mm) intake and 1.625 in (41.3 mm) exhaust." It almost sounds like the 390 has the same heads?

The 290,343,& 390 V8's all had rectangle port heads. The AMC 304 ,360 & 401's all had Dogleg exhaust ports. The valves were slightly larger on Hurst AMX heads. According to the AMC engineers & the racing guys the "Dog Leg" heads flow the best of any AMC heads. Early 71' heads also had shallow combustion chambers for higher compression.

 

[Jroch]

I took a couple of pictures of how tight the current exhaust is, is this about waht it looks like with the AMC 304 's, 360's etc? if so then I wonder if a normal pair of headers would fit?

Drivers side



Passenger Side

 

[LongHorn]

I took a couple of pictures of how tight the current exhaust is, is this about waht it looks like with the AMC 304 's, 360's etc? if so then I wonder if a normal pair of headers would fit?

Drivers side



Passenger Side

That's why most people run the fenderwell headers. The inside the frame headers that worked best for me were the "Doug Thorley Tri-Y" headers like the old "Shelby Mustangs" use to have. These are for a CJ.

 

[LongHorn]

Headers for 1972-1984 Jeep CJ5 , CJ7 and CJ8 with AMC 304 -401 AMC V8 Engine. Part number THY-605Y-C and THY-605Y-S-C. These headers are set up for dual exhaust and exit inside the frame rails.These Doug Thorley Tri-Y headers are constructed of 14-gauge tubing with 3/8-inch flanges to give you the best quality you can get in a header! Plus they are ceramic coated to give a lifetime of performance!

 

[Jroch]

Headers for 1972-1984 Jeep CJ5 , CJ7 and CJ8 with AMC 304 -401 AMC V8 Engine. Part number THY-605Y-C and THY-605Y-S-C. These headers are set up for dual exhaust and exit inside the frame rails.These Doug Thorley Tri-Y headers are constructed of 14-gauge tubing with 3/8-inch flanges to give you the best quality you can get in a header! Plus they are ceramic coated to give a lifetime of performance!

Long Horn, Thanks for the information on the heads and headers, do you think that even with the different port type "dog leg versus non" that they are interchangable?

 

[CJ]

Long Horn, Thanks for the information on the heads and headers, do you think that even with the different port type "dog leg versus non" that they are interchangable?

They are not interchangeable...

Your going to have to use manifolds or hack up a set of rectangular port headers.

Are you positive you have a 69 343? Can you get the block and head casting numbers?

 

[LongHorn]

They are not interchangeable...

Your going to have to use manifolds or hack up a set of rectangular port headers.

Are you positive you have a 69 343? Can you get the block and head casting numbers?

CJ right on that, exhaust leak city. They changed styles in 1970 when they added stroke to the engine. The later heads are a great improvement in flow
next time you need a valve job you may want to trade up.

 

[CJ]

Gotta be careful trying to swap GEN II and GEN III heads - different deck heights, center intake bolt location (can be machined to work) and bolt dia. among other things - GEN II 7/16 bolts and GEN III 1/2 bolts... If you decide to use a GEN III head on a GEN II block - you will need to either have special gaskets made, machine work on the mating surfaces or a combination of both.

I'd still like to know what the casting numbers are on the block and heads - you may be luck and have one of those weird engines from 69 that were really a 360!

 

[CJ]

Headers for 1972-1984 Jeep CJ5 , CJ7 and CJ8 with AMC 304 -401 AMC V8 Engine. Part number THY-605Y-C and THY-605Y-S-C. These headers are set up for dual exhaust and exit inside the frame rails.These Doug Thorley Tri-Y headers are constructed of 14-gauge tubing with 3/8-inch flanges to give you the best quality you can get in a header! Plus they are ceramic coated to give a lifetime of performance!

Cough... Cough... Love my Headman equal length tube (inside the frame) ceramic coated headers...

Well, loved em' on another Jeep I built... My new ones are still in the box!