View Full Version : 340 hp exhaust manifolds versus headers.

10-13-2003, 04:05 AM
I have a set of 340 high performance exhaust manifolds. I was thinking about headers and selling my manifolds. Is there an advantage other than appearance. I am assuming the headers work significantly better, but my father keeps hounding me not to sell the manifolds. And one other question while I am on this topic what was so specail about these manifolds? Other than the fact they look like a cast iron header.

10-13-2003, 09:15 AM
I have been told many times never to sell anything on a car if it was an original part.

10-13-2003, 10:13 AM
Thats a good point. You'll probably have a hard time getting them back if you ever wanted to. Keep the manifolds. Smart idea.
The flow of the manifolds for that 340/year are the best flowing manifolds made by Chrysler. The Magnums are a tie. The first Magnums exhaust manifolds were 2 1/14 outlet size.

The headers should make a nice amount of power over the manifolds. Instalation can really suck on the 1 5/8 sized tubes.
Besides (HP) power, your torque also jumps. Since the engine is making more power and breathing easy now, you'll get more miles to the gallon. Rejet the carb for best results.

Blaine Peterson
10-13-2003, 10:23 AM
The manifolds that you're talking about flowed pretty good for stock manifolds. And once the manifolds are in place theres really no muss no fuss.
Where often times with headers theres the increased underhood temperatures, low ground clearance, blown flange gaskets, etc.
But theres alot to be said about a quality set of headers that have been coated, fit well, and properly installed.

I'd still hang onto the stock manifolds though.

10-13-2003, 01:32 PM
Headers can sometimes be a really big pain in the a$$.

If you want them fine (I run headers too) but keep the manifolds.

You may regret it if you don't.:crying:

10-13-2003, 02:59 PM
I picked up a set of these that I plan on using. Would it be suicide to port these cast manifolds to get better flow considering their value? Or would it be a waste of time?

10-13-2003, 03:21 PM
You will see gains by gasket matching them to the heads.

Other than that, I don't think it's worth the effort. my .02

10-13-2003, 07:34 PM
I noticed a big improvement in performance when I went to the headers. They were a pain to install but I would never go back to cast manifolds. Hang onto them, you may change your mind afterwards. Headers do make a difference.

10-13-2003, 07:56 PM
Definately hang onto them. I remember a guy asking $600 Canadian for em this summer.
***BURP***...sorry its turkey day up (Thanksgiving) here!.Gawd I luv the stuffing....I know, it shows:D , right Doug and Dave?

10-13-2003, 08:23 PM
Thanks for all the input guys. I have decided to go with headers and just store the manifolds if I decided to go back to an original numbers matching resto, that is the main reson I kept my original cast intake. Anyone know of some reasonabley priced ceramic coated headers? I am only willing to spend $350 max.

10-13-2003, 08:46 PM
Purchase headers of your choice, sand blast them and coat with POR-15. Best bet if your not purching it done outright or fixing the old ones.

10-13-2003, 08:49 PM
Oh boy, here we go. At least it aint an A body:) $350 US leaves you alot of options. What about the rest of the exhaust? Probably have to upgrade there too. Whats on there now and what are your aspirations?

10-13-2003, 09:46 PM
well, nothing at the moment. The car is in pieces being worked on slowly. The engine and tranny just got finished a few days ago. There is no intertior in the car, it is all out and being worked on here in the next month or so. The exhaust is non-existant at the moment so I can techincally build what I want. I should add that $350 us the money I have to spend for headers alone. A local shop had a mandrel bender so I can get the exhaust later, money is not a giant issue with me (thank god for ebay selling), as I will not be driving the car till it is completely done.

10-13-2003, 10:47 PM
littlecampbell, happy thanksgiving to you too! I can hardly move, but its a good hurt. By the way, I sold my 340 cast manifolds for $100.00 about 5 yrs ago.....................STUPID ME!!!!!!!!

10-13-2003, 11:37 PM
I'm ok today. Ate way too much turkey yesterday. Went to the Northern Mopars thanksgiving campout.

They made turkey for 45 and only 30 showed. We had to make sure there were no leftovers of course. Oh man.....:help:

Seriously, I'm ok now.

LC, I don't think it shows any more on you than me LOL!

Doug, $100? You got anything else for sale?

Just kidding you man:)

10-14-2003, 07:19 AM
My 'Cuda came with headers..couldn't wait to toss em.. They droned, ran hot, and generally looked bad.

I found a set of AAr manifolds, had em jet hot coated (grey), and have not looked back.

10-14-2003, 10:45 AM
Originally posted by Mr.Mopar
I noticed a big improvement in performance when I went to the headers. They were a pain to install but I would never go back to cast manifolds. Hang onto them, you may change your mind afterwards. Headers do make a difference.

Were the cast manifolds you replaced the small block 340 high performance 68-71 versions, or some other cast manifold?

What headers did you replace them with? Can you comment further on the difference? This will be a street car but with perfomance only in mind.

I haven't put mine on...yet. Once I do, I'll have to get the exhaust replaced too, so I want to do it right the first time.



10-14-2003, 12:02 PM
Okay guys, I'm about to go off on headers again.

First off, 340 manifolds are a work of art, they work fairly well, and are equal to or better than shortie headers when the heat riser is removed and the flange area ported out to 2 1/2 inch. I ran some for a long time on my duster and had no complaints.

Headers, however, are a completely different animal. Rather than just providing a path for the exhaust gasses to exit the engine and a way to hook up the exhaust system, they enhance torque output and by so doing they increase horsepower. They perform their magic only when properly sized, have equal length tubes of enough length, and have a smooth transitory collector of the correct size.

Headers work by reflecting the pulse wave of the exhaust coming out of the port back up the tube and creating a suction at the exhaust valve, so that next time it opens, the gasses are pulled into the header tube. A second scavenge is created in the collector by the pulses of the other tubes connected to it, but only to a large extent when there is nothing of further restriction past the collector (like a muffler). These events ONLY take place when a tube sized to the horsepower and torque output of the cylinder is used and at such a length that the reflection will happen at a usable RPM.
The shorter the tube, the higher the RPM the header is tuned for. This is why shorty headers do not produce a scavenge (unless you rev the engine to about 14,000 rpm). Too large of a tube will actuall cost you power because the tube is too big maintain velocity at a usable rpm, and they actually make reversion easier, diluting the intake charge.

So what do you need for header sizing on a typical street mopar? Up to around 325 REAL horsepower, 1 1/2" tubes are ideal with a 2 1/4" collector. 350 to 425 horse, 1 5/8" with a 2 1/2" collector will make the gains where you need them on a street car without costing you top end power. So why are most small block headers sized 1 5/8" and big blocks 1 3/4"? I guess everybody's small block is supposed to make 400 horse and everyone's big block 500 horse! The 1 5/8" x 34" primary tube headers for small blocks do work well on a modified 340 or 360 (or Don's 318) with a stout cam, head work etc. But on a stocker, they do little for performance, and may even cost you some bottom end torque.

Just please give some thought as to the function of headers before absent mindedly bolting them on. Just as it is easy to over cam or over carb your combination, it is easy to over header your combo.

end of sermon.

10-14-2003, 12:07 PM
I am assuming by real you mean rear wheel power?

10-14-2003, 03:51 PM

So you are saying because the cast headers do not have long enough runners (they are like shorty headers), they won't help torque or horsepower (unless serious RPM levels), but they won't hurt either?

How much improvement would properly tuned header have over the hi-po manifolds? In my case, it's a mild 360 build with a six-pack, guessing 9-1, 915 "U" heads (don't know if they were ported) and above normal cam (unknown specs)?

I really have to tear down this motor so that I at least know what I currently have.



10-14-2003, 04:31 PM
by real I mean not imagined. I have heard of so many 500 horse small block chevies I could heave, but only a few can even get out of their own way. Bolting a tunnel ram on a stock 340 does not make it a 500 horse engine. It is very important to get the combination of parts right or you will end up with a slug.

The 340 manifolds are an improvement over the other stock manifolds due to lower restriction, headers will actually make you horsepower rather than just letting the engine make the power it could without choking on stock log style manifolds. The increase in horspower between manifolds and properly sized equal length headers is dependent on cid, engine combination etc., but I wouldn't be suprised to see 30 to 50 horse, and with proper jetting and timing even more. More importantly, the headers would increase torque across the power band making the car E.T. much quicker and be a helluva lot more fun to drive!

10-14-2003, 10:40 PM
I had the Hi-Po 340 manifolds and then sold them and installed the Mopar Performance headers. There has been quite some discussion as to who supplies headers to MP, it could be Hedman, Black Jack or some other brand. They look a lot like the old Black Jack headers that I bought back in the 70's. I had to bang them up pretty good in some areas around the passenger and drivers side torsion bars and around the power steering box and by the idler arm. I would really study the different types of headers before I installed another set. TTI seems to be the best? Hooker competition series I don't know about the fit but would like to hear back on this. As ajmopar so expertly describes, picking the right set is a task in itself but if you get it right you will be impressed.

10-15-2003, 10:30 AM
I had a set of 340 manifolds from a '73 340 I found.

I was told/informed that these were not the desireable sets like the earlier 68's and up.

Upon seeing some of the older sets, it seemed to me that the drivers side was the same, but the pass. side had the spring operated heat riser.

I didn't like the pinch the driver's side manifold has...I wasn't originally going to use headers until I saw that.

So, I got $50 whole bucks for mine. NOBODY wanted them.

I would only hold onto them if they came with the car...but, then again only if at least 95% of the car is original.

10-15-2003, 10:38 AM
I think you said you car was in pieces and you were going to headers.

I would install the headers before getting your front suspension back in place. It ought to save you a lot of fitment frustation.

I didn't do this and had to wrangle them in there, but no hammering. If the suspension is already in, at least unbolt the motor a use a jack to move it around.

Hopefully you are going to 15" rims...or have REAL nice roads where you live:D , I put a hole in mine within the first 500 miles with 14" rims. :crying: I fixed that hole and run 15" rims now.

Doug Wilson
10-15-2003, 12:34 PM
To add to what AJ said, for ideal output, the entire airflow system should be designed to function together. From air cleaner to exhaust tip. Including of course, carb, intake manifold, head flow, cam and, to a lesser extent, combustion chamber. There are some good formulae for figuring this stuff out, starting with the ones on edelbrock.com.

To do it right, off the shelf headers aren't good enough, because they are a compromise designed to work OK with most combos, be cheap to build, and have a pretty package so people will buy them, and above all to make acceptable profits for the manufacturer, WD, dealer, and install shop. Having your headers custom built after you do the math is the only way to get maximum performance.

This isn't my opinion, it's fact. The results from this approach speak for themselves.

10-15-2003, 04:08 PM
The '73 manifolds are basically truck manifolds (what my 'Cuda had). I had bought a set of 71 HP, a bit better, but both have a "center dump" design for the inboard cylinders on the driver side. Much better is the AAR T/A version, which are much more like headers.

They cost a bundle, and you need to put an adapter on the oil filter to rotate it (the AAR and T/A models did) so the exhaust pipe will clear it.

I can't say that the performance meets the needs of the 360/380 crate motor I have in there, but it should be fine for the 340 you are running, especially with a 600cfm carb..(I have the Edddy EPS 800, and contrary to many opinions here, it is not too much carb..great off idle response and low end..although what Eddy calls 800 CFM, BG would probably rate at 725 or so..)

10-15-2003, 09:18 PM
Hey AJmopar, check out this same thread on Moparts.com...interesting...:)

10-16-2003, 03:34 PM
Ive got a 340 in a streetrod using sanderson DD1 block hugger headers. Are these headers hurting performance of this engine?

George G. Leverette
10-17-2003, 04:36 PM
Mopar Muscle Magazine had an interesting article comparing headers to OEM manifolds, 340 exhaust manifolds and headers.
The results were something like 3-4 horse power for the 340 manifolds over stock and 7-10 for the best headers (TTI) over stock. This is from memory, every thing is a compromise there is no bolt on that add tremendous benefits unless the system is balanced. ( Of course the Primedia crowd can run out to Westec and generate 100 HP for $50,00 for their advertisers)

10-17-2003, 06:56 PM
That header test was a good one and made a valid point if you could see what they were doing or read between the lines.
Heres the skinny;

The engine was a create 300 HP 360 cid engine. At this point, (HP level) the power is low. Headers offer a slight gain in power and a tad more in mileage. The bigger the tube, the more power, but how much at what cost. Answer, not enuff power to justify the purchase, nominal mile gain over the cheaper small tube header.
Problems in real world use? Yes, lack of torque with the big tube header where you need and want it most.
Best bet to use? Ethier manifold or small tube header will do.

The big tube header will shine , and brightly at higher comp. and power levels. Use the tti or Hooker Super comps. , Not the small tube comps, for street strip power at a min.


It depends on your power level. There not to bad for low power levels. Under 360 HP I'd say.

10-17-2003, 07:17 PM
I switched from from Hedman headers to the Hi Po's serveral years ago on my mild 340 Duster. The rest of the exhaust is 2 1/2 inch, with crossover pipe to Flowmasters.

I just got fed up with the banged up tubes, leaking, rusting, burned wires, and general pain in the butt installation of headers on an A body.

As far a performance goes, it feels like I have better bottom end, and the rest of the powerband is very strong to 6000 RPM. They also sound awesome with the Flowmasters. They look great too, after painting. I really like them, but am tempted to try TTI's if I could afford them.

I think it depends what body style your car is. For A bodys TTI's are about all that fit properly. With your B or E body, I would try Coated Hooker headers -fairly cheap and easy install.

Moapr to ya,