Headers Vs. Exhaust Manifolds

[hemidude426ci]

So I recently pulled the motor out of my 'Cuda and am currently taking it from a 440-6 to a 512-6.  Its going to be just under 10:1 and have a roller cam.  My question is will I totally be choking this motor by going to a stock exhaust manifold vs a header?  I like the stock look and accessibility of the manifold, but will I be robbing myself of power?

[burdar]

THere's no question your going to be down on power compaired to headers.  The F.A.S.T guys make big power on manifolds but they've got alot of money into them.  You can always have yours extrude honed but that's expensive.  I guess it all depends on what your doing with the car.  If your not racing it then I guess max hp isn't an issue.

[MEK-Dangerfield]

If you are going up to 512 cubes, speed must mean something to you, right? I mean, this isn't a car you are just going to do some easy cruising in I feel. So you are definitely leaving some free horse power on the table if you don't go with full blown headers. I know the stock manifold look is nice, but if you get a set of ceramic coated headers, they look pretty good too.

[vinb]

Your 512 will need a good pair of headers to breath. Why go to all the trouble of building a engine with good power only to choke the exhaust..

My little 340 seen a big difference in power when I sent my headers out to get re-coated, I put my stock manifold's back on for a couple weeks. Man,  what a pig the Cuda was. The whole system was not balanced with the stock manifolds and the drone was really bad..

Don't even think about it, get a good pair of headers....

[tommyg29]

one word:


TTI

or actually three, but you'll get the idea

[Cooter]

Building a 512 Cu. In. engine and installing exhaust manifolds on it would be like taking shower with your raincoat on..............Screen doors on a submarine....
An elevator in an outhouse......

[Topcat]

A comparison shown here:

http://www.moparmusclemagazine.com/techarticles/mopp_0106_manifolds_vs_headers/dyno_numbers.html

[Aussie Challenger]

There is no comparison between headers & stock log manifolds, headers any day plus they look the part especially when you get the ceramic coated. If you leave the log maniflods on why not fit a 383, at least it is a BB.   
TTi everyday.   

[hemidude426ci]

Wow thanks for the feedback guys.  As the comment was made, I do care about power, and while I want this car to look as stock as possible, I don't want to sacrifice power.  I just was unsure if it would really make a noticeable difference.  Given that that's the case, Ill definitely opt for a nice pair of long tubes.  Btw does anyone have experience with a 440-6 that's been punched out to 512 and had a roller cam added? Definitely over 500' of lift and compression around 10:1.  Its going to be mated to the factory 4 spd and Dana w/4:10s.  All feedback appreciated.

[Moparal]

If you were close to my place, I could tune that 6pk for you. The promax metering plates is a plus.

[Chryco Psycho]

Port theheck out of the manifolds & try it , you will probhably have enough power , the torque will be killer & the higher RPM is where the HP will be limited

[Road_Runner]

Port theheck out of the manifolds & try it , you will probhably have enough power , the torque will be killer & the higher RPM is where the HP will be limited

How close HP-wise do you think you could get the iron manifolds to go?  I've got a set of 340 TA/AAR style manifolds I'd like to use with either the 318 or a 340 in the Barracuda but don't want to leave too much HP on the table.

Thanks, Jim

[Chryco Psycho]

I would have to look for some dyno #s , I have no direct comparisons but I think it would be fine at lower RPM , high RPM is where the big gains would be seen

[72bluNblu]

Here are some 340 dyno numbers from an article a few years back. They basically bolted stuff to a 340 and dynoed it after each mod. The first thing they did was go to an 800 cfm carb, but the second thing they did was ditch a set of 340 TA manifolds for a set of 1 5/8" Hooker headers (These are the cheaper Comp headers, not the 1 3/4" Super Comps like I run). They start the dyno at 3000 RPM, at that rpm the headers make an extra 4 hp and an extra 7 ft/lbs of torque vs the manifolds (with the carb). Not a ton, but at peak, the headers made an extra 14 hp and 17 ft lbs of torque. What I found a little strange is that it actually moved the torque peak DOWN 400 rpm vs the manifolds, peaking at 3600 rpm, and holding peak numbers longer than the manifolds.

So, with an otherwise stock 340 (just a big carb and headers), its not an insignificant change. Not a huge one, but keep in mind the more things you do (intake, cam, compression etc) the more limiting the manifolds will be.

Here's the page with the results and the header info, a little hard to read but you're comparing test 3 vs 2.

[Road_Runner]

Thanks guys, the chart shows about what I would expect I guess HP-wise between the two exhausts.  I think what all this is telling me is that if my goal is a mild gain over stock, than the stock exhaust, intake, etc. work well enough together to perform decently.  If I go with bigger heads, cam, compression, etc. I'm creating a choke point with the manifolds because they no longer flow enough to match the rest of the motor.  I'm also not sure I could bring myself to 'mess' with the TA manifolds since they are pristine and not that many are left.  I really like the idea of a stock 'looking' engine in the Barracuda, but don't want "buyer's remorse" when I start wishing for more HP/TQ when somebody spanks my 'stock' 340!

Later, Jim