Performance loss from headers to HP manifolds

Small Block Mopar Engine

  1. MrMopar

    MrMopar Well-Known Member

    Messages:
    120
    Likes Received:
    1
    Joined:
    Jul 7, 2004
    Local Time:
    3:49 AM
    I am going to instal the 68-70 340 high perf exhaust manifolds instead of the Mopar Performance headers that are currently on the car. The headers have been flattened out on the drivers side bottom 2 pipes as you all know can happen on the A body. But I am concerned about the HP loss when I do this. Putting any kind of header except for TTI's on the Dart is a real pain in the butt and am not looking forward to doing it all over again. I have the manifolds and would like to know how much power will be lost or is it going to be negligable and not really noticeable. Anyone out there do this "backwards" installation?
     
  2. Rick 5150 69

    Rick 5150 69 Well-Known Member

    Messages:
    111
    Likes Received:
    7
    Joined:
    Jul 14, 2006
    Location:
    Calif
    Local Time:
    9:49 PM
    I think you`ll notice your low end torgue will improve, the upper mid range, and top end rpm will suffer, if your not racing you`ll probably not notice, I have fixed my kids twice now, by drilling a hole and using a dent puller, and plug weld the hole and by cutting and replacing sections, easier than pulling and replacing... for now anyways..
     
  3. rumblefish360

    rumblefish360 So close, yet so far away FABO Gold Member

    Messages:
    38,379
    Likes Received:
    10009
    Joined:
    Jun 21, 2005
    Location:
    New York, on a Island
    Local Time:
    10:49 PM
    It's build dependent. 20 HP
     
  4. moper

    moper FABO Gold Member FABO Gold Member

    Messages:
    15,709
    Likes Received:
    1849
    Joined:
    Dec 27, 2004
    Location:
    eastern CT
    Local Time:
    3:49 AM
    All depends on your exact combo. I've seen less than 10% difference in published dyno specs, but I think that has a lot to do with re-tuning after the swap to optimize the maniffolds. I feel more than that when I pull the cheapie headers. But, with the right cam, you can make similar power, just not as much.
     
  5. dgc333

    dgc333 Well-Known Member

    Messages:
    4,125
    Likes Received:
    20
    Joined:
    Jan 12, 2005
    Location:
    Pembroke, MA
    Local Time:
    10:49 PM
    Long tube (under chassis) headers tend to improve the low end power so you will notice a loss through out the rpm range.
     
  6. rumblefish360

    rumblefish360 So close, yet so far away FABO Gold Member

    Messages:
    38,379
    Likes Received:
    10009
    Joined:
    Jun 21, 2005
    Location:
    New York, on a Island
    Local Time:
    10:49 PM
    Now that moper mentions it, I remember reading a write up on a 340 years ago that went from the manifolds to 1-5/8 headers with a disapointing 25 HP gain.
    Recently, (1 or 2 years ago....is that recent?) Mopar muscle did a thing on header types.
    Comp Cams has a small line of cams for use in engines with exhaust manifolds. The duration specs are wildly long for the exhaust manifolds restriction.
     
  7. MrMopar

    MrMopar Well-Known Member

    Messages:
    120
    Likes Received:
    1
    Joined:
    Jul 7, 2004
    Local Time:
    3:49 AM
    Now I am not sure if I want to do the swap back to the old HP exhaust manifolds. It is hard to turn back once you have experienced the power before. Maybe a set of TTI's will have to be in order and sell the HP manifolds to someone who is looking for stock appearance and performance.
     
  8. RPM

    RPM Superior Member

    Messages:
    3,218
    Likes Received:
    16
    Joined:
    Apr 5, 2006
    Location:
    Meridian, Idaho
    Local Time:
    8:49 PM
    keep me in mind on those manifolds....if the go for sale....

    -RPM
     
  9. 388dart

    388dart Well-Known Member

    Messages:
    547
    Likes Received:
    3
    Joined:
    Oct 26, 2005
    Local Time:
    8:49 PM
    Mr. Mopar - just bite the bullet and buy the TTIs - they are considerably cheaper in Cdn funds now than when I bought mine - albiet still expensive.
    You going to the swap meet in Reddeer on Sat 14th?
     
  10. Jim Lusk

    Jim Lusk Well-Known Member

    Messages:
    4,406
    Likes Received:
    752
    Joined:
    Mar 8, 2006
    Location:
    Fresno, CA
    Local Time:
    7:49 PM
    On a mild motor you will experience much less of a difference than on a built motor. It also depends on your purpose for the car. I'll stick with cast iron for mine.
     
  11. MrMopar

    MrMopar Well-Known Member

    Messages:
    120
    Likes Received:
    1
    Joined:
    Jul 7, 2004
    Local Time:
    3:49 AM
    I arranged to have the weekend off so I just may go to the swap meet on the 14th. Last time I went, there wasn't a whole lot of Mopar goodies around. Mostly Chevy and Ford. O.K., here is my set-up:

    340 bored .030 using stock cast 10.3:1 pistons , block decked .010
    J heads with a mild port and 2.02 intakes installed, milled .035
    Edelbrock LD340 intake with Holley 3310 750 cfm vacuum sec. carb
    Comp cams XE268 Extreme energy cam
    Felpro .050 head gasket ( needed more thickness so the valves wouldn't hit, being cautious!)
    Final comp ratio 9.8:1 The stock pistons are not near 10.3:1 as advertised.
    Mopar performance headers
    Sniper NOS 125 HP jets.
    2/14" exhaust with H-pipe into Dynomax Super turbo mufflers and tailpipes.
    3.21 rear gears
    727 trans with TF2 shift kit and 2500 stall convertor.

    Maybe I need the headers with this set-up, maybe the cast manifolds will choke it too much. More input needed please.
     
  12. moper

    moper FABO Gold Member FABO Gold Member

    Messages:
    15,709
    Likes Received:
    1849
    Joined:
    Dec 27, 2004
    Location:
    eastern CT
    Local Time:
    3:49 AM
    I think manifolds would be fine..And that 268 cam should clear the pistons by a mile, even with no valve releifs. But, running NOS thru it will really restrict things. If it were me, I'd run the manifolds without flinching a bit, but I'd upgrade to a 2.5" exh system. The XEs extra duration will help pump the exh thru the manifolds. I dont think you'll lose much unless you consider the choking from NOS use. And all that means is instead of 125 ish HP, the kit will make 100. Not a big deal IMO.
     
  13. D-mailman

    D-mailman Well-Known Member

    Messages:
    573
    Likes Received:
    13
    Joined:
    Aug 24, 2004
    Location:
    Lexington,ky.
    Local Time:
    3:49 AM
    What Rick said. Fix it. Pull'em and cut out the flat section and weld in a new piece. Always a good idea to save 'old used' headers. Never know when they will come in handy. Easy fix...you can do it, and it isn't 700. bucks. Good luck, Terry.
     
  14. Dart360Custom

    Dart360Custom Member

    Messages:
    149
    Likes Received:
    0
    Joined:
    Sep 3, 2006
    Location:
    Ooltewah/East Ridge,TN
    Local Time:
    10:49 PM

    Im fixing to do the same thing except on the car. Same 2 tubes as the thread starter also
     
  15. MrMopar

    MrMopar Well-Known Member

    Messages:
    120
    Likes Received:
    1
    Joined:
    Jul 7, 2004
    Local Time:
    3:49 AM
    Pulling the headers and then putting them back on is not an option, once they come out, they are staying out, the Mopar Performance headers fit like crap and were a real bear to get in the driver side. I guess I will put the manifolds on since I have them, and try it out. If it doesn't work out then it will be a toss up between TTI and Dougs headers. Thanks for all of your opinions.
     
  16. rumblefish360

    rumblefish360 So close, yet so far away FABO Gold Member

    Messages:
    38,379
    Likes Received:
    10009
    Joined:
    Jun 21, 2005
    Location:
    New York, on a Island
    Local Time:
    10:49 PM
    I'd do the tti's (money is just falling out of mu pockets as well <jk>) and 2-1/2 exhaust pipe with that set up
     
  17. Longgone

    Longgone John/68 Barracuda & Dart

    Messages:
    7,091
    Likes Received:
    41
    Joined:
    Jul 12, 2005
    Location:
    Newport News, Virginia
    Local Time:
    10:49 PM
    This thread touches on many things that I`ve experienced with my car. I like cast manifolds , so I talked to the techs at Comp, told them what I wanted and now I`ve got a cam that`s designed for cast iron manifolds and high compression. It makes great power across a wide rpm band. I went through the header thing and (they are for whatever reason, leaks, bad fit ,noisy) a total pain in the ass and always have been. I happily went back to my cast iron manifolds after fighting a set of chassis headers in with a big block. I agree with others here that you`ll only see a great loss in potential HP in the upper rpm range and that the build of the engine will dictate the gain of power with headers. If you plan to race the car a lot ,then I`d fix the headers with a patch. If you want a nice street machine that will still smoke `em from stoplight to stoplight then go with a cast manifold, they`re a lot less problematic.
     
  18. 1968FormulaS340

    1968FormulaS340 Well-Known Member

    Messages:
    11,541
    Likes Received:
    474
    Joined:
    Aug 24, 2005
    Location:
    St. Helens Oregon
    Local Time:
    7:49 PM
    Not an exact HP loss number but..... I went from headers and 3", dump at the rear exhaust to 340 HP manifolds, TTI 2.5" x-pipe system. My best time with headers and slicks was a 11.78 @ 118. My best time with manifolds and E70-14 (Firestone Wide Oval, Redlines) was a 13.2 @ 105. The 13.2 pass was on a Ram clutch with at least one broken pin.

    Some other changes between the two were.

    SS springs to Mopar HD springs
    Electric fan and water pump drive to stock set up
    Battery in trunk to battery under the hood


    original 340 and X heads, Ported and balanced
    Crower solid street roller cam
    Victor 340 with Holley 800 DP
     
  19. moper

    moper FABO Gold Member FABO Gold Member

    Messages:
    15,709
    Likes Received:
    1849
    Joined:
    Dec 27, 2004
    Location:
    eastern CT
    Local Time:
    3:49 AM
    I wouldnt call that apples to apples..lol..But the mph drop shows a loss of 115hp. I'd call that a little drop...but your cam I'm sure depends on scavenging effects from the headers that no longer exist, and the plenum is huge for the restrictive exh side too. So that drop doesnt surprise me at all.
     
  20. OldVart

    OldVart Well-Known Member

    Messages:
    5,428
    Likes Received:
    9
    Joined:
    May 24, 2005
    Location:
    Forestburg, Alberta, C eh n eh d eh
    Local Time:
    8:49 PM
    MrMopar, a little off topic, but are you located in Daysland? If so, I'm 25 minutes South of you in Forestburg - small world. We'll have to get together over a cold one and swap some Mopar stories some day. :) PM me if you'd like.
     
  21. Locomotion

    Locomotion Well-Known Member

    Messages:
    2,932
    Likes Received:
    468
    Joined:
    May 31, 2004
    Location:
    Florida
    Local Time:
    10:49 PM
    Here is the interesting article comparing a variety of exhaust manifolds and headers that rumblefish360 mentioned. Each step shows small increases, but they are throughout the rpm range thus increasing the all-important "area under the curve".

    I believe that a little more gear and converter, along with headers, would really help that engine, especially with the bigger valves and ported heads.
    The TTI's work very well with my 360 Commando crate engine as well as on other Magnum 360's in the class.


    Mopar Muscle Article:
    http://www.moparmusclemagazine.com/techarticles/155_0307_mopar_crate_engine_exhaust/index.html

    TTI Exhaust website:
    http://www.ttiexhaust.com
     
  22. MrMopar

    MrMopar Well-Known Member

    Messages:
    120
    Likes Received:
    1
    Joined:
    Jul 7, 2004
    Local Time:
    3:49 AM
    I did have 3.91 gears in it and it really went well, to the tune of 12.30@115 mph. But I got tired of the high rpms crusin on the highway so the 3.21's went in it. I called the Comp Cams tech line about what kind of cam to use with the stock manifolds and he said that the XE268 has enough exhaust duration to do the trick and that it was basically designed with that in mind. He did not recommend another cam to use and even stated that it would be good with the NOS. So there you have it, something that I never thought about. This has been a real good thread as far as all opinions are expressed and the learning never stops. Any input is always appreciated. Thanks guys!
     
  1. This site uses cookies to help personalize content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.