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Shorty headers for an LX: Worth it?

Discussion in 'Performance' started by Tommy Boy, Jun 1, 2017.

  1. Fast Eddie

    Fast Eddie Valued Member
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    All of a sudden a story came to mind from my dyno days at Chrysler when we were doing the rating runs ( numbers for advertising). I was running "full spread" of runs from full gross to full net (which is the way the engine is equipped with in the car) all the way to a complete car exhaust system for a 383 Road Runner engine. So I got to the last run where I had to put on the chrome exhaust tips and run a final test. We were really surprised when we lost around 5 HP by putting the tips on. So we ran the test 2 more times and the same thing happened so we just used the numbers for the test without the chrome tips. Could never figure out why it happened. When I ran the same type of tests on the 440 there was no loss so it was one of those quirks you can't figure out.
     
  2. Tommy Boy

    Tommy Boy Active Member

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    I would think changing out the mid pipes would necessarily require a re-tune because of the different cats?
     
  3. Mike V.

    Mike V. Mopar-nac The Moderator
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    No. A catalytic converter is a catalytic converter.

    Mike
     
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  4. DC-93

    DC-93 Active Member

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    Another story - on DC-93, when it was still a Charger 500, they discovered the outlet angle cut of the exhaust dumps changed lap times by up to 1/2 second per lap at Daytona!! That is huge for a simple bologna slice!
    They surmised the air going by the dumps was pulling out the exhaust pulses.
     
  5. HemiJeepMagnum

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    I am the newbee on the block and have just started snooping around a bit. Since mid 2004 I am, or have been active on several other automotive forums......Jeep (WK), early 300C, Magnum, Charger (LX), and Mercedes and am a moderator on one of them. I have both a Hemi WK (Jeep Grand Cherokee Overland) and a Hemi LX (Dodge Magnum) which are both modded exactly the same.

    I know this thread is several months old, but I just found it and thought I'd offer my two cents worth FWIW. IMO, most of the comments offered in this thread are pretty accurate in one way or another....some more than others. I'll offer my first hand experience with regard to some of the Hemi mods. and explain the results I achieved with them. When I did a mod on one, I would soon do the same mod. to the other. I did all these mods. in what I considered to be a "logical" order, so as to get as much benefit from each as possible....i.e. do the intake and exhaust before doing the cam and heads. My main goals were a moderate increase in performance and improved fuel economy. As anyone who owns one of these vehicles knows, fuel economy isn't one of their strong points. Most also know that the Hemi is a pretty well thought out engine that leaves a lot of room for improvement without seriously invasive mods. The mods. that will improve both performance and fuel economy are mods. that will improve the Volumetric Efficiency (VE) of the engine. This basically means improving the airflow through the intake, combustion and exhaust tracts so that there are as few restrictions (bottlenecks) as possible. Also, if one goes too radical with these mods., you'll pretty much kill the bottom end (lower RPM), adversely affect driveability, but gain horsepower at the expense of fuel economy. All this being said, here's my take on some of the mods., especially the exhaust system.

    1. As said, if you're going to do headers, to better manage under hood heat, coated headers is the way to go. I have titanium coated JBA shorties on the LX, and custom ceramic coated mid-length headers on the WK. On both there are wire bundles in the area of the exhaust which were previously protected by aluminum shrouds around the stock logs. Also, be aware that the LX and WK exhaust logs ARE NOT interchangeable. I've tried it.

    2. As said, installing headers on either is a giant PITA without the correct tools AND a lift. I have both in my garage and, my son and I have gotten pretty good at doing this task. One note here, if you're planning to do this job, and not have to do it over because of flange gasket leaks and bolts coming loose......with 3/8 in. header flanges, use a good quality flange head bolt (8mm-1.25X25mm, 17 each), a good quality flange gasket (I use Percy's, seal for life dead soft aluminum gaskets, P/N 66040), and Nord Lock Wedge Washers. Reference the effectiveness of these washers here: http://www.nord-lock.com/bolted/watch-the-new-junker-test-video-here/

    3. You will not get the full benefit from tubular header without a low restriction (both mine have straight through mufflers and resonators.....no switchback mufflers.

    4. If you don't want the dreaded Hemi MDS drone, you'll have to keep some sort of resonator, and stay away from "loud" mufflers.

    5. On the Hemi LX, don't expect a giant gain in horsepower/fuel economy, except above about 3500 RPM. Even then, the increase will probably not be noticeable with your rear end dyno. On the Hemi WK, it is a different story. The factory WK exhaust logs are more restrictive than the LX's.....smaller log ports and 1 7/8 in. collectors vs. larger ports and 2 5/8 in. collectors. See photo below, showing WK logs, LX logs, and my custom WK header collector with a 3 in. collector. The complete WK exhaust system netted a noticeable power increase and a 1.5 mpg increase in highway fuel economy. The complete LX exhaust system netted only a very slightly noticeable increase in power and less than one mpg on the highway.

    6. Know that most well thought out mods. that increase the VE of the engine are, at least, somewhat cumulative. In other words, they all won't give big improvements, but will all (done correctly) can provide substantial gains. Here are the mods. I have on both my Hemi vehicles, in the approximate order that I did them:
    a. SRT airboxes with and additional inlet cut into the box and channeled to behind the grill. TrueFlow air filters.
    b. BT catch cans. The Hemi's have a terrible vapor recovery system, and this helps negate the adverse effects by catching much of the oil/condensation that the system allows through. This helps keep the intake, combustion and exhaust tract cleaner than it would be without it. If in doubt, check the back side of the throttle body butterfly and intake plenum to see all the caked on oil. Believe me the rest of the combustion/exhaust tracts will look the same.....worse with dino. oil than with a good synthetic. See photo below of intake ports.
    c. Headers/complete cat. backs.
    d. Tuners. I use a Diablosport Predator on the LX and a Superchips w/Advanced Transmission Tuning Application.
    e. Frank's Racing (FRI) Sidewinder cams with 6.1 valve trains, WK advanced a total of 6* and LX advanced a total of 10*.
    f. Mopar Performance Transmission Control Module for the LX and Transgo Shift Kit, Sonnax Line Pressure Booster and my custom shift schedules/torque management settings for the WK.
    g. SLP 25% underdrive crank pulleys.
    h. Arrington 90 mm throttle body on LX and BBK 90 mm throttle body on the WK.
    i. Sultans of Spark (SOS) ignition coils w/.060 in. spark plug gaps.
    j. Total Engine Airflow (TEA) ported/polished/milled heads.

    With all these mods., when driving on the highway at the approximate "sweet RPM spot" of ~2100-2400 RPM, both the LX and WK fuel economy has improved by about 25%......LX, ~23 to 27-29 mpg and the WK, ~18 to 22-24 mpg. P10104591 (755 x 565).jpg P9040017 (755 x 565).jpg
     
    #25 HemiJeepMagnum, Oct 18, 2017
    Last edited: Oct 18, 2017
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  6. MPE426HEMI

    MPE426HEMI Well-Known Member

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    Dollar per dollar value, none of that is worth the money on the 5.7 unless you have a dedicated race car and need to use that engine size. There are better factory engine choices available. It would be better to grab a 392 car/SRT.
     
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  7. Tommy Boy

    Tommy Boy Active Member

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    Thank you for the thorough post, HemiJeepMagnum. The difference between the Jeep stock manifolds and the LX ones can be clearly seen! For $1000 and no real seat of the pants yield, this doesn't look like the best money spent.
     

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