Re: 5.7L American Racing Headers!
Wow, lots of info. and opinions on this thread....some good and some not so good. Jeff turned me onto this one and wanted me to give my input, for what it's worth.....which by the way isn't much. As he said, I have two Hemi vehicles (WK and LX) that are both modded exactly the same except the WK has a 90mm throttle body and the LX has and 85mm throttle body. Other than that, down to the custom modified SRT CAI's, they're the same.
I've been messing with almost any kind of internal combustion engines (from model airplanes, to autos, to aircraft turbines and everything in between) for longer than most of you have been alive.....well over 40 years. I've also, in the distant past, built race car chassis, racing transmissions and racing engines, so I feel I am at least a little qualified to put my TWO CENTS worth in here. A lot of stuff I'll say here has been covered in the 13 or so preceeding pages, and I agree with some of it and don't with others.....after all everyone is entitled to their opinions, even though they may be wrong.
Since this thread is about HEADERS, I'll first give you my opinion of their value on MOST newer vehicles, especially those with crappy exhaust manifolds and cat. backs, such as we have on our 5.7 Hemi's. I've not seen a much worse system on any factory semi performance vehicle as the one that came stock on our WK's. See the pix below for a comparison of the stock WK (left) 1.75 in. collector, stock LX (center) 2 5/8 in. collector, and my custom tubular headers (right) 3 in. collector that I had built over 5 years ago. If, along with an efficient low restriction cat. back, you don't think a well built header back system will make a significant improvement in engine performance (and economy), I am here to tell you that you're sadly mistaken. It's beyond me why Chrysler, or any other auto manufacturer would install a potentially serious performance engine in a vehicle and then CHOKE it up with a crappy exhaust system. After all, the engine is just an air pump, and the better the volumetic efficiency [VE] (the ability to process this air expressed as a %age), the better the engine will run, perform and provide better economy than one that is being strangled.
There are many other variables that enter into it too, not just the headers, to take into consideration when attempting to improve the VE. One needs to make sure the incoming air (intake system) is as unrestricted (and cool) as possible, cylinder heads/valves are properly sized, the valve timing (cam) is adequate for the desired purpose, the ignition system (coils/plugs/wires) is capable of delivering adequate spark at all operating RPM, and the exhaust (from header to tail pipe tip) is efficient enough to get rid of the spent gases with proper scavenging.....too small will restrict and too large will slow down the exhaust process. Our stock Hemi intake system (without the silencer and with an Airaid or SRT intake tube and a good low restriction air filter) is more than adequate to deliver more air than the STOCK 5.7 is capable of processing......which is less than 600 cubic feet per minute (CFM) at ~75-80% VE, or a little less than 660 CFM @ 100% VE. The stock airbox is capable of processing (ref: flow bench tests done on Hemi LX vehicles over on LXforums.com) just under 700 CFM.
I could go on and on here, but know that ANY GOOD LOW RESTRICTION HEADER BACK system that is properly set up on our Hemi WK's will deliver a quite noticeable difference in both performance and highway fuel economy, but in town mileage may not improve that much. On mine, with the current mods. (see signature), I routinely get 22-23 mpg (high of 24.41 mpg) on the highway and ~13-14.5 mpg in town. My quarter mile times have dropped more than a second from stock elapsed times.
Also, just installing a good header back exhaust system WILL NOT require a canned or custom tune, but also won't hurt any. With my mods. I've run the stock tune a couple times, just because everyone said it wouldn't work. It does work but is really crappy, as the stock tune can't take advantage of the better camshaft, higher RPM potential, and the transmission really doesn't like the additional power.....in fact it doesn't like the stock power either. IMO, if you want to make a noticeable improvement to your Hemi WK, the best place to start is the weakest link....the exhaust. If you want to go further, get a tuner (I prefer the Superchips with the Advanced Transmission Tuning Application), and further yet, add a cam. None of these mods. require a lot of work.....just $$$. The exhaust is, by far, the most costly.....my complete custom header back system ran ~$1400 about 5.5 years ago, the tuner about $400, and the cam/kit about $700-800. My dyno is the drag strip (I'd rather spend $$$ on mods. than dyno pulls), and I figure I've gained nearly 100 hp. as I am set up now. Next step for me would be a bigger set of heads, but they would be the most costly (~$2000) of all my mods. and only deliver about 30 more horsepower.
05 LX/RT & 06 WK/GCO, modded similarly, MDS "ON" Light, Vortex Gens, Debadged, DashHawk, BT Catch Can, SRT CAI W/Add Air Inlet, K&N Filter, Sonnax Trans Press Booster, SC Tuner W/Adv Trans Tuning App, DS Tuner, Cust tube headers w/3 in. catback, Bilsteins, SRT frt/rear bumpers, Eibach SRT Lwr Sprgs & Sways, FRI Sidewinder Cam Adv 2*, 6.1 valvetrain, SLP 25% UD Pulley, BBK 90mm TB, SOS Coils/.060 plug gaps. 20 in. SRT Reps.