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Sedans Dodge Charger Dodge Charger: Aftermarket Accessories & Performance Mods
74 messages, Last post on Nov 05, 2009 at 6:44 PM
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Replying to: losski (Jun 14, 2006 10:56 am)
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Replying to: xtec (Jun 15, 2006 2:36 pm) 
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While I haven't studied the any of the four engines that DC is putting into the Charger and its siblings, I do have a considerable amount of research history to offer an opinion as to why a large free flowing exhaust system can in many cases yield lower fuel economy and lower power at any given throttle setting. 1) Exhaust system harmonic resonance. This is a huge issue in 2-Stroke engines, and manufacturers spend considerable resources to tune the exhaust system such that the shock wave inside the header rebounds in such a fashion to actually aid in cylinder packing (volumetric efficiency). As any of you 2-Stroke dirt bike riders can attest, there is usually a fairly narrow "Sweet Spot" in the power curve where the power spikes. Said power spike is usually caused in these engines by the shock wave of the exhaust pulse rebounding off the back side of the exhaust chamber and then "pushing back" toward the exhaust port. As the intake port is almost always open before the exhaust port is fully closed, the combination of the pressurized intake charge and the rebounding shock wave leads to greater cylinder packing. 2) In 4-Stroke engines it was long ago found (like in the 1920s or 1930s) that engine efficiency (via better scavenging) was improved by opening the intake valve before the exhaust valve was fully closed, thus using the intake charge to help "Push" the remaining exhaust out. This technique is commonly referred to as "Valve Overlap", and my guess is that all of the Charger engines are so designed. 3) Assuming the Valve Overlap scenario holds true for the Charger engines, then by replacing the stock intake and exhaust system with "Better breathing" hardware, you will most likely find that the larger intake charge meets far less resistance in the combustion chamber during the period of overlap because the better breathing exhaust system is allowing too much scavenging. Said another way, with better breathing, you are effectively pumping a higher than optimal percentage of your unburned intake charge right out into the exhaust system before the exhaust valve closes. Regardless of how the engines are designed, the bet is that DC has tuned the harmonics of the intake and exhaust to match as best as possible the rest of the engine. To the best of my knowledge, the only way to successfully utilize a freer flowing intake and exhaust system is by installing a cam specifically designed to compliment the new plumbing (i.e. given the better intake flow and the better scavenging, the new cam will provide for a shorter period of overlap, or even eliminate the overlap all together). Once again, I have not researched these engines enough to know if my theory is true, so please don't quote my brief thoughts as fact. Let the discussion begin.  Best Regards, Shipo
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Replying to: shipo (Jun 14, 2006 10:36 am) Thanks for an excellent post, and allow me to add a few things. First, rest assured that any engine produced for the purpose of daily consumer use is far from utilizing an idealized harmonic resonance relationship in its intake/exhaust systems. Critical tuning such as what you are describing will exist only in the most carefully engineered and contemplated internal combustion engines (read: Ferrari, Lamborghini). The fact that John Q. Public can go out and slap a simple K&N filter on his V-8, along with a crummy Chinese exhaust system, and see a 15-30 hp increase is testimony to this fact. Trust me, DC, GM, Foad [sic], and whoever, all know how to make their engines produce more horse, but the reason they don't is simple; Engineering Economics, a.k.a., "...build the cheapest POS that will still get the job done, and get it out to the public...". The intake and exhaust systems sold with 99% of the vehicles today are produced with far more emphasis on cost reduction than they are in making power. This is (again) why aftermarket manufacturers such as Flowmaster, GHL, Corsa, etc., all can make a living - because John Q. Public is doing far more to assist the acoustic performance of his engine by removing the factory parts, than he is to hinder it. Just my two Euro. used2bfast
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Went to the dealer this morning, 7:00 am sharp, and bought the Dual Cat Back Exhaust kit (# 82209611) for the V6 3.5L Charger. Arrived at "Awesome Performance" (near work) and they started installation at 8:15 and completed at 9:00. Kit Cost $426.00 Install $120.00 (Dealer wanted almost $300.00) Sounds Great. Looks Great. I am VERY happy...... So far.....
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Replying to: discgolfer99 (Jun 28, 2006 1:43 pm)
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Replying to: losski (Jul 04, 2006 10:42 am)
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Replying to: xtec (Jul 05, 2006 2:04 pm)
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Replying to: discgolfer99 (Jul 06, 2006 3:44 pm) |
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Replying to: losski (Jul 04, 2006 10:42 am) |
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