Hi everyone. I just bought an '05 QC 4x4 Hemi in Bright Silver. I am new to the forum and this is my first post. I have been searching this forum like crazy for some info on the flowmaster replacement muffler for the Hemi. (want the truck to sound as sweet as it looks I checked flowmaster's site, but they don't show any mufflers for a 2005 Ram. Do they sell a 50 series replacement muffler for the '05 Hemi? If so, what is the part # and where can I order one at a decent price? Thanks!

 

All the kits for the HEMI I see utilize the 50 Series HD or SUV mufflers.

 

It would seem a relatively simple thing to get whatever muffler you want, of the correct inlet and outlet sizes, and any half-way competent muffler shop could do whatever necessary to install it--if the desired "kit" is unavailable.

In fact, with a cheapo exhaust pipe cutter, some adapters, and clamps you might be able to do it yourself. My new Ram hasn't arrived yet to climb under and look, but I've done this many times on other vehicles.

All the best.

 

The only thing I've heard is the rumor that HEMI's require a certain backpressure to function and develop the torque and horsepower, so if you open up the tailpipe too much, you could lose horsepower. Since the kits offer Series 50 Flowmasters and they've been made specifically for the HEMI, I would assume they are safe.

 

One more time- no gasoline engine... other than a 2-stroke is designed to need back pressure. However pipes that are to large or small will effect horse power and torque. To big can cause problems too but the talk about needing back presure is B.S.

 

But what do you think the diameter of the pipes is affecting then? Too narrow and the air doesn't move freely enough, too open and there is no resistance. Not being a jerk, I'm just curious if I'm thinking about this wrong. My degree dealt with airflow through pipes and over surfaces, and maybe I forgot something.

 

either way you look at it all your doing by putting on a different muffler is increasing the noise output, it isnt going to help you with your performance anyway, as has been discussed before, the stock exhaust was designed with maximum flow with the existing computer setup and there is little you can do by just adding a muffler to help your HP. I have cut open one of the factory mufflers and there isnt much restriction in it to begin with. If anything is killing flow, its the cats and possibly that stupid resonator. I havent taken my res off yet just because I like the stealthy approach into the driveway/garage, my garage door opener makes more noise than my truck does backing into the garage... "be very very quite" so that nobody knows that its 2 am in the morning when I came home!

 

Backpressure is a side effect. You want 0 backpressure ideally. What is vitally important is exhaust gas velocity. Too big of a pipe kills velocity at low RPMs for a couple of reasons.
1) Larger volume to fill, meaning the rate at which it moves slows down. Connect a 10' long garden hose to your faucet and time how long it takes to fill at wide open, then take a 10' long fire hose and connect it to the same faucet and see how long it takes to fill at the same rate. It'll take longer because the water (exhaust gas) velocity has slowed down drastically.
2) Larger surface area. The extra surface area means larger cooling surface. It's just like the radiator in front of your engine - bigger cools better. Gasses that cool down are contracting and becoming more dense. If you increase density but keep volume constant your velocity is going to drop.
3) Larger surface area revisited. You're also adding surface area friction by increasing diameter. A VW microbus and a cabover semi have roughly the same shape, yet the larger one has a lot more drag due to the increased surface area.

Why is this important? Camshaft profiles - overlap specifically. Your intake and exhaust valves are momentarily open at the same time and if you have a low exhaust gas velocity there is lower intake gas velocity, in a nutshell. The scavenging of exhaust gasses requires a bit of suction from the exhaust system, if you will, in order to pull the remainder of the spent gasses out of the cylinder as well as pull fresh mixture into the cylinder while the valves are overlapped. If you've got huge pipes the velocity is low and the vacuum is low as well, so it won't scavenge properly.

The flipside is that when exhaust scavenging isn't all that important - higher RPMs - you need a pipe big enough to flow as much CFM as your engine can pump. Too small of a pipe and they just can't flow the required amount of air through. Backpressure only increases with RPM.