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-   -   New Muffler = Loss of Power??? (http://www.ramforumz.com/showthread.php?t=62190)

BigOrange 09-24-2010 12:03 AM

New Muffler = Loss of Power???
 
2008 Ram w/ 4.7L
I just switched from an 18" XLerator Single 3" in, Dual 2.25" out with pipes straight out the back to a 14" Magnaflow Single 3" in, Single 3"out directly into a 3" to 2.25" Y-pipe into the existing 2.25" pipes out the back. I did this because the XLerator didn't produce the sound I was looking for. It actually made a terrible low bass drone from 1200-2200 rpm that was really annoying & really lound..... it didn't even sound like a V8!!! The problem is that I lost a noticable amount of power. The engine feels like it's working harder, and doesn't pull as much on the top end. Does this sound right for going from a 18" SI/DO to a 14" SI/SO muffler with a y-pipe? I didn't think it would make a performance difference, and the muffler guy said it would flow the same as well. Any thoughts on whats going on here? I'm also wondering if an 18" Magnaflow SI/DO would make that same deffening bass drone that the XLerator made under light ecceleration....
Also, I did unplug the battery for a while to do a computer reset, but that was 6 days ago when I had the muffler installed. Also running an Airaid Modular Intake tobe to the factory airbox with a K&N drop-in filter.
Any input, thoughts, or ideas would be great here! Thanks!

moparmanicac 09-24-2010 12:31 AM

hmm possibly the change in back pressure and the pcm needs to re learn just my 2cents

4pnt7 09-24-2010 12:50 PM

Samething happened to me. I bought a flowmaster 40 series. I lost all of bottom end. I switched to an Aeroturbine 30/30. Great mufflers.. it was a nice performance muffler. It did drone a little. Then went with an Aero Stealth 170. It was perfect for me. It was a smooth sounding muffler. I didn't loose performance. And it sounded great at wide open throttle. This was all on an 02 4.7l with more Mods.

On my 08 I'm going to use the bigtank 248. Its another stealth muffler.

BigOrange 09-24-2010 01:08 PM

would the pcm re-adjust to make optimum power for the amount of backpressure that there is now? or will I just have to get used to not having the power I had with the SI/DO muffler?

Race1Mopar 09-24-2010 04:14 PM

Back pressure is created by exhaust scavenging and how efficient it is. My guess is that's it's scavenging better and more than before, creating less back pressure. Not sure in tis engine, but in the magnum engines if you took too much of the back pressure away you lost your bottom end grunt.

AIR RAM 09-26-2010 10:14 AM

Quote:

Originally Posted by Race1Mopar (Post 318293)
Back pressure is created by exhaust scavenging and how efficient it is. My guess is that's it's scavenging better and more than before, creating less back pressure. Not sure in tis engine, but in the magnum engines if you took too much of the back pressure away you lost your bottom end grunt.


I hope you don't take this the wrong way but it sounds like you have Back Pressure and Scavenging mixed up to where they some how work together...

Back pressure is NEVER good... No engine on earth has ever needed or needs back pressure. Back pressure is a product of restriction, the words Back pressure and performance should never be used in the same sentence... the term back pressure does not belong in the performance minded vocabulary.

Back in the day when old timers did not understand the physics and dynamics of the exhaust system they would relate loss of torque to loss of back pressure simply because they went too large on the pipe they assumed they had lost some back pressure... There for they preach its importance and they have passed it on through the generations. Many people will speak about the importance of back pressure but have very little understanding on why or how it effects the system... they just know somone told them it was important. Understanding the theory of operation will help anyone put myths like that to sleep.

What they had lost was velocity. Velocity through the system is needed to keep the exhaust gasses flowing through the system... with high velocity you create vacuum... other wise know as the "scavenging effect". If you go too large on the ID of the system for the amount of air the engine can pump, you lose the velocity.... NOT BACK PRESSURE.

This velocity is pulling the gasses through the system. This effect is most important at the exhaust valve. The more vacuum your exhaust system makes the more toque you will make... but how? What is it about the vacuum and exhaust that makes toque... Hint... its not magic!

Most all NA cams are designed with an overlap of the exhaust and intake valves. This means that for a very short duration both the intake and the exhaust are open at the same time... Why? This is so your intake charge can benefit from that exhaust vacuum your system SHOULD be creating. Just before your exhaust valve closes the intake side starts to open... the vacuum on the exhaust side pulls the intake side into the cylinder effectively filling the cylinder with more air. This is a form of force induction... Not like a supercharger or turbo... but the same theory apply s. More air = more power! When you install an exhaust system that is too large it does not create the needed vacuum until the higher RPMs when the engine is moving enough exhaust to make create the scavenging effect. This is why you lose bottom end when you go too large. Its not the loss of back pressure, instead its the loss of low RPM velocity.

To get a better idea how the scavenging effect works, think of it like when draining a pool of water.
With a hose in the pool hanging over the edge from the pool onto the ground you simply create an initial vacuum on one end to get the water moving... BUT once the water is moving it continues to flow with no power source.

Think of the pool as the cylinder, the water as the exhaust gasses and the hose as your exhaust system. Go to large on the hose and it will not have the needed velocity to keep the flow moving go too small and it will be restrictive. But with the right amount of velocity in the exhaust system the vacuum created in the system continue to pull from the cylinder end.

Exhaust systems are not a one size fits all... But we are limited to whats available... so most of us have to make a sacrifice going either too large or too small. But never forget...

Back pressure = BAD (Restriction)
High Velocity = GOOD (Scavenging)

SPEED SAFE, NICK

Atlantic Blue 11-16-2010 06:43 PM

Exhaust
 
AIR RAM
Thanks for the explanation - im about to replace my exhaust with a Gibson Single system.

GTyankee 11-16-2010 08:00 PM

a few years ago during the BAJA 500 race, there was a vehicle that hauled ass across the flats it was close to the front runners on time, but, then they hit the hilly section & that vehicle fell well back, then that vehicle bottomed out & the exhaust pipes were partially dented.
that vehicle didn't finish first, but, that little bit of restriction, still let him haul a** across the flats & he didn't get passed on the hilly sections after that.
I don't know any technical stuff, but, i know that it worked

drivehard27 11-16-2010 08:36 PM

man i dont now what to tell ya i have a flowmaster and i have tons of low end when it was stock i could not rip the tires now i can rip them allday and that is all i have right now no cai or programer just a flow master 40 and i had them just replace the muffler and weld up to the stock pipe .but i will say this if i were to do it again i would get a magnaflow a friend of mine has one and it sounds deeper .i think it might just be the computer mine took about a week and about 500 miles and then it ran better i even get better mpg now

OldMoparMan63 11-23-2010 05:39 PM

Quote:

Originally Posted by AIR RAM (Post 319510)
What they had lost was velocity. Velocity through the system is needed to keep the exhaust gasses flowing through the system... with high velocity you create vacuum... other wise know as the "scavenging effect". If you go too large on the ID of the system for the amount of air the engine can pump, you lose the velocity.... NOT BACK PRESSURE.

Agree 100%. 2.5" to a 3" exhaust is the culprit. Exhaust velocity was lost, resulting in lost low end torque.


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