OE Muffler Tailpipe/Muffler/RT Exhaust Performance

[YO7_A66]

 A) Were the original style e-body mufflers (2-1/4" in, mounted beside the tank) a straight through type of design?

I have a pair on my Challenger but they are welded in place (no resonators).

 B) I am curious how much of a performance gain there would be in swapping these 2-1/4"-2" muffler/R/T exhaust tip assemblies out for an aftermarket 2-1/2" straight thru muffler with 2-1/2" R/T tips since I now have headers and 2-1/2" pipe up front before the start of the 2-1/4" tail pipe assembly.

 Thanks

[cudabob496]

since open quality/race headers will make the most power on an engine, anything you can
do to reduce back pressure downstream of the headers, will improve power, as
long as your ears can handle it. See diff below for different pipe sizes.

http://www.exhaustvideos.com/faq/how-to-calculate-muffler-size-pipe-diameter/

[Chryco Psycho]

you will see more gain going larger between the manifolds or headers to the muffler , as the exhaust cools it needs less size which is why the factory often used H pipes & larger pipes as far back as the muffler & often had smaller tips 

[YO7_A66]

  Do we know if the FAST guys are allowed to replace the stock mufflers/tips with aftermarket 2.5" assemblies?
 
 Thanks for the replies

[cudabob496]

you will see more gain going larger between the manifolds or headers to the muffler , as the exhaust cools it needs less size which is why the factory often used H pipes & larger pipes as far back as the muffler & often had smaller tips

I agree the factories use smaller tips, but it seems a smaller tip is still more restrictive overall.  In other words, the smallest diameter restriction
in a pipe with flowing water is going to limit overall flow, even if the rest of the pipe is very large. Or, given a 2.5 inch exhaust system, 2.5 inch
exhaust tips will allow more power to be made, over 2.25 inch exhaust tips. I see the benefit of a larger pipe between the exhaust manifolds and the mufflers, in that it should improve scavenging. My Cuda has a three inch system all the way back, and I think that is the best design.

[YO7_A66]

 Has anyone seen a cut-a-way of an OE muffler?
 Is it straight thru or are there internal passages?

 Thank you.

[cudabob496]

Has anyone seen a cut-a-way of an OE muffler?
 Is it straight thru or are there internal passages?

 Thank you.

since they are design to be quiet, I doubt they are straight through, but I
don't know for sure.  I suspect they are restrictive and have a significant
pressure drop. Or, if they are straight through, probably have a resonator
upstream.

The below is interesting:

http://www.exhaustsoundclips.com/cfm.pdf

I read the original T/A Mopar mufflers that curve back to exit in front of wheels, only flowed 175 cfm.

[PlumCraZRT]

I agree the factories use smaller tips, but it seems a smaller tip is still more restrictive overall.  In other words, the smallest diameter restriction
in a pipe with flowing water is going to limit overall flow, even if the rest of the pipe is very large. Or, given a 2.5 inch exhaust system, 2.5 inch
exhaust tips will allow more power to be made, over 2.25 inch exhaust tips. I see the benefit of a larger pipe between the exhaust manifolds and the mufflers, in that it should improve scavenging. My Cuda has a three inch system all the way back, and I think that is the best design.

The power difference will be immeasurable.  Exhaust is essentially considered open after the muffler since it normalizes the peak pressure waves.  Chryco is right as well, since the exhaust is cooling, the cross section required will decrease for the same exhaust velocity.

[PlumCraZRT]

since they are design to be quiet, I doubt they are straight through, but I
don't know for sure.  I suspect they are restrictive and have a significant
pressure drop. Or, if they are straight through, probably have a resonator
upstream.

I know the factory resonator was a straight-through design, but the mufflers were cut off my car.

[cudabob496]

The power difference will be immeasurable.  Exhaust is essentially considered open after the muffler since it normalizes the peak pressure waves.  Chryco is right as well, since the exhaust is cooling, the cross section required will decrease for the same exhaust velocity.

Does not make sense, ( to me that is.)  You are saying a 2.5 inch dual exhaust will make essentially the same power, whether the tips are 2.5 inches, or 2.25 inches? In that case, are you saying there will be little power loss if you have 2 inch tips on a 2.5 inch dual exhaust, or 1.75 inch tips on a 2.5 inch system.  I understand that you want the muffler at the end of the system, cause the exhaust is cooler, so it will create less back pressure, therefore make more power. But whenever you restrict exhaust diameter, anywhere in the system, you have to restrict power.

Look at the above chart.  The max flow through a 2.5 inch pipe is about 500 cfm, and is about 400 cfm for a 2.25 inch pipe.  That is a big difference.  And going from a 2.5 inch dual system to a 2.25 inch dual system causes you to lose max hp potential of about 90 hp.

[YO7_A66]

My stock exhaust consists of 2-1/4" tail pipes and muffler, then it necks down to the 2" R/T tips. This is my main concert going from headers, to 2-1/2" pipe, then down to 2-1/4" tail pipes/mufflers, then down again to the 2" tips.

 Thanks for the replies.

[YO7_A66]

 Note: I have read where the stock "round" OEM mufflers only flow around 175cfm.

 I emailed Magnaflow for the flow rate of the muffler (#12646 [6" diameter x 18" 2.5" round body], #12616 2.5" round [6" diameter x 14" body] and Magnaflow rates them at 530CFM tested at 28" of water.

I am planning on using these beside the tank with 2.5" tail pipes and 2.5" R/T exhaust tips.

Thanks for the replies.

[PlumCrazyChris]

Does not make sense, ( to me that is.)  You are saying a 2.5 inch dual exhaust will make essentially the same power, whether the tips are 2.5 inches, or 2.25 inches? In that case, are you saying there will be little power loss if you have 2 inch tips on a 2.5 inch dual exhaust, or 1.75 inch tips on a 2.5 inch system.  I understand that you want the muffler at the end of the system, cause the exhaust is cooler, so it will create less back pressure, therefore make more power. But whenever you restrict exhaust diameter, anywhere in the system, you have to restrict power.

Look at the above chart.  The max flow through a 2.5 inch pipe is about 500 cfm, and is about 400 cfm for a 2.25 inch pipe.  That is a big difference.  And going from a 2.5 inch dual system to a 2.25 inch dual system causes you to lose max hp potential of about 90 hp.

You have to remember, that the exhaust gas does not act like a liquid.  It acts like a hot air balloon...(hot gas expands) until it cools, then it contracts and fills less volume.  So with less volume, it does not require as big a pipe to keep the same back pressure.