As of now i have a 2001 5.9 automatic with stock headers, stock cat and straight 2 1/2 piping going into dual 2 1/4 piping into echo tips. It doesnt dual until it reaches the back axle. I was wondering if im losing any power with no muffler? I have noe clue if the cat is okay or even been gutted. I would like to have a muffler on it but i dont want to loose my sound. I had a single dynomax welded straight through muffler on it and it seemed to have a little more low end power, but i hated the sound....

 

your losing low end torque with no muffler

 

How so?

 

Stock engines need all the backpressure they came with, only time you can really make any power by getting rid of backpressure is when it is on a heavily modded engine, race car, or an engine that has forced induction.

 

In what way does backpressure help a stock motor?

 

You can ask me that all you want I can honestly not tell you, I do not for a fact that a couple buddies of mine who race all say the same thing, I know that my Indy with open headers lost a lot of low end torque once I took the rest of the exhaust off. I am only speaking from experience not based on technical information.

 

Well heres my go...

I know this will probably start up a debate...

An exhaust system that is extremely highflowing will not promote good torque, because at low rpm where you often find your peak torque, the exhaust gases are not flowing at optimal velocity. They are moving slower because there is not enough gas to fully fill the exhaust pipes...
The exhaust valve begins and continues to open as the piston is moving downward through the last portion of the power stroke. A very low-restriction, free-flowing exhaust system will dump the pressure from combustion out into the atmosphere. This will happen anyway, but if the exhaust system is somewhat restrictive then the combustion pressure will continue to be harnessed longer by placing force on the piston. This results in more torque and HP.....keep in mind backpressure and torque are inversely proportional.....also when someone puts too large of an exhaust on their car, it slows the low rpm exhaust pulses....another thing that slows exhaust down is cold pipes. with the pipes being cold, the heat starts exchanging into the pipe thus slowing the pulse down. with the pipe being at least the same temp as the exhaust, the heat has nowhere to go. this keeps the velocity up, until it gets to a lower temp spot and/or exits the system. this is where ceramic coating the exhaust can make a little more power.......

 

My experience and my racing buddies tell me different. Racing is really a bad example anyway. What, in the way of backpressure, do flames shooting out of exhaust pipes represent anyway? I would think an unobstructed path from the valve to the end of the pipe. It's all about the tune bud.

 

Part of that statement is precisely the theory that I have a problem with. The idea is that backpressure somehow contributes to the 'spinning of the motor' is bull****. All you have to do is consider how the valves work and sequence. The ideathat exhaust gas velocity helps the engine get rid of exhaust gasses actuallyworks in favor to the idea of less backpressure. Theonly part of the idea that I can live with is thatinstead of making it easier for the cylinders to expel exhaustgasses, you are actually helping the motor by creating aVenturi effect (same one used by Holley and later adated by Rochester). This effectcan be accomplished merely by sizing the pipes correctly.

If you have the stock y on your truck and think that you have "done away with too much backpressure" then you are dreaming.

 

Mopar your on the right track as for racing cut outs, for example...
At 6000 RPM with a shorter exhaust
pipe, (or cut-out open), will the torque be higher, or lower?
When you're talking about cutouts the distance is critical and will tune the exhaust to be efficient at one
RPM, with a tapering curve above and below that RPM. Now when you open the cut-out at 2000-3500 RPM
on the street, you notice a lack of power, Then everyone cries, "I lost backpressure, thats why I lost power!!!"
This is incorrect in the fact that by opening the cut out, youhave changed the tuning of the exhaust for the
RPM range you are using...the frequency of the exhaust does not decide how much power you make, it decides when the power
comes in. The pipe length in the exhaust has to do about when the power is made..... At 2000 RPM an exhaust pulse is 50 inches for example. If we cut a pipe to be "resonant" at 2000 RPM, it would need to be 50 inches. This pipe would only be resonant at one RPM, and one frequency. The reflected pulse at 2000 RPM will reach the exhaust port and create a low pressure area..... Someone driving around in the city would tune their
exhaust to this length because it would be moreefficient from 1000 to 3000 RPM with a PEAK at
around 2000 RPM .....SO based on my knowledge why would you put a huge exhaust and lose alot of torque to only have it available again at a unusable RPM??