Unbelievable Restriction--OEM Muffler

[dwcopple]

Originally Posted By: TallPaul
Originally Posted By: dwcopple
UAW at its finest!


Not sure what the union would have to do with this.


Ever heard the saying "you must have bought a car built on a Friday"? That is what I meant. QC guy was at "lunch" when that muffler went through.

 

[yonyon]

Originally Posted By: TallPaul
Just cut open the other end. There is a chamber where the gasses flow out the sides of the inlet pipe through tiny slots and then have to enter another pipe, again through tiny slots, flow around the other end, then through the outlet pipe. Not as bad is I thought but still VERY restrictive. I'll get some pictures up later.


So then that end of the muffler is basically a complete muffler on it's own and the other useless looking end is just an air chamber, maybe there to provide the function of a resonator.

 

[TallPaul]

Okay, a good lesson on what happens when you make assumptions. Yes, it is a restrictive muffler, but not near as bad as I initially thought. Here is the full story:

 

[SteveSRT8]

Originally Posted By: code5coupe
Originally Posted By: SteveSRT8
Some engines love back pressure. Helps keep their torque curve up.


Old wife's tale. While engines will run with lots of back pressure, there is a cardinal rule: less is more.



NOT old wives tale, well documented on dynos and drag strips across the country!

No blanket statements here. One engine may like a free flowing exhaust but another design may not. Too many variables in engine design and application prove you incorrect.

 

[mpvue]

Originally Posted By: SteveSRT8
Originally Posted By: code5coupe
Originally Posted By: SteveSRT8
Some engines love back pressure. Helps keep their torque curve up.


Old wife's tale. While engines will run with lots of back pressure, there is a cardinal rule: less is more.



NOT old wives tale, well documented on dynos and drag strips across the country!

No blanket statements here. One engine may like a free flowing exhaust but another design may not. Too many variables in engine design and application prove you incorrect.

agreed. years ago I had a '70 Nova w/ a mild 283 that I tried driving around for a few days w/ no exhaust, just open headers; NO low end power, would bog off the line.
I installed a full flowmaster exhaust, 2 1/2" pipes, crossover tube, w/ one big muffler over the axle.
it woke the car up big time! lots of low end grunt, pop the clutch and launched hard! and of course it was MUCH quieter.

back pressure is all about being well designed. the flowmaster system efficiently scavenged the exhaust, not just dumping it out faster than the engine could breathe.

 

[NateDN10]

Originally Posted By: TallPaul
Okay, a good lesson on what happens when you make assumptions. Yes, it is a restrictive muffler, but not near as bad as I initially thought. Here is the full story:

That makes a lot more sense, and is more of a typical muffler design!

 

[Bamaro]

Aren't those little holes for condensation?

 

[punisher]

Engines don't love back pressure. A pumping loss is a pumping loss no matter where it occurs in the combustion cycle.

I think a lot of the misconceptions come from people using seemingly more restictive headers/exhaust systems and picking up low end/RPM torgue in a given application vs running 2 1/4" primaries and 4" collectors on a stock engine. If you have a low duration cam, small valves, small ports, then chances are good you will pick up torque with the more "restrictive" exhaust system. "Restrictive" is in "" as it is a misnomer.

The "restrictive" system actuially allows more flow at lower RPM, not less. Higher VE= higher torque= more power at a given RPM.

 

[TallPaul]

The Ford 4.9L inline six has small exhaust valves. This was done for low end torque. It is not by back pressure, but because that engine is a low rpm engine (max 4000 rpm) and gets peak torque at 2000 rep. The small valves help low end torque, not by producing back pressure, but by causing increased velocity through the exhaust ports which helped evacuate the exhaust gasses from the cylinder, thereby causing better cylinder filling on the intake stroke.

 

[quint]

^^ Well said, both of you.

The smaller, or 'more restrictive' exhaust system that "produces backpressure" wakes an engine up because its actually creating LESS backpressure in that application......

 

[mechtech2]

Originally Posted By: SteveSRT8
You can bet that it was supplied by the low bidder.

Some engines love back pressure. Helps keep their torque curve up.

Some don't. Removing back pressure is not always a good thing. But it obviously could help high rpm horsepower a bit.


Nonsense.
No engine likes back pressure ever. Pumping losses, exhaust in the intake charge,etc..
This is an oldmyth.
It comes from small pipes often increasing low end power.
Must. be the extra restriction, right?
But that is actually due to DECREASED restriction at low end.

 

[TallPaul]

Pipes have to be the correct diameter to maintain flow velocity. In some cases that means small pipes. And since exhaust gasses cool as they travel farther from the engine you actually want to reduce pipe diameter the farther back you go.

 

[dwcopple]

Originally Posted By: TallPaul
you actually want to reduce pipe diameter the farther back you go.
yeah, because you see that all the time on race cars, OEM exhausts, and aftermarket cat-backs...:rollseyes:

 

[TallPaul]

Originally Posted By: dwcopple
Originally Posted By: TallPaul
you actually want to reduce pipe diameter the farther back you go.
yeah, because you see that all the time on race cars, OEM exhausts, and aftermarket cat-backs...:rollseyes:
Cases in point: My 2001 Ford Ranger factory exhaust had 2.5" out of the cat, reducing to 2" the rest of the way back. My 2000 Chevy cutaway chassis motorhome does the same after the cat though I think it is 3" down to 2.5".

 

[yonyon]

Originally Posted By: dwcopple
Originally Posted By: TallPaul
you actually want to reduce pipe diameter the farther back you go.
yeah, because you see that all the time on race cars, OEM exhausts, and aftermarket cat-backs...:rollseyes:


Another thing you don't see all the time on race cars: the engine spending a lot of time revving low enough to require particularly small pipes.

 

[dwcopple]

Originally Posted By: yonyon
Originally Posted By: dwcopple
Originally Posted By: TallPaul
you actually want to reduce pipe diameter the farther back you go.
yeah, because you see that all the time on race cars, OEM exhausts, and aftermarket cat-backs...:rollseyes:


Another thing you don't see all the time on race cars: the engine spending a lot of time revving low enough to require particularly small pipes.
There was more to my post-OEM exhausts and aftermarket cat-backs.

 

[SteveSRT8]

Originally Posted By: dwcopple
Originally Posted By: yonyon
Originally Posted By: dwcopple
Originally Posted By: TallPaul
you actually want to reduce pipe diameter the farther back you go.
yeah, because you see that all the time on race cars, OEM exhausts, and aftermarket cat-backs...:rollseyes:


Another thing you don't see all the time on race cars: the engine spending a lot of time revving low enough to require particularly small pipes.
There was more to my post-OEM exhausts and aftermarket cat-backs.



Glad some of us understand the HUGE variability in the engine's operational envelope.

Not many engines have the same flow at idle as they do at full throttle, eh?

The exhaust engineer uses little transducers in the pipes at dozens of different locations to effect a compromise, not perfection. And they measure back pressure (surprise!).

They simply pick a target flow and optimize to it. It could possible explain why a stock 5.7 Hemi has a smaller pipe than a 6.1.

Maybe.

 

[Josh_Putman]

Originally Posted By: TallPaul
Okay, a good lesson on what happens when you make assumptions. Yes, it is a restrictive muffler, but not near as bad as I initially thought. Here is the full story:

I can't tell from the pictures where the bearings go.