Exhaust back pressure power loss?

[MadBill]

[quote="SUPRSLO...How would you say a Magnaflow muffler acts with it's straight through design with whole found within it? To me i'd consider them a glass pack muffler as well or atleast that's how i'd describe them.[/quote]
I haven't seen inside one, but the fact that the glasspack style units are reversible is encouraging; it means they don't have any big louvers hanging into the flow path...

[SUPRSLO]

[quote="SUPRSLO...How would you say a Magnaflow muffler acts with it's straight through design with whole found within it? To me i'd consider them a glass pack muffler as well or atleast that's how i'd describe them.

I haven't seen inside one, but the fact that the glasspack style units are reversible is encouraging; it means they don't have any big louvers hanging into the flow path...[/quote]

No, no louvers in these. I have the 3.5" versions for my motor and one of the biggest reasons I decided on these was another thread here where the 3" magnaflows came out on top for not costing a 700hp street big block any power or the least of all those tested and being the quietest at the same time

[beth]

I saw inside a street Magnaflow, it was just a big open stainless oval can lined with fiberglass padding.

[JBrady]

Most of the current "race" or "high flow" mufflers are a variation of a perforated pipe surrounded by some type of absorbtion material. Borla, Dynomax, Magnaflow and many more are this style. Others such as Flowmaster attempt to manipulate the waves with mixed results.

[blown265]

any reflective surface
or abrubt change in the secondary piping should be placed where the
tuned length of the collector ends.

Would this abrupt change in secondary piping include the 'collection' of two secondary pipes into one? ie a large bore single system. We have a blown six cylinder with a 6 into 2 into 1 exhaust. Going on what has been discussed, it would suggest that our secondary tuning would terminate/reflect at this final junction. [2 into 1 point]
Going deeper, does it also follow that the use of a large volume chambered style muffler in the remainder of the exhaust would not induce a further resonating point? ie the remainder of the system after this final collection acting as an open system. [assuming enough flow from the large bore pipe and muffler]

[MadBill]

It depends on the area change at the step and the volume downstream. David Vizard covers this in detail in one of his books, I believe it's the one on buiilding Chevs for limted $$. He says the volume must be at least 10x one cylinder's displacement and there needs to be a big step in diameter, preferrably with the small pipe protruding some way into it (e.g. into an "empty can"-type muffler) for the engine to think it's exhausting into atmosphere. From this point on, the muffler will not affect the 'tune', but still needs to have minimum back pressure (<0.2 psi for zero power loss.)

[SUPRSLO]

It depends on the area change at the step and the volume downstream. David Vizard covers this in detail in one of his books, I believe it's the one on buiilding Chevs for limted $$. He says the volume must be at least 10x one cylinder's displacement and there needs to be a big step in diameter, preferrably with the small pipe protruding some way into it (e.g. into an "empty can"-type muffler) for the engine to think it's exhausting into atmosphere. From this point on, the muffler will not affect the 'tune', but still needs to have minimum back pressure (<0.2 psi for zero power loss.)

I'm not 100% but I think it has to be 8 times the size of one cylinder. I always remembered that because it was real easy to figure out for a v8 obviously

[Procision-Auto]

Would this abrupt change in secondary piping include the 'collection' of two secondary pipes into one? ie a large bore single system. We have a blown six cylinder with a 6 into 2 into 1 exhaust. Going on what has been discussed, it would suggest that our secondary tuning would terminate/reflect at this final junction. [2 into 1 point]

With limited exhaust dyno tuning, and a couple of good books under my
belt, it would be safe to confirm that the 2-1 junction will act as a mixing
point and reflect energy in the system.

Going deeper, does it also follow that the use of a large volume chambered style muffler in the remainder of the exhaust would not induce a further resonating point? ie the remainder of the system after this final collection acting as an open system. [assuming enough flow from the large bore pipe and muffler]

I'm going to make another educated guess and say the muffler will affect
the tuning even though it occurs post y-pipe. Most of the tuning occurs
within the collector in a header type system.

Any sort of connection between banks (IE: X/H and Y-pipe) will further
mix pulses and alter pressure within the system. The muffler if placed
correctly would tune the secondary portion of the exhaust as an open
ended pipe, however the amplitude of the pulses would be attenuated.

The frequency (pulse length) will not change, but reflected pulse(s) will
have less energy to make more of an impact.

[Procision-Auto]

I think I recall a value of ten times the volume from, "Scientific Design of Exhaust and Intake Systems". I'm having trouble finding that page at the
moment, but here's a quote found here:

http://www.nonoise.org/resource/construc/bc.htm

Improved quality of mufflers with longer lifetime and more noise reduction. Muffler volumes should be about ten times the volume of the combustion cylinder to be effective. Other work shows that when a very poor muffler is fitted, the exhaust noise is typically 10dB above any other noise source. Addition of an improved muffler can lower noise by 6 to 15 dBA.