Better exhaust or new cam?

[Dwight]

this is a pic of the core out of Unique's sidepides. Note the louvers.

Dwight

[Excaliber]

Don't be confused by the oft repeated "need for back pressure" to increase horse power. If that were the case, you would never see "open headers" on a race car.

The length of a header collector, in some cases, has an optimum length. One way to find it is to look carefully at the scorch marks or some other method that shows the temperature of the exiting exhaust gases. Then start cutting off the collector length until it just reaches the desired point, right at the highest temp exit point.

A two cycle engine certainly has a required "back pressure" point because of the nature of a two cycle. A properly tuned "expansion chamber" uses the escaping momentum of the exhaust to help "pull in" the fresh intake charge. That works best at near max rpm range. To some extent, this also applies to a four cycle, but not nearly as much and the "expansion chamber" becomes the "collector" on the end of the headers. No mufflers, in either case will add anything to the scavenging affect.

[RestoCreations]

A couple of points
-You will see a nice hp increase when changing from a restrictive manifold or header to a more free flowing 4 into 4 or long tube header system if you have a high hp engine. If you dont have a high hp engine, you are not going to see much of a change at all. Like was mentioned above, air in and air out. If your cylinder heads, intake, and cam are not up to par, then i would start there.

-I have seen some of these pipes that have a muffler with a flat face and then the flow hole in the center. This causes the air to hit that area like a brick wall. Its a dam, not a bottle neck. In that case, what really needs to be done is to make sure that area has a smooth transition. You can cut the muffler apart and create a smooth transition at that point. However, this requires a lot of work and might not be a project you want to tackle. Im not sure if anybody makes them with a smooth transition or if they just try to compensate the loss caused by the dam by making it smaller with a larger Internal Diameter muffler. I personally prefer the smaller internal diameter mufflers, but only if the hp loss is reasonable. I will take a 20hp flywheel loss any day over hearing loss. Look at the classic chambered website-he has a picture of reducers that make for a smooth transition-that is key. Now if only someone offered an option for 2-1/4 and 2" muffler section that would be nice.
-The louvers do catch the air when turned the correct way and make the pipes quieter/deeper, but you will also get a lot of back popping under deceleration.
-The larger louvers shown above will give a much better and deeper sound when faced the right way. The smaller louvers give the exhaust a higher pitched sound.
-The longer muffler section you can use without making the car look odd, the better.

Dwight-do you still have those inserts or did you toss them?

[CobraEd]

Originally Posted by Dwight

A muffler is a place to store air till it can sloooowly exit the muffler. The reduced speed of the air exiting the chamber reduces the noise.

Dwight

I don't believe this is correct, . . . . Uhhhhh, . . This is 100% wrong.

Exhaust gas and sound waves are two completely different things. You never want to make an effort to slow or reduce the exhaust velocity. You will lose power (backpressure). The mufflers job is to absorb and/or cancel out sound waves. The better it can absorb/cancel sound waves relative to maintaining a free flow, the better it is at its job.

Mufflers like glasspacks absorb sound waves and mufflers like Flowmasters cancel out the sound waves inside small resonance chambers within the muffler.

(just as an aside, . . . . good backpressure is like good cancer)

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[vector1]

Originally Posted by xlr8tr

These look interesting- do you have any pics? I didnt see anything on their website.

i haven't used these, just brought over from another site, thought they looked interesting. i've read the guys will make anything you want, they also have a discounted list of stuff.

[Dwight]

I removed the fiberglass and re-installed them.
It was a friends Cobra.
Dwight

[Dwight]

CobraEd, I think you use the word absorb and I used the term "place to store air till it can sloooowly exit the muffler" to describe the same thing.
All the air that enters a muffler has to exit. Nothing is absorbed. A large muffler is quieter than a small muffler on the same car.

Stock vs glasspacks (Cherry Bombs).

The large muffler has more room to store the air till it exits the muffler.
Glasspacks have fiberglass in them and Flow Master uses metal baffles to slow down the air.

This same theory is used to build/design suppressors for firearms.

I don't design or build mufflers for a living, but this is what I think happens inside a muffler.
Dwight

[CobraEd]

Originally Posted by Dwight

CobraEd, I think you use the word absorb and I used the term "place to store air till it can sloooowly exit the muffler" to describe the same thing.
All the air that enters a muffler has to exit. Nothing is absorbed. A large muffler is quieter than a small muffler on the same car.

Stock vs glasspacks (Cherry Bombs).

The large muffler has more room to store the air till it exits the muffler.
Glasspacks have fiberglass in them and Flow Master uses metal baffles to slow down the air.

This same theory is used to build/design suppressors for firearms.

I don't design or build mufflers for a living, but this is what I think happens inside a muffler.
Dwight

You cannot store "absorb" the exhaust (air as you put it) or the muffler would get bigger and bigger as you drive. You can absorb SOUND WAVES only.


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[RestoCreations]

Originally Posted by Dwight

I removed the fiberglass and re-installed them.
It was a friends Cobra.
Dwight

Why? Did he want them louder? Eventually the fiberglass builds up with so much carbon/exhaust gunk that it doesnt absorb the noise anymore anyway.

[RestoCreations]

Quote from Dwight

" A large muffler is quieter than a small muffler on the same car. The large muffler has more room to store the air till it exits the muffler. Glasspacks have fiberglass in them and Flow Master uses metal baffles to slow down the air."

Im going to disagree with you on that one when referring to the sidepipes for cobras and cobra replicas-> Larger internal diameter=more straight through flow=louder. The larger ID pipes also equal less packing material to absorb the SoundWaves.

[CobraEd]

Dwight,

More food for thought:

Picture a car accellerating at full throttle at 7,000 rpm. Lets say hypotheticaly that the exhaust is entering the muffler at 600 mph. By your way of thinking the exhaust would leave the muffler at 200?, 300?, 400mph??? I think not. That would mean the muffler was holding all that exhaust and getting bigger and bigger. If the exhaust goes in at 600mph. it comes out at 600mph.

EXHAUST has VOLUME and MASS. To store it the muffler would have to grow and get bigger as you drive. Sound waves have NO VOLUME and NO MASS. They are what get absorbed and/or cancelled out within the muffler.

I think you are trying to compare this with a gun. It is not the same thing. A gun is an instantanious discharge. Exhaust is a continual flow.


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[xlr8tr]

more food for thought: if you have 4 header pipes at 1.75 inches internal diameter each, thats a total cross section area area of 9.6 square inches. A 2 1/2 inch ID muffler = 4.9 sq in, (no wonder there is a flow restriction) whereas a 3 inch ID muffler = 7.1 sq in, a 44% increase in cross section area, but still much less than the 4 header pipes. Although there is probably a bunch of fluid dynamics math thats way over my head to add to this...

[CobraEd]

Originally Posted by xlr8tr

more food for thought: if you have 4 header pipes at 1.75 inches internal diameter each, thats a total cross section area area of 9.6 square inches. A 2 1/2 inch ID muffler = 4.9 sq in, (no wonder there is a flow restriction) whereas a 3 inch ID muffler = 7.1 sq in, a 44% increase in cross section area, but still much less than the 4 header pipes. Although there is probably a bunch of fluid dynamics math thats way over my head to add to this...

Ahhh, . . but each pipe only fires and expells exhaust when that cylinder fires. It is not continual flow. Therefore the four pipes on the one side of the car share or contend for the flow volume of the muffler. They are not all flowing at the same time.

On the opposit end for induction, all eight cylinders do not draw air through the carb at the same time. They contend for it, each taking a turn.


There is a 47 page formula that explains this. I used to have it, but my dog ate it !!!


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[xlr8tr]

excellent point cobraEd! I knew there were smarter people than me here!

[undy]

Actually, as the exhaust gases flow through the system they cool and tend to shrink in size as they move, making the exit gases a bit slower than the entry gases.

[CobraEd]

Originally Posted by undy

Actually, as the exhaust gases flow through the system they cool and tend to shrink in size as they move, making the exit gases a bit slower than the entry gases.

I agree, but as stated, that is a function of the exhaust cooling, not due to the muffler storing the exhaust.


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