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  #46 (permalink)  
Old 07-10-2007, 10:09 PM
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[QUOTE=elcaminodragster] back pressure creates torque correct???
QUOTE]

Nope, that's just a fable. If more back pressure created more torque, bulldozers would exhale through soda straws. The only time more back pressure gives you more torque is when the fuel mixture is not calibrated correctly for the extra air flow that happened when you freed up the exhaust system.

Glasspacks with louvers (or other internal projections) are restrictive because the louvers not only decrease the diameter of the internal flow path, but they cause turbulence that effectively reduces flow even more. If you want a non-restrictive glasspack, look at the Thrush Magnum. No louvers, just smoothly punched holes, and an internal flow tube that's probably larger than the rest started with in the first place. Longer glasspacks will be generally quieter, but they'll still have that blat on deceleration that some folks are so fond of.

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  #47 (permalink)  
Old 07-10-2007, 10:16 PM
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[QUOTE=jimfulco]
Quote:
Originally Posted by elcaminodragster
back pressure creates torque correct???
QUOTE]

Nope, that's just a fable. If more back pressure created more torque, bulldozers would exhale through soda straws. The only time more back pressure gives you more torque is when the fuel mixture is not calibrated correctly for the extra air flow that happened when you freed up the exhaust system.

Glasspacks with louvers (or other internal projections) are restrictive because the louvers not only decrease the diameter of the internal flow path, but they cause turbulence that effectively reduces flow even more. If you want a non-restrictive glasspack, look at the Thrush Magnum. No louvers, just smoothly punched holes, and an internal flow tube that's probably larger than the rest started with in the first place. Longer glasspacks will be generally quieter, but they'll still have that blat on deceleration that some folks are so fond of.

ok so the whole back pressure creating torque is a bs thing just like open full length headers warping valves. i got ya thanks for setting me straight . for the street tho the purples and good enough tho right??? im not going for serious performance. i think once these blow out im gonna go for the sleeper sound and performance.
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  #48 (permalink)  
Old 07-10-2007, 10:21 PM
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Hmmm...

Hey does anybody know what would happen if one were to only run resonators and no muffler. I know that on luxery cars there is a muffler Plus a resonator, thus a very muffled and quiet sound. I would think that the resonator doesnt do as much murdering of sound that a muffler does. I also take into consideration the tone of the sound produced, and Im assuming that depends on the volume of the resonator chamber.
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  #49 (permalink)  
Old 07-10-2007, 10:31 PM
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Quote:
Originally Posted by 1970Chevy
Hey does anybody know what would happen if one were to only run resonators and no muffler. I know that on luxery cars there is a muffler Plus a resonator, thus a very muffled and quiet sound. I would think that the resonator doesnt do as much murdering of sound that a muffler does. I also take into consideration the tone of the sound produced, and Im assuming that depends on the volume of the resonator chamber.

a resonator is just another name for muffler it helps newer cars be quieter. not sure about flow, power, or sound tho.
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  #50 (permalink)  
Old 07-10-2007, 10:49 PM
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Quote:
Originally Posted by 454C10
Louvered glass packs flow very poorly. And Purple Hornie's are louvered.

A Dynomax Bullet would be a better choice. It is a perforated tube design and flows almost like a straight pipe.

http://www.broaderperformance.com/mu...flow_tests.htm

i found out that the tests they did were under watter. so its not all that accurate really. for 1 the fiberglass would soak up water and 2 water clings to the metal just enough. poor water on your car and it will bead up. breath on your car it bounces off. im not trying to be a smart ***** here but those test to me dont seem all that accurate.
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  #51 (permalink)  
Old 07-11-2007, 12:14 AM
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Did it say something like 15" of water or 20" or 28"? That's most likely a reference to how much pressure (or vacuum) was used to force the air through the muffler. More pressure will force more air through per unit of time. Vacuum is just negative pressure, and it's generally measured in inches of water ("H2O) or inches of mercury ("Hg), kinda like barometric pressure on the weather report.

You'll probably see different flow rates out there for the same muffler, and it's probably due to different pressures used. There's not really any standardization in the industry, and until there is, there's always going to be some confusion.

Same deal for carburetor flow rates. Fuel injection systems and 4-bbl carbs are rated at 1.5"Hg while 2-bbl carbs are rated at 3"Hg. To add to the confusion, doubling the pressure does NOT double the flow rate, it only increases it by a factor of 1.414, which is the square root of two. So a 500cfm 4-bbl will flow 1.414 times as much air as a 500cfm 2-bbl.

Walker, parent company of Dynomax & Thrush, uses something around 20"H2O, which is pretty close to the same as 1.5"Hg, for their advertised flow rates. Vizard's rule of thumb (2.2cfm/hp) for required exhaust flow was also developed at that pressure.

Last edited by jimfulco; 07-11-2007 at 08:50 PM. Reason: brain fart
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  #52 (permalink)  
Old 07-11-2007, 11:22 AM
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Quote:
Originally Posted by jimfulco
Did it say something like 15" of water or 20" or 28"? That's most likely a reference to how much pressure (or vacuum) was used to force the air through the muffler. More pressure will force more air through per unit of time. Vacuum is just negative pressure, and it's generally measured in inches of water ("H2O) or inches of mercury ("Hg), kinda like barometric pressure on the weather report is measured in millimeters of mercury (mmHg).

You'll probably see different flow rates out there for the same muffler, and it's probably due to different pressures used. There's not really any standardization in the industry, and until there is, there's always going to be some confusion.

Same deal for carburetor flow rates. Fuel injection systems and 4-bbl carbs are rated at 1.5"Hg while 2-bbl carbs are rated at 3"Hg. To add to the confusion, doubling the pressure does NOT double the flow rate, it only increases it by a factor of 1.414, which is the square root of two. So a 500cfm 4-bbl will flow 1.414 times as much air as a 500cfm 2-bbl.

Walker, parent company of Dynomax & Thrush, uses something around 20"H2O, which is pretty close to the same as 1.5"Hg, for their advertised flow rates. Vizard's rule of thumb (2.2cfm/hp) for required exhaust flow was also developed at that pressure.
i think it was 18" of water. i still dont understand why the hell they would test a car part under water especially a damn muffler! that makes absolutely no senses.
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  #53 (permalink)  
Old 07-11-2007, 12:16 PM
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They are not testing under water!!!

and they used 15" of water as the vacuum.

Inches of mercury (hg) or inches of water (h20) is what they use to measure vacuum. They are sucking through the muffler at some vacuum level and measuring the flow.

Just like they use pound per square inch (psi) to measure flow rate on a fuel pump. And they aren't putting weights on the fuel pump to measure flow.
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  #54 (permalink)  
Old 07-11-2007, 12:42 PM
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Yeah man, those little darlins look good under there, sound nice too.....sounds alot like, dare I say; my old ford truck.....I didnt use the packs with the turndowns on the end,and I had about 2 1/2 foot pipes on the end...sounds the same tho, rock on....
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  #55 (permalink)  
Old 07-11-2007, 12:45 PM
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HaHa... under water!!!!! inches of mercury makes infinitely more sense tho.....
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  #56 (permalink)  
Old 07-11-2007, 01:17 PM
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Let's say you have a big glup in your center consel and you don't feel like picking in up because is a about 1 gallon. So you get a long straw to suck out the life giving soda. If your lips were 15 inches away from the top level of the soda, it would take 15 inches of soda vacuum to get it into your mouth.

If you were in outer space (perfect vacuum) then your vacuum gage would read 29.9" hg or 407" of water. Since hg is much heavier than water it takes more vacuum to pull it a certain distance up a tube.

15" of water is about 1.1" of hg. Not much vacuum.
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  #57 (permalink)  
Old 07-11-2007, 01:37 PM
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Can you have vaccuum without atmospheric pressure? Wouldnt it cease to be vaccuum and just be atmosphere?? wouldnt the soda just shoot into your lungs as they imploded???? at any rate your glasspacks would sound like ****t...
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  #58 (permalink)  
Old 07-11-2007, 01:52 PM
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Vacuum is the absence of pressure. So yes, you can have vacuum without atmospheric pressure. However, if you live on a planet with no atmosphere then vacuum would be atmosphere pressure.

Yes, soda would shoot into your lungs but your lungs would explode not implode.

And since sound doesn't travel in a vacuum. Glasspacks would be very quiet in a vacuum.
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  #59 (permalink)  
Old 07-11-2007, 02:16 PM
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hey 454c10,

a low cfm would mean high back pressure??? and a high cfm would mean low back pressure??? correct??? i know its a dumb question but hey im here to learn and cant learn with out asking stupid questions.
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Old 07-11-2007, 02:49 PM
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You got it.

They make a consistent pressure differential across the muffler and measure the flow. The more air that goes through, the less restrictive the muffler is.

In this case, they are sucking air through the muffler. The vacuum pump speed is increased until a certain pressure differential is created across the muffler and then they measure the flow.
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