Mufflers

Arro · Post by **Arro** » Sat Dec 08, 2007 2:19 am

Ok so someone said before that a muffler with dual 2.5" outlets doesn't flow like one with a single 5" outlet (2.5 + 2.5), but more like a 4" outlet, because it's a bit more restrictive than a single 5" airpath. I may have the comparison a bit off but you get the idea.

So how about a muffler with dual 2.25" outlets? Obviously it won't flow like a 4.5" single airpath, but will it flow similar to a 3.5" single airpath?

Just curious what people think, and if anyone might happen to have some hard data on this.

Wizzard~Of~Ozz · Post by **Wizzard~Of~Ozz** » Sat Dec 08, 2007 10:12 am

area of d = 2.5" = 4.9"2
area of d = 5" = 19.635"2

4.9"2 x 2 pipes = 9.8"2

For a 5" pipe it's 19.635"2 (or twice the size)

To calc a single pipe with the same area as 2 x 2.5's

9.8/3.14 = (3.12sqrt) * 2 = 3.5" pipe

so 2 x 2.5" pipes = 3.5" pipe. a 5" pipe = 4 x 2.5" pipes.

This is potential output, it doesn't take into account backpressures, flow dynamics etc. But all things being equal, these are the numbers I can figure out this early in the morning.. But I may have totally mis-interpreted the question. For flow rates, perhaps it would be better to look at flow rates of water, they are more readily available for plumbers. They may be in GPH, but, the rrratios should give you a rough idea.

Arro · Post by **Arro** » Sat Dec 08, 2007 1:33 pm

Nope! You gave me the answer I wanted. Thanks

03blackrt · Post by **03blackrt** » Sat Dec 08, 2007 1:47 pm

A single circular pipe, sized correctly, will always outflow two pipes with an equivalent cross-section area (assuming all other things are equal). This is because the two pipes will have more

drag

or

backpressure

or

pressure loss

whatever you want to call it. Both will flow the same amount of mass at any given temp/pressure/density/ect... one's just more efficient at doing so (has less pressure loss).

Arro · Post by **Arro** » Sat Dec 08, 2007 1:59 pm

but a muffler with 3" inlet and dual 2.25" outlets will not see added backpressure because the outlets flow equivalent to a 3.5" outlet, right?

Wizzard~Of~Ozz · Post by **Wizzard~Of~Ozz** » Sat Dec 08, 2007 2:17 pm

Arro wrote:but a muffler with 3" inlet and dual 2.25" outlets will not see added backpressure because the outlets flow equivalent to a 3.5" outlet, right?

3.2" for dual 2.25's. But all the same, the dual 2.25's output is matched to the 3" input (ie, what goes in, can get out without it being a bottleneck)

03blackrt · Post by **03blackrt** » Sat Dec 08, 2007 2:18 pm

A 3.5" will be more efficient (have less backpressure) than two 2.5". Roughly 1/3 more efficient, but it really doesn't matter much… here's why.

Let’s say a 3.5" tip "steals" 0.02psi of pressure. Two 2.5" tips will "steal" 0.03psi of pressure. This is because the two 2.5” pipes have more surface area (31ish inch circumference compared to 21ish inch circumference) on the inside of the pipe, which contributes to something called “major” pressure loss. (“minor” pressure losses are that from things such as bends, joints, valves, ect…)

So if your exhaust is at 1psi exiting the muffler (just throwing out numbers, these are in no way relevant to exhaust, just easy small whole numbers for demonstration purposes) The dual 2.5” tip will have a pressure of 0.97psi, while the 3.5” tip will have a pressure of 0.98psi. So the dual 2.5” pipes will have more pressure loss than the single 3.5” pipe.

Larger pressure in the pipe equates to less backpresser (the desire for atmospheric gases to flow back into the exahust pipe)

But both ways will flow roughtly the same amount of mass.