coladylan

Hey guys,
I have a 1997 Honda Civic CX Hatchback. It is all stock except the exhaust. It appears to have some no name chrome headers, a straight pipe exhaust (looks like 2 in) with what looks like a 18" cherry bomb/ thrush pipe where the cat was, and then another at the end with a 4" tip.

The sound is very throaty and low. Which i like. It all sounds good except when at high rpms.... then its loud. It also has a drone.

I would like to just quiet the sound, or suppress it. It doesn't need to be a crazy amount, but enough to get rid of the loudest part and the drone at moderate rpm's.

SO how can I add on or modify my system to suppress some of the loud sound?

mac25

you might want an electrically adjustable exhaust baffle.

coladylan

That is an option, but I don't really want to wire another switch, and turn it on and off. I want it always on....

I was thinking maybe a resonator? or a smaller tip (tip reducer?) or another piece I could weld in? What would quiet it down a bit?

Any ideas?

mac25

you can buy a non electric baffle, they just install on the end of the exhaust... but you might as well go back to stock, you'll have a huge exhaust designed for flow with a very small exit.

coladylan

Isn't stock pipe size 1 7/8? If I have a 2 inch, how would that be a huge exhaust flow compared to stock? Anyway... what would the baffle do on my 2 inch exhaust?

I just looked and I have 2 inch piping, but the end of the muffler (cherry bomb) which is at the very end has a 3 in end. Would making it smaller quiet it down?

mac25

there is a large difference from stock. i was stock at 1.25in and am now at 2.25, that's double the flow and way louder. you are also probabley at 2.25. why wouldn't you want the adjustable one? that way you can have it sound stock as long as you want and when you want to have some fun open it up?

coladylan

I just don't want the hassle of the adjustable... and I'm fairly certain it is 2" (i measured it)

Okay I have been doing some research and it looks like a helmholtz resonator would be a really effective way to get rid of the drone, if done right.

Does anyone know more about this? I know how it works with waves and frequency, and most of that jazz. What I need to know is how much does placement matter (ei. mid pipe, behind the end muffler, or in between) and how to calculate it correctly? (I can find the equation, and do all the math. but I want to make sure it is right). I know air speed, air density, length of the pipe, and frequency I am trying to eliminate are important.

Anyones help would be appreciated

coladylan

did some more research.

Placement doesn't matter as long as it is before the muffler.

So that leaves me with the equation...... it is a little difficult to decipher but I'm working on it.

Once again help is welcome

coladylan

Is the equation as easy as

c/f/4*12

????????

c- is speed of sound in feet per second at 400 degrees Fahrenheit (204 Celsius)
f - is frequency in hertz (sound you want to eliminate)
4- is to move the wavelength a quarter (ultimately equaling completely out of phase after reflection)
12- inches in a foot

Is it really that simple?
Does anyone know?

So if the frequency of the drone is at 150 Hz then I would need a tube that is 28.3"?