jtranizzle

Put on a Invidia 60mm TP the other week. Install was very simple, took a max 15 minutes. Sounds good, imagine a louder stock exhaust. Idle remained the same. Picked up torque through all RPMS, definitely feel a difference. Great buy...not bad for $63 (made my own CEL fix using spark plug defoulers)

whiteflash

Anyone know of a 70mm/3" Test pipe that also has a helmholtz resonator on it?

Gernby

Due to space limitations, I would be surprised if a true "Helmholtz resonator" would fit there. However, if you are referring to a "closed ended branch duct" or "J-pipe", I built some prototypes while developing my exhaust system. It was somewhat effective, but you have to really get the length right. On top of that, every exhaust system will require a slightly different length, and that length changes slightly with temperature. This one was about 30" long, and curled around under the driveshaft.

Gernby

On second thought, I think this one was 30", which was just about right for a 3500 RPM drone. I had to start bending the tip back toward the exhaust, since it was running out of room.

kchandra

Gernby - What did it do to drone? Did it impact raspiness? Kudos to you for experimenting....

Gernby

It didn't have any impact on raspiness, but it did attenuate the drone frequency. It's just a simple quarter-wave resonator. Basically, at 3500 RPMs, the exhaust pulses are at about 115 Hz. The wavelengh of a 115 Hz wave is about 10', so 1/4 wavelength is about 2.5'. This means that adding a 2.5' J-pipe causes maximum attenuation when the pulses are at 115 Hz. The problem is that some exhausts cause subharmonics that make the drone some multiple of the engine combustion frequency. It didn't take long for me to abandon the concept, and eventually found a much, much more effective approach, which I'm patenting. I truly believe the current exhaust market is going to change soon.

kolyan2k

Is this how test pipe sounds on stock exhaust ? I am looking for something a bit louder then stock, but whats on that vid is too loud for my taste. also concerned about the smell...some say no smell, others say smells like a shitty old truck....

http://www.youtube.com/watch?v=7X8ZI...eature=related

alSpeed2k

^that's a straight pipe, not a testpipe!

alSpeed2k

Oh, & yes, it smells bad!

kolyan2k

^ thanks. i am gonna keep stock for now i guess.