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As some of you may recall; I purchased and had installed a full OBX system for my '89 coupe. To say that I was displeased with the installation and resulting resonance is a very mild understatement. From 1,000 rpm, all the way to 1500-1600 the drone was so bad that I could not stand to drive the car.
I experimented with different options, including two freeze plugs in the primary exhaust tips (which helped a bit). Finally, after much search and investigation, I stumbled upon 1/4 wave resonators.
Having an IQ slightly above an apple, even I understood the theory and engineering behind this application. A sound wave travels at a specific speed through space, to cancel that sound wave, you bounce an equal (or in this case 25%) wave back at the original.
What you see is the result. Two 1/4 wave resonators mounted to the exhaust tubing at the end of the straight run, prior to the cans.
From 1200 rpm all the way to 1800 rpm the difference is amazing.
Before, at 1000 rpm the db rating was a steady 72 sitting inside the car. Now, it has dropped to 61. A 10 point drop in db is roughly equal to cutting volume in half!
These were tuned to be optimal at 1400 rpm, assuming I would pick-up additional benefit from slightly below, to slightly above that rpm range.
They work like a charm!
If interested, hit me up and I'll send you the specs, including the procedure for finding what you may need.
They are capped at the end. The theory is that the sound wave bounces-off the capped end and then travels back the length of the new tube, colliding with the sound wave traveling down the original exhaust pipe.
Think of dropping a pebble into a bucket of water - the rings/waves represent sound. When the original wave hits the side of the bucket, or another obstruction, it bounces-back against itself - thus partially canceling the wave action. Sound works somewhat like fluid.
Looks like a solution to the drone problem. Do you carry a can of "spare tire repair" in the car now that you have lost your spare tire. At least it looks like there is no room for the spare now.
Looks like a solution to the drone problem. Do you carry a can of "spare tire repair" in the car now that you have lost your spare tire. At least it looks like there is no room for the spare now.
Lol - nope, no room for the spare. Of course, it was a 25+ year old doughnut anyway. I carry a cell phone and AAA card.
I would so try that if I didn't like my spare tire so much.
Did you arrive at the tube length by calculation or published info? Also is the muffler dual outlet or did you leave it capped with the freeze plug?
There is a lengthly discussion on this on several different forums. BMW, Chevy Truck, Pontiac G8, Mustang, etc. The math works and the fix works even better. I will post the forumula on this thread.
Both tips are open, the sound around town is great, deep and raspy. And at WOT, there is a nice bark.
As some of you may recall; I purchased and had installed a full OBX system for my '89 coupe. To say that I was displeased with the installation and resulting resonance is a very mild understatement. From 1,000 rpm, all the way to 1500-1600 the drone was so bad that I could not stand to drive the car.
I experimented with different options, including two freeze plugs in the primary exhaust tips (which helped a bit). Finally, after much search and investigation, I stumbled upon 1/4 wave resonators.
Having an IQ slightly above an apple, even I understood the theory and engineering behind this application. A sound wave travels at a specific speed through space, to cancel that sound wave, you bounce an equal (or in this case 25%) wave back at the original.
What you see is the result. Two 1/4 wave resonators mounted to the exhaust tubing at the end of the straight run, prior to the cans.
From 1200 rpm all the way to 1800 rpm the difference is amazing.
Before, at 1000 rpm the db rating was a steady 72 sitting inside the car. Now, it has dropped to 61. A 10 point drop in db is roughly equal to cutting volume in half!
These were tuned to be optimal at 1400 rpm, assuming I would pick-up additional benefit from slightly below, to slightly above that rpm range.
They work like a charm!
If interested, hit me up and I'll send you the specs, including the procedure for finding what you may need.
The ultimate exhaust for older C4 CORSA, NO RESONANCE GREAT SOUND
08-15-2014, 09:50 AM
Last OBX Exhaust Update
