SloGTO
Automotive
- Apr 20, 2012
- 2
Hello, I have a 2006 Pontiac GTO. When I had my 350z, I was a big fan of Motordyne Engineering’s Helmholtz resonators for Nissan’s VQ series engines. I want to design something similar for my engine.
Initially I ordered a Corsa exhaust system. The Corsa system came with a muffler that contains a ¼ wave resonator, which is great for canceling out drone at 2000rpm on the highway. I was very happy with it; it was the perfect volume for me and worked as advertised. However, with the addition of headers the exhaust will become extremely loud everywhere else in the RPM range. I mean, it's going to be far too loud to keep my neighbors happy with me when I idle through the neighborhood at 7am in the morning or 2am at night.
Essentially, I want to design a resonator (Helmholtz or ¼ wave) for an LS2 V8 engine that will cancel out a large amount of noise at and around idle to keep my neighbors from hating me, but that won't cancel out any noise at WOT, to be welded in the exhaust.
Here’s what I have so far. I know that the LS3 engine produces a frequency of 133.3hz at 2000rpm and 100hz at 1500rpm. I am assuming since the basic design of the engine is similar my LS2 should produce the same frequencies. So since my idle is at 800rpm, I believe that I should target around 53.4 to 66.7hz for my resonator. I don’t know the EGT of the exhaust system where I want to place the resonator, because the size of the resonator will determine where it is placed in the exhaust, and that will in turn determine what the EGT’s will be for calculating the speed of sound.
Lets assume EGT of 500*F (260*C) and frequency of 53.4hz at 800RPM. (Speed of sound = 331m/s+ 0.6m/s x 260*C) So the speed of sound should be 487m/s. (487m/s / 53.4hz / 4 =2.3m) So the total length of a ¼ wave resonator for 800rpm should be 2.3meters or 7.3 feet long. And for 1000RPM, (487m/s / 66.7 / 4=1.8M or 4.2 feet long)
I have a few questions:
1. What is the best way to cut down Amplitude at idle without cutting down amplitude at WOT, a Helmholtz or ¼ wave resonator?
2. Will placing a Helmholtz or ¼ wave resonator upstream of my existing ¼ wave resonators in my mufflers affect their operation in any way?
3. Are my calculations of 66.7hz at 1000rpm and 53.4hz at 800rpm correct for frequency produced by the engine at 1000 and 800 RPM?
4. Would it be save to assume around a 500* EGT for an N/A engine midway through the exhaust at idle or is this guess too high?
5. Can someone help me with the formula for a Helmholtz resonator? I know the ¼ wave formula, but I don’t really understand nor can I find the Helmholtz one.
6. Are there any other things that I haven’t considered or don’t understand?
Initially I ordered a Corsa exhaust system. The Corsa system came with a muffler that contains a ¼ wave resonator, which is great for canceling out drone at 2000rpm on the highway. I was very happy with it; it was the perfect volume for me and worked as advertised. However, with the addition of headers the exhaust will become extremely loud everywhere else in the RPM range. I mean, it's going to be far too loud to keep my neighbors happy with me when I idle through the neighborhood at 7am in the morning or 2am at night.
Essentially, I want to design a resonator (Helmholtz or ¼ wave) for an LS2 V8 engine that will cancel out a large amount of noise at and around idle to keep my neighbors from hating me, but that won't cancel out any noise at WOT, to be welded in the exhaust.
Here’s what I have so far. I know that the LS3 engine produces a frequency of 133.3hz at 2000rpm and 100hz at 1500rpm. I am assuming since the basic design of the engine is similar my LS2 should produce the same frequencies. So since my idle is at 800rpm, I believe that I should target around 53.4 to 66.7hz for my resonator. I don’t know the EGT of the exhaust system where I want to place the resonator, because the size of the resonator will determine where it is placed in the exhaust, and that will in turn determine what the EGT’s will be for calculating the speed of sound.
Lets assume EGT of 500*F (260*C) and frequency of 53.4hz at 800RPM. (Speed of sound = 331m/s+ 0.6m/s x 260*C) So the speed of sound should be 487m/s. (487m/s / 53.4hz / 4 =2.3m) So the total length of a ¼ wave resonator for 800rpm should be 2.3meters or 7.3 feet long. And for 1000RPM, (487m/s / 66.7 / 4=1.8M or 4.2 feet long)
I have a few questions:
1. What is the best way to cut down Amplitude at idle without cutting down amplitude at WOT, a Helmholtz or ¼ wave resonator?
2. Will placing a Helmholtz or ¼ wave resonator upstream of my existing ¼ wave resonators in my mufflers affect their operation in any way?
3. Are my calculations of 66.7hz at 1000rpm and 53.4hz at 800rpm correct for frequency produced by the engine at 1000 and 800 RPM?
4. Would it be save to assume around a 500* EGT for an N/A engine midway through the exhaust at idle or is this guess too high?
5. Can someone help me with the formula for a Helmholtz resonator? I know the ¼ wave formula, but I don’t really understand nor can I find the Helmholtz one.
6. Are there any other things that I haven’t considered or don’t understand?
