whenever I get on freeway, only after about 60 mph on vacuum cruise, the car makes very specific low frequency noise. it's very reproducible and comes on at very specific speed only when there is load on engine. it sounds like that muffled noise when you're trying to blow whistle with an empty plastic bottle. AFR is fine, probably on rich side if anything. My timing is around +20-25 while cruising. just curious whether some of you have the same thing. thank you in advance.

 

I don't hear anything like this from the engine, but with the exhaust resonator installed there's a specific RPM/Load that causes a harmonic resonance which sounds like a ringing, similar to fingertip around wine glass lip

 

yea that's it. thanks! It definitely comes from the resonator which I changed recently.

finger on wine glass is much classier than whistling with an empty plastic bottle, so i'll stick with your description henceforth.

it's a ringing for sure. it resonates with my skull too.

 

You can weld an anti-resonance chamber onto your exhaust.

Maybe make the inlet/fixture to hold a certain diameter tube and then start with a long capped tube that slips in and keep cutting it shorter till you like what you (don't) hear?

 

You mean to tell me you don't like that skull vibration. Its the best.

 

That was just a "stock" picture from Google.

I was lucky when I built my exhaust out of an old JIC Spec 90 3.5" turbo back that it did not have a resonant frequency in cruise RPM.

I say lucky, because the Spec 90 it was 90% based on/recycled off of did have a bad booming resonant frequency right around 65-70mph.

Only real changes were 1ft added to downpipe for aftermarket turbo placement and changing muffler to Vibrant Streetpower 3.5" inlet/3.5" outlet muffler, a couple very minor changes in bend angle and a smaller turbo exhaust wheel.

Without the 1ft of piping added and exhaust wheel change it was better than stock Spec 90, but still boomy.

 

blue, that's a neat idea. I will have to try that. thanks.