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So the scenario is I'm with an FSAE team and we're running a Yamaha R6 with MS3 Pro. We have very strict rules when it comes to passing sound in tech ( no emissions, purely decibel limits at idle and then a set high rpm). We have done everything we can physically to reduce engine / exhaust noise with different physical components. I am curious to what techniques anyone know of to help reduce these sounds in the tuning scene. Such as retarding ignition timing? Any past experience or advice would be greatly appreactied!
I have a hard time believing you've done everything to physically reduce the noise. Have you determined the sources of noise (exhaust, intake, drivetrain)?
Have you insulated the Intake Manifold -- I know the FSAE teams often run a very large manifold, and this is basically open to the intake valves. so exterior insulation to prevent sound waves passing through your thin intake manifold (look up rock-wool, mineral wool type insulation).
If it's exhaust, then a larger muffler will always be quieter. There are lots of different designs to try as well.
You should test at different RPMs to determine if perhaps a lower RPM limit would reduce your readings.
You're giving very little to go on and, alike David, I suspect you're missing a few things.
What EXACTLY are the test conditions, vehicle stationary, drive by, or what? Is it the total noise or is the exhaust isolated?
First off, have the fuelling and timing set to minimise the throttle opening to minimise the exhaust gases - retarding as you suggest will both increase the gas volume for the same rpm, but also increase the exhaust energy that helps drive the noise. Over-advancing, short of detonation/pre-ignition, will mean more combustion energy is used inside the engine, rather than being passed out the exhaust, but it's a balancing act.
If running NA, which seems to be the thing to do, the airbox/plenum shape and construction can be a significant noise source, as can the intake to it. Using curved surfaces, possibly with internal ribbing, and creases in any flat surfaces to stiffen them up, can reduce the intake noise. If you can design the airbox/plenum intake away from the open, that would help as the surrounding components will help muffle it. Insulation, as David suggests, will definitely help but there will be a weight penalty. If it's 3D printed you may wish to look at different materials, as some will have better natural sound absorbtion than others.
With the exhaust, different materials used in fabrication may affect the ' ringing', as may different gauge materials. On that, you may wish to look at different primary lengths, collector diameters, outlet orientations to reduce the level of the exhaust pulses and/or direction. A slip-on porforated mini-muffler may make a significant difference, too.
If it' s the total noise level, go over the vehicle and make sure everything it secured in place, flat panels avoided or stiffened to reduce their 'sound board' characteristics as they vibrate.
In this instance, you have specific rpm points to work with, so you may be able to 'tune' harmonics and resonancesaway from those.
Have you actually used sound measuring techniques to confirm you will have a problem, or the locations that are contributing?
There are circumstances where retarded ignition, despite the larger total thermal energy results is less sound energy, more open throttle and soft timing can often reduce the sound intensity ar measured frequency. If it is time averaged you can even run rotational idle. There is usually a specific test angle(s) and height to the car from memory, use that to your advantage in terms of exhaust direction.