Is it possible to make 8000 rpm whisper quiet?

I was thinking about buying a engine dyno but I don't want to get pelted with rotten fruit. Anyone have experience with this?

You should also post this question over on speedtalk

Our Soundmaster cell is whisper quiet outside, we have the biggest silencers they make on it. We are less than 100 feet from residential. There are pictures on our Facebook page

Yes, but it costs money. The exhaust isn't hard to quiet down, you just need to spend the money to buy the really big hospital type mufflers.

The intake air is super noisy once the exhaust is quiet and that is harder to deal with. I worked on a job once where we installed "zero noise" air inlets and exhaust. Those things are commercially available but expensive and they take up a lot of room.

The dyno cell itself can be made fairly quiet with normal building tricks. You just need a lot of mass (concrete block walls) and dead air space as well as some sound absorber material.

Dyno Cell

Getting the exhaust quiet is not hard like Andy said, just some hospital grade mufflers. 5 years ago I think they were around $900 a piece.
Getting the air in and out without letting the sound out is the trick.
I built the room myself and it’s pretty quiet. The only time the neighbors have told me they could head it was when we had a 2200HP engine on it.

The cost of the room and the support equipment IE Fans, pumps, plumbing, electrical, VFD’s and storage tanks ran me another 25K after buying the dyno. Again, that was me (and a few friends) putting it together.

I have a old industrial building that has a boiler room in one of the basements. It seems to me the cell is already built. I would just have to remove the "locomotive" not a easy task in its self. It being in the ground I'm would kill some noise by itself. Although having a concrete ceiling might not be ideal. I was thinking I could do something with the chimney and some industrial suppressors.

I'm just dreaming I guess

This still applies:

https://board.moparts.org/ubbthreads/ubbthreads.php/topics/2053550/re-sound-deadener.html#Post2053550

My real life professional experience on this topic is in recording studios, rehersal studios for hard rock bands (like Manowar, from Wiki "In 1984 the band was included in the Guinness Book of World Records for delivering the loudest performance"), and concert large portable generators, all related somewhat to your issue.