Dyno Cell- Exhaust extraction vs Fuel tune

[revvedmoto]

Well, this is a multi-faceted question that may change the direction of my dyno cell build. I've been googling different questions I’ve come up with while planning my dyno cell build. Between construction methods, soundproofing, and ventilation systems there seems to be very limited info out there. This forum and a few others had a few promising threads so I figured I would ask my questions here.

To Start I bought a used dynojet chassis motorcycle dyno earlier this year but after a dozen or so uses I started getting some noise complaints. I currently have the dyno in a metal shipping container where the whole side of the container opens to the world. I pretty much have been running this thing outside and it reverbs pretty good on the metal container. I'm still on the fence if the dyno will be left in the container and try to kill the reverb and exhaust note or if I'll be moving it into a room in my shop. All the bikes I tune will have an aftermarket exhaust pipe that arent very quiet which leads me to my first question.

During my exhaust quieting/extracting research, I came across two setups. Most seem to have a hose and funnel setup sitting a few inches from the exhaust but would make little to no difference in the sound department. This is also the method that dynojet recommends. The other method I've seen they slip the hose over and attach it to the exhaust, extracting the exhaust and sound. All these setups seem to be engine dynos.

I like this idea, but I have two concerns one being damaging someone’s exhaust by rubbing the finish. The second, assuming I’m powering this hose with an inline fan and then out a silencer, could the vacuum created potentially affect how the bike is tuned?

My thoughts were to wrap the exhaust in something soft and slip an oversized hose over the exhaust in the hopes of alleviating some of the pressure and hopefully collecting the majority of the sound.

I'm curious what you guys think, am I overthinking this, Is there a better method to extract the exhaust without affecting performance?

 

[BrianPetersen]

The suction from a normal ventilation fan isn't going to be sufficient to make one whit of difference to how the bike runs, no matter whether it's a funnel past the end of the pipe (high possibility of leakage of exhaust into the dyno room ... think carbon monoxide here) or a larger-diameter soft cushioned thing fitted loosely over the end of the muffler.

I know someone who did what you're doing, a couple of years ago. He built a full enclosure around the dyno (and bike, and computer monitor, etc) with a door that closes around the back after the bike is rolled in and put on the dyno, and the whole thing is sealed with noise-absorbent material (sorry, don't know exactly what he used) around every wall and the roof and the back door and the edges are sealed. With the back door closed, it is totally sealed except for the exhaust and make-up air openings. The exhaust fan draws out through another enclosure filled with sound-absorbing stuff before it gets to the fan ... I think he just jammed it full of fiberglass batts, this is sitting on top of the main dyno room with the hose (~ 6") hanging down. The exhaust fan volume is considerably higher than the engine exhaust volume because you also need lots of make-up air volume for engine cooling; heat build-up is still a problem (he made it so that it's really easy to open the back door so that this can be done between runs). Make-up air comes in through another centrifugal fan that blows at the bike's radiator through a flexible duct that can be aimed as needed. Every path for noise to get in or out, needs to have that noise blocked or absorbed. And I mean EVERY path.

His neighbors haven't complained.

 

[gruntguru]

Seal the pipe to the exhaust outlet but make sure you have a big step-up in diameter (at least 20%) otherwise you may affect the tuned length. Check the backpressure in your added system - less than 1 psi is fine.

je suis charlie

 

[enginesrus]

I would never have a dyno in a stick built shop. It needs to be in a total fire proof installation. Concrete or block building.

 

[CWB1]

Noise control out the stack will always be a struggle for engine testing, anybody outside within 1/2 mile of every facility I've been at knew when we were testing and complaints weren't uncommon as neighbors' windows opened and outdoor activities commenced in summer. My best advice is to locate your shop far away from residences in an industrial area.

Yes, cell exhaust stack pressure is typically controlled to remain slightly negative as it impacts performance. Funnels are prob your best bet for connecting to fancy exhaust tips but there are other methods like bland clamps and slotted sleeves.

 

[ant180]

I can give some first hand experience here.

I built a chassis dyno cell in my old shop using 2" thick steel faced foam core sandwich panel ("Cool room panel" here in oz) for walls and ceiling. I had serious issues with noise inside the cell, but never got around to installing sound deadening on walls and ceiling. I had a few cars loud enough in there to cause issues with hard disks on computers, and intermittent issues with TV type displays. Ear plugs and muffs over the top were barely enough.

The cell was built somewhat to keep the noise down for the neighbours but mainly to allow me to have ample airflow, ensuring the supply of plenty of makeup air whilst keeping the cell at a slight negative pressure and keeping ambient heat as low as possible

Makeup air entered via a ceiling opening approx 4' x 4', positioned in front of the car. The opening had walls approx 3' high built around it, and then a large box maybe 8' each side built on top of that. an opening on one side of this box approx 12" high by the full 8' wide allowed air in, whilst making sure sound had to bounce off multiple surfaces lined with foam and cloth to deaden the noise.

Exhaust air exited by a 3' diameter 15kw 3phase axial fan above the ceiling at the rear. This was ducted out the roof (maybe 20-25' high) with sheetmetal 3'x3' HVAC ducting. On top of the roof was a sheetmetal bend, with a turn approx 110degrees, and a bit of a hood to keep rain mostly out.

A VFD on the exhaust fan was absolutely vital, as 15kw of airflow is a shit load! Id usually run the fan way down, and turn it up via remote only for the duration of a pull on the bigger cars.
I also used a big approx 8kw centrifugal blower fan aimed at the radiator and blowing under the car. Dont underestimate how hot an exhaust gets under sustained load unless there is plenty of airflow on it.
Noise outside with all doors shut was fine in an industrial area, but no way would it pass in a residential.

If i had to get the noise down further, i would have lined the exhaust stack with sound deadening material, and perhaps constructed it like the intake stack, with multiple lined surfaces for the waves to bounce off on their way out.

One other thing. Dont assume all your noise is exhaust noise. Most angry NA engines make a load of induction noise. Even if you seal the exhaust up into giant mufflers, you still have the intake to deal with. Id do what is needed to get the cell closed off and deal with the noise in the stacks as needed.