Dyno room exhaust muffler and impact on tuning accuracy

After being their part time tuner for some period, my local garage had finally decided to purchase their own (second hand) dyno to support my tuning work and will be delivered later this month.

One of the problem we are facing right now for setting up the dyno room is noise as there are sensitive neighbors nearby. Due to building restrictions, the room may only be built with light materials meaning sound deadening will be a problem. Our proposed solution is to use a reducer/coupler to connect 8" flexible piping to the vehicle's exhaust tip and route the exhaust through some form of industrial muffler (or fabricate our own from barrels) before venting the exhaust gas out from the room. Other than muffling the noise, this would also prevent exhaust gas from contaminating the intake air as all exhaust gas will be ducted directly out of the room by the sealed piping.

My concern now is, now much restriction would such a system add to the exhaust? Will it be sufficient to throw off the tune completely once the system is removed or would the effect be minimal?

We have ZERO experience at building a dyno room so any other inputs will be greatly appreciated. Thank you!

I built one out of two stacked barrels, 6 (I think?) 1" perforated tubes down the centerline of the long axis, and then packed with lava rock. It's loud, but makes running rotaries on the dyno doable in the residential area behind the shop. Also, the longer the exhaust/8 inch tube you're planning on using the better.

Thanks, yes we might go the fabrication route if industrial silencers are too expense. Rather than lava rock, we will probably try some insulation or exhaust packing materials. How hot does your barrel get? I am wondering whether normal insulation material would handle the heat.

When you said the longer the tube the better, do you mean better sound deadening right? As in theory, the longer the tubing, the more exhaust restriction it would generate.

With your setup, do you experience any significant impact on in how the engine runs/accuracy of the tune once the restriction is removed?

Well, it would be cheaper to buy a whole lot of ear plugs for neighbors and give it away for free)

Jokes aside - you have a quite difficult thing to solve. The exhaust pipe should not be too different in height as that will create a differential pressure ( since hot gas always goes up ) thus some exhaust suctioning which in its terms will effect on engine VE. So both ends of your dyno exhaust extension pipe have to be at the same elevation level although the middle part can be lifted somewhat if required by building design. It also will have to be large enough not to cause a restriction - from what I've seen it is usually 3-4 inches in diameter...

@MGV101 Yes, better sound deadening when we run our longer runs depending on which dyno I'm running on. The can doesn't get crazy hot, but its certainly warmer than you'd want to lean against :P. Only time I've scorched the concrete was having to jimmy rig a secondary catch for a divorced wastegate that put a bend far too close to the ground.

Last but not least, for us, there're negligible power/accuracy differences within reason. That said, on track with a proper sealed air box running on the banking at 170 there's a bit more airflow and lower temps that'd be quite difficult for me to replicate.

Provided the exhaust ducting it large enough, there shouldn't be a significant problem - remember, when the vehicle is driven the pressure around the exhaust exit is going to be varying as well. Rather than having the ducting sealed to the exhaust, I may run them as slipped over the exhaust, and open, to check if the exhaust drives the fumes through the ducting or if there is sufficient back-pressure to 'stall' the flow - that would also give the potential to draw cool air into the ducts that will help damp the exhaust pulses that cause the noise, but may also allow an extraction fan to be used to help draw on the exhaust gases.

Just to clarify, is this an engine or a chassis (wheel or hub driven) dyno'?

Are the building restrictions because of local regulations, or land-lord concerns? There are relatively light sound absorbing materials available, but cost and availability may be a problem for you, but shaped foam blocks can certinly help. You could try applying some anechoic chamber principles to help control the noise in the room/enclosure, too, as any sound reduction will help.

If it is possible, especially with roller dyno's, it may be worth checking if the rig can be rubber mounted, - many are set/bolted directly to concrete, but any imbalance may cause vibration that can be felt some distance through the ground.

Are you planning on having the exhaust exit through the roof?

Forgot, have a look through these - https://www.google.com/search?client=firefox-b-d&q=how+to+build+a+dyno+room%3F

A lot of guys who were fabricating their own mufflers for rotaries here in Australia were using an insulation product called rockwool which had similar sound damping to fibreglass but significantly higher temperature rating. If you do barrels I would look into it.

I would be inclined to use larger diameter ducting and an inline fan to suck from around the exhaust tip and exhaust through the roof of the building for both personal exposure to fume and noise as well as any tuning related recirculation issues. A steel impeller radial fan doesn't require anything sensitive in the gas flow and will generally draw ambient air across the bearing/shaft/"seal" area into the housing if there is a bit of clearance. You will see plenty used on all sorts of fume extraction systems, often mounted outside the back wall or on the roof of a building.

Thank you M:EP, good to hear it does not effect tuning too much.

Gord, we have a wheel driven dyno. And our concerns are both, landlord and local regulations. However, I think roller noise should be acceptable but I'll still look into the dyno mounting. The neighbors should be ok to put up with some noise as long as it is not excessive.

Yes, barrels is the most likely method here, just need to see what damping materials are available to us.