Finally a dyno run!

[bruce]

Finally got to do my first actual dyno run (well somewhat actual) with my dyno . . . all I can say is I have a new toy to play with now and ALOT to learn! LOL

Found some things I need to change on my dyno build somethings need to be changed others re-visited to find better ways and others things worked better than I imagined.

One big thing is the exhaust evacuation, need to come up with a better plan on that one. I am not able to have my dyno as a permanet setup/room so it has to be portable. I am using a flexible automotive exhaust pipe and running that into a tractor trailer muffler. Problem is the area where it connects to my straight pipe out of my engines. (wasn't thinking about taking pics when I ran the engine sorry). I was using a peice of high-temp sleeve material between the flex pipe and my exhaust pipe, it just blew out. The flex pipe is just slipped over my exhaust stack. My exhaust from the engine goes and and straight up.

How critical does this connection have to be?

Do I need a gap, can it be a tight fit on the pipe?

How much larger in dia should the evacuation pipe be so it does not have an effect on my engine exhaust?

I can not just run a straight pipe, my neighbor doesn't care for me now so I need to quiet this thing down somehow and the tractor trailer muffler does quite well

I'm kinda just brainstorming here on the forum . . . thoughts anyone?

[bruce]

I'm quite happy with the ability to manually control the load using the variac until such time when I can upgrade to automatic load control or should I say how to cheaply do it with ebay purchases of the right parts. I think I have most of the parts now just have to figureout how they all work together.

Only concern I have with the telma is the rpm's and spinning those big ole cast iron plates on it. It's rated up to 8000rpm's but I have to say it is kinda scary running it at 4000rpms so I can only imagine what it would be like at 8000! I'm seriously thinking of setting up a reduction somehow to slow it down.

If it was bolted to the floor it would be alot less scary LOL I have some re-engineering on my dyno framework I want to do to make it less scary and easy to adapt to the rollers I plan to build for my chassis dyno add-on. I built my frame so engines could be bolted on either side of the telma so rotation was not a problem. The telma must rotate in one direction only.

I need to add a temp sensor to the telma also, one more gauge to watch . . . it got warm but not hot. Made about 6 pulls, course I was only working with less than 25hp.

One other thing is adding on a starter/ring gear to the dyno itself, using the engine starter is hard on it since it is turning the telma and engine. Not really that bad but don't like putting the strain on the customers/my parts like that. Something from a small 4 cylinder would probably work.

[Tony]

Bruce, I have no dyno, but I have been thinking a lot about how to solve some of these exact same problems myself.

Noise is a very big issue for me here too, but I have some very long term evil dyno plans myself...

The basic problem seems to be how to get rid of the noise and the exhaust gas without introducing any extra artificial back pressure on the engine. So the first thing immediately after the open engine pipe should probably be a sufficiently large open (acoustically lined) expansion chamber. Something larger than twenty times the single cylinder capacity of the engine should work according to some reference books I have here, and that is not inconveniently large.

That should feed straight into a high capacity exhaust extraction blower. Following that, a suitably large absorption muffler. But the secret ingredient to the whole thing is a variable area throttling device right at the muffler outlet.

If you can deliberately restrict the exit area of the muffler, it will definitely hold back a lot of the noise through reflection, and greatly reduce fundamental frequency pulsing. The trick is to have something that automatically opens and closes, without flutter, to hold some fairly low fixed back pressure inside the muffler. Less than 0.5psi works very well, but slightly more back pressure than that would make it even quieter.

With a bit of ingenuity it should be possible to automatically control the extraction blower and the outlet restriction to hold exhaust pressure inside the expansion chamber (that the engine sees) at atmospheric pressure. while maintaining a sufficient back pressure inside the muffler over a wide range of engine operating conditions. I have carried out some rather interesting tests here on all this, and it all works rather well.

I can go into all this a bit deeper if anyone is interested.

Bruce, can you use the gearbox that is normally attached to your engine to drive the dyno ? That would be a lot safer.

One other idea, placing the starter motor on the dyno itself is an excellent idea, but a fairly powerful starter will be required to overcome the inertia of those big heavy rotors. One way to overcome that, and save some money would be to use multiple starter motors instead of just one. There is no reason why two, or any number of starters cannot be arranged around the ring gear and operated simultaneously. And you can use low cost secondhand starters off some smaller common engine, instead of a horribly expensive giant sized "special" starter motor.

[MMack]

Last year I built a system to silence the a air powered venturi. You pump compressed air in to a chamber and it blows out an annular ring creating a suction through the middle. They are like 105 db normally. We put it in a box lined with armaflex insulation. 1" thick in an 18" cube with the venturi in the middle. There is a 4-6" gap in the tube that feeds the product in. As the sound waves expand out of the venturi, only a small portion go into the exit pipe several inches away. I sounds simple, but it works. The exit is at or below ambient, 75 db for that area of the factory. It is so quiet that the folks don't realize and leave it on and are using a ton of air!

Mike

[Tony]

Yes indeed Mike, a relatively large chamber, lined with acoustic absorbent material, and having a relatively very small exit area will be extremely effective over a very wide frequency range.

[gofaster]

I picked up a 5" muffler for a diesel truck, and a length of 5" exhaust tubing. The new muffler was about $50, surprisingly the tubing cost more! I also picked up a flapper type rain cap. I picked up some garage exhaust tubing and various adaptors as a kit from ENCO. I'll let you know how it works out.

[MMack]

I have seen some exhaust clamps at some street rod shows that allow you to butt splice the pipes. The clamp is a 360 degree wrap that clamps each pipe seperately. This type of clamp may help. I think Jegs or Summit carry them.

Mike

[Thomas Vaught]

One of the guys I worked with at one time lived on a piece of lake front property. The House was on the top of the hill, the lake was on one side of the hill and a large garage was on the other side of the hill. He did a lot of turbo boat stuff for people.

He made his own dyno (about 2000 hp at 7500 rpm). Very similar to a two drum Stuska. http://www.stuskadyno.com/xs-211.html]http://www.stuskadyno.com/xs-211.html[/URL]

But back to the set-up.

He made a very large water tank which he buried in the hillside, he pulled the water to fill the tank from a deep well at the beginning of each dyno season.

He also dug two tunnels INSIDE the hillside and routed the exhaust from the turbos into the tunnels. No noise to bother the neighbors after the Earth Mufflers did their deal, the actual exhaust came out away from the homes. Tony's deal of routing his exhaust flow from his flowbench through the drain system works the same way.

Tom V.

[86rocco]

I know of someone that's using a similar "engine muffler". In this case, it's a 30" culvert about 25 or 30 feet long buried a couple feet underground terminated at a dry well to get rid of any water that might otherwise accumulate and a 10" vertical pipe to vent the gases. I've never actually heard it in operation but I'm told it's very quiet.

[Tony]

Underground is definitely the way to do this.

Right now I am feeding the exit air from my flow bench down a storm water drain, and it is wonderfully quiet.

A very good buried muffler can be made from a long length of about two foot diameter concrete pipe, filled with old car tyres. This works surprisingly well, it just needs a vertical exhaust stack at the outlet to restrict the exit flow area, and it should be very quiet. Nothing to slowly rust away either.

[dragv6]

While were on the subject of mufflers, How much of a risk is an explosion inside them from unburnt fuel, specificly methonol fuels?

[Tony]

I haven't heard a car backfire for a very long time. I think it would be even more difficult to do on a dyno, unless there was a very serious ignition problem.

[Thomas Vaught]

The culvert drain with the tires sounds an awful lot like some Sniper Noise Suppressors I have used in the past. The ratio of the discharge pipe to the 24" diameter pipe is about right too! LOL!

Tom V.

[BCjohnny]