Building an affordable engine dyno

[Tony Castronovo]

After nearly twenty five years of stellar service our engine dyno, "known as Betty" has passed on to the point that she is so worn out, she had to be put out of commission.

She couldn't handle the relentless testing of the XForce engines over the past couple of months, and the 100 hour test was just too much.

Anyway, all kidding aside when I designed Betty I tried many loading devices from water to electric (eddie-current) but both either was too difficult to control, or they couldn't bear the high RPM's that our engines deliver.

All that time right in front of me was a dyno that both you and I have used many times and didn't even know it. Amazingly it was designed for this very use. The back pack blowers are the perfect engine dyno as their design is one where you are trying to move as much air as possible with the limited horsepower at hand.

The more air allowed in the inlet of this (impeller) designed unit means more load on the engine, due to the increased compression taking place. So to control the load you simply have to reduce, close, or allow all the air in the intake.

To do this I simply made a slide valve or a gate that enabled me to open or close the inlet and let the desired air in, thus controlling the load on the engine. Shut off has very little load, mostly rotating mass and friction which is minimal by design.

The rest was easy, all we had to do was run the boat with the desired prop and an on-board tach, put it on the dyno and open the gate ( with a RPM meter connected to the engine ) until the RPM's matched.

Now to say that we can read horsepower would be a wrong, but we were able to make very close comparisons between propeller and engine, which in my book was even more valuable information, and served the purpose testing over 25,000 engines that most of you may have owned.

After many test sessions we could dial the "dyno / comparitor" (my machine my name) to represent loads so close to reality that we hadn't had to do a customer water-test for two decades. If the engine performed properly the dyno told us so.

This brings us to today and a new dyno we are currently building, and I would like to share this information with all of you. Because of our new inline 52 cc XForce engine making so much power we can no longer safely use a back-pack blower impeller, so I started to source other viable products in leu of making it ourselves.

I thought what out there can handle 10 horsepower and 15+ K RPM's, yet have little to know resistance pre-loaded that works with an impeller.

You guessed it! A Turbo Charger. After testing a couple we settled on a giant Garrett turbo with a 4" inlet and with some modifications we have found what I believe to be the most durable "spinning wheel" known to man.

The hardest thing to do is just that, "the hardest material we ever cut" It took 6 hours to cut the turbine wheel off the hot section of the shaft. I believe the two are assembled as a whole during a second operation casting process, and it was the hardest @hit I ever cut.

Then we added the PTO ( square female end fitting to the shaft end ) forget taping it, didn't even try. Drill it and put an threaded insert and be done. Be sure that there is no run-out when installing the fitting, and please don't weld it, it will not last forever, and you do not want to anneal the turbine shaft.

At this point Tony Jr. has the water system plumbed, turbine mounted, and a radiator to cool the engine water back to the source tank.

The next thing to do is make a universal engine mounting system, followed by a new intake gate, ( Hint ) a 4" RV crapper valve works real nice... It has a wide range of adjustment.  For this cause as a RV owner there are only two ranges when it comes to these valves, closed and get the Hell out of the way.  Pretty soon WHH will have a new and improved DYNO-Comparitor that should last allot longer than I will in this business.

Enclosed are some build pictures showing how you too can make a great little machine at a fraction of the price of a computer dyno, that can test your engine work and performance gains or losses even when there is snow on the ground, and even provide more useful  information. I know, I own one of those $6,000 dyno's.

Which brings me to today January 24th 2012. Damn it's 80 degrees here and we had to turn on the air, gotta love those solar flares. I wonder where Al Gore is these days? Probably spending his money in the tropics, from what I hear they are not effected by Global Warming.

Give it a try, I'm sure the Chinese will...

Tony C.