Injector Sizing calculations - Electronic Fuel Injector sizing

[Greg]

I've been looking to make an engine dyno for a while now and after reading posts here I was ringing around some truck wreckers to try and find a telma retarder. When I explained what I wanted it for the bloke I was talking to said he had an old water brake chassis dyno that I could have for $500. Apparently it has had new seals etc fitted at some stage but they just dont use it any more. My plan is to use the water brake from this dyno as the power absorber and maybe upgrade to an electronic load cell to measure the torque.

I take it from looking around a bit on the net that these are still used and seem to work well. Space is not an issue and either is making up the chassis to mount the engine etc.

To measure power from what I have learnt you use the formula:

power(in hp) = torque(in lbs-ft) x rpm/5252
(I hope thats right, everything I learnt was in metric units, kW, Nm, radians)

So all I need to do is measure how quickly the engine accelerates against a certain torque? What I am wondering is do you need to keep the torque constant and how do you do this?

Also, has anyone had much to do with a water brake setup and is there anything I need to look out for when I go and look at it?

One other thing I was thinking of was to mount a flywheel/flexplate and starter motor on the water brake end so I dont have to fiddle around trying to mount bellhousings and starters to engines without block mounted starters. Does anyone see any problems doing it this way? I suppose the weight of the flywheel will be extra weight for the engines to turn but I suppose this can be factored out in the calculations?

Last thing (this is turning into an essay rather than a post!), does anyone know of an affordable computer sensor/software setup for reading and calculation?

[98-1074649673]

Wow thats a few questions!!

For an indepth book on dynos pickup a copy of Engine Testing Theory and Practice, Michael Plint & Anthony Martyr ISBN 0768003148 One whole chapter on design of connecting the dyno to the engine! Explains in depth the harmonic effect on cranks from dyno running if not connected correctly.

Load cells can be purchased off eBay along with digital meters to read them after you get the dyno working manually then go digital. Cheap? LOL don't think so u get whatca pay for I am finding. I have not gone digital yet. And this all depends on the level of accuracy u are looking for? Cheapest way I have found is a DAQ card and dump the numbers into Excel and do your own spreadsheet, course this intails learning Excel and how it works with a DAQ card? Personaly I will probably go with something commercial for digital since I lack the knowledge to do all this work.
"Do what u do best, pay someone else to do the rest"

Water Brake dynos use water and lots of it!! It has to be cooled so you need to have a large tank and a pump that will supply the brake with the correct amount of water all the time.

A water brake will do static testing ie one rpm and one torque reading move on the next rpm range and measure torque etc . . . search on the net for more info on all this LOTS of info out there that explains it in more detail than this non-engineering student can LOL

Will this water brake take the rpm of a direct engine coupling? If its on a roller dyno its probably made for lower rpms? My eddy current unit is rated for 7000 rpm's with short bursts to 8000 being ok but no sustained testing at that rpm.

Hope I've answered more questions then I created for you? Least that should be a start . . .

[84-1074663779]

As Bruce says, a water brake is best for static dyno testing where the dyno holds the engine at fixed RPM points.

RPM measurements can be made with the engine tachometer which can be checked for accuracy by strobing the engine flywheel against a fluorescent lamp at certain RPM points.

Torque measurement can be done by making a torque arm on the dyno push on a brake master cylinder. A decent accurate large scale pressure gauge (calibrated in psi ?) can be calibrated to read directly in foot pounds. It is just a case of getting the arm length and bore diameter sorted out.

A pencil, paper, and calculator are pretty low cost as well.

It is not high tech, but it is simple and doable. Numbers on a computer screen can end up being expensive, and may not be any more accurate. But it might be something to work towards in the future.