The dyno home page
Updated: 6 -Jan 99
Version 0.3
History:
0.1 original edition
0.2 added info and progress on my dyno
0.3 added inductive pickup info
Conditions of use
The information in these articles remains copyright to their respective owners. In the case of my efforts, it is available for non commercial use under the following conditions:
It is not to be sold or used for commercial gain. A lot of people have given knowledge and time to this project, and I wouldn't like to see them miss out.
I want copies of plans or drawings or photos of the finished product.
If you do your own data aquisition software or hardware, I would appreciate a copy of it. I will even pay a reasonable amount for it.
Introduction
Some progress has been made - see the first photos on the DIY inertia dyno page. At present nothing has been done for over 2 months, since I have been flat out at work, so it is in bits again after painting. I need to reassemble it soon and finish the covers for it (for safety if nothing else). The data aquisition side works after trouble with a faulty timer card, but the software "needs work" and is still clunky with some aggrivating interface issues. Pretty bug free though.
If you want to build a dyno, there are a couple of options, the retarding force can be either a brake (usually water, electric or hydraulic) or inertia. If you want some info on "how-to" an inertia dyno, click here.
What's a dyno anyway?
The best answer to this is to go to:
and also read:
Building an inertia dyno
In theory, an inertia dyno is the easiest to build, as you are measuring the acceleration of a large flywheel or drum. The key is in the software and the data aquisition side, making this more of a software problem rather than a mechanical one.
I have made some progress on this, which is outlined on the DIY inertia dyno page.
Dynopower in the UK sell plans and hardware and software to make a full house commercial grade dyno. This would probably be the best option if you plan on making your living with it.
For some background reading, the SAE have a paper 1994 Motorsports Engineering Conference Proceedings (paper no: (942478) which includes this article by Prof. Gordon Blair on "acceleration testing a kart engine". It has all the maths you need for it.
Another must read site is at TDK Motorsports which covers how to make a flywheel based dyno for kart engines, using the Performance Trends DataMite for data aquisition. Thanks to the first class effort by TDK, I won't go so much into the DAQ side of the dyno. My software and hardware was done by Andy Cree, who is also interested in doing others. The price was $NZ800 (Approx $US400) for the software and timer card and pickup, which I though was reasonable.
While the engine RPM can be estimated from the drum speed and gearing, it is best if you can pick it up directly. This can be done via a connection to the low voltage side of the coil, whihc is the way most aftermarket tachometers connect. I have thought of getting a cheap tacho from the auto parts store and gutting it to provide the electronics. The other way of getting engine RPM in real time is an inductive pickup from the spark plug lead. This has a lot of problems with noise, and this page may help.
One area of interest is using a soundcard to record the engine firing pulses, and processing those to get RPM figures. Try Streetdyno or Homedyno for info.
For an inertia dyno on a slightly smaller scale, have a look at this one for model boats - has some good stuff.
You can make a small dyno using a hydraulic pump as the load. In my case, it has a tank of hydraulic oil, with a 50GPM Cross gear pump (50HP). The line coming out of the pump splits with a return to the tank,which has a fixed throttle valvve in it. The other line goes through a pressure guage and an adjustable throttle valve. Changing the throttle valve opening adjusts the load. There is a rev counter on the pump (pump rpm is proportional to flow), and power absorbed is flow (rpm)x pressure x constant. You can buy (expensive) combined pressure and flow meters which will almost let you read this off directly.
Problems i have found include:
The oil gets hot and this makes it thinner after a long run
the pump is old which makes it inconsistant under high loads
the load on the engine makes it run very hot which makes cooling a problem.
Here is a post I saved from earlier on...
From rgstruve@dmacc.cc.ia.us Tue Jan 09 07:43:36 1996 From: Richard Struve <rgstruve@dmacc.cc.ia.us> Date: 8 Jan 1996 19:43:36 GMT
jvwillou@students.wisc.edu wrote:
> There are several different kinds of dynamometers; water dynos are just one of them but that's the type I'm by far most familiar with. >Nothing more, nothing less. I'm a machinist and have built a 100cc V-4 two stoke. How could I make a little dyno to measure power of this. >I suspect it makes around 10 hp at roughly 10000 RPM. I suppose I could literally use a brake rotor and caliper to capture the torque.
That would work, but a far more simpler way would be to couple a hydraulic pump to your engine, keeping in mind the maximum RPM of the engine and pump respectively and gearing accordingly. Use a pump capable of handling a little over 10 hp. Pipe the outgoing flow past a pressure gauge and to a needle valve. Out of the needle valve to a flow meter, and return it to the reservoir. With the needle valve open, you will get flow without pressure, this will relate directly to RPM. A little experimenting will yield a conversion factor to calculate RPM from the flow. Closing the needle valve will result in pressure being created. Now you have all of the physical parameters necessary to calculate power, force, distance, time. The equation to calculate power will be:
HP = GPM x PSI x .000583
If you know the pump displacement, the equation for torque would be:
Torque(ft-lb) = PSI x pump displacement(in cubic inches) /24pi
Keep in mind, that these only work for positive displacement pumps. An old worn pump with internal leakage will directly affect this system. Also, there will be some error due to heat loss in the fluid. It all depends on how accurate you want to be. Spend more money, you can get more accuracy. A piston pump will be more accurate than a vane or geroter pump.
Hope this helps
Dick Struve
If you are interested in building a hydraulic brake dyno, keep an eye on this page (brake dyno for Briggs motors).
Building a water brake dyno
Carl Shipman: Performance tuning, Tab books, 1973. Has a bit of a chapter on how to build a water brake dyno (1mb zip) from a water pump, good for up to 100hp. It is long out of print now and almost impossible to find a copy. The link is a reprint of the relevant bits of it.
This page shows how to make a dyno using a Telma electromagnetic retarder. These are a braking system used on large trucks to slow them going down hills, in addition to their standard brakes.
There aren't many books on this subject, but there are a couple which are useful:
Carl Shipman: Performance tuning, Tab books, 1973. This has a chapter on how to build a water brake dyno from a water pump, good for up to 100hp. I think this is long out of print now.
Larry Atherton: Desktop Dynos : Using Computers to Build and Test Engines. Bk&Disk Edition Paperback, 128 pages Published by Voyageur Press Publication date: September 1,1996 Dimensions (in inches): 10.87 x 8.33 x .48 ISBN: 1884089232
Anthony Martyr, Michael Plint. Engine Testing : Theory and Practice. 3 Edition Hardcover, 401 pages. Published by Butterworth-Heinemann Publication date: July 1,1995 Dimensions (in inches): 9.53 x 6.35 x .87 ISBN: 0750616687. This book covers the setting up of a dyno test cell and how to interpret the readings. Not so much for the home handyman dyno operator and more for researchers and developers, but still worth a read. A new verion is coming out "soon".
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Build Your Own Low-Cost Data Acquisition and Display Devices . For tech heads - how to do DAQ on the cheap. Computer and electronic now how required.
Dyno makers
engine modelling software and engine development stuff
Visual dyno - a performance estimator for PC's which can estimate a performance curve.
The home dyno - if you get sick of waiting for me to upload the plans, then this might be useful. It records the engine RPM and calculates the HP from the acceleration.
StreetDyno. Same as Homedyno, it records the engine pulses via a soundcard or other audio recorder.
Smartkart isn't really a dyno thingie - it is a datalogger and an interesting one at that. If you are into data aquisition for motor racing, then this page also has links for the DAC mailing list - a low volume but high quality list on the subject.
Race & Competition Motorcycle Tuning Resources. Collection of software for 2 & 4 strokes
Performance Trends Automotive and Racing related computer software & data loggers
Softengine Products engine modelling software
Miscellanous dyno based links
Ducati performance dyno page Dyno testing of Ducati bits and pieces
Lots more motorbike dyno charts, with a neat little plotting applet to display and overly them.
Exhaust Theory How exhausts work