Why dyno test an engine?
There are better reasons to dyno test than just to get a horsepower number to brag (or be embarrassed) about. So what are they?
To get accurate horsepower and torque numbers.
A computerized engine dynamometer accurately measures torque and rpm and then can accurately calculate horsepower.
How are accurate horsepower and torque numbers used?
Knowing the horsepower and torque gives the engine dyno operator or engine tuner a solid basis for making changes in the engine's tuning or to the engine itself. This is simple. If horsepower and torque go up the change was likely correct, if they go down the change was probably incorrect. Here are some variables that can be tuned this way; carburetor size and jetting, intake manifold selection, cam grind and timing, ignition timing and advance curve, the headers primary tube diameter and length, collector diameter and length, and carburetor spacers. Check out "Dyno test results; Amsoil vs Petroleum (15K)" and "How to use dyno test results" as examples.
A dyno is an ideal place for the first run of an engine.
At RevSearch we prelube the engine being tested before EVERY start and post lube after every shutdown. The dyno's starter will not work without engine oil pressure. We can also pre-heat the engine. Engine break-in routines specified by cam and ring manufacturers can be accomplished under controlled conditions. Blow by can even be monitored as the piston rings seat.
Exhaust gas temperatures are recorded.
Exhaust gas temperatures (egts) are so important they deserve their own section. Egts are even more important than horsepower and torque numbers for tuning carburetor size, carburetor jetting, fuel distribution, and carburetor spacers. Look at the graph below. Which piston might melt? Yes, #3. How would you find this out without dyno testing? You're right, usually when the engine melts a piston. Have you ever heard of THAT happening?
For a record of your engine's performance.
After a dyno test we give you a bound booklet full of detailed information about each individual test, baseline weather conditions on the day of the dyno testing, space for you to record engine build information, and many easy to interpret graphs of your engine's performance.
What about the computer dyno programs?
We have one of the popular computer dyno programs and it will give you a rough idea of what your horsepower and torque will be. But what about tuning? An engine dyno is just another tool (however, an important one) to use to get an engine running the best it can possibly run. A computer dyno program is no help with this.
Does dyno testing wear out the engine?
Speaking with the voice of our experience, not any more than normal running. There is the idea that dyno testing wears out engine bearings. We have proven this to be a myth. For example, our first engine, a Dodge 360, had 40,000 miles on a stock bottom end (except for forged pistons), stock 1973 heads with 50,000 miles on them, and sat for over ten years before becoming the dyno system/dyno operator test engine. It was then pulled over 140 times when finally an intake valve head got hot enough to soften and sink up into the cylinder head. After this it would not run above 4900 rpm without floating that valve. (This was caused by a lean condition because of additional carburetor spacers. The lean condition resulted in high egts and was noticed during the test. I won't make the mistake of ignoring that again!) The majority (99%) of the tests were full throttle sweeps, run from 5500 rpm to 2500 rpm. Because of a fuel distribution problem cylinder #2 EGT was always above 1500º(the header tubes would glow red hot!!). We have since learned how to deal with these fuel distribition problems. When this engine was disassembled no unusual wear was noted, in fact the bearings, both main and connecting rod, were re-usable (and were re-used). Unusual was the fact that four of the pistons were physically hitting the heads during all the miles and dyno testing!! (A teenager put it together). One could say dyno testing was not unusually hard on this engine. However, any engine new or used, can break. There is no way to know what a re-conditioned or used part (for example connecting rod) has been through. Over revving or assembly mistakes can break any part or cause stress that will break it later.
If you have any questions please e-mail me the current address is on the RevSearch Home Page.
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