This post was prompted by an adamant idiot, although he thinks he is an engine development "genius". (geniass? ?) BTW, not a guy from this board/community.
It is also a duplicate from my thread, How do I make my engine better, Racing Engines 101. What can I say, more guys read the midge . . . . .
Validation of your DATA . . . . .Everyone,
Please excuse my rant . . . . .
I get sent dyno data/flow bench data for analysis, on a regular basis. Some of the data is "useable", some is not. Dynos & flow benches can vary,
BUT, there is a "reasonable" amount of variance that
should be accepted. As with ANY pieces of "scientific testing equiptment", there needs to be
maintenance and calibration for continued
accuracy and repeatability.
Think about that for a moment . . . .
One of the things that can be done to validate data is "cross-checking". What I am saying is:
If you have dyno data and flow bench data, these pieces of data can be "correlated", to determine relative accuracy for both sets of data.I do this on a regular basis for data that I generate, and for data that I analyze.
(This is aimed at normally aspirated engines, but the formulas can be modified for blown engines.)
This is what you can do:
A) Don't just flow test the bare cylinder head(s). (You test all the ports, right?
) Test the
entire inlet tract.
2) Convert from airflow to
"potential" bhp using the following formula:
BHP = observed cfm * power coefficient * number of cylindersPower coefficient flow in inches of water 0.430 10
0.350 15
0.272 25
0.257 28
Airflow should be through the
complete inlet tract, AND,
should be the average of all cylinders.
There is a more complete conversion chart in Harold Bettes' book listed below. BUT, be aware that flow testing at very low test depressions can be misleading.
d) IF YOUR ENGINE IS WELL DEVELOPED AS YOUR AIRFLOW, dyno test results should
"reasonably" agree with the
"potential" calculations.
1) If the numbers agree, great. The dyno and flow bench you are using are reasonably well calibrated and accurate.
2) If the dyno numbers are lower than predicted by the airflow:
a) Most likely, more development is necessary to "capture" the airflow potential. OR
b) Perhaps something is out of calibration. This is easy to check, and there is no excuse to avoid it.
3) If the dyno numbers are significantly higher than predicted by the airflow:
a) Something is wrong, somewhere. Either the flow bench or the dyno is inaccurate and need to be tested for accuracy. You should test both for repeatability as well.
b) If your "back calculation" check from C/bhp results in airflow numbers far in excess of what is "normal" for your valve size(s), then something is royally screwed up.
Two books that every racer should have (and have read), explain these processes better than I can are:
1) "Engine Airflow" by Harold Bettes
2) "Dyno Testing and Tuning" by Harold Bettes & Bill Hancock
These books may prompt you to begin to digest some of the more technical collegiate texts from my reading list.
Fordboy