A dyno is a handy and helpful tool, but don’t consider it to as the be all and end all to your on-track performance. Not only do all dynos read slightly differently, but you will get different reading depending on the method the operator uses. Also the conditions will play a role, having your car tuned and making a million horsepower at 9 o’clock at night doesn’t mean you will have a million horsepower at midday the next day.
With this in mind, a dyno should be used for back to back testing of components and tuning, and before you get to this point the basics should have been checked. At anywhere from $150 to $200 per hour having a flat battery, running out of fuel, or having the engine dump the contents of its sump on the floor, isn’t money well spent.
On the subject of fuel, it is wise to make sure your car is dyno’d with the fuel you normally run. On an initial run for a carby, you may find you will have to change float levels at the racetrack after your trip to the dyno to deal with cornering flat spots. This will affect your mixtures to an extent.
These items specifically relate to air density. Most of the front runners will tend to have at least an air density gauge with them when they dyno their car to assist in understanding the test conditions. Others will run their own lambda sensors in the exhaust. Peak hp readings will be taken after final jetting/tuning. Lambda (or CO) readings along with the air density readings will also be taken down.
At the racetrack, as the air density changes, calculations will be made to the jetted carb depending on what you have weather-wise on the day. Sometimes these changes may be in the region of .025mm to .05mm. Therefore, it is important to remember that the hp readings given are only a snapshot of the conditions of that time but can be of great value at the racetrack if used correctly.
Jetting the pilot circuit, the main circuit, the air correction circuit, or why cars foul plugs in the pit at Wakefield Park are all technical topics in themselves, as well as the difficult carby we run, how the restrictor plate leans off mixtures on throttle opening leading to the reason of fouling plugs.
These will be left for another time.