Many of us have seen and heard a Dyno power run. The power runs are part of tuning but a lot has to happen to get to the power runs. Large numbers of vehicles are presented for Dyno tuning with faults. Many of these faults may not even be noticeable during normal driving. By design the dyno places high loads often at high speeds on the vehicle. This and the data logging capabilities reveal unknown faults that will prevent tuning from being performed and need to be rectified. The issues may not necessarily be engine related either. We are going to run over some of the common issues we see during our dyno precheck or are discovered during the dyno tune. We are going to focus on 3 things, Fuel system, Ignition system and Engine.
This is going to seem basic, fact is dyno tuning uses fuel. We want to tune your car using the fuel you will most often use. Race fuel will get you a bigger horsepower number but the tune will be optimised for that fuel. So we need fuel in your tank and the fuel you will use every time you drive the car. When it comes to flex fuel that adds an extra element in that the tune is performed on the base fuel and then corrections are tuned for ethanol content. Performing a flex fuel tune will require your everyday fuel and the highest Ethanol based fuel you will use. Most likely this will be E85.
So now we have the correct fuel in the tank, we perform mechanical checks in the engine bay, Engine oil and coolant levels want to be perfect. New engine oil is not necessary, the fluids just need to be in good condition. If it doubt have the fluids and or filters changed. Visual checks are also performed, items like fluid leaks, cooling system hoses, drive belts, fuel lines and for turbo applications intercooler and boost control plumbing. Now you might be thinking what risk is small oil leak. When running on the dyno large amounts of load at high speeds are experienced. This generates localised heat that can ignite any oil that gets onto hot components.
Next is to go more in depth doing a compression test and leak down test. In the, event of low compression or excessive leak down a tune will not be successful. While the spark plugs are removed for the compression test they are inspected along with other ignition system components. This is a good time to consider what spark plug gap will be required. With the engine check performed we move on to correctly setting base ignition timing. To achieve this the timing marks need to be clearly visible. Similarly base fuel pressure needs to be checked and set correctly if adjustable. Often this will require a fuel pressure gauge to be fitted.
Moving on from the engine, checks to driveline components like clutch, uni joints, CV shafts and wheel bearing are required. No matter whether a hub or chassis dyno these driveline parts will experience high load and speed. If a clutch is slipping during normal use, slipping will definitely occur when operating on the Dyno.
When using a chassis dyno, tyre condition and age must be considered. Any defects may cause tyre failure resulting in damage to the vehicle and dyno. When tuning on a chassis dyno the tyre pressures are increased above the normal road use pressure. Since we are talking about tyres, generally harder compound tyres are better. Vehicles producing larger power may need stickier tyres to prevent tyre slip. However stickier tyres with absorb power resulting in a lower reading.
When using a hub dyno tyres are no longer relevant. The only issue seems to be when lock nuts are fitted and the wheels cannot be removed to allow mounting on the dyno.
Now we are ready to load the vehicle on to the dyno and make some noise. Even though all the visual checks have been performed the stress placed on the components when under load can reveal weaknesses. Weak ignition coil, incorrect injector sizing, weak fuel pump or even low voltage output from the alternator are issues we see and for the turbo cars the intercooler system may pass a visual inspection and still have leaks occurring under high boost conditions. All this can be logged on the dyno so corrective action can be taken.
This is just a brief look into what needs to happen for your successful tune to occur.