Building the turbo Aston Martin V8 engine: Some reverse engineering.
Previously we found out the Aston Martin V8 engine ‘breaths’ pretty well even in the high RPM. We determined this by dynoing the car. The torque was constant up until the rev limit. All aspects in an engine determine the general performance of the engine, but there is one main item in the whole engine that has the most influence on the characteristics of the engine and that is the valve opening and closing timing.
Opening and closing the valves is controlled by the camshafts. On the Aston V8 engine these camshafts are turned with the camshaft chains. The timing on the exhaust camshaft is fixed, the timing on the intake camshaft is constant variable. The variable valve timing is controlled by the ECU. For every certain RPM and load the valve timing is set so that the intake valve will close when the engine has done its full intake breathing. Bear in mind the engine will still suck in air while the piston has already passed bottom dead centre. The intake air is having a certain velocity entering the engine, and due to the weight of the air it keeps on moving even when the piston is going up!
The Aston engine is already engineered to precision, so we can better use the OEM settings for camshaft timing and adjust from there, than trying to make something better ourselves. To determine the camshaft timing, we put a moroso timing wheel on the crankshaft and checked where top dead centre was, with a measuring device into the sparkplug hole:
After determining the exact position of Top Dead Centre, we put the measuring gauge on the bucket for the intake valve. The intake camshaft can be moved to an advanced position by oil pressure, but when the engine is in a non running state, the camshaft always defaults to the fullest retard position. This position is the normal position for engine idling, as well as for the high RPM. The advanced position is only used from low RPM to the middle RPM.
Knowing the exact intake timing, we put the measuring tool on the exhaust camshaft and measured that one up.
Now we do understand camshaft timing is important information and can be valuable to those that need to assemble an engine and do not know these values. Here is what we measured:
Intake open: 46 BTDC (in full retard position)
Intake close: 90 ABDC (in full retard position)
Exhaust open: 60 BBDC
Exhaust close: 75 ATDC
Next step in our project: Disassemble the full engine!