Interference Engines
Manufacturers usually produce interference engines because they are looking to squeeze a little more performance out of their high compression small displacement design. In and interference engine the valve opens further into the combustion chamber than a non-interference engine.
This is great for engine performance because the extra distance the valve opens into the chamber allows more of the air/fuel charge in. This can also be negative because if the timing belt or chain breaks both the piston and the valve it strikes can and will be damaged. 
In a non-inference engine the lift on the camshaft is sufficient to open the valve and allow air into the chamber without opening so far that the valve will strike the piston should the camshaft suddenly stop rotating. This is not true with an interference engine where the camshaft has more lift opening the valve further into the engine. If the timing belt were to break in an interference engine the fully open, stationary valve will be struck by the moving piston resulting in internal damage.
There is an excellent timing belt guide offered by Gates. This guide will tell you if the engine you are working with is interference or not. www.gates.com
