There are a few different types of timing sets out there, each for a specific application. Pat will also go over why each set is used for each application. Keep in mind these parts are for performance bullets, not stock engines.
In the 1960s, roller timing chains were introduced. There were 2 different types available: a single roller and a double roller. A single row has one row of gears on the sprockets and as you would imagine, a double roller has two.
Most original equipment push rod engines including current ones us a single row timing chain. A good example is today’s LS. It uses a single row because it doesn’t require a lot of spring pressure to run the valve train and is a more compact setup on the front of the block.
When the valve spring pressure is significantly increased along with the power output and rise in the RPM ceiling, a double row chain will control the valve train better because it spreads the load between two sets of gears. The engine’s cam timing will then be more stable.
Keep in mind both single and double row timing sets will stretch over time. In addition to affecting the cam timing, in extreme cases, it will affect the ignition timing by as much as 3 or 4 degrees. At that point, the engine is dangerously close to a catastrophic failure because the chain is ready to break.
As far as materials go, most hot rod types are made from regular cast iron. But the pinnacle of timing sets are the bullet type, both on the crank and cam gear. These are typically fully adjustable.
If you were hotrodding in the ’80s, then you probably remember hearing what a gear drive setup sounds like. There are advantages and disadvantages for a gear drive. On the good side, they are extremely accurate when controlling the position of the cam since there is no stretch involved. The downside is they are slightly too obnoxiously noisy in their operation and induce mechanical residence into the valve-train sometimes causing issues in extreme performance applications. They are still available for popular engine combinations so if you like that high-pitched whine, these might be for you.
One of the ultimate timing set ups is a belt drive setup. These are specifically engineered to provide accurate cam timing, ease of adjustment, and have great longevity.