I brought up cam timing a while back on FI motors and was basically told I was wrong and that our cams are rather ideal for FI. Consider the following.
Here's a graph I hand copied out of Corky Bell's book Supercharged. When I say copied, it's ***** on accurate, to scale, etc. It shows cylinder pressure vs. crank angle. I do believe his graph is inaccurate. It shows cylinder pressure for a naturally aspirated engine going to zero around 105* after TDC. There's no way. Just think about it. Everything I've ever read, and everyone I ever spoke with that was knowledgeable on this subject will tell you the exhaust valve opens while there is still pressure in the cylinder. Granted his graph was meant to illustrate the difference in cylinder pressure's for a NA and FI motor. The bottom line after peak pressure is his line. The one above it is the one I believe is more accurate. I highlited it but it didn't show up when I scanned it.
If there's still pressure in the cylinder why would you open the exhaust valves, letting it out? Surely it's doing work, pushing the pistons, and making HP. While that is true, the engine has to expel the exhaust gases on the exhaust stroke. This takes power for the piston to push all of the exhaust out. Welcome to pumping losses. Usually the exhaust valve is timed to open such that pressure in the cylinder is minimal and doing little work. When the exhaust valve opens, exhaust gases still under some pressure poor out of the engine, which reduces pumping losses. The exhaust valve timing is modeled around striking a balance between these two such to maximize HP. Our exhaust valve opens at 127* after TDC (ATDC).
Let's assume an arbitrary value for cylinder pressure when the exhaust valve opens. Say 100PSI. Mazda engineers determined opening the exhaust valve at 127* ATDC resulted in maximum power. Now let's turbo charge this motor. As Bell suggest, and many others, cylinder pressure is up later in the power stroke due to the increased amount of oxygen burning. As his graph suggest, a FI motor will have more cylinder pressure at any given crank angle over a NA motor, as well as carry cylinder pressure further into the power stroke.
If this is so, then it sure sounds like our exhaust valves are opening too soon. A lot too soon. I am going to assume our motors are at the arbitrary value of 100PSI cylinder pressure when the exhaust valve opens. Now that this motor is FI, we have more than 100PSI in the cylinder when the exhaust valve opens. More like 300-400 PSI. Looks like ideally we would hold our exhaust valve closed a bit further through the power stroke and capitalize on the the higher cylinder pressures that are present later in the power stroke between 127* to say 140* ATDC.