Ignition timing

The only cam timing event that makes a difference to compression is the closing of the intake valve in relation to pistosn position in the stroke. That means by it being changed, the cylinder pressure is directly altered. The simple simple deal is centerlines set rpm ranges and shape of power curves, and lifts and ramp speeds depend on port flow characteristics. All of them interact with each other in both positive and negative ways. You cant change one to get something without giving something else up. What we call "long duration" means the openning and closing points of both valves is later in each's relevant part a stroke cycle. That means the intake cycle is tuned to use the inertia from higher rpms to fill the cylinder, and the exh is open longer for the same reason. That means at low rpm, the intake charge is no longer still moving into the cylinder when the piston starts to come up from bottom dead center off the intake stroke. The negative effect is reversion, or intake charge being pushed backwards up the port by the piston's upward motion. One way to "fix" low speed is to add power to the intake (to add inertia to the charge) by making the static compression ratio higher. That's why cam companies list a "minimum compression ratio" for each cam. And why the idle and emmissions gets bad when you dont have that higher static ratio. Another way to address the problem is to add initial timing. If the chamber design is huge (for the bore size), and there is little tumble and squish effect, and the fuel is fast burning pump gas, adding timing can help. If you go too far trying to add timing, you can get into problems because today's fuels burn so fast, the heat and pressure they create when firing goes away before the piston is in a position to really put the force on the crank. That's around 17-20° past TDC on the firing stroke. The mixture burn speed is critical to initial timing. But every engine, and every home town, can be different. That's why I say start with what he said, but try other things. I have gained a lot by limiting initial and slowing down the advancing in heavy cars with fast burn chambers. It's not "conventional", but it works. The power levels are where they should be, and the cars are drivable and snappy. It's all part of tuning the package.