...Except even with a tuned PCIII you're still going to have the 'Popping' BECAUSE of the Pulse Secondary Air Injection Check Valve (PAIR Valve, aka smog reduction system). The reason the unburned fuel explodes in the ehxuast pipe is because air (or rather the oxygen in the air) is being introduced into an environment that is devoid of oxygen (Burned exhaust gasses cositing mostly of CO2 and water, as well as some sulfates). The fuel cannot burn unless there is oxygen present. The PAIR valve facilitates this introduction and without it, the unburned hydrocarbons would travel down the pipe cooling itself and eventuall out into the cool atmosphere where it can be consumed by other things that require air.
The PCIII helps, but to get rid of the 'Popping' you MUST remove the Pulse Secondary Air Injection Check Valve. the popping happens all the time even without a louder S/O, you just never hear it. i've had many a discussion with other experianced engine tinkerers and the collective answer to the issue is oxygen. fuel cannot burn without oxygen.