Here's a situation, a car that is currently running optimal. Dyno proven 78whp, could fall back to 74whp if electric current disruption occurred, which its settings were reside at conventional RAM currently. In order to further improve its power output, below are the mod list that has proven on multiple dynoed vehicles.
1) Extractor:
A. 4-2-1 extractor to replace stock 4-1 short runner cast iron extractor, which its O2 sensor located at Y joint instead of cylinder 3. Expected power up 5whp
B. 4-1 long runner, which O2 sensor located at cylinder 3. Upside is, minimum mod is required, does not need to change O2 location & the product is cheap, widely available & compatible with all Campros. Down side is, O2 reading inconsistent. Low end & mid range compromised. Expected power up 3-5whp depending on RPM range.
2) Mid box:
A. Twin chambered resonator, to replaced stock single chambered resonator. Expected power up 0whp but to have even more silence output + benefit of force feedback due to long runner extractor got the tendancy of lag. Its expected to reduce throttle lag after extractor mod combined with twin chamber resonator.
B. Swirl flow bullet. Induce high suction power, great benefit for mid/high end. Cheap and widely available. Expected power up 1-2whp. Due to swirl flow design has some barrier, low end output/response is expected to be acceptably good, but exhaust noise will sound like FART. If u r not sure how it sound like, go to your kitchen, floot your sink and let loose of the clog. Pay attention towards the end of the water evac, that's exactly how a swirl flow sounded like.
C. Straight flow bullet. None blockage exhaust flow. Sounded garang and great benefit for mid/high end RPM. Expected power up 3-5whp on top end, but least expect on lower rpm range. Intense traffic condition on low RPM pickup could feel the car juddering if rear muffler is not well feedback.
3) Muffler:
A. Waja CPS single chamber twin tip muffler. Does not compromise with exhaust noise but induce higher exhaust flow compare to stock 3 chambered muffler. Benefit for after 4krpm. Expected power up 3-5whp depending on the extractor/mid box setup.
B. S-flow. Does what a straight flow do, less noisy and can benefit from mid/high end. Expected power up 5whp.
C. Straight flow. Has to be bundled with chambered mid box, otherwise power loss. If everything is setup properly, expected out put 5-8whp at top end.
The above are based on multiple vehicles input, stage by stage dyno test results. It could be bogus as dyno wasn't done on the same day. Note that temperature & humidity can affect engine output, given different fuel can produce different kind of result, hence the "actual" output is only meant for a rough reference. Take this "test" as a survey for future reference.