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I'm wondering if "race-prepped" motorcycles are the best source of modification ideas/guidance for people who ride motorcycles on streets.

If one engine has VTEC and the other does not do you think these two engines might need a different airbox configuration?

[stepping into shithole] Man.... I know I'm going to regret sticking my toe in this shit hole...... RC51 - have a very similar flapper in their air box. It is interesting to note that I never saw a race-prepped RC51 with an active flapper (including Honda supported teams). However street-going RC51's sold by Mother Honda that were subject to EPA regulations did come with an active flapper. I don't think anyone has ever found the "smoking memo" signed by Soichiro, but the common consensus is that the flapper exists solely to satisfy an EPA noise regulation that are done at a certain RPM that is determined by an equivalent speed determined by gearing, or something like that. Many posters here and on the RC51 sites have modded the flapper and I don't recall anyone posting any evidence that the mod resulted in any repeatable changes in performance. It has been years since I've read any of these discussions, so I'm going off memory. Google "Motorcycle Flapper Mod" and you'll have a week's worth of reading on the subject across about 5 product lines and thirty motorcycle forums. I personally buy into the noise control thought (and my calibrated Mk 20 eardrum confirmed intake howl). Consider this.... The marketing teams would have "variable intake" on every piece of literature if it even resulted in 1 hp or 1 lb/ft benefit.... never saw a pamphlet that mentioned it. I've also never saw a dyno curve that showed any difference between before/after either. I thought this discussion ended at least fifteen years ago. Go figure? [stepping out of shithole/]

I did a write up here on using PlastiFix

Health, world peace and a good haul over the festive season and in 2019!!!

I don't understand, 1998 5g has v.a.i & no vtec, 2000 5.5g has v.a.i & no vtec, 2003 6g has v.a.i & vtec, 2007 6.5g has v.a.i & vtec, 2014 8g has v.a.i & vtec, 2018 has ??? & vtec And with what airbox.. the same yes?

I heard that the EPA fired their motorcycle intake noise regulation from the "grassy knoll".

My "normal" mileage for my 1998 VFR is 40-44mpg on 93 octane. Only mod is Vance & Hines SSR2 slip on. If that were my bike it would be a huge red flag. I monitor my mileage for two reasons 1. Curiosity 2. Great indicator of driving habits and or motorcycle health.

Okay, just in case I'm missing something here: You're saying that performing a mod to make the flapper valve stay open during low Rpm/low "demand" situations (instead of closing as it was designed to do) somehow delivers more horsepower in the higher RPM/high "demand" conditions (during which the flapper was always programmed to be open anyway)? I'm confused.