Flapper Mod
pic courtesy of Sir
James & Andy B (www.hondahornet.co.uk)
Very simple to do:
| 1. Remove the seat & left side panel |
| 2. Remove the 3 screws that hold the airbox lid on |
| 3. Remove the hose from the vaccum switch & plug the hose with suitable sized screw or bolt. You can then tuck the hose behind the intake air temperature sensor that is attached to the airbox directly behind the vaccum switch. |
Update 03/23/02
| I still don't have any dyno testing done nor do I have any dyno time scheduled anytime within the next couple months, but I did disconnect & plug the vacuum line & I believe the results are definitely positive along with that I also believe this was done by Honda for no other reason than to keep the noise down for EPA testing! The induction roar is howlin' mad now especially at freeway speeds & the bike no longer has a surge of power at 5500 rpm, but it is not because you are losing horsepower it's because it is making the power curve more linear & producing better power below 5500 rpm so when the power picks up at 5500 rpm you no longer feel it as an increase since the power flows much more smoothly now. I put over 100 miles on the bike this morning & will not be reconnecting the flapper door. |
Since this mod is so simple I strongly urge any of you to disconnect & plug the vacuum line & try it for yourself. If you don't like it then put it back on... I will dyno test the mod as soon as I get an opportunity, but without trying to brag I have hundreds of people that will attest that I can feel increases & decreases in power especially when jetting or remapping a bike even without the aid of a dyno. It's just one of those things that comes natural to me. |
I am very interested to hear from UK Hornet owners & the reason for that is because on the UK spec'd RC51/SP1 the ECU that controls the flapper valve (very similar to this one) opens & closes at different rpms than it does on the US Spec'd RC51/SP1. Having said that UK owners did not report the same results when performing the flapper mod on their SP1's nor did their dyno charts show the improvement like they did on US dyno tested bikes. At the same time they reported no ill effects either. Any way if
any of you guys/gals across the pond want to test this
& report your results to me I would love to hear from
you |
| This is a flapper door actuated at certain rpms that cuts off the the majority of the air flow to the airbox! On the RC51 disabling and/or removing this mechanism in the ram air tunnel yielded more linear power delivery (we believe that on the RC51 it was put there for noise abatement issues so that it would pass EPA testing & not performance related as Honda claims because it runs better without it & it is very likely that it was put on the 919 for the same reasons as the induction noise is the loudest part of the 919 & the EPA has gotten real strict lately on noise emissions) I'll disconnect it on my 919 & give it a try as soon as weather permits. If initial testing is favorable I will then dyno test it as well. |
| Where this type of testing gets tricky is in the fact that dyno testing will only give you full throttle acceleration results & mods like this may hinder a full throttle run, but be beneficial to a partial throttle roll-on etc... That is when you have to weigh out which you need more. Most people don't ride their streetbikes around pinning the throttle to the stop & if they have to give up some WOT acceleration in return for better lowend or midrange roll-on acceleration or throttle response they usually will. |