Ok, I noticed that my H23A has a dual stage intake manifold with both short and long runners. Can someone clarify exactly what happens? I know that the long runners are used in the low rpms and then it switches to the short ones in the high rpms. At what rpm does this switch happen? Is it an instantaneous changeover or is it a gradual switch? Do both sets of runners stay open in high rpms or are only the short ones open with the long ones closed? What kind of mods can be done to this little system if any? Is there any gain to disabling the butterflys to allow both sets of runners to continuously stay open throughout the entire rev range? Tell me some stuff please!! Oh yeah, i rode in my friend's 89 accord lxi which also has a dual stage intake manifold and you could feel/hear the crossover point which was at 4,900rpm. I cant decern it in my car. Is there a way to make it more decernable?? If so...I wanna know...cuz it felt really neat...similar to vtec.
From 0-3800rpm the short runners are closed by the butterfly valves. Once the engine is at 3800-4000rpm there is enough manifold pressure to open the butterflies. So from about 4000rpm up all eight intake runners are open.
You can unplug the vacuum hose from the actuator which will make the butterflies stay open all the time. The upside is that you will get the extra power at a lower rpm (about 3000 instead of 4000), but you sacrifice low end torque. You wont gain any horsepower, it will just be available sooner.
On my car at least, I can hear the changeover at about 4000rpm. It goes from normal sounding to scream.
Originally posted by red92si From 0-3800rpm the short runners are closed by the butterfly valves. Once the engine is at 3800-4000rpm there is enough manifold pressure to open the butterflies. So from about 4000rpm up all eight intake runners are open.
You can unplug the vacuum hose from the actuator which will make the butterflies stay open all the time. The upside is that you will get the extra power at a lower rpm (about 3000 instead of 4000), but you sacrifice low end torque. You wont gain any horsepower, it will just be available sooner.
On my car at least, I can hear the changeover at about 4000rpm. It goes from normal sounding to scream.
Mine is definately audible as well. Sounds like it gets a kick in the pants.
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Gone, but not forgotten...rest in peace Jon.
when I had the IM all apart I just removed all the plates
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1992 Prelude SI Type SH EBP VTEC BB1 SiR H23 DOHC 4th gen Type-R BB4 Milano Nordic Mist F22 JDM-spec 5th gen Type-S 4WS H22 EDM Mugen edition
Disabling the butterfly valve will make your already hungry for torque 4 cylinder starving. The whole point of the system is to broaden and flaten the torque curve which is the main goal of anyone who is tuning a motor. Hondata claims on their website that on average about 8hp is lost when disabling the butterfly valve in the low end. Hondata is one of the most reputable Honda tuning companies that eats and sleeps tuning hondas on dynos with different ECUs. So i would like to believe them as a reliable source of information.
I wouldn't touch it if i were you, unless you are going to FI your car.
ive got intake header and exhaust and my crossover is NOT audible whatsoever! is my thing even working? like i said earlier...it was noticeable on that 89 accord...you'd think it would be noticable on mine. could there be some kinda vaccum leak or something or is it simply not noticeable. well...you guys say it is noticeable so i must have a problem. i want mine to be noticable too. what should i do?!
Heres how you can check if they are working... when the car is off, check the position of the butterfly valve on the drivers side of the intake manifold. Turn the car on and let it idle... go and check the butterfly position again.
When the engine is off you should be able to move the valves by hand, when the car is on at idle, they should be rigidly set in the "closed" position.
im one step ahead of ya. ok i found where the little actuator thing on the side of the manifold is. i was able to turn it over 90degrees. i let my friend turn my car on. no change in position but i couldnt turn it by hand again. i told him to slowly increase rpms and watched it. it suddenly flicked open at just below 5,000rpm. we then took it for a nice long high speed drive around the back winding roads of town in which i was constantly downshifting and reving to redline around curves through 3rd and 4th...passing through the point where the butterflies would open and we noticed no difference at all. i guess mine just isnt noticable because obviously it is operating properly. oh well, thanks for your help anyways guys.
no problem... I wish we could help. It is a wierd case because they seem to be working on your lude, but there is no audible or physical change in engine reaction. Good Luck to you.
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