I was reading this mod and was thinking about trying it but I wanted to know if there was anyone that tried it and wondered if it messed up the a/f ratio since the engine is getting more air int he lower rpm?


All Si and VTEC Preludes have a dual stage intake manifold, similar to what twin cam B16 and B18 motors have. Why the H23 Prelude motor has it is beyond me cuz the two stage manifold is usually part of the VTEC system. A normal manifold has 4 runners, one for each cylinder(on a 4cyl). The dual stage manifolds have 8 runners in the top two sections. At low rpm's, only 4 of the 8 runners are "open" and at a certain rpm, a set of flapper valves opens up to allow more airflow which results in more hp. Why don't they just have all 8 runners open full time? Simple, too much air will result in a low end power loss. So until ~4800rpm you have 4 runners open, then at 4800 a set of flapper valves opens and you have 8 runners all the way to redline. The runners have a diaphragm that controls the opening and closing. The diaphragm has a vacuum line running to it and at 4800 where there is enough vacuum pressure, the diaphragm opens the runners. Ever notice how your Si at around 4800 drastically changes sound and it sounds like the car is going to explode? Well that changeover in sound is the manifold opening up.

This is what the middle section of the manifold looks like with the flapper valves. The silver diaphragm on the left side is what controls them. Until 4800 they are closed, but after 4800 they open up as shown in the picture. All the small piping and fittings are for Nitrous so don't look at those. So what's the mod? Simple, if you want more power sooner, unplug the vacuum line that connects to the diaphragm. Now the flapper valves will always be open at all rpm's. Yes, you will lose a little bit of low end power, but you will gain power sooner(above 3700) as a result of them being open. 4800 is a good rpm, but it's possible to take advantage of the 8 runner design before 4800 and by unplugging the vacuum tube, that's what you're doing. Since racing always takes place above 3000 or so rpm, you won't have to worry about losing low end power. After all, why else would you want your car to be faster if you're not racing it??

This is where the flapper valve is located on the engine. You can see it's between the brake master cylinder and the left side of the upper intake manifold(attached to the manifold actually). There is a line connected to the top of it, just unplug it so it hangs or cap it off. I have **** retentive people asking me all the time if stuff will get into the vacuum tube if it isn't capped off. Let's be realistic, the opening is smaller than 1/8" wide, do you think that with the hood shut, something will bounce around in the engine bay and land inside the tube which is tucked under the manifold?? Hell no. Unless your car sinks to the bottom of a deep lake, you're not going to get any water or dirt in there. Besides, that tube BLOWS are out when the engine is running, how is something going to get sucked inside there if there's 40lbs of air pressure blowing out of it constantly?


from

http://www.92lude.com/flapper_valve_mod.htm

 

All that does is loose low-end power. It's also been covered a billion times. I've done it and it's pointless.

 

OK - if you do the flapper valve mod - can you just use a VAFCII controller to add more fuel in the lower rpms? I want to do this.....

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by matty c &raquo;</TD></TR><TR><TD CLASS="quote">This is where the flapper valve is located on the engine. You can see it's between the brake master cylinder and the left side of the upper intake manifold(attached to the manifold actually). There is a line connected to the top of it, just unplug it so it hangs or cap it off. I have **** retentive people asking me all the time if stuff will get into the vacuum tube if it isn't capped off. Let's be realistic, the opening is smaller than 1/8" wide, do you think that with the hood shut, something will bounce around in the engine bay and land inside the tube which is tucked under the manifold?? Hell no. Unless your car sinks to the bottom of a deep lake, you're not going to get any water or dirt in there. Besides, that tube BLOWS are out when the engine is running, how is something going to get sucked inside there if there's 40lbs of air pressure blowing out of it constantly?
</TD></TR></TABLE>

It's a vacuum line, stupid. That means it is drawing air in. If it isn't capped off you'll idle funny because you have a vacuum leak, and it will also suck in unfiltered air, which is full of dust and dirt. to people who give advice they don't even understand.

 

^^first you should know where that vac line comes from....there is a solenoid, and a vacuum box....the vacuum box recieves vacuum from the intake manifold, and it goes through the solenoid when it opens at the set rpm....which has a filter btw......

this is a worthless mod.....covered one hundred billion times....they are fine how they are.....in fact that manifold will never perform noticeably better than it already does unless you do some SERIOUS work to it....

you are better off getting a custom jg sheetmetal one when you get some money, they are proven to put down good hp, and dynos show it....the euro r does okay but is a pain in the *** to install....

 

the dual stage manifold has dick to do with vtec buddy.

 

^^^^- in response to whO

 

wow.... I love it everytime this post comes around... Its better than the usual ones though.

This mod is awesome btw.... Its proven to loose low end on the dyno, the butt dyno, and really wont help you at all. In reality, unless you have a FI application or serious N/A this mod wont be worth your time... Which is exactly 3 seconds...

BTW... This is the second post from 92lude.com today thats put me in tears. I think I'll buy the domain preludericer.com and give it to them for free...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by SiRLudeVtec &raquo;</TD></TR><TR><TD CLASS="quote">^^^^- in response to whO</TD></TR></TABLE>

see the bold part...


<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by matty c &raquo;</TD></TR><TR><TD CLASS="quote">

All Si and VTEC Preludes have a dual stage intake manifold, similar to what twin cam B16 and B18 motors have. Why the H23 Prelude motor has it is beyond me cuz the two stage manifold is usually part of the VTEC system.
http://www.92lude.com/flapper_valve_mod.htm</TD></TR></TABLE>

like i said, zero to do with vtec. i have it. i have a b21...its defenitely not vtec. the b20a and b20a5 have it, again not vtec, so what makes you think its associate with v-tec?

 

flapper valve mod? I always knew them as dual runners. I disconnected mine (running a p28), so now the open under wot by vacuum and I can tell you that it makes absolutely no difference, except a little less low end power. don't worry about it, and leave your flappers alone.

 

"flapper-valve-mod" is more commonly known as "get-rid-of-any-low-end-torque-and-gas-milage-that-I-may-have-had-with-no-benifits-whatsoever-mod"