reading on Bradys H23A website about a small mod that helps top end power that involves unplugging a vaccuum line
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. 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 rpms, 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 diaphram that controls the opening and closing. The diapram has a vacuum line running to it and at 4800 where there is enough vacuum pressure, the diaphram opens the runners.
So what's the mod? Simple, if you want more power sooner, unplug the vacuum line that connects to the diaphram. Now the flapper valves will always be open at all rpms. 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.
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(attatched to the manifold actually). There is a line connected to the top of it, just unplug it so it hangs or cap it off
1) Where is this on the engine in english? (a pic with a large red arrow would be cool heeh)
2) Would the F22B have the same / benifit from it ?
the f22 doesnt have the secondary valves and the mod doesn't really help at all... you lose low end and the top end just starts to come in a bit earlier
Research before you reply boy. The F22B DOES have the secondary intake runners. I have done the mod and can tell no significant different, the exhaust just sounds deeper at the lower RPMs.
NeilSkinner, i will take a pic in a little bit when i go outside of the vacuum hose that is necessary to unplug.
You don't gain power, you only lose low end torque. It's a pointless thing yo do unles you're pushing a lot of power and having them closed at low rpms is hurting you.
I also tried it and say that it is pointless....It made daily driving worse and only could tell the difference on the entrance to the highway
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DO NOT buy from The Drop Shop in Hudson, NH! Jon at the drop shop has taken money from customers and refused to deliver merchandise or give refunds for a year now!!!!!
Yes, I agree and I didn't care for that either. It's loud enough.
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DO NOT buy from The Drop Shop in Hudson, NH! Jon at the drop shop has taken money from customers and refused to deliver merchandise or give refunds for a year now!!!!!
yep this mod is a waste of time, when I changed my engine the bypass valve and vacuum tank had the lugs snapped so no vacuum, meaning the secondary butterflys were open all the time.
The car ran like a POS, while I was waiting for the spares to come in I actually cable tied the butterflys shut
Ok vtec was a little quieter but the car ran so much better
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(a pic with a large red arrow would be cool heeh)
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