I would like to know if there is any way of connectiong the secondary intake runner butterflies to the VTEC solenoid so that whenever the vtec engages the secondary butterflies would simultaneously open. I'm using the Hondata P28 ECU on my 1993 Prelude Vtec. PLease help. I'm trying to save myself from purchasing a rpm switch.

 

Are those the one's that open up at around 5500 rpms? If so then yeah you can, but I donno how I just remember reading it somewhere, sorry.

 

The secondary butterflies are supposed to stay closed until 4900 rpm's. Just get an MSD RPM activated switch to turn it on.

If you used the VTEC control wire, you would need a relay to make it work. Power is sent to the intake bybass to hold them closed, then at 4900rpm's it's turned off to let them open. The opposite is true for the VTEC solinoid.

 

If you want it to stay open at all time. Disconnect the Vacuum that goes to IAB ( Intake Air Bypass ). Why do you want to buy a switch, Isn't the P28 from a Non-vtec computer, I know the SI version has the IAB also

 

P28 : 92-95 OBD-1 Civic Si/Ex
They did not have secondary butterly valves, so the P28 doesn't support it. Since it doesn't support it, they already stay open all the time. Like I said, sending power to the butterfly valve solenoid closes them. If no power goes to the solenoid, they will just sit open.

 

*5100 is what I meant.. that's when I notice.

 

You can leave the valves open all the time, like the other guy said, pull the hose on the IAB intake diaphragm.. plug up the hose with something, just to keep it clean.. Now understand, doing this makes a loss of 15+ hp to the wheels before vtec... Honda wouldn't have done this secondary valve thing for no reason... you want backpressure to get some low-end power..

My friend did jumped on the dyno and tested this, leaving the valves open, and compared to stock.. the difference was that leaving the valves open all the time produced nasty horsepower losses, and there wasn't any gains.. the stock setup is the way to go..

Jay

 

What about if I leave the secondary runners closed? I have the JG Pro Series head package.

 

DirtyLude.......could you send me a diagram of how I can do this using a relay?

 

Has anyone ever thought about chopping off the framing for the butterflies? I was considering hollowing a spare intake manifold out.

 

As of the Honda shop manual (Helms) the IAB butterflies open at 4,700RPM. Unless you are "needing" more airflow like with a forced induction application, or turning considerably higher RPMs, removal of the IAB butterflies or them staying open full time will cause a drop in low end torque plus a top end horsepower loss.
The IAB butterflies help build torque at lower RPMs.


[Modified by H22Si, 12:36 PM 1/30/2002]

 

You can try this:

The VTEC (blue) wire is comming from the ECU on the bottom and both IABSOL and VTEC wires are heading toward the solenoids out the right. The red wire needs to be a switched power source. You can use one of the yellow/black wires that goes to the ECU for this, if you can't find another source. The black wire goes to ground. The black box is a bosch style electrical relay and the black lines are the tabs that come out of it.

When the VTEC wire is powered it will disconnect the IABSOL from power, opening up the butterfly valves for high RPM use. When VTEC is not powered, the IABSOL will be connected to power and close the buttefly valves.

I've never tried this. I've never seen it done by anyone else, and my electrical background is nill, so don't blame me if this blows up your ECU, your car, burns down your house, and has an affair with your significant other.

 

Actually instead of running to ground you might want to cut the VTEC wire, attach one end to the tab on the right of the relay as it's shown and one end to the left of the relay.