Of course I've searched on this, but the only info I've found is either permanently open, removed, etc. I've found nothing about making them open sooner. I'd like to get them to open up ~4100 instead of ~4900. Anyone heard anything about this?

 

Check the end of this thread out, things came up like a shift light, vtec controller, or some other sort of rpm activated switch.

https://honda-tech.com/forums/honda-prelude-4/iab-diaphragm-slow-open-close-2510389/

 

Ya know, I read the first half of that thread, but it didn't seem to apply to my question. So I stopped reading before it got good. The shift light/RPM switch is an intriguing idea.

Now, I have a question about IABs. I know it's an on/off system, but is it solely based on RPM? Or does the TPS come into play? I think it's just RPMs but I'd like to know for sure before I do anymore research into hacking the system.

Dixxon, you obviously have a good grasp on physics, but how is your electrical background? Any suggestions on how to wire it up?

 

It's just RPM.

And it's not 4900 AFAIK, more like 4600.

 

I'm trying to cure my 4k-4.5k mess. Anything think IABs opening sooner would help? I know setting VTEC to 4100 would help, but I really don't like the idea.

 

I don't know if that's really a mess. I'd expect that hump is caused by your intake giving you a boost in that area.

Maybe opening the IABs sooner would help boost power in that area.

If you really want to mess around it's possible to manually actuate the IABs if you feel like standing over an engine at full power (they spring open).


super edit: or even better, run once with them open, once with them operating normally, see what you get.

 

I think moving your vtec engagement usually cleans up and can smooth out the powerband. A tuner could accomplish what you want I think without modifying your IABs. They are vacuum controlled I believe though so you could install a solinoid switch that opens and closes the IAB. That solinoid needs to have an activation method though being electrical which would be controlled by something that senses vacuum or something that reads RPM. Vacuum switch could work but I think it would be alot harder and more involved. Rpm activation requires it to be setup through tuning ie. nos activation or similar.

 

Well, I don't like the fact that torque and power both drop once I hit 4k. Especially since 90% or more of my driving is done between 3k and 5k. I think either the engine is choking for air or it's mechanical (cams).

VTEC is already dropped to about 4600-4700 and I don't like the idea of going lower. The "tuner" only adjusted the A/F ratios with my VAFC. I kinda doubt his abilities. The IABs are vacuum controlled. The vacuum is controlled by the existing solenoid & diaphragm. So the thought is wiring a shift light to the solenoid to have the solenoid close and the IABs open at ~4000 RPMs. Though, if the engine isn't choking for air, this won't cure the dip.

 

Well run with the IABs open on the dyno and see if it makes more power there. Try changing intakes while you're there.

And yeah, if you want more power down there also consider lowering VTEC.

But I don't think anything is terribly amiss.

 

cams would not cause this. The only way to fix it if the cams were causing it would be by lowering VTEC more- something you don't want to do.
I replied to your other thread with the solution I told you earlier.
Offer still stands

 

Of course it's the cams, if he had some S2P1-like primaries he'd make tons of power before VTEC, heh.


edit: And yeah, hijacking the solenoid with some sort of RPM based output would be great I'm sure, but the stock ECU might not appreciate being separated from the solenoid.

 

The ECU can lick 'em. But seriously, from what I've read, disconnecting the ECU from the solenoid does not cause a CEL.

 

Cool. I left mine plugged in just in case. Not that I use a stock ECU ever, these days.

At any rate, if you really want some answers hit the dyno again and test IAB open/closed/normal, VTEC from as low as, say, 4000 RPM, and intakes if you got them. Then you can go and modify stuff as needed.

Although I'm continuing to not see this as a "problem" per se. It looks pretty much like a normal H22. Though 173whp STD isn't a whole lot.

 

it might be useful to know what mods you have done thus far and what your tuning goals are, just smoothing out the power curve? Have you done I/H/E etc?

 

generic CAI, 2.5" crush bent exhaust, hytech replica header, tuned with a VAFC.
Its a slushbox as well. Not that it makes that much of a difference, but figured I'd throw it in for good measure

 

I see a large drop in TQ to be a problem. I know it's close to a standard H22 dyno, but I don't want a standard H22 plot. My baseline was 159whp STD, or 156whp SAE. 173whp STD = 169.5whp SAE

Mods are:
Generic CAI w/ K&N filter
Hytech replica header
Custom 2.5" crush-bent exhaust w/ Carsound cat

My goal is to get rid of the loss in power and torque between 4k and 5k. Basically, smooth out both curves. The only tuning option is my VAFC-II.

 

I don't want a standard H22 plot either, but you (like me) both have pretty much the definition of standard H22s so I wouldn't expect miracles. But do go and try some things and maybe you'll get what you want...

 

what i would do is use a meter and find out what voltage the solenoid gets to tell it to open (it could be in the manual too)... then do some calculations to find out how much resistance it would take to modify that voltage to get the IABs to kick in sooner

 

the solenoid cuts power to make the IABs open

 

Get a hex editor and a ROM reader. Download the .bin file, then go to PGMFI.org and find the memory address for the opening rpm and rewrite the ROM. That's what I did on my old H22 and the G23.

That's the most economical way for me.

 

I figured something like that was possible. Thank you very much. Now, sadly, most of that is going to be over my head. Do you happen to have a writeup, including where to get a ROM reader?

 

I wasn't under the impression that the chips used in the OBD2 ECMs (he has a SH) were particularly inexpensive...if someone has even publicly mapped out the OBD2 codebase like that.

 

Aw man, A Blue Lude! Why you gotta go and screw up a good thing like that. OBD2 FTL. SH FTL. Get a 5 pound LSD to replace the 80# ATTS unit and an OBD1 conversion harness like the rest of the world. Then you'll be golden.

Either way the benefit from the IAB opening at the proper time only nets you like 3 HP for about 1000 rpm of the whole band. And it's located at one of the most useless parts too. No power because there's no displacement and you're only about 4000 rpm away from peak where you should be.

Sorry Kronn. It's a no go unless you're willing to adopt a different ECU. Go with some RPM switches or yo might be able to wire it into VTEC. Not ideal but close.

 

So, I've read a lot on this and found a few people who bypassed the solenoid and plugged the diaphragm directly into the IM. According to their posts, this would cause the IABs to open ~3500 RPMs. It sounds like a good idea, so I checked how easily I could do this between dyno pulls.

As you can see from the picture, the previous owner never removed the intake resonator or vacuum hose. So, my plan is to unplug the hose from the resonator and re-route it over to the IAB diaphragm (green line). Any comments?

 

Follow-up question: For the three vacuum ports coming out of the IM in that area (1=plugged, 2=intake, 3=CC), does it matter what order they are in?