I was planning on using a pr4 ecu (92-93 DA 5 spd) for the obd1 conversion along with hondata. I have been offered a p28ecu(92-95civic 5spd). Now I have been told this is a better ecu to use, but have never been told why. I dont see why one ecu or the other would make a difference once it has been modified by hondata, as long as it is an obd1. If someone can better explain why one would be better than the other, not necessarily the two I am personally debating between, I would greatly appreciate it.
I’ve asked this same question, and nobody here seems to be able to answer it? If you find an answer please post it because I would like to know as well. I’ve been searching for the past week and still haven’t found a satisfactory answer.
I can’t tell you why in your situation it would be better but for other ECU’s some have knock some don’t and some can control the secondary butterflies used on GSR and H22a motors. Thats all I could think of, HTH.
Originally posted by Blackteg
I can’t tell you why in your situation it would be better but for other ECU’s some have knock some don’t and some can control the secondary butterflies used on GSR and H22a motors. Thats all I could think of, HTH.
no that wasnt what I was looking for, but thanks anyway
I think it just has to do with the fact that 99.999% of the people who chip an ecu use the p28–it’s already an obd-I vtec ecu, all it needs is to be chipped for DOHC programming (in most basic engine-swap cases) and you’re good to go. Also probably has to do with how easy it is to get a p28–they’re friggin everywhere. 
Oh and interesting tidbit #836 for today: The secondary butterflies are NOT controlled by the ECU–they’re controlled by vacuum. The ecu merely pumps a little additional fuel–and if you have a chip of any sort, especially most n/a chips, you’ll be dumping more fuel anyway. So honestly a p28 chipped to DOHC with more aggressive fuel mapping up higher will be right at home with a b18c gsr engine. 
I dont think you guys are understanding the question. WHY is one ecu going to work better than another, not which one, after hondata is installed.
or maybe I’m not asking the question correctly :think:
Originally posted by zoomintegra
[B]
Oh and interesting tidbit #836 for today: The secondary butterflies are NOT controlled by the ECU–they’re controlled by vacuum. The ecu merely pumps a little additional fuel–and if you have a chip of any sort, especially most n/a chips, you’ll be dumping more fuel anyway. So honestly a p28 chipped to DOHC with more aggressive fuel mapping up higher will be right at home with a b18c gsr engine. 
[/B]
just another tidbit, A chipped P28 will not control these secondary butterflies - they will stay open all the time which is not good.
Why? Because running the stock GSR intake manifold with a chipped P28 ECU, which doesn’t control the secondaries and leaves them wide open will make you lose about 10ft. lbs. of torque! This has been dyno proven (thanks to Joe.R/honda-hybrid site). So, it’s not a good idea leaving the secondaries open. I hear how a lot of people think that leaving these butterflies open will make a GSR/B18C engine more Type-R like…that is a load of hog poop
just a FYI
Originally posted by GOLDENCHILD
[B]just another tidbit, A chipped P28 will not control these secondary butterflies - they will stay open all the time which is not good.
Why? Because running the stock GSR intake manifold with a chipped P28 ECU, which doesn’t control the secondaries and leaves them wide open will make you lose about 10ft. lbs. of torque! This has been dyno proven (thanks to Joe.R/honda-hybrid site). So, it’s not a good idea leaving the secondaries open. I hear how a lot of people think that leaving these butterflies open will make a GSR/B18C engine more Type-R like…that is a load of hog poop
just a FYI [/B]
last time i checked, the ECU had nothing to do with vacuum pressure. it’s VACUUM PRESSURE which actuates the secondary butterflies, NOT the ecu. I think perhaps you have the actuation of opening and closing them confused with the dumping of extra fuel (running rich without them open will obviously cause loss of power). i’m merely going on what Tony Palo has told myself and others on honda-tech. I have a feeling the crew chief/engine builder for the Jotech/Tran/Norwood team knows his stuff. :shrug:
Directly from Hondata’s website:
The IAB or secondary intake runner is a set of butterflies in the intake manifold of B18C and H22A engines. The P72 ECU controls the IAB, but other ECUs do not. If IAB control is lost by swapping ECUs then the engine will always run on the shorter intake runners, typically losing 8 hp from 3,000 to 5,500 rpm.
the butterflys are controlled by vacuum. The vacuum is controlled by a solenoid. The soleniod is controlled by the ECU.