alright so ive searched the FAQ's, all the write ups, and practically the whole internet and cant find anything on the obd0 situation for my mini me i am going to do. The y7 motor that is in the car is running the stock Si obd0. Im doing a y7 block with y8 vtec head w/ p29 pistons into my 91 civic si. so i got a couple questions....

Since my y7 head is using the obd0 Si distributor, could i also use it with the y8 head?

What ecu will i need to get?

could i use my stock Si intake manifold on the y8 head?

And since the head is going to be ported and polished with new valves and valve springs, what kind of numbers am i looking at with the mini w/ basic bolt ons? I know im not expecting a drastic gain in horses but i heard this swap will help out a little bit. Anyone got any dyno numbers?

 

keep in mind that i already have most of the necessary parts for the swap, the ecu and obd0 situation is the only thing keeping me from going through with the swap. any helpful advise is welcomed

 

Yes, the OBD0 distributor will work on the Y8 if you plan to keep it OBD0.

If you do not have AC, then your PM6 Si ECU can be chipped and reflashed with a ROM that will activate vtec via the AC line and have slightly different fuel/ign mapping for the upper rpms.

If you want to keep AC, then a PS9 (automatic D16A6) ecu will use the shift signal to activate vtec.

There is some difficulty finding these roms for OBD0 though. Ideally you'd want the Y8 fuel maps as a baseline.

As you might have found out, timing can be tricky too, since the Y7 and Y8 motors make use of the knock sensor that the Si ecu ignores.

While you could use the Si IM on your Y8, it will not allow it to breathe enough in the upper vtec rpms, causing it to pretty much perform the same as the Y7 or maybe worse.

 

ok so theres not a stock ecu from another civic i can use? Would it be more worth it to switch it to obd1 if possible?

 

The P28 (D16Z6) ECU is the popular starting point for OBD1 mini-me's. The costs of switching to OBD1 can add up quick:

wiring harness adapter
distributor adapter
OBD2 distributor
4-wire O2 sensor

That can be around $350 more or less depending on how you source it. The big advantage though is that once you have that OBD1 ECU you can chip it for tuning, and there's lots of support for OBD1 tuning compared to OBD0.

I went through all these options over the last year, trying to figure out what to do, too, and decided not to go through with it.

 

D16Z6 ECU is a P28, not P29 - P29 is JDM OBD1 DOHC ZC ECU

 

Corrected, thanks!

 

ive read on a write up that i can use an obd1 z6 distributor on the y8 head, and my buddy has a obd0-obd1 jumper harness hes lettin me have. so if im correct all i need is a p28 ecu?