What is the main purpose of converting to OBD1 from OBD2 on a D16Y8 motor? Are there any HP gain without tuning the ECU? Can I use the existing P2P ECU to get it tuned or chipped by Hondata?

 

P28 has a little more agressive fuel and timing maps, a lot is associated with the base timing between the 2 ecu's. P28's are however most common chipped, and they are still kinda cheap

 

I already bought the P28 ECU + harness. I was pretty sure to have Hondata (s100) tuned/chipped the ECU. But, I have I/H/E only. How much HP gain I can expect?

 

Don't use the Hondata S100, spend the extra $30 for the S200. More reliable and also expandable so you can add options later on.

It is VERY difficult to find people who modify OBD2 honda ecus. It's expensive to do, there's no socket so you cant just swap chips afterwards, and if you want changes later on you have to have the whole service done over again. Also, OBD1 gets rid of secondary O2 sensor and the P28 doesn't require the knock sensor or crank fluctuation sensor to be hooked up. It's just better! It's not that you get big hp gains just by using it, but it allows you the potential for it.