I have a 99 civic si. I dropped in a jdm b18c gsr, (completely stock) and everything went great. Its been about a week and a half and no check engine lights. Hear is the deal. When I use the stock b16 ecu it feels pretty powerful, but when v-tec kicks its very very quiet, but you do feel a mass amount power and you can tell its working. I tryed a gsr ecu and its the same.
With the stock b16 motor the vtec hit very hard and was very loud, and this one hits hard its just very quiet.
I don't know I was just asking out of curiosity if anyone have heard of something like this. It works great so i guess nothing needs to be fixed, it was just unusual to me.

 

GSR motor's have the secondary butterflys that engage at about 3800 (i think thats the right RPM) and then VTEC at 5700. If its not wired properly, the motor will run bad, and as you said, sound quiet. their called the IAB's, and unless your using a GSR wiring harness, they will need to be wired by hand.

 

Ya i see what your saying. I actually em running a skunk2 manifold on it with the b16 wiring harness, But i used to have a gsr integra and i ran the same intake and never had any problems. I don't know. Like I said I know its engaging because i can feel the power diffrents