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I've been doing a lot of searching on here and around the Web and nothing is really coming up for me except on a few hypermiling sites. I see a lot of people dropping the D16Y8 their 96-00 Civic HX cars but never anyone putting a D16Y5 into their 96-00 EX.

I'm pretty particular about my mileage so I keep a pretty good running total on what I get. Right now, I average 32.7mpg in my Y8 running 20% city / 80% hwy @ 65-70mph.

Again, being mileage friendly, I started to do my research about what I could do to get better mileage. Upon my research, I found that A LOT (meaning 70% or more) of the mileage people are getting out of their 96-00 HX is 40-42+ mpg. I've even seen readings as high as low 50s.

My thought is: what mileage could I get if I swapped an HX motor into my EX Civic?

I would keep the EX transmission and just buy what I need. So far, I understand that I need an HX (D16Y5) engine with complete intake and exhaust manifolds, a new wideband primary O2 sensor (HX is 5-wire, all others are 4-wire), D16Y5 wiring harness and HX ECU (P2N code).

I also understand that the HX motors were all OBD2A from 96-00. So, would I need some kind of jumper harness to make the HX computer work, without a check light, in my '00 EX (OBD2B)?

What's everyone's thoughts on the mileage I might be able to get with having the HX motor but still having the EX transmission? How much would having the EX transmission hurt my gas mileage?

I hope I posted this in the right spot in the forum. This seemed like the most appropriate place. Please let me know if I should move it to somewhere better.

Thanks in advance! Have a great day!
 

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Don't use the HX harness. Reuse your EX and modify as needed. Because it kept the OBD2A ecu layout it won't be compatible with your chassis. Use a OBD2B to OBD2A jumper harness.
 
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