Injector CCs & MPG Increase
 

I have a manual '97 Civic HX with 151k miles. Im currently considering a fuel system cleaning and/or injector upgrade. Ive read mention of upgrading from 1 to 4-hole injectors for better fuel delivery, but Im unclear as to whether any increase in injector CCs will improve or decrease fuel efficiency.

For the record, I'm currently achieving roughly 34mpg doing mostly city driving, which is about 4mpg less than the factory rated 38mpg city. The engine is mostly stock excluding a Magnaflow header/cat combo, K&N air filter, & '02 RSX Type-S muffler. I'd like to maximize my MPG and at least average around the stock ratings. Your suggestions will be appreciated.

I have a 98 hx and I just upgraded to the 4-hole injector. I haven't had time to run many miles under controlled circumstances, but my car really snaps to a start and runs really good. I did a couple of 36 mile runs today and got 58mpg @ 65mph on split 60/40 freeway/rural. Setup just about like yours with exhaust system and headers. I need a few tanks to evaluate further. Good Luck

How many MPG did you average before the injector swap, and how many CCs are the newer Injectors?

The problem with going to larger cc injectors is that low flow rates become harder and harder to control with the bigger injectors get. Idle and low speed driving suffer.

Going with a new generation injector will help. Try to get something from a junk yard that is as close as possible to the size you need. You will likely need the newer electrical connectors too.

As far as I know no one has done any testing between new gen versus original injectors.