Gas Mileage Question: Si vs Hf Ecu w/ CX motor in 91 CRX Si

[chethewitt]

My dad and I put a 95 CX motor w/ Hf trans into a 91 Crx Si.

We did this for fuel economy...we were hoping to get 55+mpg. So far, mileage has been kinda disappointing as he's only getting 40mpg. (In a stock Crx Si w/ 13inch wheels/tires my dad has been able to get 47mpg, using hyper mileage techniques.) Keep in mind, he lives in NW Ct where the roads are not flat and straight like they are here in FL. He also doesn't do much highway driving so the 47mpg he was able to get with his Si is quite impressive. Basically, he knows how to drive a car to get maximum efficiency out of it...

Currently, the setup is as follows.

Cx Motor. (8v head like HF motor - bone stock)
91 Si Intake Manifold (Head matched to intake ports)
91 Si Exhaust Manifold
No Catalytic Convertor
HF Transmission
Si Ecu

Now, what can we do to get better fuel economy. Would going with an HF ecu yield better results? We're assuming it would, given the 8v head design shared by the cx and hf motors.

In any case...suggestions are welcome. Thanks!

[Ryland]

You have an intake from a 1.6L engine that is designed to run at 3,000rpm at highway speeds on a 1.5L engine that is designed to run at 2,000rpm at highway speeds, same with the exhaust, when you get a chance compare the intake on the civic CX to what you have and do the same with the exhaust, they didn't make them smaller because it was cheaper.
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