STD cam a good idea in DX with HF transmission?

[StorminMatt]

About six weeks ago, I swapped an HF transmission in my 1989 Civic with the hopes of seeing better FE. And let's just say that the results have been most disappointing. I recently did a 100 mile drive. And mileage was a MISERABLE 28MPG. This is VERY significantly worse than either my B18C5 CRX OR what this car was getting with an SI transmission. Now originally, this car was a STD. But it now has a DX cam and ECU. Do you think I could actually see better mileage if I was to swap the cam and ECU back to the STD stuff? I can tell you that just by looking, the STD cam is MUCH smaller. I would think this might mean more efficient operation at the low revs that the HF transmission causes the engine to spin. What do you think?

[GasSavers_Erik]

What kind of mileage were you getting with the Si trans? Are you doing city or highway driving? I think the HF will do worse in the city because you have fewer low speed gear choices. 28 is pretty low though. If you were driving less than 35 mph most of the time, then the Si trans might be the best one for you.

When I put an HF trans in my 87 Civic DX about a year ago, it took a tank for me to learn the new shift points. You might give it another tank or two and see where you are then, if you are concerned that its geared too high, then you might try a highway trip in 4th gear instead of 5th and see if the mileage gets better.

It would be pretty easy to swap the ECU though- that might be worth a try before going to the trouble to swap the cam.

Does it seem like it has a decent amount of power at low rpms? (around 2000 rpm)

[kamesama980]

bigger cams=higher rpm power=higher geared trans. all these things work together and are interrelated. If you've got big cams and not revving it using them, you lose out in both power and economy.

I'm not sure of the plurality of your cams so use whatever number is applicable

[FritzR]

I think it would be worth a shot. You would want to make sure the valve timing is set the same as the STD. The DX motor has max torque at 3800 rpm where the STD at 3000. With the DX motor and the HF trans you would probably get the best mileage at 80 MPH in 4th gear. From the D series wiki, notice how close the specs are for the first two.

D15B1

(Same as the D15B2 engine, but with a mild camshaft, and a restrictor plate between the throttle body and intake header)

* Found in:
o 1988-1991 Honda Civic Hatchback
+ Displacement : 1493 cm?
+ Bore and stroke : 75 mm X 84.5 mm
+ Compression : 9.2:1
+ Power : 70 hp (52 kW) @ 4500 rpm & 83 ft?lbf @ 3000 rpm
+ Valvetrain : SOHC (4 valves per cylinder)
+ Fuel Control : OBD-O DPFI

D15B6

* Found in:
o 1988-1991 Honda CRX HFx
+ Displacement : 1493 cm?
+ Bore and Stroke : 75 mm X 84.5 mm
+ Compression : 9.1:1
+ Power : 62 hp(88-89) 72 hp(90-91)@ 4500 & 83 ft?lbf @ 2800 rpm
+ Valvetrain : SOHC (2 valves per cylinder)
+ Fuel Control : OBD-0 MPFI

as compared to the DX motor
D15B2

* Found in:
o 1988-1991 Honda Civic DX/DLX
o 1988-1991 Honda CRX DX
o 1992-1995 Honda Civic LSi Hatch/Saloon (European Market)
o 1990-1995 Honda Concerto (European Market)
+ Displacement : 1493 cm?
+ Bore and stroke : 75 mm X 84.5 mm
+ Compression : 9.2:1
+ Power : 91 hp (68 kW) @ 4900 rpm & 119 Nm @ 3800 rpm
+ Valvetrain : SOHC (4 valves per cylinder)
+ Cam Gear : 38 tooth
+ Fuel Control : PGMFI Dual Point
+ Redline : 7000 rpm