D Series Honda Motor Questions?
 

Is the only difference between the 88-91 D15B2 bottom end and the D15B6 bottom end 4 valve reliefs in the pistons as compared to 2? In other words would the CRX HF head work on a DX bottom end, with a tiny loss in compression due to the extra 2 valve reliefs?

Some specs from the wiki

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) @ 5500 rpm & 83 ft?lbf @ 3000 rpm
+ Valvetrain : SOHC (4 valves per cylinder)
+ Fuel Control : OBD-O DPFI
+ Transmission : LSD

[edit] 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)
+ Displacement : 1493 cm?
+ Bore and stroke : 75 mm X 84.5 mm
+ Compression : 9.2:1
+ Power : 100 hp (75 kW) @ 6000 rpm & 119 Nm @ 4500 rpm
+ Valvetrain : SOHC (4 valves per cylinder)
+ Fuel Control : PGMFI Dual Point
+ Transmission : LSD

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 @ 3000 rpm
+ Valvetrain : SOHC (2 valves per cylinder)
+ Fuel Control : OBD-0 MPFI


The other question is like it says in the specs above, is the Hatchback motor,
D15B1 really just the same as the DX motor, D15B2, but with a different cam?
I know it also has different intake manifold and injection but according to the part number the ones off my HF motor are the same. I'm just trying to match up the torque specs for a replacement motor for my CRX HF.

I think you are risking valve to piston interference issues if you were to put a 4 valve head on an HF lower end. You'd have to change the pistons to match the head. Plus the compression ratio would be wrong.

I wouldn't put a 4 valve head on the HF. Look for a CX head or another HF head.

I wouldn't put a 4 valve head on the HF. Look for a CX head or another HF head

Thanks again SVOBOY. I managed to get a good HF head otherwise I'd be buying yours. That's backward though I was wondering is the HF head, 2 valve, would be OK on the DX motor, 4 valve? Also as the 2 engines have the same bore, stroke, and displacement the only compression loss would be a tiny bit due to the 2 extra valve reliefs, right?

Oh, yeah, it'd be fine...sorry, I got a bit confused...

The D15B1 also has a close-coupled cat like the D15B6, though the exhaust manifold runners are larger on the 'B1... I assume to match the larger 2-valve exhaust ports. Of course, that makes no difference whatsoever if you're just using the bottom end. :)
I'm pretty sure the HF uses thinner connecting rods, probably to reduce reciprocating mass... But again, that makes little to no difference here.