What makes an 87 CRX HF motor HF?
 

What's the difference between the 87 CRX HF, DX, & Si Motors other than the fuel injection? I've read conflicting information about the displacement. Some websites say 1.5 and some 1.3 on the HF.

My chiltons manual shows:

the 87 1.5 crx Si as being D15A3, this is the fuel injected model. 91hp at 5500 rpm, 93 ft lbs at 4500. 8.7:1 compression

the 87 1.5 HF has a carb. 58hp at 5500, 80 ft lbs at 2500. The HF motor is listed as having 26 degrees BTDC timing. 9.6:1 compression, Not clear on how many valves it has.

For 87 there is also a non HF 1.5 liter listed .This is the motor with the CVCC head that came stock in my 87 Civic DX. 76 hp at 6000 rpm, 84 ft lbs at 3500 rpm. D15A2. 9.2:1 compression. Timing is 20 degrees BTDC.

87 1.3 liter D13A2 had a carb (not sure if it was CVCC) 60hp at 5500, 73 ft lbs at 3500, 10:1 compression, same bore, shorter stroke than 1.5L

Look for the engine block code near the thermostat housing- this will tell you if its the 1.3 or 1.5. If its fuel injected, then it has to be the 1.5.

There is no 1.3 HF motor listed for 1987.

The timing (26 degrees for HF engine) sticker under the hood might be a good way to tell the HF apart from non HF (20 degrees BTDC) if the motor is original.

The 1.5 CVCC motor will eat head gaskets until you fix it with a specially designed replacement. Thankfully, this head is not prone to cracking.

In 1984 there was no CRX HF, insted it was simply call the DX 1.3, and the other one was the DX 1.5, no base modle, and the regular civic 3 door (hatchback) was avalible as a DX 1.3, DX 1.5 or S 1.5 (befor the SI exsisted), a 4 door sedan, and two trim leavles of the wagovan, all civic engines for 1984, including the 1.3 were cvcc, I belive this was the only year that a 1.3L CVCC engine was sold in the US.
The 1987 CRX HF engine has a CVCC head as well, altho the part number for the head is differnt between the HF and the DX, differnt cam shafts, along with the blocks being differnt (DX block costs around $45 more as well), they use the exact same clutch, but differnt fly wheels (lighter on the HF), the carburators are simaler enough that they use the same gasket set, but differnt jets, chokes, and while looking under the hood you noticed right off the biggest difference, the HF has a silver alluminum air cleaner houseing, while the DX has a black painted steel air cleaner houseing, the HF also has a plastic valve cover, insted of black painted steel, I've also heard rumers that the HF only had one compresion ring, and one oil controle ring, insted of two compresion rings and an oil controle ring, the price of a single set of rings for the HF is around $21, while a set for the DX of the same year is $51, so there is less of something in there.

I'm wondering if I could swap the HF engine and tranny into and 87 CRX Si using the Si fuel injection for maximum fuel economy. Or, could I just use the tranny and the cam? Any thoughts there?

You might as well leave the Si engine in there and just change the trans. The fuel injection/Si intake won't work on the CVCC head of the FE engine.

The CVCC cam is different (extra lobes for the extra CVCC valves) from the Si cam, I don't think they would be interchangeable- but I could be wrong

Check out this web site
https://www.redpepperracing.com/forums/
Yes it can be done but you will have swap out the CVCC head and replace it with the SI head. Unless you did some major tuning of the computer I belive you would lose economy. There is a reason Honda went with the CVCC head on the HF

After trying this sort of thing, I have to wonder how much a transmission swap alone will help. I swapped from an SI transmission to an HF transmission in a Civic DX hatchback. And in the process, I lost TONS of acceleration, but did not gain ANY MPG. That's right. Nothing Nada Zip. I would therefore say that you would only lose if you swap an HF transmission into your CRX SI.

swapping an HF engine in to an SI body is going to be kind of skechy, as you are going to need to swap the ECU (yep, it has one) and all 56 vaccum hoses.
I've never checked on the gearing of the early SI, but it might be worth going with a DX tranny, as the HF is going to be way way to much, I think the fuel injection was pretty close to what honda kept useing in fallowing years on the rest of the 1.5L civics, so check in to improvments that had been made as years went on, the SI head is going to be closer to the VX head then the HF head, altho I don't think any of them are interchangable.