Honda CRX Forum banner
1 - 12 of 12 Posts

·
Registered
Joined
·
26 Posts
Discussion Starter · #1 ·
I got an HF with a D15B2 out of a DX due to the fact the original motor blew up on me...I want the good gas mileage for this being a daily driver. Now could anyone tell me if I could just bolt the 8 valve head on the B2 block, or would I have to change a few things?
 

·
Registered
Joined
·
122 Posts
Im pretty sure you would need a few other things like

1) The proper ecu (use the one that came with the head your using)

2) You are gonna need a different timing belt

3) new head gasket, head studs

4) youll wanna use the intake manifold, injectors, throttle body, fuel rail that goes originally with the head

5) must check for valve clearance and compression issues

6) May have to change the distributor to the one that was used with the head ur putting on

.......im pretty sure all this must be addressed
 

·
Registered
Joined
·
26 Posts
Discussion Starter · #3 ·
Im running the HF ECU on the B2 now, I have the HF distributor still, and i used the PGM fuel rail and injectors and everything on the B2 motor also. So could i just use the head studs off the old motor and all i would need is a head gasket, timing belt, and to check valve clearance?
 

·
Registered
Joined
·
96 Posts
im not too sure of this so someone please correct me quickly if im wrong... but the b2 (dx) has 4 valve reliefs per piston and the b6(hf) has only two. i can only imagine the valves from the hf head slapping the pistons because of the clearance issue unless you used the hf pistons on the dx block as well. same reason you can use an hf block and dx/si head.
 

·
Administrator
Joined
·
16,562 Posts
ender_ said:
im not too sure of this so someone please correct me quickly if im wrong... but the b2 (dx) has 4 valve reliefs per piston and the b6(hf) has only two. i can only imagine the valves from the hf head slapping the pistons because of the clearance issue unless you used the hf pistons on the dx block as well. same reason you can use an hf block and dx/si head.
The dx pistons have more valve reliefs than you need with an HF head. Why would there be a clearance issue? HF valves are by no means larger than dx valves, and they certainly don't have more lift.
 

·
Administrator
Joined
·
16,562 Posts
Yeah the HF valves are in the corners of the combustion chamber, to promote swirl. This gives a better air/fuel mixture which results in a more efficient combustion, and also evacuates the exhaust gases easier. This is the same concept stemming from the original Civic CVCC (compound vortex controlled combustion). :)
 

·
Registered
Joined
·
122 Posts
u can use the old head bolts but its not recommended to.... if you can get all of them out safely and delicately and the threads look in good shape still then i would say your ok. But pick up a few anyway incase one breaks or strips threads on the way out..... u never know.
 

·
Registered
Joined
·
317 Posts
it may be a real dog, because the DX has flat pistons, and the HF has domed pistons. I would think it would have really low compression.
It will probably run just fine, but be really really slow!

Good Luck, and here's a few pics of some HF pistons.



 

·
Registered
Joined
·
58 Posts
just to share my two sense, i really do not think you are going to see an increase in fuel mileage by converting back to an HF motor. I drive an HF Crx and i bought it bone stock, original drivetrain in great working order still, i'd say it probrably got about 40mpg, maybe a hair better if i did a ton of highway driving but i rarely am on highways. I then swapped the Hf motor for a d15b7 using a Pm6 ecu from an '88 Crx SI but i kept the HF tranny, i swear to you my gas mileage increased no joke. My theory is that the fact that the HF motor is so unbelievably underpowered causes you to be full throttle most of the time just to get it to move anywhere, and adding an engine that was still efficient but just a little more powerful allowed me to use much less pedal input during regular driving, basically you don't have to constantly strain the motor out all day long. it was'nt until i swapped out the HF transmission for an SI one that my gas mileage dropped drastically so i'm a true believer that the gas mileage that the HF is claimed to get is all in the tranny, not the motor.
 

·
Registered
Joined
·
26 Posts
Discussion Starter · #12 ·
yea that does kind of make sense because it would take a little biut to get desired speed where as with the dx motor now its only about half throttle if that and it gets about the same....and i agree its ALL in the tranny because i drive the actaul HF car with the B2 (dx motor) with the hf trans and a 91 DX and the rpm ranges are way different because the way the trans is geared
 
1 - 12 of 12 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top