I wanted to do a cheap upgrade since I have to get my timming belt change soon. I was wondering if anyone out there knows if the Si Head will bolt right on to a HF bottom block? I have a 91 HF and I have a SI head with the intake manifold and ecu in the garage. What I wanted to do is replace the HF head with the Si head, I know that there wouldn't be a significant gain in power but compare to the HF, it would really help when your trying to pass a big rig on the free way. If this can be done, what do I need? Does anyone have any links I can refer to?

Thanks

 

yes it will bolt on but ull have issues when 4 of ur valves are slaming into ur pistons....now some one onece told me that HF motors have teh indents for 4 valves but no one has yet to prove this the only way u can know for sure is to take off ur stock HF head and look if it has 4 indents then u can go ahead and slap a SI head on upgrade to teh si intake manifold and run the si ecu the HF injecters may also be different i do not know for sure but i dont think they are....u can run ur stock distributer and stock everything with this even if u dont swap rthe head u can just use the intake manifold and throtlebody with the si ecu and ud be good for some extra power but id open it up and prove what pistons the HF has

 

Do you know if the HF header will fit the Si head?

 

d series parts are d series parts. especially external ones.

yes the header will fit.

ever heard of using it for turbo.

 

yeh teh head is asthetically the same has spaces for the extra valves but they were not machined out....and ud be using the short block the long block includes head ditributer intake etc...ull want to use the si intake and throtle body also and ecu keep us informed

 

I would keep the HF ECU
The only difference between the ECUs is the Rev limit...
The Hf valve train might start to get valve float after the stock 5,500 RPM limit
But if I am wrong the Si ecu will give you some access to the power in the top end that you will have gained with the Si intake.

 

oh and the fuelmaps arent different either come on the pm6 is worth putting in

 

HF ECU, I put one on my car one day for laughs, and man does it suck. Its like such a downgrade.

 

they only have two valve releifs in them, i have a HF block in my garage with no head....

 

I have helped my friend do an SI head swap on his HF. Had 4 valve releifs.
He did another hf/si swap couple months later for another car, also had 4 valve releifs in the pistons. Actually, i never once saw an HF piston with only 2 releifs, besides pics that people posted here. I'm pretty sure it has to do with the year of the motor.

 

Hey RioNinja, did your friend have any problems with the HF/Si head swap? Did he notice any major power gain? I should be getting my HF from the body shop in about a week or so (its being painted eternal blue with blue perl) and I'm trying to get everything ready for the head swap. Just wanted to thank everyone for their input....Will keep everyone posted.

If anyone is interested in adding power windows to their crx, let me know. I've converted my HF's and my bros dx (civic hatch) manual windows to pwr, I'll post some pix later.

 

No problems. The cam timing was off slightly, since the block height is different. Most of the power is towards the topend. due in part to the advanced cam timing. Its a huge difference over stock HF. Even though the motor is smaller, you should be almost as fast as a stock SI if you swap intake manifold/ecu/exhaust/etc.

Keep in mind that you might have a motor w/ 2 valve releifs, in which case you would have to swap pistons as well. IMO, then its not worth it. For all the money it would cost, you can just find an complete SI motor. Hell, i see people give them away if you look hard enough.

 

Got an 88 HF short block with only 2 .

 

If you want the HF to feel quicker just loose the crappy *** tranny. It won't be a rocket ship but better than a regular HF. An HF bottom end isn't all that strong either, you'd be better off just swapping in the whole Si motor and tranny. ECU too of course