How much horse power would i have/gain if i put a Si manifold from a hatchback in my stick crx 89 hf

 

Not a whole lot. The HF engine is only 8v and not designed for power. You can purchase a D16A6 from an 88-91 Civic/CRX Si for less than $200. It is a direct swap (no wiring involved). Trying to upgrade the HF engine is pointless, as it's not what it was designed for.

 

either way the HF engine is already mpfi, so there is no point in swapping to a si IM. You still have the 8 valve motor either way.

 

You can put a dx pm5 head on it with the si intake manny and pm6 ecu and get a noticeable increase. Do a search for bisimoto. He had d15b6 with an 8 valve head that ran 10's in a hf.

 

Goi for a si tranny. It will be the best upgrade you ever do to a hf short f throwing it off a cliff. It would be hauling some hf *** then! Never actually tried but i belive with just the tranny it would move ok since it is so light and si gears Are short.

 

uhhhh.... yikes. You can put it on, but please, please, please, don't try to race anyone. That's just sad, and it would make us all look bad. 6 hp at most.