HF to SI swap. What's needed

I have a 1991 HF that's burning oil. I have access to a 1989 SI engine. What will I need to make it work properly. I plan on using the hf tranny for now. (just a commute car.) As far as I can tell it should bolt right in. Should I use the SI or HF harness and which ECU should I use? Which flywheel? I want the engine to be ready for the SI tranny and other upgrades when I get them, so I want the engine to run as well as posible and not like a beefy HF. I have heard you can use different harnesses and ecu's but it can effect performance. By the way the si engine is comming with the harness and ecu.

Well you are in luck your HF is the same wiring as the Si. Put the Si motor in using the Si intake and injectors but you need to find a PM6 ECU (90-91 ecu allow you to use chips to upgrade or even later go OBD1 yes OBD1 with a OBD0 ecu). Thats the only difference in the 2 as far a wiring. It should all be plug and play. If you use the HF ecu it will run very under powerd and lean you could possibly do damage to the motor. So get a PM6 ecu.

So I should not use the ecu out of the 89 SI?

If you have the 89 ecu use it. If you have to buy one buy a 90 91 thats all I was tryin to get at.

Thanks. I do have one, but I found the newer ones on E bay for $50.00. It looks like the only difference is that the chips are changable on the new ones, so it's eaier to upgrade right?

Thanks. I do have one, but I found the newer ones on E bay for $50.00. It looks like the only difference is that the chips are changable on the new ones, so it's eaier to upgrade right?

You will only be able to upgrade the 90 91 ecu the 88 and 89 are not upgradable with a chip.

Thanks for all your help! Looks like this should go real smooth now.