[91civichatch2571]

Originally Posted by AbsolutelyClueless

I have a 1990 Civic SI hatchback with 300k on the motor. time to retire it and either rebuild it, replace it or "upgrade" it. The cost delta between stock and 25 more ponies is too small to ignore. So...

I've read the faq, searched the forums, consulted the stars, and glanced at the tea leaves yet I still have a few questions.

The Faq list these direct bolt in performance engines:
D16A6 or SOHC ZC - 108hp, great upgrade from DX/LX engine. cheap.
JDM D15B - welcome to VTEC. nice peppy engine, 125-130hp
D16Z6 - quick, with bolt ons should be able to beat allot of other sport compacts, 125hp
D16y8 - same as D16Z6 but 127hp
DOHC ZC - quick, similar performance to SOHC VTEC but DOHC NON VTEC, aftermarket support not quite as great as SOHC VTEC, 130hp

Someone Define "Bolt in"?

If I get a D16Z6 or a ZC can I use my existing tranny? ECU? wiring harness?

Are all Z6's the same? if not which year should I get?

Which Clutch package? 90 civic si? or donor car?

I'll be doing the swap myself but want very little down time. I don't want to be running around looking for this hose, that plug, and god knows what else.
I want simple, quick, seemless and clean.
BTW, I'm not going to racing or even pretending to. This is a commuter, run around town car. When I want to get the polices attention, I'll take the Jag.

The term "bolt in" means that you dont need to spend $300 on new motor mounts, you can use your existing motor mounts. Which engine you choose (if you choose to replace it) is completely up to you. Personally, out of all those I would probably pick the D16Y8 because it will most likely have lower mileage than most of the rest, its a common engine so the aftermarket support is good, and its pretty peppy. All of those engines listed will bolt up to your tranny. For the ZC's (SOHC and DOHC) you can use your stock ecu, but the rest will require different ones. If you get the SOHC ZC, you can use your existing wiring harness and I think you dont even need to modify it. With the DOHC ZC you will need to add a couple wires but its pretty easy. When you get an engine with vtec, you will need to add a few more wires and find a way to activate vtec via an RPM activated switch, or an VAFC or something. The Z6's im pretty sure are all the same. As for the clutch, yes you will get one for a 90 Si if you stick with that tranny. I think that answers most of what you asked. If you have any more questions about a specific engine or just a general question, feel free to ask, theres a lot of knowledgeable people here that will be glad to help you out. And by the way, welcome to AF