Honda CRX Si JDM ZC Swap
|Last updated: 5/26/06
|Email comments or questions to Eric Sanborn
I completed this swap in the first few weeks of December 2004. Our old engine had about 190k on it and was sucking coolant somewhere. I thought it might be the water pump. It was due a timing belt anyway so I decided to fix it. When I needed a breaker bar to get the spark plugs out I decided it was actually time for a new motor. Since we painted the car a year or so ago it was coming time to freshen up the drive train anyway. I had researched ZC swaps a few years ago, but the stock engine was doing so well we could not justify the expense. The engines are now harder to come by and more expensive, but as you will see below I still feel worth it.
For those not in the Japanese car community the ZC is a double overhead cam engine that came in the Japanese domestic market (JDM) CRX SiR. It is similar by not the same as the engine that came in the late 80s Acura Integra. The engine makes about 20 more horse power than the stock US market CRX Si engine did. The story goes that due to emission legislation in Japan engines are pulled after only 40k to 50k miles. Therefore these JDM engines are supposed to have only about that many miles. Now since there is no way to prove that then it is anyone's guess how many miles they really have.
I got my engine from Woodfins in Richmond, VA. They turned around and got it out of a yard in NC. Cosmetically the engine is a wreck. If I were to put the 190k engine next to it on a stand and ask you to pick which one has "40k" and which has 190k 10 out of 10 people would guess wrong. It had a chipped flywheel pulley (discussed later), dented oil pan, 2 broken off vacuum lines, broken TP sensor, rusted up fuel pressure regulator and unusable throttle body. As a result I reused a number of times off the old engine like the fuel rail and throttle body as well as a number of brackets. My recommendation to someone buying an engine is to get the yard to email you a picture of the engine you are getting. I would not have purchased this one. However as you will see later the engine runs like a top so some time put into refinishing the valve cover should work wonders in cleaning up the engine cosmetically.
Engine it its ugly form. Soon I hope to blast and paint the valve cover.
Compared to my Audi swap of a turbo engine this was a walk in the park. The ZC pretty much bolts in where the Si engine was. I chose to upgrade to the 90/91 clutch setup which is 212 mm diameter instead of 200 mm. At the same time we got a 6.5 lb Fidanza aluminum flywheel. I had figured the stock one would be at the end of its useful life. It was rather blue and scored a bit so I think it was a good choice. As I recall the stock flywheel was 22 lbs when I weighed it. This whole upgrade is tougher for those with 88 CRX Si cars as the number of splines on the transmission is different than the 89-91.
Below is a list of things that are different between the two engines when it comes to installation:
The ZC appears to have a power steering pump although my engine came
with zero accessories. As a result the crank pulley is a bit
different. The Si pulley has a damper of some sort in it. My
ZC pulley was quite banged up, but the pulley was so much lighter (about 6
lbs) than the Si pulley I chose to touch up the chips and reinstall it.
The most notable difference with the new engine is how smooth the car drives. I am still running just the stock Si computer and it is amazingly smooth. The only problem currently is a strange idle fluctuation when you first come to a stop for maybe 10 seconds. This was not there for the first week, but is now. Mid range power feels improved somewhat while power above 5000 rpm is quite an improvement. This is definitely the engine that should have come in the car from the factory.
So far fuel economy has been lower than I hoped, but the motor had a bad thermostat in it that was stuck open. I have changed it now and hopefully there will be an improvement. The old engine averaged about 36 MPG with our mixed driving. The first full tank through with the new engine was 30.5 MPG. My wife has a small road trip planned soon so that should be a good test of highway fuel economy.
On a side note I will never again build an engine without an aluminum flywheel. Then engine revs so easily and I am sure it has contributed to how smooth the engine is.
I noticed the number of hits on this page has gotten fairly significant. I feel bad I have not put any updates on it in ages. We probably have about 10,000 miles on the ZC engine. I don't have the figures in front of me,but I believe it has settled about at about 34-35 MPG with around town driving. My idle fluctuation turned out to be a nicked wire in the distributor. Sometimes on hot days when the engine is just turned on it idles low, but other then that it is just like you would expect with a new car.
The car pulls like a freight train above 4500 RPM. Between the light flywheel and the light car it took me some time to get used to how fast it reved in first gear. I was often hitting the rev limiter. Above about 5500 the car puts down some black smoke. I think this is because the stock Si computer doesn't give enough ignition advance. The stock computer also has a lower rev limit. To fix both these problems I am planning to reprogram the ECU with the help of the knowledgable people at pgmfi.org. I am trying to get an extra ECU so I don't have to take the car off the road while I work on it. I plan to load the JDM ZC original program as a first step. Then I will likely add the USB functionality and along with my Wide Band confirm everything is perfect.