How to swap a 92-95 1.6L SOHC VTEC into the 4G civic/crx

An easy, no-weld swap for your tired 1.6L or 1.5L is the 1.6L SOHC VTEC from the 92-95 civic Si/EX and Del Sol Si. And with the popularity of the DOHC VTEC swaps into the 5G civics, there alot of the SOHC VTEC motors available for good prices. (Is any reason the 96-97 EX motor won't work also? Let us know.)

A big thanks to Lag_boy and mechanic b for the information. This article was based on Lag_boy's original article.

Updates at the bottom [click to jump]

The basics

• First determine the parts you will need. This depends on what model civic you have, and how hard you want to work:
  • Si option 1: Using your existing intake and ecu.
    Requires: SOHC VTEC block, head, VTEC solenoid, and distributor. You'll have to make your own VTEC controller.
  • Si option 2: Using SOHC VTEC intake and ecu (requires a lot of re-wiring).
    Requires: SOHC VTEC block, head, intake, VTEC solenoid, distributor, engine wiring harness and ecu w/connectors.
  • DX option 1: Using a 88-91 Si intake and ecu. Matt's DX to ZC wiring how-to will help you modify the existing harness for the Si ecu.
    Requires: 88-91 Si intake and ecu, then see Si option 1.
  • DX option 2: See Si option 2.

  Note concerning smog laws: Option one or two should have no problem passing strict smog tests, like they have in California, as long as the new engine is in good condition, runs and idles well and all the 4G emissions equipment is being used. But is it technically 'smog legal' to use the 4G Si intake and ecu with the 5G motor in a 4G body? That's a little fuzzy for a Si, and really fuzzy if it is a DX. More investigation will be done, but consider yourself warned. And don't forget the golden swap rule: Motor, ecu and emissions equipment must be the same year or newer as the car it is being installed into.

• Transmission: The 89-91 Si and DX (and probably the HF) transmission will bolt to the SOHC VTEC motor. That’s why this swap works. Three of your stock motor mounts are on the transmission, dramatically simplifying the install. Si transmissions will yield faster acceleration, but the DX has lower RPM cruising and a higher theoretical top speed. The choice is yours (i.e.: if money's tight, use what you got!). The 88 transmissions reportedly do not work because they have a different number of teeth on the spindle.
  Also, you can upgrade to the 92-95 pressure plate, clutch and flywheel, but you can't mix and match these components with 89-91.

• Required tools and stuff (beg, borrow, stea...):
  • The service manual (the Helm manual, not Chilton's!!) for your year civic/crx (covers both DX and Si), and a 92-95 Civic manual if you are going to use the VTEC ecu.
  • Engine hoist, or several helpers with really strong backs
  • Digital multi-meter for trouble shooting error codes, if they occur
  • Soldering iron, or crimps, and high-heat electrical tape
  • Lots of metric tools

• Find a 92-95 SOHC VTEC engine.
  Maybe one of your 5G friends just upgraded to DOHC VTEC power and is looking to sell his SOHC VTEC motor to cover some of the cost?
  Good prices from your local auto yards should start around $500 for at least the block and head. Try to get the VTEC solenoid (around $40 from H.A.P.) and distributor, too. The 92-93 and 94-95 distributors are different, so make sure you get the right one for the head. The 4G distributor can be modified to fit, by drilling the holes bigger. With this mod you lose the ability to adjust the timing by turning the distributor, resulting in a fixed stock timing setting.

• With Si/DX option 1, the only sensor to modify is the coolant temp. sensor on the 88-91 which has a two prong connector. It is located on the rear of the block by the oil pressure sensor. On the 92-95 there is just a bolt to fill this hole, since the sensor on the 92-95 was moved near heater hose. Just swap out the bolt with the sensor and be careful not damage the prongs.
  

  this is the 88-91 coolant temp. sensor which you will place in the block of the 92-95
  here you can see #16 is the 92-95 coolant temp. sensor it screws into the 92-95 thermostat housing(not shown)

  With Si/DX option 2, since you are converting to the newer motor's complete engine wiring harness and ecu, you don't have to worry about this.

• Before you install the motor, it is the BEST time to install a new clutch, as well as the EASIEST time to replace the timing belt, water pump, and tensioner. You'll kick yourself later if you don't take care of these now.

• To install the motor, remove the drivers side mounting bracket from the your original motor. Bolt this onto the new motor.
  
  The sketch on the left shows the bracket that you bolt to the timing belt side of the block, the sketch on the right shows the driver's side engine mount.
  At this time, you should install the intake, and attach the transmission. If you are changing over to the 92-95 Si engine wiring harness, you probably will want to do that while the motor is out of the car.

• You can now install the new motor, in reverse of removing the old motor. Follow your service manual!
  • Si option 1: connect every thing the way it was before except the distributor.
  • Si option 2: Using the SOHC VTEC engine wiring harness and service manual, connect everything.
  • DX option 1: Use Matt's DX to ZC wiring how-to will to modify the existing harness for the Si ecu. Connect every thing as if it was an Si except the distributor.
  • DX option 2: Using the SOHC VTEC engine wiring harness and service manual, connect everything.

  For Si/DX option 1, you can wire the SOHC VTEC distributor to the old wiring harness, and retain the ability to advance and retard the timing at the distributor. Or you can use a drill to make the 88-91 distributor fit the 92-95 motor, and probably lose the ability to adjust the timing.

• Now that the engine is in place, install intake tube and filter, the header, axles, and anything else you took out. Double check your fluids and all the critical bolts and parts. Are you ready to try it out? If you're ready, then start it up. Did it work? Trouble shoot and eliminate any error codes you may have. If you had no error codes before you started, you should not get any now, IF you connected everything correctly.

• If you are planning on using the VTEC ecu, now is the hard part. The ECU connectors for the 5G Civics are different than the 4G Civics. Thus, if you use the VTEC ECU, then it's necessary to cut off the 3 ECU connectors of the 4G car, and solder up all 45 or so wires to the ECU connectors (with some wire coming out of it) of the 5G car's ECU. This will require a bit of time, since the ECU pin locations all have different codes(letter/number)for both cars, and most of the wires are colored differently.

• It's VTEC time! The most simple VTEC controller would be a toggle switch wired to the solenoid. But that would be rather inefficient. But if you're in a hurry, it'll let you test that the VTEC is working. You can design your own VTEC controller with a MSD rpm switch PN-8950 and PN-8671 which will give you a range of 4600-6800rpm to activate the VTEC.
  
  Another low cost option would be the Autogage (by Autometer) ATM-2302 Tach with built in shift light. The shift light could be wired to trigger the VTEC solenoid, its infinitely adjustable from 1K-8K RPM and costs less than $80. See Matt's VTEC controller article at the Integra Performance Page for more info.

Updates

Q: Can someone clarify in detail what I need to do for an '88 CRX??
Can I retain my '88 tranny? Will the difference in splines be a problem?
Can I use an upgraded '92-'95 clutch, plate, and flywheel on my '88?

A #1: (by [Ed])
The 88 splines are different, you'll need an 89-91 tranny if you want to use the 89-on flywheel/clutch. Or swap the 88 flywheel to the new motor.
The site(s) forgot to mention you'll need to trim the timing belt cover a bit to fit the bracket to the driver-side mount. Rest of the mounts/brackets will be the ones of your CRX.
That water temp "sensor": the hole is not there in some of the 5g motors (in fact, none of the 5g motors I have have a mounting hole). That sensor is actually the thermal switch for the cooling fan. 5g's have them mounted on the thermostat housing...just extend the 4g wiring to the new location and use the 5g connector (I used the 4g engine wiring harness).
If you plan on running the 5g ECU, remember to bypass the injector resistor box, because it's not needed.

A #2: (Mechanic_b)
92 sohc vtec block have the coolant fan switch at the back of the block and the rest of the sohc vtec is located the thermostat housing of the vtec block. The timing belt does need some trimming on the front side of the engine underneath the 88-91 bracket so that it will clear the timming belt cover. One of the options you can make is if your're thinking of upgrading the clutch anyway but wants to use you're existing tranny. Just get some high performance clutch disc and pressure plate your 88 tranny and you can use your si flywheel. The only reason why we suggest 89-91 2g Crx and 4g civic is because you can just upgrade it to a bigger in diameter stock 92-95 clutch disc, pressure plate ( from the dealer preferably )and the same flywheel ( which ever year you're gonna use because 4g flywheel is different from 5g flywheel). This option is only if you're in a tight budjet for better holding power which will cost you 'bout $180 for the clutch kit at the Honda dealer. I use to have this set-up and still able to pull 13.1 et with single fogger nos. I upgraded it to ACT clutch now. Sorry they don't make one for 88 model, I think......