View Full Version : How to: Swap from SOHC to DOHC

07-30-2003, 11:30 AM
Following the demise of my wife's SOHC due to rod-knock, *pours a 40oz* I swapped a DOHC KA in it's place. In this post, I will tell you how

I cover how to swap a S13 DOHC motor into a SOHC equipped S13, as well as parts necessary.

1. Source parts needed for swap (full parts list is at bottom of post).
2. Ensure you have adequate tools, space, equipment, time and money to accomplish this.
3. Source a motorset.
4. Yoink old motor from chassis. You can unbolt the motor mounts from above or below. Guide the motor out, making sure it doesn't damage
anything on it's way out. I'd pull the tranny at the same time as well, in case you're going to be utilizing the same transmission ,so that reinstallation will be much easier.
5. Remove A/C lines. You will have to get custom lines made if you want to keep A/C, or make a custom bracket for your SOHC compressor.
6. [OPTIONAL] Remove any other engine bay items like AIV, airbox, etc. and prepare engine bay to your liking. (clean, sand, paint, nothing, etc)
7. Move SOHC power steering lines over to driver's side & install DOHC power steering reservoir -OR- install S13 DOHC power steering lines.
8. Replace SOHC throttle cable with DOHC throttle cable. Two bolts at the firewall behind the accelerator (and remove the accelerator to make life easier.
9. Pull SOHC engine harness. You can either cut it at the firewall, leave it intact and pull it thru the firewall (into the engine bay), or whatever is easiest for you. Don't throw it away just yet - you may want extra wiring, or to keep the connectors for future use.
10. Install DOHC engine harness. Reverse of above.
11. If you're doing a manual swap, NOW is the time to drill out the place for the clutch master cylinder, install it, and run the hardline down.
12. reinstall everything you took out to prep the engine bay, like AIV, airbox, cruise control, etc.
13. Prepare your new motor. This means whatever maintenance you'd like to perform on it before it goes in, i.e. water pump, vacuum line
replacement, thermostat, reseal oil pan, timing chain job, belts, etc. It's about 11ty billion times easier working on an engine when it's OUTSIDE of a car.
14. Slide your slick new DOHC KA into it's new home. Again, watch your clearances. You don't want to damage anything or scratch that fresh new paint, right? Make sure you attach your heater hoses during this step. It'll make life MUCH easier.
15. After getting the tranny mount in and bolted down, tighten down the motor mounts. This is important, as your engine can sit cockeyed and still be tightened down at the motor mounts.
16. You're getting close! Reinstall your clutch fan (or not if you have electric stuff), and install your radiator and fan shroud. Install your Upper and Lower radiator hoses at this time.
17. Start connecting the harness to the motor. Now is the time to do a clean job of installing the wiring.
18. Finish installing everything else, like intake piping, sparkplug wires, etc.
19. Your engine bay SHOULD be complete. Now it's time to address swap wiring.

1. Locate the body harness (under dash harness that attached to the ECU) that attached to your old harness. Cut the old connector off (the one that attached to your SOHC harness) and attach your DOHC body harness connector. Just match the colors! There will be some wires left over. These are for the SOHC's diagnostic plug, and are unnecessary. Please note: Your car will NOT be able to hook up to a CONSULT tool. To accomplish this, you must get a body harness with all the correct DOHC wiring. This is why we cut the body harness connector off, and not the engine harness connector.
2. I recommend using a soldering iron, shrink tubing and electrical tape as opposed to butt connectors. It makes for a much cleaner job, and a cleaner electrical signal.
3. You need to swap out your tach if you want one that works. No wiring is involved, but it must be done. Simply pull your combination meter (gauge cluster) and remove the three screws behind the tach. Lift and separate. Installation is reverse of removal.
4. You should also extend the wires that go to the PS line sensor and connect that to your subharness. It's not necessary, but it's a good

Parts needed:
S13 DOHC KA (or S14 KA with OBDI lower intake plenum, S13 DOHC distributor and S13 DOHC coil & others)
S13 DOHC engine harness & body harness connector.
S13 DOHC MAF, intake piping, coil, tachometer, power steering reservior and hoses (low pressure), throttle cable (and cruise cable if you have it.), engine-side brake booster vacuum hose, engine/transmission subharness (if swapping from automagic).
Optional: S13 DOHC power steering high pressure lines

A few sidenotes: S13 AIV system is same/same. Nothing needs changing there. For cruise control, the cable length is dependent on the motor. DOHC cruise control can't use the SOHC cable without a weird custom bracket.

For my swap, I used a '95 KA, adjusted to behave like a '92. I used a '92 exhaust manifold, EGR tube, distributor, lower intake plenum, coil, and vacuum routing. To eliminate the secondary butterfly vacuum line, I pinched it and sealed it. I performed a fully stock swap. No EGR or AIV elimination, no intake or cams or otherwise.

PS. Please note that I did all this by searching for information on how to do it. I'd never previously swapped a motor before. Also, feel free to remind me of steps that I missed, info I left out or didn't address, or other constructive criticism.

This info is intended solely for the users of Zilvia, and is copyrighted 2003 by me, Kevin Pratt. Any use for the purposes of monetary gain and/or reproduction outside of Zilvia.net is prohibited by me without prior approval and/or compensation.

07-31-2003, 02:42 AM

08-04-2003, 10:30 AM
ok.. i'm sending this into the FAQ for posterity.
send me a PM if you see anything I missed.