So you own a 2001-2003 Honda Civic EP3 and want to find out how to swap a K20A2 into it. Although your Civic shares the same engine layout, there’s a few things you need to make your K20 EP3 Swap go smoothly. What’s the difference some may ask? it’s still the DOHC i-VTEC engine from Honda.
The difference is simple. Whereas the K20A3 is still a DOHC innovative i-VTEC engine, the K20A2 from the Acura RSX is far superior. The variable valve intake system that makes up Honda’s i-VTEC works just on the intake cam on the K20A3. The K20A2 however utilizes both intake and exhaust side of the variable valve technology.
Because these two versions of the i-VTEC engine exist, many EP3 owners look to swap in the K20A2.
Doing so allows them to take advantage of both cam profiles and gets more bang for your buck modification. Just because the engines are basically the same however doesn’t mean that the RSX engine will just bolt right in.
There are significant differences that you will need to take into consideration. This will allow you to easily bolt in the K20A2 engine into your Civic Si.
K20 EP3 Swap components
Power Steering Pump belt changes– Before you drop that RSX engine into your Civic Si, you will need the old idler pulley from your EP3.
Use this idler pulley to replace the RSX power steering pump.
K20A2 ECU – You can get away with using your EP3 or stock Honda Civic Si ECU here of course. However you should take it easy and keep the RPM below 4000. Before you can use the Acura RSX Type S ECU, you will need to have the anti theft removed or your key reprogrammed by Acura / Honda.
Shifter modifications – Depending on your setup you may need slight modifications to your EP3 shifter base to reach reverse. This will enable you to re-use your factory linkage while retaining the same throw.
Exhaust changes – If you want to use a RSX Type S stock exhaust manifold and midpipe, they won’t properly fit without welding. Instead turn to a DC Sports Ceramic Race header or an out of the box aftermarket solution to fit things together in your K20 EP3 Swap.
Engine harness – When getting your K20 EP3 swap done, you can either elect to modify your EP3 engine harness or just swap in a RSX Type S harness.
If you retain your factory wiring you will need to make provisions for the reverse lockout.
Axles – Unless you are swapping RSX 5 lug hubs and brakes as well, you can stick with your factory EP3 axles.
Belt – Changes to your power steering pulley and the idler pulley will make your old accessory belt not fit, and an RSX one won’t either. Instead use a 64″ ribbed belt to complete your K20 EP3 swap. You may be able to get away with using your old EP3 belt, but it’s not recommended.
Have any questions for this K20 EP3 swap guide? leave them for us below and let us know!
If im keeping my stock Ep3 trans to i still need to change the harness? since i wont have to deal with the reverse lockout?
What are you swapping from? If you have an EP3 already and are retaining the transmission, you are covered for the reverse lockout, reverse lights and switch!
Will it pass California smog with those headers?
Hi Sargon, which EP3 headers are you aking about specifically? If you are looking to officially pass California SMOG or BAR your vehicle, the only one that will truly pass smog is the factory unit unfortunately. This is because the main catalytic converter is located in the stock header unit.
Good luck!
I have a 03 ep3 i put a k20a into and im still useing my ep3 5speed transmission and wiring harness an ecu…but i keep getting limp mode at 4k the codes im getting is…
P1106
P1259
P0325
I was told i need to have my ecu flashed by honda to run the k20a today…so any advice would be greatly appreciated
Thanks!
Hi Todd, thanks for reading my Ep3 swap guide.
No, you don’t need to flash your ECU at the dealership, it’s a better investment to look into a Hondata KPro or something along those lines. However you’ll need to deal with the check engine codes that are stored in your ECU. Let’s take a look at your K series check engine light code problems :
P1106 Barometric Pressure Sensor Range/Performance – Check your MAP sensor, or the wiring. If you’ve recently swapped the engine you may have gotten a bad sensor.
P1259 HONDA VTEC System Malfunction – VTEC errors can stem from a variety of issues most of all the P0325, leave this code for last.
P0325 OBD-II Trouble Code: Knock Sensor Malfunction – This knock sensor is either dead, or there’s a problem with wiring.
Luckily to fix your K series swap problems it won’t take a ton of work. Start with the MAP sensor and here’s a few links to help.
How to Test the RSX MAP sensor
How To Test K series VTEC
How to test K series TPS
K series RSX ECU Pinout
Hope that helps! Thanks for reading!
So the pump needs replaced with the idler & switch to 64inch belt is all?
Or does the other idler also need to be changed?
You will need to change the belt and the idler to ensure proper operation in your K20 swap. Hope that helps and good luck!
So the EP transmission fits just so on the K20
Hi Noor, yes depending what starter and vehicle you are swapping this into the EP transmission will fit on a K series engine just fine.
Thanks for reading my K swap guide!
How much does Swap usually run? Just for the a2 and parts? Got a knock in my a3 and it’s looking like it might be ttime to swap if possible.
Hi Craig, thanks for reading.
This swap will depend on cost, but it’s pretty effective in your EP3. If you aren’t upgrading clutch, drivetrain or exhaust components, you can get away with under 2000 invested if you play your cards right.
Good luck
I have an 04 ep3 with a k20a and kpro I have been running the stock ep3 trans for a year now just got the npr3 trans. I have a harness that came with motor but the third plug that does not plug into the ecu is not correct moatible with car connection. So does reverse lock out have to be wired independently if so can you explain the wiring pin locations . Also I have seen people hot knifing a sliver from there gearshift underside is this what you mean to reach reverse.
Hi Dion, okay interesting project there. So the harness you are talking about is from your factory harness, and you lack the ability to control reverse lockout. can you take a pic of the harness itself and what you are missing on the EP3 lockout?
I am looking into get my a2 BARD in Cali. With the oem type-s headers you said it needs to be welded?
Hi Jon, thanks for reading my Honda swap guide.
With OEM style headers, you will need to cut the flange off and weld it back on for a true plug and play solution. The issue arises from the length of the OEM headers, and you’ll need an exhaust shop to weld it up for you. Hope that helps!
Ok… so I have the 03 EP3. If I retain my ecu but have kpro will I be able to resolve the RPM issue you mentioned? I really don’t want to invest in kpro again on a new ecu.
And I don’t necessarily need the wiring harness if I maintain the factory 5 speed? I’ll only need that to prevent lock out issues if I get the 6 speed… correct?
Thanks!
Hey John, yes you are correct. And if you have a KPRO and your original EP3 ECU there’s no reason to upgrade again.
Thanks for reading