Sorry again if this has been asked to death if so admins can delete this post, I've researched things for weeks now and I can't seem to find any supporting evidence or continuation of success.

I have a CSX 5-speed which is a K20z2 engine. I've been considering changing out the camshafts to a K20z3 (Civic Si) or a K24 (Acura TSX) but I was told I can't because only the intake side has vtec.
My question is, since my crappy K20z2 engine is essentially the same as the RSX base K20a3, can I use the camshafts from the K20a3 to swap into my K20z2 or would that be pointless?
I guess my questions would be:
1) Would there be any gains such as low end torque since my K20z2 only redlines at 6800? and
2) Would I pass smog if I do this?

P.S I'm not considering Kpro or anything, I know. I'm just using stock ECU for now.
Thanks in advance!

 

The K20Z2 and K20A3 cams are essentially the same... swapping them would be pointless.

1) Same cams produce the same results. If you were to install a pair of RSX-S or TSX cams, which would require new rocker arms and extensive modifications internally, you WOULD lose low and mid-range torque AND the engine would run poorly because running "VTEC Killer" cams is VASTLY different from the mild cams that you have now and your ECU doesn't know that swapped cams..
2) You will NOT pass smog... and a tuning solution would be required to make the engine perform properly.

 

@JRCivic Thanks for the heads up!

What if I were to install a TSX or k20z3 camshaft only for the intake side and leave the exhaust side alone? Would that work at all or should I just leave the engine alone and move on?
Thanks!

 

Nope. Leave the engine alone and move on.

 

Haha. Gotchya. God I hate my k20z2 engine so much. It's the crappiest of all K series. xP

 

It is disappointing that Honda chose to create the "Econo-K" engines... appearing nearly identical to the performance models to the untrained eye on the outside... but are so very different on the inside. Your unwillingness to swap ECU's, or convert to a tunable engine management system, basically eliminates your ability to modify your engine internally. If you would by willing to use a PRB ECU, you could install a USDM K20A2/Z1 or K20Z3 (or equivalent from other markets) and pick up a ton of power... and have true 3-lobe VTEC operation. When you start mix-matching internal parts, you MUST have a tunable ECU (like adding K-Pro to your current ECU).

 

Won't that fail smog by changing the ECU like that? PRB is RSX type s right?

I've been trying to go sleeper and strictly all OEM for my k20z2 because I'm a bit too old now for aftermarket stuff. When I was younger I would go crazy on my DC2 type R and my 2000 Civic Si. Now I'm more of a subtle sleeper so to speak. To be frank, this is what I've done to my k20z2 so far and I have to admit it has tremendous torque for an engine that only does 6800 redline after these modifications. I suppose just like anyone, the addiction to do more and go farther is quite strong and i thought it was possible to pass smog with the camshaft intake swap or something but I don't know much about internal engines:

*K20z3 6-speed + LSD transmission swap
*FD2 Type-R flywheel + K20z3 friction disc + K20z3 pressure plate swap
*K20z3 exhaust header swap + K20z3 catalytic converter swap
*Mugen Si catback sports exhaust (not the motorsports one, the genuine Honda upgrade from 2008 mugen si)
*Mugen Si quick shifter
*most importantly, an Acura TSX intake manifold RBB.

I had to research the intake manifold one for weeks because I came to the conclusion that going RBC (civic si) or type R (RRC) manifold would be a waste since again I only redline to 6800. The TSX manifold gave me tons of low torque which when swapping to 16 inch RSX Type-S wheels made me finally chirp 1st, 2nd and 3rd to my surprise.
*I tried considering maybe a J35 throttle body but also found out it was a waste of gas? I'm not sure on that one yet.

All these mods I've checked and re'checked with Blu-Driver Bluetooth to make sure there were no error codes nor check engine lights. And so far so good. I know I can pass smog with these mods so far. And that's how I started taking interest in possible camshaft mods if possible.

 

What year is your CSX ?

 

2010


Cleanest engine bay I could make

 

OK, scratch what I suggested above. I would locate a K20Z3 (or similar in other markets) and an ECU from a USDM 2007-11 Civic Si and plug that in. You could use a Hondata FlashPro to program an appropriate tune into your stock ECU to run the K20Z3... this would be the easiest way to add significant HP. All of your current parts would be usable. If it was mine, I would buy a 2006-08 USDM K24A2 (TSX) engine, a 2007 CRV right side engine bracket, and a K24 header designed to fit the 8G Civic chassis (your current header might fit, but it may rub against the cradle/sway bar because the K24 engine is 19mm taller) and tune it with a Hondata FlashPro.

 

I might consider the K24A2. This is the TSX RBB intake manifold I swapped out for. I got this information from the Honda Element Club where they would often do this modification on their engines. Look how much beefier the plenum is!



Here's another head scratcher I was theorizing. Japanese automatic FD vehicles has the same part number as the header I have on my CSX on right. It looks nearly identical to the K20z3 header on left. But at the end there's no separator as you see on the bottom. I tried to ask in 8th gen forum if the Si header was sort of like a 4-2-1 compared to 4-2 without that 'half-moon' thing at the end. Turns out measuring the circumference of the runners was a difference of 12cm and 11cm respectively. But yet, the shape is exactly the same. Even the exhaust manifold shield cover is the same part number! And as a bonus the CSX Type-S also uses the same header part as the Si.



Anyway, I've got a lot more research to do. Thank you for the helpful tips

 

Registered here just to answer to this thread
No, k20z2 is not the crappiest engine. It's actually pretty descent from the point of gradual upgrade. What does this mean:
It's RBC head (like k20z3) which means it already has the castings for the lost motion assemblies. Essentially it is a k20z3 running with a k20a3 rocker assembly.
Knowing this you can put FN2 camshafts (and rocker assembly) with VTC 50, flash it and get around 180hp/185Nm (considering the rest is stock). Then you do headers, intake, tb, change block to k24 with higher compression etc etc. With your already existing upgrades.. well, I'd love to see what can you get.

 

I'd love to but I need to pass smog emissions here in california. So I'm doing everything subtle while getting some performance without flashing ecu. =(

 

If you need to keep it California smoggable, your best option would be Civic K20Z3. Pretty much plug & play, you'd be able to BAR the car simply as a Civic Si without much fuss, and you'll have the best of all the K20 stuff that was ever offered in the US. You won't be able to pass off a K24A unless you get an inattentive or ignorant smog guy, and those are becoming rarer by the minute as the state cracks down more and more.

Clean CSX though!

 

@Acura_CSX99
Are you able to confirm what part number stamp is on your stock k20z2 cylinder head? semi curious about this K20Z variant.

 

Hello I would like to share my story and information in hopes that others can find it useful and I'm also hoping to learn some things. I have a 2008 Acura CSX with the k20z2 in it and 5 speed manual transmission.I purchased an ecu from a z3 and had it programmed to my ignition/ key.I was able to drive and operate the car normally while I saved up for Flashpro. The flashpro works as it should and I started off using the completely stock tuned calibration, only adjusting the injector size and times to match my specs in the z2/a3 until I am able to get an rbc with injectors and the transmission gear ratio to match the 5 speed transmission. I also switched from MAF calibration to MAP, making sure to determine WOT, disable p0101 etc... The goal one day is to have a z3, but for now I'm doing what I can with the z2. I have cat delete, stock header and exhaustStock intake with throttle body spacerZ3 throttle bodyH22 egr block off plate (k20z2 has egr)Throttle body coolant delete (my throttle plate has not frozen at intake temps of 25f in -25 weather here in Canada.)8th gen si flywheel, competition clutch kitHybrid racing detent springs and selector springsAcuity shift cable bushingsAcuity shift base bushings Today I discovered the fd2 Asia Civic 155hp calibration, which is also a k20z2. Hondata has informed me the calibration is no longer supported and they don't recommend I use it. I do not want to use the calibration specifically. The question I have is, should I use the stock tuned - base map for the z3 like I did in the beginning and continue to data log and road tune my fuel tables based off of that? Or should I import cam angles, ignition tables and fuel tables from the Asia Civic calibration? To get in to a bit further detail, if the answer is yes, that I should be using the cam angles and ignition tables from the 155hp Asia Civic calibration, should I also bother importing the other parameters like coolant temp compensation, lambda values, cranking fuel etc or is it okay to just import the cam, ignition and fuel tables? I notice that there are many changes between the completely stock tuned calibration and the completely stock tuned map calibration (race) as well. The reason I do not want to use the Civic Asia calibration is that there aren't as many options/ parameters as there are with the canada/ us civics like adjustable launch control and a few other things I've noticed. To summarize, I'm just trying to figure out the best direction to go with this setup.

Stock tuned calibration (z3/si), converted to map with those ignition and cam values to start and tune fuel from there

Stock tuned with all settings and parameters imported from Stock tuned race map calibration (si/z3) minus injector differences and tune fuel from there

Stock tuned with cam angles, ignition tables imported from Asia Civic calibration (z2/ base) and street tune fuel from there

Thank you in advance for any advice and help

 

Sorry for the loooong *** delay (also posted in the wrong reply 🤦‍♂️). I finished everything. And @JRcivic1 was right. I got real VTEC by using 2008 TSX camshafts + RBC VTC 50 intake camgear. I also had to source an RBB solenoid and the VTC spool valve assembly. Also I used a CSX-Type-S ECU (exact same as a Civic Si) ECU and an Si engine harness and a FlashPro.

I'll try to keep it as short as possible since there's a ton I did within the 2 years and some really interesting finds along the way. It turns out the k20z2 cylinder head for the Canadian only 2006-2011 Acura CSX (non Type-S) is the exact RBC-1 cylinder head as an 8th gen Civic Si cylinder head and CSX type-S cylinder head. (Only thing missing are the entire upgraded valve trains + upgraded assembly shafts/rockers + lost motion springs. In fact, the k20z2 has the castings for the lost motion springs except no springs! There was a mention of this from a post decades ago on some guy trying to upgrade his automatic Asian FD civic to an FD2 before he stopped updating. Here is a photo I took of my cylinder head as proof:

It turns out the stock assembly shafts, springs, plus the camshafts are the EXACT same part # as the k20a3 RSX base.



I don't even know where to begin next because I made so many modifications. But along the way, I also upgraded the valve springs, retainers, keepers, seats, assembly shaft, assembly rockers, valve adjustments. Took out the EGR assembly and capped it with an OEM plate. Had to change knock sensor to match the fittings from the Si engine harness. I ported an RBB intake manifold, and also port matched it to the fuel plenum and to the TSX throttle body (i know i know, RBC or RRC intake is milles better). But I'll explain later.

I finally had the confidence to pull my cylinder head and replace all the springs to an FD2. I think FD2 springs have the same part # as Civic Si.



I also did a light pocket port. How did I do this? Another long story, but in a nutshell I tried to port an RBB3 TSX head in 2024 and completely F*cked it up when attempting to remove the valve stems and then re-installing new valve stems. All that re-drilling and honing what a waste of 4 months and money. But I learned so much from that experience.

I also ended up with an genuine FD2 transmission (crazy story on how I ended up with this), also ended up with a complete FD2 exhaust system that perfectly fit with an FD5 chassis. (fd2 exhaust header + fd2 catalytic converter + fd2 pipe A + fd2 pipe B + fd2 exhaust muffler).
Then I got FD2 control arms, FD2 RRC crank pulley, using the same FD2 flywheel, clutch plate, and pressure plate from earlier, FD2 airbox and tube + resonator, FD2 fuel injectors. And then I finished it off with the smaller twin-block spoon calipers as it fit the stock brake discs! And got CE28N wheels to lighten everything up even more.




So now it really hauls *** throughout the power band while staying quietly OEM. But I was having the longest problem with FlashPro because I just didn't know how to use it. After increasing it to 7600rpm I was later told I could safely go up to 8000 but I must have a proper tune. The question is is it safe? Well some say it is, some say no. There aren't any oil squirters down there, (I haven't personally checked) But I heard you don't need it, some say you do... some folks use the RSX base block with missing squirters etc. Anyway with a little help here and there and by reading as much as I could research I'm almost done with the fuel tuning using MAP tuning. And instead of trying to rice it out like I used to do with my other Hondas/Acuras in my younger days, I decided to keep it 100% sleeper except for the lighter wheels and brake calipers. I love how unassuming my sedan looks, until I floor it.




Engine bay.



Only thing I regret is not using a tsx k24a2 lower block for the ultimate franken-build. But so many times my gf threatened to leave me because she hates this car. I keep telling myself okay 'one more' modification then no more I swear. I suppose I need to stop here for now. 💖

 

Great job. Enjoy.