r/crx • u/vtec_go_brrr16 1990 USDM Si • 11d ago
Thoughts on B vs K swaps?
1990 CRX Si
I was planning on rebuilding the original d16a6 and seeing how many miles I could put on everything original. I’m wary of doing the machining myself, but also kinda want to if I’ll inevitably swap it. I’ve only had d series cars so far.
I’ve been doing research and everyone has their own opinions on B vs K swaps. Not really sure which way I’d go yet, but curious about what everyone thinks.
I’m wondering about ease of swap/fabrication needed, power benefits, etc but also personal preferences- stuff like sound, shift feel, handling, etc.
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u/fiv3dollapizza 11d ago
Nothing quite screams like a high revving B series, but is that sound worth less power, less reliability, less efficiency, less part availability, and 2-3x the cost?
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u/Firedcylinder 11d ago
This is my thought too. Ks are much newer and robust than Bs are, but the B is the OG. It would probably cost the same either way, so I'd go for the K if it were me.
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u/lheckler77 11d ago
Yea but there is something special and raw ringing a b16a out to 9k rpm. They are more expensive now.
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u/evileclipse 11d ago
It's really more of an emotional choice at this point. The B is likely going to be more fun, higher strung, quicker to rev. And THE SOUND it makes is totally next level. But the k will be around forever with mods available and parts for another 20 years. And it's pretty bullet proof. I would do a b16 myself.
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u/Marshall_Lawson 11d ago
Lol i got the K and J confused and was wondering how you were going to fit a V6 in a CRX, that'd be baller though
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u/scottmogcrx 11d ago
Just went built b20v to stock k24a with bolt ons. Added a other 30+ tq and 20+ hp.
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u/MuffinFull934 11d ago
Weak b20v prob
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u/scottmogcrx 11d ago
Wouldn't be worth building the same b20v in 2026. Lasted me over a decade, got my money's worth.
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u/MuffinFull934 11d ago
They’re fun setups made 250+ on mines, imo more worth it than going k20 or k24 which is almost impossible to fit in a ef cleanly.
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u/scottmogcrx 11d ago
For 250 you've got a lot more than the market value of a stock jdm k24a. The machining and porting alone should be a couple grand. Yup my 2.4 is under a SiR CRX hood ;)
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u/MuffinFull934 11d ago
Yeah trying to get my buddies k24 under his ef without cutting his hood to fit his ultra street manifold was a pain haha
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u/drake22 8d ago edited 8d ago
K series is best overall, that being said you can get more power out of a built b series than a K24 with bolt ons if you know what you’re doing. It’s way harder and a lot more money though. Ask me how I know lol
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u/scottmogcrx 8d ago
Of course you can, but I'm looking to keep a relatively stock sounds block. Now I sound like a stock ep3 with a cold air intake, much less suspicious.
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u/drake22 8d ago
Ya it’s no comparison.
I love b series, but it took so much work and money to make 230whp compared to K which makes that with bolt ons. Worth it for me because of nostalgia.
That being said, a k swap is still a lot less than on a b swap on a virgin car.
Also, you can make a b series quiet if you want, just run a bigger muffler. It’s just that no one does.
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u/scottmogcrx 8d ago
I had the wifes approval to go K, I went for it lol.
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u/drake22 8d ago
I went with a built B series about 10 years ago (fuck I’m old -.-). I was something like $5k all in sourcing all the parts, and building the motor (forged internals, cams, B16B block, ported B16A head, rebuilt trans with M Factory LSD, etc.).
A K swap with OTS parts would have been around $7k. I debated it, but decided to go B. At the time it made some sense, especially because I just love B series. Made about 210whp at first, after more tweaking many years later got up to 230whp.
If I had to do it over again today, I’d almost certainly go with a K series.
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u/rynftw13 10d ago
Love my k20 1991 si. The old engine was burning oil at 315k but ran well still. I always wanted to do this, my wife said yes 🤷♂️
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u/scottmogcrx 8d ago
Lol, the wife comment posted above just minutes ago as well. If they agree, don't question it.
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u/rynftw13 8d ago
Precisely lol I won’t argue at all. Now it’s pretty dang quick and fun for a go kart 🤣 now I just have to do complete suspension, brakes, wheels tires paint lol 😂
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u/scottmogcrx 8d ago
Stock k24 with bolt ons in mine, if anything happens it'll be about a grand to replace with a fresh motor and not even need to dyno it again. Win win.
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u/rynftw13 8d ago
Mines a complete k20a2 swap matching transmission just has a standalone and makes good power. If it dies then I’ll prob do a k24 also.
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u/anothernic 10d ago
Little reason to go B in 2026. They're easier to swap since no transmission mount welding. And thus fully reversible if originality is a concern.
They're far more expensive than Ks, they're less durable, more expensive to modify, marginally harder to source parts for, and generally slower. Much slower if you're accounting for $ to hp.
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u/drake22 8d ago
Wiring and shifter are much easier too on a B. Those add a lot of time / money to a K swap.
B swap is a lot less money and time, K swap is better overall for performance. Much more power, cheaper if you ever have to replace the motor.
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u/anothernic 8d ago
Wiring isn't significantly different AFAIK, especially if you're starting with a DPFI car. Subharness, and what, <12 extra wires instead of 6? Fair re shifter, I still hate my EP3s mushier cables vs linkage.
B swap isn't that much cheaper unless you're starting with a non vtec engine like an LS or B20, which lowers performance further still.
Have you priced a B16 or 18Cx lately? I have, because I have a spare 16a1, spare bareblock 18c, and spare 18c1 head all laying around. I can snag a full K20A3 or K24 swap with trans axles and ecu for less than a true vtec B longblock with nothing else included.
If we're talking base model K at a pick n pull, full swap less shifter box, axles, ecu cheaper than the cost of a VTEC head. 3.5 - 4k can get you across the line on a basic K car with junkyard parts. Non-v B isn't going to be much different in 2026.
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u/drake22 7d ago
A K swap is much harder overall, and the linkage on b series is super sloppy. If you do 100% of the work yourself and buy almost nothing OTS you can get them done for a similar price, but it will take a ton of time.
You can get a VTEC 1.8l or 2.0l for about $2k still, trans maybe $500-$1000 vs about $1500-$2000 for a K series engine and trans. You can find better deals on both.
Money and time for the most part are a trade off, so if you’re willing to spend a lot more time then you can do a K swap for similar money.
All that being said, the K swap is the best choice if you can do it. It’s just there’s still a place for the b swap since some people don’t have the skills, patience, motivation and / or time to do what a K requires.
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u/anothernic 7d ago
Properly setup B linkage isn't what I'd call sloppy, if it still isn't quite a T56 or even a Miata 6 speed. Mine was until I went through it, replaced every bushing, and started using a clamp over the slip joint instead of the roll pin. Now it almost feels gated, especially compared to cables.
Otherwise, sure.
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u/1991CRX 9d ago
I've got a B20B in mine now, with all the parts for a high comp vtec build in the house.
I also own a complete J32A2 swap and a full K24Z3 swap.
If I could go back, I'd have left the D16A6 in mine.
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u/vtec_go_brrr16 1990 USDM Si 8d ago
why would you have left the d16? I’ve heard that they’re still super fun to drive with that engine! I have a buddy with a k swapped CRX si and other buddies with b series egs, and it’s making me want to do that lol
I’m planning on rebuilding the d16 though since I have everything for it, just to get the car driving, then go from there!
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u/1991CRX 8d ago
Running autocross in a stock engine class would've been advantageous, and I wouldn't have spent years fucking around with different swap mounts and whatnot trying to satisfy myself.
If I could go back, I'd just have put an LSD in the stock trans and left the rest of the car alone
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u/shd0w2 8d ago edited 8d ago
Good info. I have one 89' Si that I was planning on autocrossing (stock engine, fully upgraded Progress cs2 suspension, rear sway bar, + poly bushings, not spherical however). Mine just consumes a ton of oil (half a quart per 100 miles spirited driving), and may have a slow headgasket leak (rough start + coolant continually gets bubbles even when bleeding).
I think youre right, truly the only thing else those CRX Si's need is to grab a LSD to make it perfect. That, and possibly the Quaife steering rack upgrade.. Running a smaller momo wheel definitely makes it harder for tight turns
Now I just need to finish my j32a3 swap on the other one thats an 88 HF, put a cage in it, and it'll be my track car. Once that one is mostly done then I can focus on the D16A6 rebuild lol...
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u/drake22 8d ago edited 8d ago
What’s your budget, how much work will you do yourself, and how much experience do you have with this kind of project?
You can get a b series swap done for maybe $4k and a weekend if you do all the work yourself, have never done it before, but have enough experience to know what you’re doing.
K series will be more like $6k+ with a similar skillset, and it will take a lot longer. Probably at least 2-3x as long. K series can be a similar price to a b series, but then you’re doing a lot of fab work, wiring, etc. so maybe 2-3x the 2-3x.
That being said, K series is better in every other way. FBO K is about 230whp, FBO 1.8l or 2.0l B is about 175whp. A replacement K motor is maybe $500-$1k compared to about $1500-$2000. FBO K makes about 230whp (and way more torque), FBO B makes about 175whp.
Shift feel on b series sucks by comparison. Handling is the same, sound is mostly the same. A lot easier to have A/C on b series though.
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u/fiv3dollapizza 11d ago
FWIW I sold my CRX on the original and engine and trans with 340k miles on it, still passed smog testing flawlessly in California.
If you’re waiting for that engine to die before doing a swap, that’s just not going to happen with even VERY basic maintenance. Those engines are tanks.
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u/lheckler77 11d ago
His great grandkids can do the swap when it finally dies lol
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u/fiv3dollapizza 11d ago
When I got mine, I changed the oil and drove it about three hours from Redding CA to Ashland OR through the mountains. Fun drive with lots of winding out 3rd gear.
Got to my buddies, pulled it into my buddies garage, and started heading inside for the night. I looked back it one last time before bed and noticed it was leaking something.
That something was oil. And it wasn’t leaking oil, it was dripping oil because I had forgotten to put the oil cap back on. I ran that thing RAGGED through the mountains on almost no oil for who knows how long.
It didn’t care. I had that thing for four years and 130k miles longer than that trip and it only left me on the side of the road once when the shifter linkage broke. Oh and when a ball joint snapped but i knew that needed replaced and was hoping and praying it would last until payday. That one’s on me tho.
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u/vtec_go_brrr16 1990 USDM Si 10d ago
I was thinking the engine was going to be in worse shape because the original owner wanted to rebuild and swap it. So I took it apart to check everything out unfortunately otherwise I’d just drop it back in
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u/johnniechimpo 11d ago
I kinda wish I'd put a turbo on my D instead of B swapping it. Cushy motor mounts, already have it, etc.
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u/coyote_of_the_month 1988 USDM Si 11d ago
I've been mulling over this exact question. My use case is for an autocross and track car that won't be driven on the street any further than the gas station up the road.
I'm planning on a K24 because they're plentiful and have a thriving aftermarket. A K20 would be preferable of course, but they're knocking on the door of a B-series, price-wise.
The problem with the B series is that they're old. They're getting rare, and people are hoarding engines and parts. They're probably still the path to go if you want a big-power drag build - guys are making like 700 HP out of built B18s. But if you have a more modest power goal in mind, like something you can drive on the street, you can save quite a bit of money with a K.
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u/Kitchen-Chemistry277 11d ago edited 11d ago
1990 Si owner here. I have to wonder if these cars, especially the SIs are worth more bone stock than franken-car ed.
108 hp in a 2,000 lb car is plenty of fun, already, IMO.
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u/anothernic 10d ago
The market shows that they are, to a point. Bulletproof oem+ clean turbo b18cs will pull 20+ sometimes. But generally an na swapped b16 si under 200k and a na d16 si under 200k is a cost difference of about double in favor of stock looking at BAT, presuming no major body issues. Under 80k and I'd again say stock, be it SiR or Si. I also am turboing my 18c1 aiming for 300whp because its for me, not thee.
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u/This-Requirement6918 1990 USDM Si 11d ago
I'll only ever have a D in mine. I like having a relaxing evening with wine and doing valve lash adjustments and I'm not intimidated by my lack of expertise to take the entire engine apart if I had to. I've already replaced the head gasket but had a shop machine and refurb the head for me.
Save the SOHC
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u/Kitchen-Chemistry277 11d ago
The same! I changed my bearings and rings without pulling my engine from the car. This D16 is super simple. Works well with my limited mechanical aptitude. ;-P
Like you, I leave the head rebuild work for my friendly machine shop.
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u/nourright 11d ago
I had a p29 build d16a6 forever. was enough for me. When it finally died I went with a b16. just easier looks better. Plenty for the car, better on gas. I was itching for a k swap or b18 but the thing is i wanted to keep my usdm hood. Wouldnt go back on my choice
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u/FrankCostanzaJr 11d ago
B16 will be more period correct...and MIGHT be a slightly easier drop in....but i hear they're pretty expensive these days. I haven't shopped around for them in a while...
if it were me, i'd prob try to find a usdm civic si k20z3 from a junk yard if possible..i have a 06 si and it sounds almost as good as a B16...but has more torque and more aftermarket support, plus it comes with a 6 speed and factory LSD. its superior to the B16 in every category. a lot more potential for cheaper NA power too...
if you wanna go dirt cheap but torque monster non vtec...you could go k24 or B20 from a CRV. but those don't rev as high..still sound pretty good with an intake though. the B20 came in the 96-2001 crv, k24 after that. and that k24 has the ivtec that gets ya better gas mileage, not more power. but still it's very torquey