Let's talk about K-swaps

Also interested in any continued research if people have new information- I've heard horror stories of weird vibration induced gremlins on some K series race cars.  True?  Dumb anecdote I latched onto?

In reply to ¯\_(ツ)_/¯ :

You have to delete the balance shafts and people rev the nuts off them. They destroy dbw throttle bodies and anything w/ no isolators. A lot of people make them work to great effect, but you'll want a paint pen and nut/bolt the car frequently if it's a race car. I'm not sure if it matters as much for a street car that's not going to be reved to the moon as frequently. 

this is good detail but at what point is the K swap too old? I Know B swaps are still happening and have happened for a long time but is the L swap of the current era turbo honda the right approach now? how soon will these junkyards dry up. I fear this is the life of the current EJ series for subarus given the platform changes over the decades. 

In reply to fidelity101 :

They put the K motor in a lot of things and they're good w/ little refreshing and not many changes. I don't suspect we're close to drying up from a motorsports perspective for a while.... The one in my Supra was a straight from the junkyard build w/ a few updates.

This one was built as an endurance car - it's redline was set to 7200 and it made 215whp. No undue vibrations at that RPM and it lasted as is. 

fidelity101 said:

this is good detail but at what point is the K swap too old? I Know B swaps are still happening and have happened for a long time but is the L swap of the current era turbo honda the right approach now? how soon will these junkyards dry up. I fear this is the life of the current EJ series for subarus given the platform changes over the decades. 

The k24 in the CR-V alone accounts for about 700,00+ k series. Supply will be fine for a while

I would love to K swap my wife's Honda HR-V. Some 6 speed AWD and a little turbo action would make that thing acceptable over the 1.8 CVT AWD.

My K swap is still in progress, so I don't have personal experience yet, but the trend in broken K24s seems to be those that are modified for more power and/or pushed at high RPMs.  My intent is simply to enjoy the ~215 HP of stock K24 in my Miata.

Vibration is a thing, but no surprise when the process includes removing balance shafts.  It's a track car, so it gets a full looking over between events anyway...  

In reply to Rodan :

I do have personal experience with the type of build you're describing. I didn't say it couldn't be done, but you have to stay ontop of it - those thing's vibrate like crazy at 7500+rpm. There's a reason the endurance racing car was set to 7200 - if you can get enough power lower down you'll last a lot longer. 

In reply to accordionfolder :

Yes, I have every intention of keeping the revs below 7500.  And I'm putting together with the vibration in mind... witness marks, thread locker, etc.  

In reply to Rodan :

At that level if it's a healthy engine it'll last a long time - everyone likes to rev them to the full 8200 and... that's a lot. 

I've run my stock junkyard K24A2 in endurance racing for a few years with barely a hiccup (one injector went bad), 205 whp, shift at 7k, it doesn't even burn any oil.   The power is enough for what I'm doing, and not having to touch the engine is really nice.  

In reply to Sonic :

Which ECU are you using? And in which car for that matter? 

I'm a big fan of the "find an oe engine that makes more power than you need and then turn it down" recipe. Most people can't build a better motor than a modern factory. 

There are a few companies claiming huge numbers out of NA k24s, like 375 hp.  But I have never seen a dyno chart on them, are those numbers realistic or reliable?  I would like to play with one some day, my last experience was with an element that burned oil & set vtech faults.

In reply to accordionfolder :

I don't remember the ECU code, but it is from an 05 Element, then K Tuner for tuning software.  I put in a 50 degree VTC gear but didn't use the extra range in the tune apparently.  Has basic breathing mods all homemade but a fairly small Accord cable throttle body.  All this was in an EF Civic hatch for most of the run time, now in an EG hatch.   

Why do balance shafts need removed?

In reply to Lof8 - Andy :

For a Miata swap, they need to come out to allow an oil pan profile that fits over the steering rack/crossmember.

Caperix said:

There are a few companies claiming huge numbers out of NA k24s, like 375 hp.  But I have never seen a dyno chart on them, are those numbers realistic or reliable?  I would like to play with one some day, my last experience was with an element that burned oil & set vtech faults.

That sounds like a high strung, short-life motor to me, probably a drag race-only one.  It's expensive to build once, and then you get to do it again when it wears out quickly.

Low 200s seems to be what most people get out of a K motor when they're looking for a motor with the kind of life and manners that you could drive it on the street.  It's true of either K20 or K24, IIRC it's the same head so makes the same top end power, but you get more torque with the K24).

Rodan said:

For a Miata swap, they need to come out to allow an oil pan profile that fits over the steering rack/crossmember.

They also cost you a fair chunk of power, I believe.

In reply to codrus (Forum Supporter) :

I wouldn't be surprised if removing the balance shafts frees up a little power.   Most of the K24s are rated ~200-205hp, and Miata swaps are routinely getting ~210-220 whp.  Exhaust and tuning probably contributes to that as well.

190-220whp NA junkyardable makes my wankel cry

In reply to fidelity101 :

haha - Yeah, that's why it's ubiquitous and a bit annoying at times, but it does work for not a lot of money. It isn't as easy as the internet makes it seem, but definitely a well documented swap. 

fidelity101 said:

190-220whp NA junkyardable makes my wankel cry

I just bought a 2011 civic si to play around with, and it's very annoying how much better this engine is than the duratec lump in my NC miata. I struggled to get 170whp on that with full bolt ons and tuning, but the K20 can hit 200-220 and parts are cheap. The K wipes the floor in terms of usability too, the stupid thing is as smooth as 1500rpm as it is at 8200. 

I have so many questions...why is it so good? Why can it still rev past 8k with a balancer? Why doesn't it shake when lugged? Why do other manufacturers even bother building I4's when they should use honda engines under license? Why didn't I get one of these a decade earlier?

The "secret" with K motors is the head.  They flow extremely well.  And with a CNC port (aka 4Piston) they do even better.  Also in the head is the second gen VTEC system with phasing on the intake.  Low rpm cam gets you the driveability and torque, while the cam advance fixes the emissions.  High cam gets you all the power the head can take.

As for NA power #'s, they've gone up over 450hp now.  Here's some off-the-shelf builds: https://4pistonracing.com/collections/complete-engines

That 400hp motor is a 2.5l, which is a bored out K24.  If you stroke it, you can go to 2.7l and get 480.  I've seen a legit dyno chart of one making over 500.  Lots of little details to get there.

From a grassroots standpoint, the sweet spots are these:

1) Basic bolt-on/tuned K24A2 225hp.  06-08 USDM TSX motor with K20A2 oil pump and cam phaser (50VTC).  Needs good intake/header/exhaust/tune.  Drag Cartel DIC's will add another 10 hp easily.

2) Built K24/K20 Frankenstein 265-280hp.  High compression forged pistons/rods.  Big cams. K20 head.  CNC ported head will support 10-15 more if your compression is high enough and the rest of the build generates it.

12.5:1 compression can be tuned to run on 93 premium w/o knock.  E85 can support upwards of 15:1.  These motors LOVE compression. 

I have lots of dyno charts I can share for the value of various mods.  It all has to work together to get maximum value.  I also have boxes of shiny blown-up "Gifts to the God of Speed".  Many lessons learned.

One more thing on builds...

Awhile ago I realized that Honda was selling brand-new, perfect bore blocks and cranks for cheap (assuming you aren't paying MSRP).  You take an 03 Accord block, add in the crank (which is now the superceded and superior R40 part) and you now have a perfectly machined base for a build.  Select a piston/rod combo for the desired compression and put it all together.  Very easy.

Somewhere along the line, 4Piston picked up on this and started offering the same thing ==> https://4pistonracing.com/collections/short-blocks/products/4p-k24-in-stock-short-block

They will also sell you a completely brand-new 300+hp engine, nothing machined or used, for under $10K. 

In reply to Andy Hollis :

What engine management do you use on your K swapped cars, and why did you choose it?  Thanks!