Extreme Engine Tech: Building the Ultimate K24 Part 1 The Cylinder Head!

by Mike Kojima

Modding late model Honda/Acura engines is somewhat problematic lately.  Take for instance the late model K series engine.  Once probably the best naturally aspirated inline four cylinder production engine by far, the K motor in its latest variant, the K24Z7, is a neutered, decontented version of its former self.  Found in the current 2012 and up Honda Civic Si and the Acura ILX, the K24Z7 still boasts a decent 205 hp and 174 lb ft of torque. This is slightly better power and much better torque than the much acclaimed bone stock K20A2 that everyone knows and loves.

However, the modification potential of the K24Z7 is infinitely less than the older motor.  The new engine loses Honda's famed VTEC system on the exhaust cam side and even worse, has a very inefficient log type exhaust manifold cast as part of the cylinder head.  These production changes were probably done to reduce the cost of the engine and improve emissions. Making torque and power through gains in displacement and sacrificing the free revving goodness that the K engine was known for.

The K20A2 was known for its ability to become a 250 whp all motor street screamer with bolt on parts and make gobs more power NA with internal mods.  With a 2.4 liter bottom end it was possible to make nearly 300 NA whp on pump gas with daily driver niceness.  When turbocharged the engine could produce 400-550 hp in very super streetable pleasant to drive form on pump gas. 

Now the question is, can we do this on a late model engine with off the shelf, easily obtainable parts without any exotic work and one off custom parts? We think so and we asked the folks at Motovicity to help us.  If you didn't know, Motovicity is one of the largest wholesale distributors of performance parts in the country with an extensive inventory of performance parts in stock. 

We pitched our idea at them, to build the ultimate late model K motor with these constraints.  It had to be streetable, built for pump gas, no E85 or race fuel dependent compression ratios or turbo selections, The engine had to be built to be responsive with decent bottom end and manageable turbo lag.  We are talking about power that is in by 3000 rpm and strong till 7500 rpm, not a turbo that is just getting started at 5000 rpm and inefficient until you hit 20 psi. 

Most of all it had to be built with off the shelf parts, no exotic and custom parts that take months to come, costing mega dollars and are often the downside of building really big power engine. Motovicity not only thought this was a great idea but also opened their entire inventory for us to pick and choose from.

So remember, this isn't the ultimate import drag race big power build but it is the ultimate obtainable and daily drivable build.  Check it out!


When You're Done Read Part 2 and Part 3 of the Build!


We started our build with brand new parts fresh from Honda.  In retrospect, this probably wasn't the most practical way to do things because when you buy a head from Honda, it is not a complete head but a bare casting that you have to buy a bunch of separate parts for.  Not an inexpensive process at all.  For the average person, It's cheaper to work with complete assemblies sourced used.  The first thing that had to go was the stock K24Z7 head with the integrated log exhaust manifold and no exhaust side VTEC.  Although you can easily and effectively turbo with the stock head, we wanted to run an efficient turbo manifold to get the most out of our engine.  We initially considered the K20A2 head but were concerned about having to deal with oil passage and head gasket compatibility for the VTEC system which controls lift, duration and phasing of the intake cam unlike the stock head that has VTEC and variable phasing only on the intake side.  Although this isn't too big of a deal for us, we wanted to meet our goals with an easy bolt on approach. For an easy bolt on, we chose the K20Z3 head.  This is the head found on the 2006-2011 Honda Civic Si. It has VTEC on both the intake and exhaust with variable phasing on the intake side. Another good thing is that it has a conventional exhaust manifold so we can bolt up a trick 4-1 tubular turbo manifold.
The K20Z3 head has the good flowing intake ports that the K series engine is known for.  Good flowing ports will enable us to reach our turbocharged power goals without expensive and time consuming porting and head work.
The combustion chamber is a fast burning low included angle design that is very beneficial for turbocharging. The valve seats are hardened which is great for the Supertech Inconel exhaust valves we will be running. The head's valve seats are pre machined and ready to go but we will be having Portflow Design do a performance valve job with a radiused seat and a deep throat cut. Although is isn't a fully ported head, it is about the ultimate flowing valve job and perfect for what we want to do with our streetable turbocharged engine. 

Here is a quick video Portflow took of them machining our head on the super bad ass Newen valve seat machine.  The Newen cuts a smooth radius as a CNC machine doing away with conventional cutters.  You can program any valve seat contour and the Newen cuts it.  Portflow uses the Newen to blend the valve seat into the port, then cuts a smooth continual radius to the seating surface. This flows way better than any conventional multi angle valve job.  A good valve job is about 50% of the flow increase potential on a K motor head.
Here is a closer look at how the Newen cuts a continual smooth radius from below the valve seat, blending the valve seat to the port, up to the valve seating surface itself.  An amazing valve job that is difficult to replicate by hand.  It is done with 100% repeatability quickly.
The exhaust ports are the good flowing K engine tunnels from years gone past without the dumb integrated exhaust log manifold of the current engine.  Turbocharging will more than make up for having stock ports.  There isn't a lot of good information about how this lash up of head to bottom end works as there are a grip of different K motor variations on the net so we will find out!
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Posted in: Magazine, Tech, Engine
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Monday, May 25, 2015 10:45 AM
"For an easy bolt on, we chose the K20Z3 head. This is the head found on the 2004-2008 Acura TSX."

The K20Z3 head has more VTC adjustability and better flow than the K24A2 head that you guys are speaking of.

The K20Z3 is from the 06-11 Civic Si's.

The K20Z1 is from the 05-06 RSX Type-S.

K24A2 comes in two forms. I think it's the 08 and up TSX motors (K24A2's) with bigger camshafts.
Monday, May 25, 2015 11:47 AM
I was hoping for an all motor build that didn't involve swapping heads. But I guess tons of people probably already did that.
Mike Kojima
Mike Kojimalink
Monday, May 25, 2015 12:21 PM
An all motor would suck with the integrated log manifold. It would be difficult to get much more power beyond bolt ons.
Mike Kojima
Mike Kojimalink
Monday, May 25, 2015 12:24 PM
We are running the K20Z3 head.
Der Bruce
Der Brucelink
Monday, May 25, 2015 4:15 PM
Classic MotoIQ people!

I was really hoping that last paragraph was going to say something about being dropped in a new project Lotus or super lightweight EK, or maybe even a TSX, but I might just have to enter to win!

In depth and great!
Monday, May 25, 2015 7:30 PM
I was hoping this would show me some effective upgrades to my K24Z7. It was pretty a pretty expensive buy at ~$22k, but it did come with a free Si. I think this is a little beyond what I was planning. Good stuff to see, though.
Mike Kojima
Mike Kojimalink
Monday, May 25, 2015 7:47 PM
The head, a good header and cams with an ECU like a Hondata will really wake your car up.
Tuesday, May 26, 2015 7:42 AM
I'm extremely ignorant on this car - can the factory ecu handle the ex cam vtec on the z3 head? Using the hondata flashpro, of course.

We have the annual obdII plug-in testing here in Houston. Simplicity is key.
Tuesday, May 26, 2015 7:49 AM
I love how we're getting two engine builds, from opposite directions. A block up S52 and a head down K24.
Mike Kojima
Mike Kojimalink
Tuesday, May 26, 2015 8:07 AM
It uses one solenoid for the Vtec and one for the VTC so yes.
Tuesday, May 26, 2015 10:16 AM
Cool build Mike, and great article..!
Wednesday, May 27, 2015 9:20 AM
Any particular reason why assembly lube wasn't used to lubricate the parts during assembly? I've had good results using both assembly lube and standard engine oil, but I'm curious to know as to why Howard chose standard engine oil for this build.
Wednesday, May 27, 2015 9:30 AM
Maybe it's just something fairly heavy, like 20w50?
Mike Kojima
Mike Kojimalink
Wednesday, May 27, 2015 10:18 AM
Because oil works fine?
Wednesday, May 27, 2015 10:35 AM
I'm assuming this gets pre-lubed with the oil pump or an external pump before first startup?
Shane Laake
Shane Laakelink
Thursday, May 28, 2015 10:29 AM
I never realized cam shafts were still made from iron. Is this common? Seems heavy.

Great read btw
Thursday, May 28, 2015 10:50 AM
Good wear characteristics, easy to machine and grind, easy to cast, and cheap. That's a hard recipe to beat with most other cost effective materials.
Friday, May 29, 2015 6:14 PM
What does the lost motion plunger do?
Wednesday, June 03, 2015 7:33 AM
It provides preload to the center rocker arm when not in VTEC.

Nice article, whoever wins this is extremely lucky.
Wednesday, June 03, 2015 10:59 AM
Whoever wins needs to wrap a Caterham around it.
Mike Kojima
Mike Kojimalink
Wednesday, June 03, 2015 11:53 AM
I have lost plenty of engines to balance shaft failure even in mild performance use so I feel that this is a very prudent thing to do.
Tuesday, June 30, 2015 6:22 AM
what do you have to do in order to have the perfect connection matting the block and head together successfully?
Wednesday, December 30, 2015 8:45 AM
Awesome project Mike, Nice to see the oems leaving bolt patters the same so you can make frankensteins like this
Wednesday, December 30, 2015 10:33 PM
Concerning the balance shafts and all that, why does Honda not have a cross plane crank? I.e., a crank where the con-rod ends are at 90 degrees to each other?
Mike Kojima
Mike Kojimalink
Thursday, December 31, 2015 12:40 AM
All production inline 4's that I know of in cars are flat cranks. The only production in line 4s I know of with a cross plane crank are Yamaha R1 motorcycles.
Thursday, December 31, 2015 6:19 AM
@Wheelz: Pimary vibration gets a lot worse with a cross plane 4, unless you go to very high RPM. That's the reason most applications use a flat plane. Secondary vibration is better at very high RPM with a cross plane 4, which is why the YZF-R1 uses it. It also uses balance shafts to help with other effects from odd firing order because of the cross plane config.
Mike Kojima
Mike Kojimalink
Thursday, December 31, 2015 11:37 AM
In MotoGP the cross plane cranks supposedly had power delivery characteristics that were an advantage.
Saturday, January 02, 2016 1:50 AM
The crossplane for the yzfr1 was develop to create a more linear power delivery. A regular flat plane inline 4 on a motorcycle has the power pulses to far spread out for going through turns. They wear out the tires faster and with the spacing of the power delivery, you cannot get back on the throttle as fast as a crossplane. I've ridden lots of bikes and the crossplane is definitely the smoothest going through turns.
Saturday, September 03, 2016 4:36 AM
@RotaryKnight- it's actually the opposite- the flat plane I4 essentially "smears" power delivery; crossplane makes the power delivery "lumpy" which helps the rear tire dig and make more power. These little things add up at 0.5hp/lb.... ha, that's like 1500-1750hp in a normal car.

Mike Kojima
Mike Kojimalink
Saturday, September 03, 2016 10:49 AM
On cars, the flat cranks were found to help traction and it was something from the 90's and early 2000's that helped Ducati among others but with the advent of the electronic era of bike racing the cross plane crank was found to be an advantage.
Anonymous User
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Tuesday, September 06, 2016 10:42 PM
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