Not too long ago, we released an article and video covering the Honda K20A vs K20C and a lot of you guys responded pretty positively to that, but the one you guys also asked for a similar piece of content covering the different versions of the K20C.
After all, these two engines are incredibly similar, they’re both apart of the K20 family and they’re both apart of Honda’s new turbocharged engine lineup.
Now what’s this particularly interested is that both of these engines are the only turbocharged K20 engines available in the USA. Overseas Honda also offers a K20C3, but that’s a topic for a different time.
Realistically there are also two versions of the K20C4, one found in the Honda Accord and one found in the Acura RDX.
The differences between the Accord and the RDX K20C4 are so minute that’s it not something we’re going to cover in this. So, for the rest of the article, we are going to refer to the K20C1 found in the FK8 Civic Type R and the K20C4 found in the Accord Sport or Accord EX-L.
Before we get into the real differences between these two engines, we should cover some for the basic information. Both of these engines are 2.0L liter turbocharged engines with an aluminum block, aluminum head, dual-overhead-cams, Honda’s VTEC system, direct injection, a 9.8:1 compression ratio, and both engines are known for being pretty strong.
Different Forms of VTEC
It should be noted that both K20C1 and the K20C4 don’t use VTEC the same way a K20A engine. Where a K20A engine will have VTEC on both the intake and exhaust camshafts with VTC on the intake cam, the K20C1 and C4 only have VTEC on the exhaust side with VTC on both camshafts.
The dual VTC part of the system allows valve overlap to be adjusted at any moment, resulting in much greater efficiency and better performance.
The reason for not having VTEC on the intake side, is that both engines are turbocharged which means they don’t need variable lift on the intake side since the turbocharger will force air into the cylinder and that small extra amount of lift will make no difference.
Power output for the C1 is 306hp and 295lb-ft and power output for the C4 is 252hp and 273lb-ft. If you’re looking at the aforementioned Acura RDX C4, power output is slightly higher at 272hp and 280lb-ft.
Starting from the top-down, we’ll look at the differences in the cylinder head first. Both engines use nearly identical castings and both of them use cast-in exhaust manifold that so many people seem to hate.
One of the most obvious differences between the heads is the different base plates for the high-pressure fuel pump and the C1’s addition of a vacuum pump.
The vacuum pump was likely added to the C1 to reduce oil blow-by since the C1 has a higher redline and runs more boost pressure. It’s also possible Honda added the vacuum pump to help the C1 pass emissions, but it’s hard to imagine that it wouldn’t pass emissions without the vacuum pump.
Another important difference in the cylinder head is that camshafts are different. The difference in camshafts is probably to help the C1’s larger turbocharger spool up faster as well as help the C1 make more peak power.
The power curve of any engine is larger determined by the camshafts, so the C4 probably has camshafts which are designed to help the C4’s smaller turbocharger make more low-end and mid-range power.
The intake valves on the C1 and C4 have different part numbers, however, I was unable to find any information on how they are different. The exhaust valves on the C1 and the C4 are both sodium-filled.
Sodium helps to cool the entire valve which lets both engines run a bit leaner without making the exhaust valves too hot.
The intake manifolds are nearly identical as far as I can tell, and the throttle bodies are the same on both engines.
As far as the direction injection system, both engines are almost completely different, with the C1 having the entire fuel system built around having tons of flow to support the power it produces, and the C4 having a fuel system designed for improved fuel economy and efficiency.
The high-pressure fuel pump, fuel rails, and injectors are different between both engines.
Arguably the most important difference is the different turbochargers. Since the K20C1 is designed for use in a high-performance application, it has a larger turbocharger that is capable of producing more peak power. On the C1 you’ll find an MHI TD04 turbo and on the C4 you’ll find an IHI RHF5 turbocharger.
The smaller turbo on the C4 helps provide more low-end and mid-range power, ultimately making more usable power since you aren’t going rev your engine to redline all the time on the streets. Unfortunately, the smaller RHF5 turbocharger on the C4 becomes a big limiting factor when tuning.
You can push a small turbo like the one found on the C4 to spin faster and make more peak power, but you’ll end up with superheated air temperatures which pretty much negates any increase in boost pressure and will greatly reduce the life of your turbo.
You’ll see this same issue on many Ford Ecoboost engines which also use very small turbos like the K20C4.
Of course, since each engine is packaged into different platforms, they have a unique intercooler and intake piping, however, the intercooler cores are very similar as far as sizing.
Cylinder Blocks and Internals
Looking at the bottom end, there are some notable differences, but both engines are very strong. Starting with the connecting rods, both engines use forged steel connecting rods according to Honda’s press releases and as far as I can tell, they’re the same part number.
There are reports of the connecting rods being different between both engines, but considering they use the same part number and are identical in the parts illustration, I’m pretty sure they’re the same.
The pistons are different, with the C4 using a pretty common flat-top design with valve reliefs cuts. The C1 pistons use a more complex D-cup dish which is likely done to help reduce detonation since the C1 runs more boost.
Both engines have piston oil squirters which simply spray oil at the bottom of the piston dome to help keep the piston cool.
The crankshafts appear to be different, with Honda referring to the C1’s crankshaft as “ultra-lightweight forged steel” and the C4’s crankshaft as “super lightweight, high rigidity steel crankshaft”
Upon closer inspection you’ll find that both engines have the same part number for the crank and in-fact use the same crankshaft.
As far the blocks go, they’re nearly identical except for the crank position sensor, but they are different part numbers.
Which One is Better?
The summarize all this information remember that the C1 has a bunch of small changes to make it more suitable for a high-performance application. The most notable differences are the fuel system, camshafts, turbocharger, pistons, and tuning.
To put it simply, the K20C1 is stronger and capable of producing more power than the K20C4.
I wouldn’t call them the “exact” same engine as many people and publications have in the past, however, they’re extremely similar and I think it’s safe to say that they’re about 90% the same or more.