The 2018 Honda Accord ditches the V6 in favor of a 2.0-liter turbocharged four-cylinder as its most powerful engine option. It’s been heralded at many outlets—including admittedly this one—as being an Accord with the Civic Type R’s engine. While it is based on that motor, the newly released parts catalog reveals many significant differences that go beyond early reports of a smaller turbocharger and less aggressive tune.
Car & Driver had a chance to speak with Honda chief powertrain engineer Terunobu Kunikane, who shared a few details about the changes they made to update the engine for Accord duty. He stated that the pistons, turbocharger, fuel system, and tune were some of the main changes made but the newly released parts catalog reveals that the engines are significantly different.
We can go even deeper into the catalog to find out what’s different and if it’s possible to tune the Accord to Civic Type R power levels.
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Starting from the bottom of the motor, the first difference we see is that the Accord oil pan has a lighter casting and a much smaller baffle plate. This is likely a move to save weight since most Accords won’t see time at the track that would require the level of oil control that we see for the Type R.
The cylinder block castings and accompanying parts appear to be the same except for the crank position sensor and cover. Even though they look the same, the Accord block lists for $996.32, while the Type R block is actually cheaper with a list price of $922.74.
The crank position sensor differences are explained once we look at the crankshaft and piston diagram, which shows that both engines uses the same exact crankshaft but each has a unique crank pulser plate,which is to count the number of engine revolutions.
The chain drive sprocket, the bearings, and thrust washers are shared between the engines, while the crankshaft pulley is not.
The differences in the the pistons are confirmed by the diagrams. The Accord piston is a fairly standard flat top design with valve reliefs cut into it while the Type R piston shows a more complex D-cup dish which is likely necessary to reduce detonation for the more aggressive tune. The changes to the Type R pistons are not cheap as they list for $216.67 which is five times more than the list price of the Accord pistons.
Both engines use the same piston wrist pin which means that the pistons could be interchangeable but the connecting rods are different, with the Type R units being almost twice to cost of the ones found on the Accord.
The cylinder head castings are very similar, and show the cast-in exhaust manifold along with rockers and valve guides that are exactly the same across both motors. The most notable differences are seen in the base plates for the high pressure fuel pump and the addition of a vacuum pump on the Type R engine which is not present in the Accord.
These types of pumps are used for various purposes ranging from emissions reduction to performance improvement and in this case they are likely used to provide better piston ring-sealing in order to reduce blow-by.
Each of the engines has a unique set of cams, but the the cam gears and the rest of the chain drive are almost entirely the same. The other notable difference is that the cams on the Type R appear to have a dowel pin to fix the cam gears while the ones on the Accord do not.
This might be a protection mechanism due to the higher spinning nature of the Type R engine. The valvetrain is mostly shared, but the Type R intake valve is different and lists for triple the cost of the Accord intake valve which likely notes a difference in design.
The intake manifolds appear to be slightly different but based on the shared intake manifold and throttle body gaskets they appear to be constructed in a similar manner with inlets and outlets being the same size. They are also fairly inexpensive with both coming in with a list price of less than $100. The throttle body is exactly the same for both engines.
Honda added balance shafts to the engine on the Accord in order to reduce vibration and make it run smoother. Since these shafts are integrated into the oil pump assembly, the pumps between two engines are completely different. Even with the addition off all of these extra parts, the pump assembly for the Accord is still cheaper than the version for the Type R.
As noted in the Car & Driver post, fueling is different as the Accord system is designed for economy while the Type R system is designed for heavy flow in order to maximize performance. Almost every single part of the fuel system is different, from the high pressure pump, down to the fuel rail, and injectors.
The Type R uses a MHI TD04 turbocharger that is designed for top end power, while the Accord uses a smaller IHI RHF5 unit which is designed for smoother power across the band while maintaining fuel economy.
Almost all of the parts are unique to each turbo including the inlet pipe which is a visible cast aluminum piece in the Type R and a plastic piece in the Accord. Although the pipes do not interchange, the “Earth Dreams” sticker is available separately for about $13 if one wanted to spice up their Accord engine bay.
The intercooler cores appear to be of a similar size but the overall assemblies are different as each unit has unique endtanks, inlets, and outlets. Due to the nature of how each engine is packaged, the piping is different along with the manifold pressure sensor.
The Accord also adds an air temperature sensor on the inlet pipe side which is not present on the Type R. This sensor measure the temperature of air after it has exited the intercooler which can allow for a more granular tune for fuel economy. The Type R appears to use a combination sensor that measures flow and temperature on the turbo inlet side which is common on many turbocharged cars.
There are some other small differences but the rest of the engine is mostly the same across both of the models. The changes made to the engine for installation in the Accord are fairly significant when it comes to tuning, as the Accord engine was not really built with performance in mind.
Changes to the engine programming are likely possible and we will likely see tunes that approach 300 HP at the crank but there will be limits mostly from a fueling and boost standpoint. Since the fuel system was designed for economy, there will be a limit to how much boost can be added before the fuel system can no longer match it without detonation.
The smaller turbocharger will also prove to be a limiting part as adding more boost will force it to run hotter and it will reach a point of diminishing return at some point. The differences in temperature and crank sensors will also be a stumbling block as the differences will likely cause tuners to have to write the software from scratch instead of being able to port the software from the Type R.
The good news is that the intercooler is sized well for any upgrades. so it likely won’t require any changes for a tune. And since the exhaust arrangement on the head appears to be the same, there is a potential to install the bigger turbocharger from the Type R onto the Accord engine.
Hopefully this puts some of the speculation and rumors about the 2.0-liter to rest and gives everyone a good idea of just how different the engines are. And maybe it gives you a useful guide if you want to start messing with it.
Bozi was born in the land of the Yugo but grew up flipping Chevys in the Southeast US. His automotive background ranges from running a used car sales and service facility to building junkyard LS engines and fixing endurance cars. You can find him on Twitter and YouTube.