The Temple of VTEC Asia Short Technical Overview Series

Honda's R20A Engine for the New CR-V

When Honda launched the new CR-V for the asian market, they surprised fans by replacing the K20A engine that powered the out-going 2nd gen CR-V with the new 2.0l R20A SOHC i-VTEC engine. This engine first debutted on the JDM Honda Stream and is a stroked version of the 1.8 R18A SOHC i-VTEC engine that was introduced with the new Civic. While JDM and U.S. versions of the CR-V features the K24A DOHC i-VTEC engine, the R20A was chosen for asian CR-Vs specifically to cater for what Honda deems as the unique requirements of the Asian market. Nevertheless, the fact that Honda chose a 'single-cam' R20A to replace the 'twin-cam' K20A of the out-going CR-V have raised quite a lot of talking points amongst car enthusiasts. Hard-core Honda enthusiasts will of course know well by now that a SOHC engine, especially one designed by Honda may not necessarily loose much - if any - even in a direct comparison against a DOHC engine. This is especially true for specific applications, some of which will even favour a SOHC engine over a DOHC. The L-Series that powers the City and Fit/Jazz is a very good case in point.

In the media-drive event that accompanied the launch of the CR-V, Honda Malaysia brought in the R&D engineer who was primarily involved with the R20A engine to conduct their technical presentation of the CR-V. This proved to be a very good coincidence and needless to say I quickly grabbed the chance to have an in-depth discussion with the engineer on the R20A engine as well as the rationale behind the decision to choose the R20A for the new CR-V.

In this tech overview, I will take a look at the R20A and its design features, using materials and information that often may not be available elsewhere. This is because I had the opportunity to spend close to a hour with the R&D engineer in an informal environment, discussing the merits and disadvantages of the R20A, in its specific application on the new Honda CR-V. Armed with knowledge from that session, in this article, I will try my best to highlight the technologies and innovations that have gone into the R20A engine. At the same time, I also hope to be able to explain Honda's rationale in choosing this engine to power the new CR-V, rather than continuing to use the K20A.

Horses For Courses

When the new CR-V was launched here in Asia, I received numerous feedbacks from car owners and even some Honda enthusiasts questioning the replacement of the K20A with the R20A. The K20A is of course an excellent engine and this makes its replacement all the more painful to Honda enthusiasts used to the excellence of Honda's DOHC VTEC engine. I put forward these feedbacks to the Honda R&D engineer as part of my attempt at passing customer - especially Honda fans - feedback to Honda R&D. Because of this, he made an extra effort to try to explain to me the rationale behind Honda's decision to replace the DOHC K20A with the SOHC R20A.

In a nutshell, the R20A is chosen to power the new CR-V from the viewpoint of it being a total package. The keyword is the fact that the CR-V is an SUV, with the base version not having any sporty-biased high-performance pretensions at all. It is a case of clear market segmentation. For Asia, Honda's target market means that they do not expect CR-V owners to demand high-power, high-revving capability that perhaps a Honda Civic owner might demand (for e.g.) Intended - and expected- usage of the CR-V will typically involve family-based outings, trips to the DIY shops, maybe even a little bit of off-roading and similar activites - with no-one really expected to be taking the CR-V to the race-track for a weekend 'track-day' or for some drag-racing. So high-performance from the angle of 'sporty' is not a pre-requisite when Honda sat down to decide on an engine to power the new CR-V. But make no mistake, from Honda's point of view, the R20A is 'high-performance', but this is from the viewpoint of it powering an SUV - and the sensible and expected application of such a vehicle. Thus the R20A is chosen because it has a good balance of virtues - good driveability for typical SUV driving conditons balanced with good fuel economy, reliability and ease of maintainance, and a more compact size and lighter weight. As such, the R20A as a package, offers the better compromise of power, fuel economy, size, weight, complexity and ease of maintainance.


Being the same series, the R20A exploits the same SOHC i-VTEC implementation as the R18A. For a thorough discussion about this new VTEC implementation, refer to our special TOVA Technical Overview of the R-Series SOHC i-VTEC implementation.

To briefly recap, in terms of the camshaft/valve-train, this implementation is basically that used in the 'power' SOHC-VTEC implementation of the old D-Series, e.g. the 130ps SOHC VTEC D15B used on the EG and EK Civics. However, Honda R&D engineers brings a new twist to this implementation. In the old D-Series implementation, a middle cam-lobe works on the intake valves and offers higher valve lift and longer opening duration, to generate more power at high rpms. In the R-Series i-VTEC implementation, the middle cam lobe is again bigger than the standard cam-lobes. However it is now an 'economy cam' lobe instead. In an unusual reversal of roles, by making the intake valve opening duration extremely long, the lobe holds the intake cam open way into the piston up-stroke portion of the cycle. In operation, this will expel a portion of the air-fuel mixture back into the intake manifold. It's like overfilling a bucket with water and then pouring away the excess fluid in order to get just the amount we want.

With this technique, the desired amount of air-fuel mixture is obtained in the combustion chambers without the need for an almost closed throttle butterfly. In fact, the throttle body butterfly can be kept fully opened and is effectively dispensed with, in the SOHC i-VTEC economy mode. This reduces pumping losses significantly and improves engine efficiency and thus fuel economy.

Technology Overview

On to the rest of the engine. In terms of construction, the R20A and the R18A are basically similiar except for some detailed changes. Both engines shares the same cylinder head and valve train and according to the R&D engineer, apparently even their camshafts are similar as well. The R20A block is slightly different from that of the R18A as the R20A comes with a balancer shaft and so its block will have additional casting for the balancer shaft.

Both R20A and R18A in fact shares the same pistons. The crankshaft and con-rods are of course different due to the longer stroke of the R20A. A additional difference in the crank is the use of steel 'shims' or crankshaft braces on the R20A compared to aluminium ones on the R18A. This is for added strength and durability, to counteract the extra stress from the longer stroke of the R20A.

Like the JDM Stream. the CR-V's R20A features a variable intake manifold with 3 stages of operation instead of 2 on the R18A. The use of 3-stages is for smoother torque delivery. However, the settings on the CR-V's R20A are different. Additionally the CR-V's R20A features an additional refinement. The Honda R&D engineer drew a chart for me from which I made the diagram on the left. 1st stage starts with the intake runner length setting at 'short' and changes over to 2nd stage 'long' runner settings at 3,200rpm. 2nd stage changes over back to short runner settings, the 3rd stage, at 4,700rpm. The CR-V's R20A features an additional refinement in the engagement of the 1st and 2nd stage, with a variable changeover based on throttle position. With TPS of 75% and above, 1st stage is engaged from 0 up to 3,200rpm. For lower TPS values, 1st stage is not activated and 2nd stage is used all the way from 0 up to the changeover to 3rd stage at 4,700rpm.

A variable intake manifold is also used on the out-going CR-V's K20A engine. While the K20A uses rotating ball valves to switch between the long and short intake runners, the R20A reverts back to the more traditional butterfly valves. The activation of the butterfly valves are by hydraulic pressure but is controlled by the ECU (obviously as 1st stage is dependent on both engine rpm and throttle position). In the standard 'long' runner setting, the butterfly valves are closed. The intake air from the throttle body and plenium now takes the 'long way' around, flowing through the curved intake runners to the intake valves. In 'short' setting, the butterflies are opened up. This provides a 'short-cut' for the intake air to by-pass part of the intake runners on its way to the intake valves. During the launch of the CR-V, Honda Malaysia had a cut-away R20A engine as part of the display. This had a cut-away intake manifold as well which Honda had thoughtfully coloured the inside of the intake runners blue. The photo of the cut-away intake manifold on the right clearly shows the intake manifold design, the butterfly valves and how they combine to create the short and long intake runner configurations.

Variable intake manifold designs such as this typically makes use of the resonance effect. When the intake valves opens and closes, it causes pulses to be produced in the intake mainfold. These pulses are effectively sound waves, produced at different frequencies depending on how fast the intake valves opens and closes, which of course directly depends on the engine rpm. So at different rpms, a slightly different frequency of sound waves is induced in the intake manifold. By varying the length of the intake mainfold runners, two different resonance points can be produced to cater for the different sound waves produced. When a resonance is acheived, high pressure points are produced right at the intake valves so when they open, more air can be pushed into the combustion cylinders leading to better filling of the cylinders and of course more power.

While good for power delivery, the sound waves and resonances in the intake manifold also produces noise. So like the R18A, the CR-V's R20A has similar 'sonic tuning' implementations in the intake (air filter) system to dampen the noise from the induction resonance and for the R-Series to also deliver a better sounding engine note especially at WOT.

The R20A's ECU is mounted on engine bay for advantages of shorter wiring harness. It is sealed by a special epoxy for protection against heat and contaminants from the engine bay. In the engine bay, the R20A is mounted very low. This is mainly for the benefit of a low Center of Gravity (CoG) but is also because that's the only way to get the driveshaft to the level of the driving wheels and so avoid excessive drive shaft angles. Remember the CR-V is a pretty tall vehicle.

The 'real-time 4 Wheel Drive' (rt4WD) system is basically the same implementation as that on the out-going 2nd Gen CR-V. To recap, this system makes use of a viscous coupling clutch to transfer power to the rear differential. It is 'real-time' in the sense that it engages only if there is a speed differential between the front and rear wheels. With real-time 4WD, the CR-V functions as a FWD under normal driving conditions. Under tougher conditions, if the front wheel breaks traction, it will be spinning faster than the rear wheels. When that happens, the viscous clutch has a hydrualic circuit that engages the clutch plates to transfer drive to the rear wheels. On this new CR-V, the viscous clutch has been improved to transfer an extra 20% torque to the rear when the front wheel begins to slip under the same conditions. Max distribution of torque between front and rear wheels is still 50:50.

The R20A is mounted in the engine bay with new improved engine mounts. There are two new 'torque-rod' engine mounts, one on top-left (where the timing chain is) and one behind the engine (where the exhaust manifold is). The remainder 2, for side and transmission are also new designs with increased body structure rigidity. The new torque-rod mounts features a 2-stage 'double vibration insulator' which works on two planes - both horizontal and vertical. This offers superior damping over the older mounts and insulates against vibration from the engine getting into the driving cabin during driving. With the new engine mounts, the amount of vibration from engine that is transfered to the cabin has been reduced from between half to less than 1/3 over the engine's operating rpm range.

The R20A is mated to the same '2nd generation' 5AT gearbox as the R18A on the Civic. This gearbox features 5 gears with ratio optimized for the CR-V. Another feature of this gearbox is its new 4-pinion open differential. Meanwhile the gearbox's casing rigidity, gear transfer capacity, bearing capacity and gear capacity have all been improved. The gear ratios are 2.785, 1.684, 1.128, 0.772, and 0.592 for 1st, 2nd, 3rd, 4th and 5th respectively. Reverse ratio is 2.000 and final drive is 4.500.



On paper, the new R20A engine actually fares pretty well against the out-going K20A engine - in the context of the CR-V (i.e. R20A as used on the new CR-V versus the K20A as used on the 2nd Gen CR-V). Both engines are approximately 2.0l in displacement, the R20A being 1c.c. smaller at 1997c.c. compared to 1998c.c. for the K20A. While the K20A was a square configuration (bore and stroke are equal), the R20A on the other hand is a greatly under-square design, with bore and stroke at 81.0mm X 96.9mm. By general rule of thumb, an undersquare configuration will offer superior low and mid-range torque compared to the square configuration, with some compromises in power delivery at high-rpm. Both the K20A and R20A offers a variable length intake manifold and both engines are tuned for smooth torque and power delivery rather than outright max power. Then the R20A also has the benefit of the new SOHC i-VTEC mechanism that offers excellent fuel economy during light throttle cruising conditions.

In terms of specifications, the R20A again compares quite well to the K20A. It delivers a max power of 110kW or 150ps at 6,200rpm with a max torque of 19.4kgm at 4,200rpm. The 2nd gen CR-V's K20A for the Malaysian domestic market meanwhile was rated 156ps at 6,500rpm, 6ps more but with the same max torque of 19.4km at 4000 rpm. However, note that this is for the Malaysian market and for most of ASEAN, the 2nd gen CR-V was actually rated at the same 150ps as the R20A. Thus, 2nd gen CR-Vs in Thailand, Singapore and so forth were all rated at 150ps instead of 156ps. But single figures like max power or max torque don't tell the whole story of course. With the R20A, Honda engineers has been particularly successful in exploiting the advantages of the undersquare design to deliver an overall better midrange torque/power delivery than the K20A. The chart on the left is cropped from a photo of one of the presentation foils of the technical overview that was presented to us (media) during the new CR-V launch as well as the media test-drive. Note how the torque curve of the R20A is smoother than that of the K20A to the extent that the R20A actually delivers slightly superior torque in the crucial areas of the mid-range rpm band. Bearing in mind the R20A CR-V is only offered with a 5AT, a superior mid-range is more important than outright top-end power and this is exactly where the R20A wins over the K20A in terms of power delivery.

With regards to performance, the R20A also has an advantage over the K20A in that it is now mated to a five speed automatic gearbox while the K20A had to work with a 4AT. The extra gear allows a much better spread of the ratios over the effective rpm range and with the new CR-V's overall kerb-weight being maintained the same 1540kg as the 2nd gen CR-V, the R20A actually drives the new CR-V better - stronger drive in the low gears but more relaxed in the high gears especially in cruising conditions. We will be talking about how the new CR-V drives and performs, in detail, in our forthcoming review here on TOVA.

May 2007
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