The Temple of VTEC Asia
Short Technical Overview Series

Honda's new R18A Engine

After briefly covering the new K20Z engine for the Asian Domestic Market, we now take a similar look at the new R18A engine that was launched with the new 8G Civic. This R18A engine is a more 'univeral' engine in the sense that it is being used in the new Civic throughout the world and not just Asia alone. There is likely tons of technical information on this new engine in car publications and internet sites all over the world. However as the materials for the R18A in this article are derived from the same technical overview presentation which the K20Z review was based on, this article may hopefully contain new and useful information for the reader who might still be seeking R18A information. As with the K20Z article, a similar comment applies to most of the photos in this artcle, with regards to their (lack of) quality and alignment.

In the technical presentation, Honda calls the R18A their "all new 1.8l i-VTEC". The engine is designed to work in conjunction with the new 5AT gearbox and like the K20Z also features Drive-By-Wire as part of its key technological features.

i-VTEC - "Same but Not The Same"

While there's much 'reputation' to be gained by being first on the block (i.e. being the first to publish a technical overview), doing this article at so late a time (after everyone else has more or less published their 'reference' review on the R18A) did allow me to make an important observation. This is that there seems to be some confusion about the i-VTEC mechanism on the R18A. Many seem to continue to think that i-VTEC on the R18A functions in a similar way to the VTEC mechanism in the original SOHC-VTEC engines like the D15B or D17A. This is not completely accurate and I hope I can correct this with this technical overview series.

The new R18A engine is a 16-valve SOHC design with a new 'i-VTEC' mechanism. This new i-VTEC mechanism is a cause of much confusion amongst even hardcore Honda enthusiasts. Basically when i-VTEC was first launched by Honda, they made a statement that i-VTEC = VTEC + VTC". This however is not true when applied to the R18A. As a SOHC design, it is not a trivial matter to implement an effective VTC mechanism to the R18A, not the traditional VTC which seeks to optimise intake and exhaust cam opening overlap. This is because a SOHC head uses a single camshaft for both intake and exhaust valves so the VTC's mechanism of rotating the camshaft on its axis will not work as it will affect both set of valves. So the important thing to bear in mind is that on the R18A, i-VTEC does not equal VTEC+VTC. There is no VTC and thus no continous variation of intake and exhaust valve opening overlap. The i-VTEC mechanism basically is similar to the SOHC-VTEC mechanism on the D15B and D17A of old. However, this is where the similarity ends. i-VTEC on the R18A does not merge two torque/power curves together. Rather it switches the R18A engine between two entirely different modes, a normal 'power' mode and a fully docile 'economy' mode. Furthermore, when and whether to switch is not determined by simple parameters like engine rpm alone but rather by a combination of parameters, most importantly parameters used by the ECU to decide if it should 'open' VTEC or not. So the 'i' in i-VTEC actually stands for 'intelligent' meaning a new generation of SOHC-VTEC which responds to actual road and running conditions, rather than the traditional one which works more or less mainly on engine rpms alone. VTEC on the R18A does not always engage - if the proper conditions are not reached, the engine might never enage VTEC at all.

This article is not the best place to dwell into intricate details about the new i-VTEC implementation as it's done on the R18A engine. To fully explain the R18A's i-VTEC implementation will take up too much space and detract from the original objective of this article which is a full technical overview of the engine, not just the i-VTEC mechanism alone. Meaning while the R18A spots 'i-VTEC' prominently, i-VTEC is not its sole technological showcase. The whole engine is actually a showcase of state of the art thinking and technology. A planned follow-up technical overview article will do a much better job. In that article, I will be using materials supplied by Honda for this purpose. i-VTEC on the R18A represents a whole new way of thinking and is truly a step forward. However in this article, we shall focus more on the overall technical detials of the new R18A engine.

Design Objectives

Like the case with the K20Z, the Honda R&D engineers clarified their design objectives for the new R18A engine in the technical overview presentation. The R18A is described as an 1.8L i-VTEC '4V SOHC' with a 'new' i-VTEC implementation. These objectives for the R18A are

Responsive Acceleration :
and "Torquey performance thruout the rpm range'

Naturally the baseline for comparison was the 1.7l SOHC-VTEC D17A engine in the outgoing 7G ES-Civic. Recall that this engine delivers a max power of 130ps and a max torque of 15.8 kgm from a 1.7l SOHC design using the traditional 12V/16V VTEC mechanism. The new R18A engine, with an additional 100 c.c. of engine capacity and exploiting new technologies delivers a max power of 103kW or 140ps. This is 7kW or 10ps extra power over the D17A. Max torque is 174Nm or 17.7 kgm which is 19Nm or 1.9kgm more than the D17A. So while the difference in displacement is only 100c.c., relatively the R18A delivers a lot from it.

Similarly with the K20Z, the saying 'a picture speaks a thousand words' applies here with this R18A as well. Honda supplied a similar comparison chart in the presentation, comparing the power and torque curves for the D17A and R18A. However in the PR materials for the R18A i-VTEC, the same chart is available but in a much higher 'publishing' quality. So I used the better chart which is reproduced on the left and like the case with the K20Z clearly shows Honda's objectives and how it has been achieved with the R18A.

Like the case with the K20Z, the focus with the new R18A is 'torque' and its delivery across the rpm range. Looking at the comparison chart on the left, we can see how much more torque and power the R18A delivers over the D17A. In this case, the comparison of the max-torque figure is even misleading as the R18A peaks in torque at a different rpm than the D17A. So the largest increase in torque that the R18A delivers is at its max-torque point and the increase at that point is actually greater than 1.9kgm (around 2.5kgm based on crude visual estimation).

Of greater significance is how the R18A delivers a lot more torque/power than the D17A over the entire rpm range. This starts from the idle rpm and continues on to the redline. Based upon visual estimation, the increase in torque is at least 10Nm. When coupled with the new 5AT gearbox, this translates to greatly improved performance.

This then is what the Honda R&D engineers listed as their achievement for the R18A - (as compared to the D17A) the R18A achieves both power performance and superior fuel economy (more on the fuel economy in the i-VTEC tech overview article later).

Key Acheivements of the R18A engine (Honda's view)

Honda R&D listed 6 key achievements for the new R18A engine. These areas, along with the technologies used to achieve them, are explained in the technical presentation and listed below.

1. Fuel Economy + Power

The R18A delivers a new level of fuel economy but yet more power than the D17A. This is achieved by using the following technologies:

2. Increased Torque

For improved driveability, Honda has been concentrating on torque on their newer engines. Actually more torque at a specific rpm directly means more power at the same rpm but the common term used by car enthusiasts nowadays in that 'torquey' implies more acceleration (due to more power across the rpm range) while 'powerful' can often mean a 'torqueless' engine with all the power coming in at high rpms. In this case, the objective and achievement of the R18A is more torque throughout the rpm range (as compared to the D17A) or alternately and equally as correct, more power throughout the rpm range (take a look at the power chart above to see what I mean).

Specific technologies used to achieve improved torque are listed as

Of the two items, the new variable length intake manifold is one of the core components of the R18A that is responsible for its torque/power delivery so we will take a closer look at this.

Variable Length Intake Manifold

While the R18A does not rely on traditional VTEC mechanisms to deliver a broad torque/power band, it instead exploits the principle of intake tract resonance to deliver more or less the same result - that of merging two different though relatively narrow torque curves together to a combined curve that is delivers high torque across a much broader rpm band. This is achieved from the new intake manifold which features two sets of intake runners (from the plenum), effectively a variable length intake manifold.

The principle of variable length intake manifold depends upon the resonance of air inside the intake tract. Intake tract here includes the intake manifold and the air-filter system, i.e. from the air-filter right up to the intake valves. When the intake valves open and close, they create air pulses which flow along the intake tract. These air-pulses or sound waves are responsible for the intake roar (or noise, depending on who makes the engines). The frequency of the sound waves is determined by how fast the intake valves are opening and closing - how fast the engine is spinning or engine RPM. An engine spinning at 3.000rpm will create a sound wave at roughly 50Hz.

All sound waves will have resonance points which depend upon the frequency of the sound (or alternately, its wavelength). These are known as the resonance frequencies. When the wavelength for the resonance frequency coincides with the length of the intake tract, high pressure points will be created at the intake valves, higher than atmospheric pressure. This will help in the filling of the cylinders. More air means more fuel can be injected and this means more power. So all engines will feature a specific peak in torque (or power) which is influenced by this resonance frequency. For many Honda engines with a standard intake manifold (e.g. the B16A), this resonance frequency is usually around 3,000rpm. This is also why when we replace the standard air-filter with an open element system, we can destroy the mid-range torque of the engine if we do not make sure that we place our fancy new air-filter back in the same place as the original air-filter box of the stock intake system. This is because if we place the filter too close to the intake manifold, by using a very short metal pipe for e.g., we will effectively change the length of the intake tract and thus the resonance frequency it supports (a short intake tract will have a higher resonance frequency).

The principle of a variable length intake manifold, usually with dual runners like the one used on the R18A is that they make use of two sets of intake runners. One set is designed to have a resonance at a lower frequency (or engine rpm) while at a higher rpm, a 2nd set of much shorter intake runners will be used. This shorter intake runner will of course feature a resonance frequency which is higher. So the 2 sets of intake runners will deliver more or less two separate torque peak or effectively two slightly different torque/power curves. By using the same technique as with VTEC, by selecting the right point to activate the 2nd set of runners, we will be able to combine the two torque/power curves together to deliver a single curve which delivers torque/power across a much broader rpm.

One limitation is that dual runner intake manifolds do not have the same 'bandwidth' as that delivered via valve timing. Also the actual length of the intake runners are constrained by physical space so the two torque curves won't be spaced too far apart. So there are constraints to how far apart the two torque curves are as well as how 'wide' an rpm range they cover. Thus while in principle we can deliver the same benefits with variable length intake manifolds as with a traditional VTEC mechanism, in practise, we cannot work across the same very wide rpm range as VTEC. This is partially (not totally) why the R18A does not have a very high redline.

3. More compact dimensions

In pursuit of their "Man Max-Machine Min' principle, Honda has been introducing smaller and smaller engines. The new R18A is no exception and features a more compact size than the outgoing D17A, despite delivering an extra 100 c.c. of engine capacity. Honda R&D listed two areas for this achievement:

4. Quiet Operation

Engine 'noise' at both idle and when operating has been reduced with the R18A which Honda attributes to the use of a new Lower block construction for the engine block.

The new MAF sensors

5. Emissions

Acheiving lower emission levels (ULEV and ZLEV being the target) is the other target Honda has for their new range of engines and to deliver a new level of (low) emissions, Honda has employed the following with the R18A :

  • 2-bed catalytic converter located immediately after the mainfold
  • "Leading-edge" control systems : DBW and airflow sensors

    Similar to the K20Z, the R18A employs MAF (mass air-flow) sensors in the air-filter box as well as the exhaust manifold to supplement the MAP sensor in the throttle body. In the Q&A session, I asked about the rationale in using both types of sensors. Honda R&D says they allow them to meter the air-fuel ratio in the engine a lot more accurately than just using either sensors alone and this is crucial to allowing them to achieve more efficient combustion of the a/f mixture, directly leading to more power, better fuel economy and lower emissions.

    6. Reduced Weight

    Besides being smaller in physical dimensions, the R18A is also lighter than the D17A which Honda attributes to

    1. Aluminium VTEC rocker arms
    2. integrated cylinder head and exhaust manifold (meaning they come casted as a single item)
    3. Plastic head cover
    4. High strength cracked connecting rods. The conrods are now casted as a single piece and then 'cracked' apart at the proper place. This gives a very close contact patch when they are bolted over the crankshaft)
    5. plastic intake manifold, a 'trick' borrowed from the L-series engines

    Some of the parts above, (such as the aluminium rocker arms) also reduce the weight of the internal working components and help in reducing internal power loss.


    Both the K20Z and this R18A engine feature a new Drive By Wire (DBW) system which Honda says allows them to deliver "Exhilarating (throttle) Response" from the R18A engine. A very enlightening explanation was given when Honda R&D showed in the presentation a comparison of the acceleration versus throttle pedal position for the Civic 1.8S.

    Note that the VW Bora is being used as the benchmark. While the 'target' remains the Toyota Altis, Honda is also targeting the 'continental' alternatives with this new Civic, hence the use of the VW Bora when tuning throttle response. Within Asia, it is generally held (whether correctly or not) that the continental marques deliver good 'driving feel' so cars from VW, Peugeot, Audi and so forth have been examined during the R&D of this new Civic.


    NVH is another area which Honda R&D focussed on in the development of the R18A. Specifically they looked the 'High frequency range', i.e. how much 'noise' the R18A delivers in the higher frequencies.

    The graph on the left shows their achievement in this area. Honda R&D itemized the following areas as being the main focus during development:

    • Intake Sound
    • A New "Torque Rod Mount" system

    In addition, to reduce intrusion of outside noise into the cabin, Honda also employed sound insulation techniques.

    A new 'torque rod mount' system was designed to supplement the standard engine mount system. This system consists of an upper and a lower torque rod added to the engine-gearbox package and helps to reduce vibration and twisting of the engine during application of throttle. The net result is the reduction of 'booming noise' from the engine in the high frequency range.

    For sound absorption, this was done through a new "soundproof package" which helped in 'Improved Quietness' via the reduction of outside noise intrusion. These was done using double door seals and a special 'Sound absorbing door hole seal' which is a special hole opened up inside each door which serves to cancel out outside noise through resonance (see diagram).

    There is also use of sound absorbing materials for improved sound insulation, specifically in the roof lining and the use of insulating floor carpets.

    When Honda launched the new 8G Civic, they made a lot of reference to how much attention was paid to details - to regain back as much of the 'Civic DNA' of old as they can. One of the most important areas in this case was the sound of the engine, or rather how the engine sounds when pushed hard. Honda made lots of reference to how they actually tuned the engine sound when designing this new Civic.

    In the area of engine sound, the target was to generate a 'Linear Engine Sound Output'. The D17A's sonic 'signature' was severely lacking (to be frank) in this area. So the new R18A was literally designed to 'make all the right noises at the right place' ! Honda characterized it as 'Sporty Intake Sound Tuning' (to improve the 'sonic quality' of the intake roar) and one of the places they paid a lot of attention to was in the specific tuning in the intake system (air filter system) by the use of 'optimized intake parts'. This comprises 4 main areas, identified in the diagram above on the left and which are :

    1. A 'silencing device' for frequency change in the air-filter box
    2. optimized Air cleaner SHAPE
    3. Optimized duct length - note how the intake duct is twisted
    4. A 'silencing device (for) frequency change' put in the middle of the intake duct, specifically for the tuning of the engine sound !

    The sonic tuning involves the reduction of engine sound during low-rpm operation and an increase of the "High rpm intake sound", i.e. roar of the intake at high rpms was increased. The overall target was to produce a more linear engine sound during WOT runs. The achievements in this area are identified in the graph on the left.

    So the idea is that the engine should be quiet when baby'ed but be suitably 'noisy' when pushed hard - clearly catering to the wishes of Honda enthusiasts ! After years of being told by us (enthusiasts), it looks like Honda R&D finally understood that the sound of an accelerating (Honda) engine is an extremely important and integral part of the Honda driving experience.

    The careful attention paid to the engine sound during WOT runs for both the K20Z and R18A are explained by the term 'Linear Engine sound output' and is highlighted in the graph below.

    Interior sound level at WOT for Civic 1.8S Engine sound achieved level for front seat middle sound

    Like the K20Z, the R18A is now designed to work in conjunction with the new 5AT gearbox as a 'package'. The specific areas of improvement for the new 5AT have already been covered in the K20Z technical review so we will not be going through it again here.


    During the launch of the new Civic, it was clear that Honda is quite proud of what they have managed to achieve with the new R18A engine for the new 8G Civic. What should now be clear from this article? Remember that 140ps max power output from a 1.8l engine can rightfully be considered 'very high spec', ignoring the standards set by Honda themselves with the original B18C engines. This can be supported if we compare the R18A output with those from competitors including 'high specification' twin-cam engines of similar size. For e.g. the 1.8l DOHC Twin-Spark engine used in the Alfa Romeos are delivering 140ps as are the 1.8l DOHC EFi engines used in the local (Malaysian made) hot-hatches like the Proton Satria GTi and Proton Putra. This is also comparable to the 1.8l Toyota Altis (138ps) and superior to the 1.8l Nissan Sentra (130ps).

    Coupled with potentially exceptional fuel economy (for a 1.8l engine) and specific characteristics targeted to please long time Honda enthusiasts, it is clear how technically advanced the new R18A engine is.

    I was truly impressed by how much technology was in the new R18A when I sat through the presentation. Ignore common misconceptions that 'SOHC means low tech while DOHC means high tech'. Owners of the new 8G Civic 1.8S should be proud and reassured that their new 1.8l SOHC i-VTEC engine is truly 'state of the art' !

    September 2006
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