The new 8G Honda Civic that was launched throughout Asia earlier this year featured a 2.0l DOHC i-VTEC engine, coded K20Z. This 'new' engine is a development of the K20A used in the original 7G Civic 2.0 i-VTEC sedan that was exclusive to Asia. The new K20Z+5AT engine-gearbox combo in the new 8G Civic 2.0S features Drive-by-Wire, important gains in noise reduction via sound proofing techniques and finally an attention to 'linear engine sound', i.e. how smooth and 'encouraging' the engine sounds to the driver when doing WOT runs. While both engines features the same max power of 155ps, the K20Z do feature some important improvements over the K20A. In this short TOVA technical overview, we highlight the important elements of those improvements. The source for the information in this article comes from the technical overview presentation that was done by the Honda R&D engineers from both Honda R&D Japan and HRT or Honda Research Thailand, based in Ayutthaya in Thailand. This presentation was given during the special media test drive event that I attended as part of the launch of this Civic for Malaysia.
All of the technical photos used in this article are sourced from shots of the presentation material taken using my Fuji digital camera as they are being shown on the screen. Consequently, the quality of the photos are patchy at best while many of the photos have alignments that are not 100% accurate. Unfortunately while Honda do not prevent us from taking the photos, they also do not seem comfortable in giving us a copy of the presentation materials as all previous requests have not been entertained. So this is the best that I can do for this article.
As pointed above, while the new K20Z and the older K20A features the same max power of 155ps, the K20Z has been specifically improved for daily driveability and for use with an automatic gearbox. In the presentation, Honda characterized this as a target of 'big improvement in middle and high torque'. The key point to note is the emphasis on torque. This is exemplified by the new max torque for the K20Z, 188Nm or 19.2kgm; this being a large 12Nm or 1.2kgm over the K20A, over 6% more torque. However, as usual, just a single max-torque figure cannot tell the whole story. I find the best means to illustrate the target that Honda had for this K20Z is the side-by-side comparison of the power and torque curves of both engines that Honda showed in the presentation. This is reproduced on the left below. The blue coloured curves are the power and torque curves for the original K20A while the red coloured ones are for the new K20Z.
Note 
how the whole power curve for the K20Z has been shifted to the left, meaning that power is now being delivered earlier in the rpm band. Even more enlightening is the torque curve comparison. The original Civic 2.0 i-VTEC's K20A had a torque curve that is reminiscent of the Bseries DOHC VTEC engines of yonder years. That is the torque curve shows a distinct 'two hump' or two peak points. Looking at the blue torque curve, we can clearly see that the engine merges two individual torque curves together, with the changeover at around 4,000rpm. Meaning we can clearly see how VTEC is combining two distinct torque curves into 1, to deliver, as the propaganda says, 'two engines in one'.
In actual usage, this gives us the very nice 'VTEC surge' - i.e. once VTEC engages, there is a nice resurgent urgency in the pull from the engine. We can see this as a result of the sudden surge in torque after 4,00rpm. In actuality, on the original K20A, this surge has been amplified by the falling torque curve before VTEC engagement. Put in another way, there is a 'hole' in the torque curve at around 3,000 to 4,000rpm, before VTEC engages. This is why in actual usage, we can actually feel a lacklustre response from the engine before the VTEC engagement point. I think many ET1 Civic 2.0 i-VTEC owners will agree with this.
If we look at the red curve, which is for the new K20Z engine, we can clearly see the great pains that the Honda R&D engineers took to 'fill up' this 'hole' in the middle of the torque curve. In this case, they more than fill it up, the torque now peaks in that region, which incidentally is the crucial mid-range rpm band where an engine spends most of its time in when running with an automatic gearbox. So in usage, the new K20Z will 'pull all the way to 4,000rpm' before acceleration starts to taper off. However, that's not all. Note the much higher torque in the high-rpms, after 4,000rpm right until the engine redline of around 6,500 to 6,800rpm. The K20Z delivers more torque -and power- than the K20A throughout the whole rpm band.
To achieve this improvements, the K20Z engine features several detailed improvements. There are 5 main areas highlighted in the presentation which are listed briefly below.
1. New Intake Manifold with Resonator
The K20Z features a new intake manifold design that features a 'torque-up' resonator (resonance chamber) that delivers improvements in low and mid-range torque. This resonator is what is mainly responsible for the nice peak in torque in the midrange of the new K20Z engine.
2. New Camshafts
In addition to the new intake mainfold, the K20Z features new camshafts with profiles that are specifically designed to complement the resonator in the intake manifold. These two combines together to deliver the high-rpm power output and torque improvements that we see in the power/torque chart above.
3. New exhaust manifold
The exhaust manifold is a new 'even runner length' design that features a high (exhaust gas) flow rate. Even runner length means that the individual runners of the manifold are all equal in length. An even runner length exhaust manifolds features convoluted runners which twists and turns. This ensures that all 4 runners are of equal length. The new exhaust manifold design helps to deliver high power and torque.
4. Drive-by-Wire (DBW)
The K20Z features a new Drive By Wire (DBW) system that features an electronically controlled throttle body. DBW means that the throttle (gas) pedal is no longer directly connected to the throttle body via a throttle cable. Rather there is an electronic sensor that detects the throttle pedal position. This sensor feeds the position into the ECU which then electronically sets the throttle opening using logic and parameters built into the PGM-Fi program. Honda says that their reason for choosing DBW is the flexibility that it offers, especially in letting them create 'acceleration feeling', i.e. smoothness and linearity in pickup.
5. Additional MAF (Air-Flow) Meter
Finally the K20Z features additional MAF sensors or air-flow sensors in addition to the standard MAP sensors. Used together, they offer more accurate A/F control that can be afforded by just the use of a MAP sensor. Thus the air-fuel ratio in the engine and combustion efficiency can be more accurately maintained and this allows a smaller cat to be used - thus less precious metal required which to Honda represents an important 'cost-down' - lower manufacturing costs.
The new engine-gearbox 'package' means just that, the K20Z and the new 5AT gearbox have been specifically revised to complement each other. According to Honda, their 5AT gearbox that makes up the other important half of the package is designed to offer top shifting quality in its class along with a reduced size and enhanced efficiency.
Honda lists three main areas where the new 5AT gearbox has been improved. The first area is in the shifting quality and feel. The 5AT features both close and wide gear ratios carefully implemented amongst its 5 gears, a direct clutch pressure control to offer better engagement of the automatic clutch and special attention paid to coordinated control with the new DBW system.
The 2nd area is in improved fuel efficiency (and better power delivery). All 5 gears now features lock-up clutch control, delivering friction loss reduction in all gears. This delivers improved fuel efficiency and better power delivery (less power lost in the gearbox means more power delivered to the driving wheels) which I intend to confirm this when I take the Civic 2.0S for my full review by having it dyno'ed.
Finally, the new 5AT gearbox features a significantly reduced physical size. This is acheived through a new gear layout - the 4th and 5th gears now shares the same placement while the torque converter is now a new 'ultra-flat' small diameter design. The new 5AT is now just 356mm in width (thickness) and slightly over 80kg in weight.
Top In its 'Class'In the presentation, the objective for the new K20Z+5AT engine-gearbox combo is articulated to be 'top acceleration in its class'. As a hard-core Honda enthusiasts, this of course quickly caught my eye and naturally I seek further clarification. The 'in its class' that is emphasized is actually the sporty sedans in the ASEAN market. The market leader in this segment, for ASEAN is the current generation Toyota (Corolla) Altis. So the Honda R&D target is to defeat the Toyota Corolla Altis conclusively and to ensure that the Civic remains superior to what the next generation Toyota Altis is expected to be. In addition, the new Civic is also intended to offer a viable alternative to the European sedans in the same market segment, again for ASEAN. These European sedans are exemplified by VW, Peugeot and Alfa Romeo 2.0l sedans.
This then is the reason why the current specifications of the Civic 2.0S, re 155ps max power and just a 5AT option is deemed sufficient. To endure the Civic 2.0S to the market segment of Honda enthusiasts in the ASEAN market (Honda's own views of what these enthusiasts wants and needs), Honda R&D added the specific features like HID, sequential shifters, and so forth to the Civic 2.0S.
This then concludes this quick technical overview of the K20Z. The same technical presentation also contains the same technical information for the new R18A engine. That will be the focus of the next article in this series.
Wong KN
September 2006
© Temple of VTEC Asia
