Turbocharging the EJ Civic 1.6L SOHC VTEC

Our last article on the HKS light pressure turbo project Civic garnered a lot of interest. That base car was a non-VTEC Civic, with the HKS turbo generously upgrading its max power to that equivalent to an automatic B16A Civic but with vastly superior midrange pull. A lot of readers have written to me asking for more details of the car. However, most of them were driving the VTEC version of the 1.6SOHC Civic instead. The prototype of the HKS kit was actually done on such a model, a Malaysian domestic market EJ8 Civic VTi. Consequently it would be of interest to many to know the result on that car. Since I had access to the car, I thought that the obvious follow-up article would be this.

The owner of that Civic, Mike, bought the car because it was the highest spec'ed EK-Civic available in the local (Malaysian) market at the time. As the top model, it uses the 1.6SOHC VTEC engine, spec'ed to deliver around 125ps. Red-line was a high-ish 6800rpm. The car was sold only with an automatic transmission and carried the high-performance flag for the Civic range during the EK Civic generation's life-cycle for Malaysia (1996-2001). Unfortunately, after a few months driving around, Mike was already feeling a lack of midrange pull from the engine. The car was used for daily driving to and from work, a round trip exceeding 100km, 90% of which is a 5-lane highway travel. Mike told me of many 'encounters' with the competitions, typically the larger engined cars which unfortunately tends to bully their way around such roads. As a result, he quickly developed a yearning for more power.

A brief experimentation with the typical route of drop-in mods quickly told Mike that it will not yield the kind of power gains that he was looking for, which is power gains all through the rpm band of sufficient magnitude to allow him to handle the larger displacement cars (2.0l-2.2l and higher) on an equal basis. However, Mike's timing was good because Aerotech, the HKS specialist for Malaysia was just finalizing the initial design of the HKS low-pressure-turbo kit. Thus the opportunity to prototype the kit on Mike's car gave significant cost savings - both to Mike who got the kit at a huge discount, as well as Aerotech since they were able to have a portion of the prototype's development cost covered.

1.6SOHC VTEC Low-Pressure-Turbo (LPT)

I got to know Mike just after he took delivery of his car a few days before. The prototype turbo-kit in his car was basically the same as that covered in our previous article on the Malaysian 1.6SOHC non-VTEC auto Civic. It is after all, the basis for that kit anyway ! Mike's car is of course an SOHC-VTEC version but both engines are very similar in design so the kit was the same, except for one item - the exhaust manifold.

In a 4 cylinder engines, the power strokes do not overlap. Therefore in a turbo-charged 4-cylinder, the exhaust manifold to which the turbo-charger is connected to will need to maintain a steady, consistent pressure to ensure that the turbo-charger spins at a consistent speed. Special attention was paid to the design of the exhaust manifold used in the prototype kit, which was based on that used in the HKS B16A low-pressure-turbo kit. The manifold has the exhaust from cylinders 2 & 3 and 1 & 4 tied together before feeding together into the turbo-charger. This initial manifold was built out of small sections of steel tubes welded to together to form the design. The intention was to test out the design on the prototype and to then use it to create the mold with which to make the final cast manifold for the proper kit.

In the event, I have to report that Mike did encounter problems with exhaust leakage from the manifold. The very high exhaust pressure and temperature at the manifold often made the welding points crack at several places. There were a few return trips to re-do the welds. Other than that though, the prototype kit works exactly as designed which is extremely well. In the final production kit, the exhaust manifold is a cast-iron item. Based on data from the prototype kit, the design was able to be simplified into a "4 to 1" design, with all 4 cylinders feeding their exhaust into a single point before feeding into the turbocharger. When the cast manifold was available, it was quickly retrofitted to Mike's car. With the cast item the problem with exhaust leaks encountered with the prototype kit was then fully solved.

This prototype kit also uses the same HKS FCON-4 tuning computer as the HKS demo car. In fact, the tuning done on this car was even more extensive than that on the demo car since a lot of basic research had to be done. Of special significance is the boost level. Many days of testing were done before deciding on a boost level of around 0.3 bar. However, as explained in the demo-Civic article, a problem with turbocharged automatics is the shift-shock. Since automatic transmissions allows the driver to be on full throttle even during the automated gear shifts, there will be a shock as the next gear engages. And with a turbocharger, this will lead to a spike in the running boost. At one time, a boost level of as high as 0.5 bar was recorded during shift-shocks and the engine and gearbox were clearly stressed more than is desirable. At the time of the prototyping, the relief valve solution was not thought of yet. In the end, very careful tuning and setting were used to keep the shift-shock boost to 0.36bar.

A Super Powerful Auto VTi

The dyno chart of the car as delivered is reproduced on the left. As usual, the original, base dyno chart was reproduced together with the turbocharged version for comparison. The stock car, with the benefit of a HKS Super Power Flow filter dynoed at 90ps at the wheels. With the reference 30% power loss figure, this works back to around 129ps at the engine, tallying extremely well with the specified 125ps stock power with the benefit of an open-element filter. Of special note is the profile of the stock dyno graph. Note the obvious change in the curve at 4500rpm. This is the VTEC changeover rpm and proves conclusively that the VTEC implementation in the Malaysian Civic VTi is a power oriented one.

After tuning was completed, the turbocharged version delivered 117ps at the wheels. Working back to engine power, this topped 167ps. The HKS LPT upgraded the power of the 1.6SOHC VTEC engine to almost that of the much higher spec'ed auto B18C !! This was a massive achievement and is confirmed by the automatic B18C DB8 Integra which dynoed at 118ps at the wheels featured in our Beyond Stock article on the baseline reference for the B18C.

Comparing to that car's dyno chart, it can be seen that this turbo 1.6l SOHC-VTEC has more power in the low-rpm. Power at 3000rpm for the 1.6l turbo was almost 70ps while the auto B18C delivered less than 60ps. This carried on in the midrange as well, the 1.6l turbo generating >70ps at 4000rpm while the auto B18C did not achieve 70ps. VTEC cuts in at 4800rpm for the B18C and this gives generous benefit to the engine allowing it to match the 1.6l turbo's power at 5000rpm and above. Of course the B18C have a superior rpm range, capable of revving to around 7500rpm, almost 1000rpm higher than the 1.6SOHC VTEC. Viewed in this perspective, the HKS kit's upgrade to the 1.6l SOHC VTEC was huge indeed, allowing it to overcome a 200cc displacement deficit as well as a lower spec'ed configuration (SOHC vs DOHC), ultimately only losing out in the ability to rev to very high RPMs.

As with the project Civic, this prototype kit also impressively duplicated the stock engine's power chart by lifting it by 27ps almost all throughout the rpm range. Equally interesting is that the turbocharged curve even has the slight power surge when VTEC activates the wilder cam profiles at around 4300rpm !

The Driving Experience

Mike was one of the first members of my Honda club. As a result, I had extensive experience with his car. All the time that he had it, I was impressed with how responsive and powerful the car felt. Although an automatic, the power delivery was very impressive, especially when VTEC opens the wilder cams. I was also treated to many stories of road encounters that Mike has on his way to and from work. As described, Mike's daily commute to and from work is around 100km of mostly highway travel. As a result, he tends to have more than his fair share of encounters with rude or impatient drivers, especially suffering in the hands of those which have larger engines. In the event, Mike were now able to dispatch with all of such 'nuisances' with ease :- probably most of them were taken by absolute surprise from the sheer speed of his turbo-charged VTEC Civic; as can be seen from the photo, externally the car does not give away any idea of what's underneath the bonnet - a real sleeper of a Civic indeed !!

My personal experience with all-out driving of this car was an even more interesting event. My friend from Singapore, coincidentally also name Mike, drove his EG9 to Malaysia on a business trip. We met up, the two Mikes, and a couple of others for a drink on Friday night and subsequently "itchy feet" got the better of us and we ended up "testing" one Mike's turbocharged Civic against the other Mike's EG9. That EG9 is the 160ps Singapore version, 5 speed manual and generously equipped with a complete complement of bolt-on mods; Tanabe header & exhaust, Akimoto filter, SFC a/f regulator, adjustable fuel pressure regulator, an aftermarket ECU that raised the rev-limit to 9000rpm and even a very mild head polish. That car as reported elsewhere here on Beyond Stock, delivered around 137ps at the wheels at that time (we had that test before the car went for its dyno-tuning session which netted it the 5ps gain at the wheels).

I drove the turbocharged 1.6SOHC VTEC with owner Mike as the passenger. The EG9 had its owner Mike and two other of our friends onboard. In the event, upon peeling off to join the main road, the two cars were neck to neck. Although the EG9 was ultimately slightly faster, it couldn't overtake us even on the main road. The midrange superiority of the turbo-charged 1.6SOHC VTEC allowed us to easily build up an initial lead, despite the large disadvantage of the automatic gearbox, and even with wild cams screaming until 9000rpm, the EG9 still could not overtake. On the next round, we started behind the EG9 and I was surprised that I could keep up closely with it.

That "test" was an impressive one, especially when we consider that the turbocharged 1.6SOHC VTEC is an automatic car, with a redline of only 6800rpm and therefore much lower gear ratios when compared to the NA EG9, a 5 speed manual B16A complete with the close ratio 4.4 final ratio gearbox. In an all out race, the EG9 with the superiority of the 5-speed manual gearbox and higher power at the wheels will ultimately win, but it would needed an extended high-speed chase to achieve the victory. Indeed, had the EG9 been an automatic like the SOHC-Civic, it would have been easily defeated !

Conclusion

Owners of 1.6SOHC VTEC Civics are probably a fair bit more performance minded than that of the ordinary 1.6SOHC version. The VTEC implementation did allowed a broader powerband to the stock engine, even a mild bump in the power when VTEC engage the wild cams. But it is the HKS light pressure turbo that really brings the car to life. This prototype Civic was every bit as responsive as the demo Civic but more powerful and a broader power band to boot ! The car was able to take on all of the common "nuisances" Mike had the misfortune to encounter on his daily work commute. In the end it is particularly telling that the only car that could satisfy Mike when he decided to upgrade his car was a manual DC2 Integra SiR.

For readers in Malaysia, to get more details about the HKS Light Pressure Turbo bolt-on kit for the 1.6SOHC and SOHC-VTEC EK-Civics, contact Aerotech at 60-3-79556112. The cost for the kit is relatively high especially for a one-time outlay but for those who demands such large power increases, it is the only way to go short of changing the engine.

Wong KN
July 2001
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