Isuzu Philippines kicked off their 2019 fuel economy challenge competition this month, continuing contests they held last year with Isuzu vehicle owners among their dealers, this time with fans from Isuzu vehicle clubs.
Like in 2018, this year’s competitors from numerous car clubs, along with members of the motoring press, would drive a single lap around a 4.2km loop starting and ending at the main entrance of the Isuzu factory in Laguna Technopark. With different groups on several weekends, car club and media drivers compete separately on the 4×2 and 6AT variants of either the D-Max pickup or the mu-X SUV, both with the new 1.9 liter RZ4E turbodiesel efficiency engine.
Veterans hands-on on a new engine
Continuing the contest series with car club members is a shrewd move by the country’s leading truck brand, holding contests that put the 1.9 liter RZ4E, their newest and smallest turbodiesel, front and center among people with first-hand knowledge of the sporty D-Max and mu-X utility vehicles that mount larger engines in past and present variants.
The RZ4E engine featured on Isuzu fuel eco challenges since last year was introduced also in 2018 as Isuzu’s first turbodiesel that departs from the 4J engine series from which they’ve drawn the 3.0 liter 4JJ1 as well as 2.5 liter 4JK1 and 4JA1 engine models for the D-Max and mu-X along with their discontinued Alterra and Crosswind line-ups.
And, while the RZ4E’s 147hp peak power and 350Nm of max torque put it in good standing against these 4J engines, its diminutive 1.9 liter displacement could be cause for skepticism, especially when powering Isuzu’s mid-sized D-max pick-up and mu-X SUV, and particularly among current owners who drive former and current variants with larger 2.5 and 3.0 liter engines.
| Engine | code | 4JK1-TC | 4JJ1-TC | 4JJ1-TCX | RZ4E |
| Introduced | mo-yr | Sep-14 | Oct-15 | Sep-17 | Mar-18 |
| Emissions | level | Euro 3 | Euro 3 | Euro 4 | Euro 4 |
| Displacement | cc | 2499 | 2999 | 2999 | 1898 |
| Bore x stroke | mm x mm | 95.4 x 87.4 | 95.4 x 104.9 | 95.4 x 104.9 | 80 x 94.4 |
| geometry | over-square | under-square | under-square | under-square | |
| Compression ratio | x : 1 | 18.1 : 1 | 17.3 : 1 | 16.5 : 1 | 16.5 : 1 |
| Peak power | hp / rpm | 133 / 3400 | 160 / 3200 | 173 / 3550~3650 | 147 / 3600 |
| Peak torque | Nm / rpm | 320 / 1800~2200 | 380 / 1800~2200 | 380 / 1800~2200 | 350 / 1800~2600 |
City mileage simulation
Appropriately, since the 4×2 6AT RZ4E D-Max and mu-X variants are ideal for daily commutes in heavy traffic, Isuzu’s fuel eco challenge simulates city driving more than it does highway cruising. The contest runs happen on wide concrete roads that could be busy with Laguna Technopark’s regular car and truck traffic, and on which a 40km/h speed limit is strictly enforced as well. With max speeds allowing 6-speed gearboxes to barely gain third gear, the contest at least approximates first world city driving if not the kind of standstill conditions regularly endured by local motorists.
Interestingly, despite these restrictive driving conditions, competitors have turned in some numbers that actually approximate highway mileage figures. Last year, Isuzu vehicle owners from among the brand’s dealership ranks recorded 20.7 and 17.6km/l on winning runs with the D-Max and the mu-X, respectively. This month, on the initial leg held on August 3, members of the mu-X OP car club started the contest series with impressive mileage scores of 18.1 and 16.9km/l for the D-Max and the mu-X, respectively. And these numbers stand to be improved on by subsequent contest runs happening with other clubs in August.
Refined next-gen diesel
A top scoring driver from the mu-X OP club observed that while the current 3.0 liter 4JJ1-TCX Euro 4 engine option is rated higher, the new 1.9L RZ4E does deliver enough power and torque–more than on the larger 2.5 liter 4JK1-TC initial engine offering on the mu-X SUV. Another top scoring driver added that the RZ4E is also very responsive, answering crisply to every light tap on the accelerator pedal–the new engine remaining as responsive as the short-stroke over-squared 2.5 liter 4JK1-TC despite the RZ4E’s return to a diesel engine’s typically long under-square stroke.
The exceptional mileage figures they scored and the increased power density and responsive revving they observed point to RZ4E innovations such as improved combustion chamber geometry and pistons made lighter with carbon-fiber segments (keeping the under-square diesel responsive to accelerator inputs).
We ourselves participated in the first leg contest on August 3, and here we confirmed an observation we made on a previous, week-long test-drive: the RZ4E is so refined, you’d mistake it for a large, naturally aspirated gasoline engine from the driver’s seat and from behind closed windows. And, quite appropriately, the RZ4E’s adequate, fuel efficient and smoothened power seems well fitted to city-friendly 4×2 6AT variants of the D-Max pickup and mu-X SUV, the utility models that Isuzu has pioneered at turning into iconic passenger car alternatives.
