IMG20151113165354We dive deep into the details of the JATCO-sourced automatic transmission on Crosswind XUV and Sportivo variants, and come back up with a notion on how to get acceleration that’s closer to how you’d feel it with a stick-shift.

Impressive with its economy, although limited to an 83hp rating because it tops out quickly, the 2499cc 4JA1-L low-boost turbodiesel on the Crosswind packs a big 137lb-ft of peak torque behind that measurement and accelerates quickly enough through a diesel’s typical short-shifting regimen. But that’s with a manual gearbox. The same engine feels very different, sounding more revvy while delivering less acceleration, on the XUV and Sportivo variants with their JATCO-sourced automatic transmissions.

XUV and Sportivo variants of the Crosswind have bigger, heavier tires, of course, but the difference in performance seems to be caused more by the tall gear ratios on the wide-gapped 4-speed automatic, by the high-stall ratio of its torque converter, and of course, by having to delegate shift control to the gearbox. Isolating it to these factors led me to try a technique derived from that of veteran Lancer A/T owners.

Crosswind-power-curve
Power contour of the Crosswind’s 4JA1-L low-boost turbodiesel

On those sporty Mitsubishi sedans with a 1.5L MIVEC engine and its peaky torque curve driving a 4-speed auto, experts have been surging the accelerator to 3000rpm—the lower edge of the engine’s peak powerband—and then promptly letting off on the gas as soon as the car starts accelerating. This charges the powertrain’s flywheel, cranking in momentum that’ll then deliver smarter acceleration—a surge to quickly overcome the car’s inertia coming off a stop or a slow cruise.

Now, on the Crosswind with its diesel-engine torque curve, the powerband’s meat is from 2000 to 3500rpm. Torque starts at 50% of peak at 1000rpm, climbs rapidly to 88% at 1500rpm, then reaches its 100% figure at 2000rpm before tapering down to 95% at 3000rpm and then to 90% at 3500rpm.

Isuzu Crosswind Gear Ratios
 Gear 5-speed M/T 4-speed A/T
1st 4.122 2.784
2nd 2.493 1.544
3rd 1.504 1.000
4th 1.000 0.694
5th 0.855 n.a.
Final 4.100 5.125

Problem is that getting a Crosswind A/T to that 2000rpm threshold takes some doing. Rolling out easy from a 750rpm idle will see you triggering an upshift to 2nd gear very quickly at just 10km/h. When that happens, your revs which had been climbing steadily to 2000rpm will drop back down to 1500rpm and stay there while the engine deals with a fairly tall 2nd (1.544:1) and then with an early direct drive 3rd gear (1.000:1).

Consequently, on a Crosswind with an automatic gearbox, you’ll find that engine revs gravitate to 1500rpm and it takes a fairly deep stomp on the gas pedal to get the tachymeter needle moving again. Now, if you give into the urge and stomp on it, you won’t just reach 2000rpm but will likely overshoot. This makes for a disconcerting, obviously wasteful, rev up with much slippage in the torque converter.

I do suggest that you wait until you’re in 2nd gear or higher before pumping up the revs from the default 1500 up to or above 2000rpm.

That slippage is necessary, tolerance for wide differences between impeller and rotor speeds translates into multiplied torque—indispensable at slow hauling speeds. But it’s not something you always need, and, to be frank, it makes for an inelegant ride, the engine roaring while making acceleration look dismal in comparison. While the Crosswind’s JATCO automatic transmission does have torque converter lockup (creating a hard link between impeller and rotor when the latter’s speed is within 5% of the former), this kicks in only at around 80km/h, late in the acceleration game and only after the upshifts that finally got you to 4th gear.

IMG20151108110233Now, instead of lamenting this state of things in the torque converter, that hitherto black box that makes stop-and-go traffic crawls far more tolerable, the slippage can be exploited to let you stroke the accelerator. This would be the equivalent of feathering the clutch and stroking the gas pedal to surge up revs on a manual gearbox. Instead of stomping on the gas pedal, give it a two or a three-count pump, quickly charging the flywheel with enough inertia to counter and overcome that of a slow-cruising Crosswind.

A two-count pump—one, a short shallow stroke on the gas, followed quickly by two, the sustained, but just slightly deeper press on the pedal than before you started—will get your revs from 1500 rpm to just under 2000rpm very quickly. A three-count pump—two quick and shallow strokes followed by a third, sustained and slightly deeper pedal push—will get you over 2000 and nearer to 2500rpm smartly enough.

IMG20151108154613In geek speak: because the torque converter has a high-stall ratio, because it permits and harnesses a lot of slippage, those shallow throttle pumps will speed up the flywheel and impeller in spurts to cavitate the transmission fluid and not yet incur hydraulic resistance. In other words: the pumps let you “slip” in a rev up in quick stages.

I do suggest that you wait until you’re in 2nd gear or higher before pumping up the revs from the default 1500 up to or above 2000rpm. It’s an easy state to recognize. As long as you’re at 10km/h or higher, you’re out of 1st gear and ready to, well, pump things up. Why? It just works out smoother, without the early shift-bump up from 1st gear knocking you off your game.

Then, after a two or three-count pump has put you quickly in the zone between 2000 and 3500rpm, without the hoopla of a roaring engine driving a torque converter with mounting slippage, that’s when you do the Lancer thing and start thinking of easing off the gas pedal as you feel the momentum come on line. You’ll find that easing off the gas is more responsive, can be done with more precision.

End of it all, on a Crosswind with an automatic gearbox, reaching or going beyond that 2000rpm threshold with this two or three-count pump tactic will get you smarter, surprisingly quieter acceleration. You’ll see.

IMG20151108154653

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One thought on “The Pump: getting smarter acceleration from a Crosswind A/T

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