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The Troopy hauls ass with an AXT Turbo.

Words and photography by Mark Allen

Let's reiterate something I said a month ago - a 4.2L diesel Troopy will never be a standing quarter-mile contender - I still stand by this statement. Hauling around the countryside in anything but top gear tends to wear a little thin after a while, and I still stand firm on that one, too! So, after having punted about the countryside in my (speedy) slug-box 1HZ AXT turbo-powered Troopy for the best part of a couple of months and clocked up just shy of 10,000km, surely I'd be happy with an extra 40.1 percent in power and 39.7 percent in torque. Well, yes and no. While the AXT turbo kit has transformed the Troopy into a much more comfortable touring vehicle that can tow caravans, car trailers and camper trailers without a hassle, more power is never enough. Of course, there are provisos here; more power at the risk of cooking an engine is not what I'm on about here. I wanted to find out if I could pump more safe power out of a 1HZ engine and - here's the big bit - not use more fuel in doing so.

Yes, we all know that to provide more power means dumping in more fuel to create a bigger bang, but bigger bangs usually equate to bigger fuel bills - as if we aren't paying enough at the fuel pumps already! You will remember from part one of this AXT turbo fit-up that I asked the guys down at the Melbourne head office of AXT to fit and tune, but not play too much with anything else on the system. In doing so, they easily managed massive results in power and torque (nearly a 40-percent increase on both). My pre-turbo fuel economy was on average 14L/100km for around-town and long-distance touring. After the turbo was fitted, I was getting more like 15-16L/100km in similar circumstances. I have left the Troopy as it was when I first picked the AXT turbo install up all in the name of keeping the testing fair and even - right down to leaving the roof racks on, which I would normally take off while not in use to save on fuel.

One thing I have noticed about the AXT Garrett T3 water-cooled turbo fit and basic tune was the increased black smoke on take-off and under load. While speaking to Daryl Aston (head honcho at AXT) about the smoke issues, he recommended I go the whole hog for injector replacement and tuning - which is what I intended doing. So, while the excessive black smoke issue is not a turbo or fitting fault, there is one part of this standard system that can be changed to gain even more power and (supposedly) use less fuel! A visit to West End Diesel in Sydney's Wetherill Park saw a run on its dyno to assess what my engine was doing on the inside. As expected, my engine was pumping out bloody good power and torque figures but was over-fuelled at lower revs and under-fuelled at higher revs.

A boost compensator is the key here, as any engine can only be tuned (unless it has a factory boost compensator) as an average adjustment. What the boost compensator does is, as the name suggests, compensate the amount of fuel that is required for the revs and boost on hand. Low revs need less fuel and high revs need more fuel than the average setting. West End Diesel managed to squeeze an extra 11.1 percent (9.2kW) and 8.2 percent (40.3Nm) from the AXT turbo set-up without compromising safety. In fact, it will be a hell of a lot safer as it's not being over-fuelled down low, which can result in overheated pistons in the 1HZ. The claims in fitting a boost compensator are up to a 20-25 percent increase in power and torque - that's way over what an intercooler can lay claim to and far cheaper! The fitting of a boost compensator comes in at $1350 - compared to an intercooler at anywhere from two-to-three grand. As an added bonus, the boost compensator also claims to improve fuel consumption.

Seat-of-the-pants driving tells me exactly the same as West End Diesel's dyno figures. Down low I have lost a little oomph (slightly), but once you get going, the heavy Troopy hauls ass big-time. It kind of feels a little like a slingshot effect now; a good, solid take-off followed with better and better acceleration as the revs climb. The fuel economy was the next big check; first tank returned 14.8L/100km, while the second put a smile on my dial - 14L/100km. Now while that may be nothing startling, it basically returns my consumption to pre-turbo economy figures - proof that you can have your cake and eat it, too! Editor Pat will be pleased that I can now get out to the back blocks, do my job, return quicker and easier, and at the end of the day give him a smaller fuel bill - winners all round!

EXHAUSTING
At the time of fitting the AXT turbo, I kept the factory original exhaust and muffler set-up so as to check on what effect changes would make at a later date. As well as changing the exhaust system for power increases, I was also keen on making way for extra tanks where the factory (very large) muffler used to reside. For those that aren't familiar with the routing of the OE system, it runs from the block on the driver's side, down the driver-side chassis rail to just behind the driver. It then bends at 90û to the passenger's side and bends another 90û to the rear to exit out the rear left-hand side. Along this route is a smaller resonator near the block, followed by a 44-gallon-sized muffler on the passenger's side. The new route now comes out of the block on the driver's side (can't really change this part), then runs the full length of the driver's side to exit on the rear driver-side corner. This, in effect, has left me with a massive area under the rear passenger's side for another tank later on. Instead of the resonator/huge muffler combo, I now run two straight-through hotdogs on a 2.5in system.

Why a 2.5in instead of a 3in pipe? Firstly, lack of physical room to fit the larger pipe prevented it. Secondly, the larger-diameter pipe is much thicker walled, thus much heavier - as if the Troopy wasn't heavy enough already! Thirdly, the cost of the larger pipe is a few hundred bucks more (mine totalled $500). Fourthly, it was recommended that a 2.5in pipe would do the job I needed so long as it wasn't restricted, hence the mandrel bends and straight-through hotdogs. Initially I was going to run a single hotdog as the muffler but dreaded the thought of the constant drone on long-distance runs. While I do love the unhindered 'ballsy' noise of an unmuffled turbo-diesel (the turbo acts as a muffler), short play trips would be fine, but long trips would be a bloody nuisance. So dual hotdogs, one under the driver's seating position and one at the rear, were given the nod. The end result is a system that certainly sounds different (read: better) than standard, allows the engine to rev out easier and isn't annoyingly loud.

TEMPERATURES
With the last (almost) 10,000km that I racked up with the AXT turbo kit, not once has the dashboard temperature needle budged - not one bit. I haven't been giving the old 1HZ 'clunker' an easy time either. It gets driven to and from work in Sydney traffic (don't I hate that), flogged on weekend play trips in the sand at Stockton, mud in the scrub and rocks while out on photo shoots. It also serves duty towing camper trailers, trailers and caravans. To not have the engine temperature rise at all serves testimony to the engineering and design that has gone into the manufacturing of the T3 Garrett-based AXT turbo. I'm still kicking myself that I didn't serve the AXT turbo treatment to my Troopy sooner - ah well, a fella has gotta live with his mistakes, hey!

DOLLARS AND CENTS
The Advanced 4x4 Turbo Systems (AXT) kit for a 1HZ 78 Series Troop Carrier rounded out at $3190 plus $550 fitting. The aftermarket exhaust system set me back $500, while the boost compensator was $1350 well spent. Fitting adds approximately $560. For more information on a turbo fit-up for any brand of 4WD, give AXT Turbo's head office a call on (03) 9793 7740. It'll give you all the goss on your particular model and direct you to your closest outlet/fitter Australia-wide. Also, have a look at www.axtturbo.com.au.

AXT GARRETT T3
The Garrett T3 turbo is a water-cooled affair - claimed to be far superior in reliability as it's able to maintain a constant temperature and won't get so hot as to cause damage. The kit includes oil and water teflon braided hoses, which are rated to 4000psi. AXT utilises a powder-coated, cast-alloy ducting to minimise airflow restriction and maximise heat dissipation. A split (two lots of three-cylinder banks) cast-iron intake manifold is used to allow for expansion and contraction, which eliminates the chances of manifold cracking.

NUMBERS
Boy it's hard to compare dynos with dynos. Regardless of all the hype about being able to compare a vehicle on one shop's dyno, then directly compare it with that in another shop's, some things just don't go to plan. Hence why we always compare before-and-after figures from one dyno only and then calculate a percentage increase to show what's really happening. The overall percentage increase is more beneficial than the outright kilowatt or Newton-metre numbers here. Before-and-after figures on West End Diesel's graph show us an increase of 11.1 percent power (9.2kW) and 8.2 percent torque (40.3Nm).

While this falls short of the claimed 20-percent increase, West End Diesel was instructed to be light on the power-increase figures while concentrating on improved fuel economy when fitting the boost compensator. The tech guys at West End Diesel ensure us that if we could let them have their wild way, they'd see much larger increases than shown here. So far I have achieved about 1L/100km better fuel economy, combined with a sizeable increase in power and torque, so I'm laughing!