The Toyota 1HZ is an engine developed by Toyota Motor Corporation for the Toyota Land Cruiser and the Toyota Coaster Bus of 1990. It replaced the previous (2H) heavy duty engine which was being used in older Toyota Land Cruiser models. This engine generates more power and torque than previous diesel Toyota Land Cruiser engine. Despite being 25 years old, the 1HZ still sees use in Landcruiser 70 Series production worldwide with the exception of Petrol-only markets and Euro 4 and Australian markets, where the 1GR-FE and 1VD-FTV Turbo-Diesel is supplied respectively. A popular engine in the 80 series Land Cruiser and replacing the 70/75 series 2H in 1990.

If you run a Toyota Land Cruiser with the 1HZ engine, you will know two things about it: It’s very reliable and, it could do with more horses to help it along. If you agree, read on…

As reliable as the 1HZ engine is, it can be broken! I have owned four 1HZ Land Cruisers and of the four, only one of them wasn’t underpowered… because I turbo-charged it. But this is not as simple as it seems.

The trouble with the 1HZ is that it was never designed for being turbo-charged and when Toyota did build a turbo-charged version of it, they made some major changes to the piston design. They did this because the standard pistons have very thin crowns, and what this means is that the high-pressures created by a turbo can, and in most cases will, blow a hole in the top of one of the pistons. I say in most cases because after-market turbo suppliers cannot help themselves in trying to get the most power increase so that they can boast about their achievements and sell more turbos. This has lead to blown pistons, but by then, in most cases the warranty has expired.

Overheating is another issue. Some Land Cruisers like the 105 wagon have huge radiators, and can handle turbo-charging without problems. But the 70-series Cruisers do not, so one has to be more careful, or add intercoolers. But the moment there are intercoolers and oil coolers, the entire modification begins to get over-complicated and the legendary reliability of the 1HZ begins to diminish.

I looked for three years at all the turbo chargers available, and there are several of them, and to the surprise of many in the 4×4 world, chose the one that is the cheapest. Not because of the money saving but because I believe it will have the least effect on reliability, which to me is more important than the extra power being delivered. It is made by SAC. I have now run it for 40 000kms, done five expeditions and no issues whatsoever.

The SAC turbo is simple! And this is what I love about it. Some who look at the installation suggest that it’s crude. Yes, I suppose it is. The turbo induction pipe has no elegant bend (it’s a squared off tube at an inefficient 90° angle) and there are no expensive look-good components to woo buyers. The turbo charger is controlled by a simple spring, that opens the waste-gate at approximately 0,7-bar. Anything above 0,9-bar for long periods, the Toyota engineers tell me, will blow one of the pistons within 100 000-kms for sure. They reckon, without having done any lab tests, that at 0,7-bar, I am absolutely safe, as long as the exhaust gas temperatures don’t peak, too often.

That brings me onto an addition, which surprisingly SAC does not offer, and that is an EGT (exhaust gas temperature) gauge that warns me when temperatures peak. Anything above 700°C for more than a minute or two will damage the turbo-charger and eventually the valves. Temperatures peak on long hills at high speed exaggerated by high ambient temperatures. One of the ways to reduce EGTs is to replace the exhaust with a larger-bore one, with a more efficient exhaust manifold. What this does it let the hot gasses escape easier, and cools it down faster. SAC also offers a head work, where they grind the head, allowing the engine to breathe more efficiently. I have not tried this so cannot report on the power increase or temperature decrease, but my gut tells me it may not be worth the expense, even though some improvement are probable.

So, in conclusion, if you are thinking of turbo-charging your 1HZ, avoid the turbo-makers who boast of the most power output, because truth is, it’s easy to get lots more power out of this engine, but at a huge cost to reliability. Look for one who’s focus is adding more power but are prepared to compensate power output for reliability. My SAC turbo adds an extra 22kW power output and I cannot remember how much extra torque but the improvement in overtaking performance, which is where the 1HZ seriously lacks, is excellent. Not earth-shattering, but it makes this a much, much nicer vehicle to drive. And the turbo-whine creates a nice, reassuring whizz that I really like.

Fuel consumption has increased. Pre-turbo I achieved a better than average 12L/100kms from my 1HZ. Now I get about 14L/100kms and can creep to 16L/100 kms on long stretches with a heavy load and bulky roof-rack… Still far better than the similar petrol engined vehicle and still acceptable. But the old saying applies here: If you have more horses, they have to be fed.

The Toyota 1HZ is a 4.20 l (4,164 cc, 254.1 cu-in) six cylinders, four-stroke cycle water-cooled naturally aspirated internal combustion diesel engine, manufactured by the Toyota Motor Corporation.

The 1HZ engine has a cast iron cylinder block with 94 mm (3.7 in) cylinder bores and a 100 mm (3.94 in) piston stroke. Compression ratio rating was 22.7:1. In 1998, the 1HZ engine received a reinforced cylinder block and crankshaft, new pistons and glow plugs, the compression was reduced to 22.4:1. Since 2002 the engine is equipped with an EGR system.

The motor has a cast iron cylinder head with the single overhead camshaft (SOHC) with two valves per cylinder and indirect injection design.