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The GT-601 gas turbine-powered Macks

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The GT-601

Developing a gas turbine for vehicular use posed unique challenges, as vehicular operation encompasses a wider operating envelope than aircraft or stationary gas turbine operation over a limited altitude range.

The GT-601 vehicular gas turbine incorporates variable turbine nozzles for engine braking and gear shifting, as well as its conventional use as a temperature trim device.

The GT-601 was designed to work with a manual clutch and transmission, or with automatic transmissions (with torque converters omitted).

To meet the challenges of vehicular operation, the GT-601 incorporates features not found in previously designed gas turbine engines.

  • 2-Stage Compressor - To meet the high specific power requirement not obtainable with a single stage compressor.
  • Radial Inflow Gas-Generator Turbine – Minimum cost solution for equivalent performance/life trade-off. Cooled radial stators considerably cheaper to fabricate offered possibility of later transition to ceramic stators
  • Two-Stage Power Turbine with Two Stages of Variable Stators – Higher Efficiency – Reduced diffuser loss-turbine /recuperator. Requirement to match with manual transmission dictated need to decelerate turbine during gear shifts in 2 seconds. Only two stages of variable stators will suffice.
  • Multi-Module Recuperator – High specific power dictated the pressure ratio. Pressure ratio mitigated against rotary regenerator – leakage incompatible.
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Mack Turbine Truck

Commercial Motor / June 27, 1969

Another American vehicle manufacturer has entered the gas-turbine league. Mack Trucks unveiled a prototype turbine-powered truck to its executive earlier this month. The truck uses an industrial gas turbine engine made by The Garrett Corporation, a Mack associate; both Garrett and Mack are part of The Signal Companies Inc.

In announcing the development, Mack states that the prototype is intended to provide the firm's engineers with data needed before the introduction of pre-production test models. Data to be obtained includes acceleration rate, intake and exhaust silencing requirements and general performance information. No information is given on the turbine, such as output and type, but the unit is coupled to a modified Allison semi-automatic transmission in a standard Mack forward control chassis (F-model).

There is added interest in the Mack development given the agreement signed at the end of last year by Garrett and Cummins. This covers a joint program between these two companies to explore the feasibility of gas turbines for trucks and construction equipment. It was stated at the time that Cummins would handle marketing of such units.

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Owner Operator / Sept-Oct 1978

A new gas turbine engine for trucks, the GT601, is being developed by Industrial Turbines International (ITI), a consortium of Mack Trucks, Inc. and Garrett Corp., American firms, and one German company, Klockner-Humboldt-Deutz AG. All have extensive backgrounds in worldwide truck engine manufacturing.

The GT601 is an all-metric design that ITI refers to as a recuperated cycle free power turbine engine in the 300 kW to 560 kW (402 hp to 750 hp) shaft power class.

The engine weighs 988 kg (2178 Ib) and measures 1492-mm (58 3/4-in) long, 1038-mm (41 -in) wide, and 1119-mm (44-in) high.

All engine accessories are gear driven, and include the starter, lubrication pumps, fuel pump, governor, and an air pump which is used for starting only. Likewise, all vehicle accessories (brake air compressor, air-conditioning compressor, alternator, and power steering pump) are gear driven.

Aeromechanically, the engine consists of a gas compressor section, a recuperator section, a combustor section, and a power turbine section.

An electronic computer oversees engine operation for minimum fuel consumption.

At its commercial rating of 410 kW (550 hp), the GT601 should have an overhaul life of 10,000 hr in over-the-road truck use.

The lack of belt-drive accessories and water-cooling system contribute to low maintenance, and there is easy access to engine components.

The variable stator, free power turbine design makes transmission requirements relatively simple. Though laboratory test-cell and in-vehicle evaluations of the GT601 have just begun, results to date look very good.

In combustion tests, the GT601 produced 3.7 g/bhp-hr nitrogen oxides and hydrocarbon; the carbon monoxide content of the exhaust was 0.076 g/bhp-hr.

Installed in an 80,000-lb tractor-trailer combination (Mack R-795S), the engine accelerated the loaded rig from a dead stop to road speed using only top gear of a 5-speed manual transmission. Initial fuel consumption results are in the area of 238 g/kW-hr (0.39 Ib/hp-hr), which is within the diesel engine range.

If all goes well, production of the GT601 could begin as early as 1981.

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Debut for Gas-Turbine Macks

Commercial Motor / May 1, 1982

Two gas-turbine powered Mack trucks made an appearance at last week's Gas Turbine Conference at Wembley

The GT 601 turbine is produced by Industrial Turbines International, a consortium comprising Garrett and Mack of the USA, and Klockner Humboldt Deutz of West Germany.

The gas turbine is particularly sensitive to ambient air temperature, hence the qualification that it develops 410 kW (550 hp) at 29°C (85° F).

At sea level, with an ambient temperature of 15° C (59° F), the GT601 is rated at 475 kW (638 hp).

The turbine-powered Macks are both 6x4 tractors, a forward-control Cruise-Liner and a bonneted Super-Liner.

They have been brought to Europe to demonstrate the potential of the turbine to military authorities as it is also produced in 520 kW (700 bhp) form for use in a light tank.

To be compatible with automotive transmissions, the output drive speed of the GT 601 is 2,600 rpm compared with its generator and power turbine speeds of 37,000 and 26,000 rpm respectively.

The highest temperature recorded in the engine is the 1,040° C (1,900° F) at the turbine inlet.

According to engine load, the temperature prior to the stainless steel heat exchanger (or "recuperator" in Garrett terminology) is 650° C (1200° F) and 315°C. (600°F) after it.

One of the advantages claimed for the gas turbine concept is that it is far lighter than equivalent high horsepower diesel engines. At the Wembley exhibition, Garrett was quoting a weight of 998 kg (2,200 lb) for the GT 601 compared with 1,360 kg (3,000 lb) for a 600-plus horsepower diesel engine.

The GT 601 has been designed specifically for heavy trucks (30 tons plus) where it is claimed to achieve 10,000 hours between major overhauls.

At a gross weight of 80,000 lb (approx 36 tons) in U.S. tests, the Super-Liner achieved 56.5 lit/100 km (5 mpg) compared to 62.7 lit/100km (4.5 mpg) at 100,000 lb (45 tons) and 70:6 lit/100 km (4 mpg) at 120,000 lb (54 tons).

The Gas Turbine Conference was organized by the American Society of Mechanical Engineers and the Institution of Mechanical Engineers.


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NOx Emission Controls for Heavy-Duty Vehicles: Toward Meeting a 1986 Standard

Motor Vehicle Nitrogen Oxides Standard Committee

Assembly of Engineering

National Research Council


Another promising alternative engine for heavy-duty applications is the GT-601 gas turbine being developed by a consortium of the Garrett Turbine Engine Company, the Mack Truck Company, and German engine manufacturer KHD (Klöckner Humboldt Deutz AG). This a very large engine rated at 550 horsepower in commercial applications.

It’s emissions of hydrocarbons, carbon monoxide and nitrogen NOx have been measured at 0.05, 1.89 and 3.13 g/bhp-h respectively, on the steady-state test cycle.

At its most efficient operating point, it has a brake-specific fuel consumption of 0.393 lb/bhp-h.

Its particulate emissions have been reported as 0.33 grams per kilogram of fuel.

Using the best fuel economy figure of 0.393 lb/bhp-h gives a minimum brake-specific particulate emission rate of 0.38 g/bhp-h. (Of course, the actual emission rate over the test cycle would be greater than this, and no direct comparison with the 1986 particulate standard of 0.25 g/bhp-h, on the transient test procedure, is possible.)

The developers of this engine are optimistic about its introduction in the latter half of the 1980s, but they recognize that this high-powered engine’s uses will be limited. Initial applications are expected to be in on-and-off-road applications such as logging and mining. The first application in trucks would be in a Class 8 trucks operating on rugged terrain.

This particular engine is cited here because it is currently undergoing on-road evaluations in a truck. Future use of this engine will obviously depend on its ability to meet NOx and particulate standards, as well as on its fuel economy as compared to that of the diesel engine it would replace.

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The GT-601 gas turbine was produced by Industrial Turbines International (ITI), a joint venture between Garrett AiResearch, Mack Trucks and KHD (Klöckner Humboldt Deutz AG) established in 1972 to produce purpose-designed gas turbines for heavy trucks.

Klöckner Humboldt Deutz had been producing gas turbines from 1956. In 1980, the KHD gas turbine unit was renamed KHD Luftfahrttechnik GmbH and sold to BMW Rolls Royce in 1990, now known as Rolls Royce LLC and a major producer of jet engines.

The GT 601 was a free-turbine all-metal engine with a fixed boundary recuperator. More than 7,000 hours of operation were accumulated, including more than 2,000 hours in highway trucks. These engines demonstrated the feasibility of fixed boundary recuperators along with superior torque compared to diesels of similar rated power, easy cold starting, and the ability to survive limited foreign object ingestion.

While the initial chose power range was 450-638 horsepower (335-476 kW) for heavy trucks, ITI later created a 550-750 horsepower (410-559 kW) engine range to better target the tracked military vehicle segment.

Installed in the experimental XM723 mechanized infantry combat vehicle (the forerunner of the Bradley fighting vehicle), the GT-601 was mated to a Detroit Diesel Allison X-300 four-speed automatic transmission with the torque converter omitted.

GT-601 Development History

1974 – Initial design work begins

1976 – Final design completed.

1978 – Production of early prototypes. Results proved the GT-601 to be highly reliable.

1979 – The first GT-601 underwent endurance testing in a Mack R-795S 6x4 tractor.

The U.S. Army Tank Automotive Research Development and Engineering Center (TARDEC) and ITI sign a one million dollar contract to identify gas turbine power as a viable powerplant for tracked military vehicles. Specific test programs were created for the U.S. Army’s XM2 infantry fighting vehicle and XM3 cavalry (scout reconnaissance) fighting vehicle, requiring a power increase to 750 horsepower.

1980 – Gas turbine truck testing (Mack Trucks) at the U.S. Army Yuma Proving Ground in southwestern Arizona.

1981 – A 638 horsepower GT-601 installed in a 45,000 pound XM723 mechanized infantry combat vehicle (MICV) underwent TACOM Phase II demonstration testing at the General Motors proving grounds in Milford, Michigan from August 17 thru November 5. to demonstrate the characteristics of a Garrett GT601 gas turbine engine mated with a Detroit Diesel Allison X-300 transmission without a torque converter installed. Virtually no engine-related problems were observed.

Combined with additional U.S. Army testing of the GT-601 in M2 infantry fighting vehicles, Mack 6x4 tractors, and M-48 main battle tanks, over 6,200 miles of feasibility study was done.

1982 – The GT-601 completed 1,000 hour qualification testing, and testing using multiple types of fuels.

1983 – The GT-601 powered XM723 underwent TACOM Phase III demonstration testing at the General Motors proving grounds in Milford, Michigan from January 4 through 18, March 24 through 30, and completed June 7 through June 9, 1983.


  • Vane Braking - The U.S. Army concluded that the distinct advantages of gas turbine “vane braking”, a feature unique to the GT-601, provides enhanced drivability as well as the ability to maintain low speeds on downgrades without vehicle brake application.
  • Inlet Blockage - The engine showed no adverse affects from a 55 in-H 20 inlet depression other than reduced power output
  • Maximum Braking - Power turbine inertia does not have any adverse affects on the gear train during vehicle braking.
  • Forward-Reverse-Forward Maneuvers - This maneuver did not adversely affect engine or transmission integrity.
  • Gradeability - The GT601-powered vehicle demonstrated the ability to maintain a balance speed approximating computer predictions on a 60-percent grade.

The positive experience prompted the U.S. Army to arrange for additional testing at their Yuma, Arizona proving grounds to evaluate various inlet filter systems and demonstrate the GT-601’s ability to operate in extreme sand and dust conditions.

The GT-601 was installed in additional vehicles for testing including the General Dynamics Land Systems Division Electric Vehicle Test Bed (EVTB), a “Chieftain” main battle tank from the UK’s Royal Armament Research and Development Establishment, French AMX-30 main battle tank, Israeli Russian T-55 main battle tank, M-109 self-propelled howitzer (at Yuma and Fort Sill Proving Grounds), and a Weasel air-transportable armored fighting vehicle and M-48 main battle tank from the Federal Republic of Germany.

1987 – Sixteen prototypes had been completing logging over 60,000 miles. Development costs reached US$90 million. The GT-601 gas turbine has been extensively tested by the United States, Britain, France, Israel and Germany. ITI hoped for orders to refit M-47, M-48, M-109, AMX-30, and German main battle tanks, as well as orders related to power generation, industrial and marine power.

ITI estimated the military spec GT-601 in mass production would cost US$250,000 per unit.

Reference: The XM723

From 1958, The U.S. Army was imagining an infantry fighting vehicle that, with substantial armament and greater protection than the M113 armored personnel carrier, would allow the armored infantry squad to fight from the vehicle. In 1964, the Army initiated a development effort for a mechanized infantry combat vehicles (MICV) to include an interim vehicle, the MICV-65 (XM765), and an objective vehicle, the MICV-70.

After rejecting the XM765 AIFV derived from the M113, the Army gave FMC a contract to develop a superior version. In 1972, the Army awarded FMC $29.3 million to design, develop and fabricate three prototype MICV-70 vehicles, a ballistic vehicle, 12 pilot vehicles, and associated systems engineering, product assurance, and test support.

The MICV–70 project led to a purpose-built vehicle, the XM723 MICV, armed with light cannon and a machine gun in a one-man turret, and provided with vision devices and firing ports for the mechanized infantry squad it carried.

Prototype to the Bradley Fighting Vehicle, the XM723 operated with a crew of 3 and carried 9 Infantrymen. The turret was armed with a 20mm cannon and 7.62mm coaxial machine gun. The design had a novel laminated steel / aluminium armor which was relatively light but gave improved protection against small arms fire up to 14.5mm.

The XM723 prototypes were completed in 1975 and owed some design heritage to the US Marine Corps Amtrac series of vehicles, rather than the M113. Although the Infantry (XM2) and Scout (XM3) variants of the MICV were still mechanically identical, they were envisioned as having different weapons stations. The infantry version was to continue with the one-man turret as planned. A dual turret version was planned as well.

The scout version with its reconnaissance mission placed a premium on observation for the commander. The original MICV arrangement, with the commander stationed in the hull behind the driver and beside the turret, was unacceptable. Thus the Scout version was to have a two-man turret so the commander could be stationed at the highest point in the vehicle with a 360-degree field of view. And in addition to the cannon and coaxial machine gun, the Scout version included an optically-tracked wire-guided (TOW) heavy antitank missile launcher.

In 1975, the Army rejected two prototype designs for the Scout version and began developing the prototype XM723 as a cavalry vehicle. The Army combined both cavalry and infantry fighting vehicle requirements under the Mechanized Infantry Combat Vehicle program in 1976. At the same time, an army task force new program called the Fighting Vehicle System consisting of two vehicles: the XM2 Infantry Fighting Vehicle and XM3 Cavalry Fighting Vehicle.

The XM723 was designated the XM2 for the Infantry Fighting Vehicle requirement and the XM3 for the Cavalry Fighting Vehicle requirement. FMC was awarded a contract to produce the modified vehicles. Based on recommended changes to the XM723, the M2 Bradley Fighting Vehicles was manufactured and fielded in the early 1980's.







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  • 6 months later...

A few amendments to the otherwise excellent information on this topic. I was the project engineer for the GT-601 installation in the R model. My team at the Engineering Development and Test Center in Allentown, PA installed the engine in 1979-80 and modified the vehicle accordingly. The technicians and machinists at the ED&TC were absolute masters of innovation and deserve huge credit for their work. The vehicle was eventually driven out to Phoenix where AirResearch was HQ and extensively tested in desert and mountainous conditions (up to Flagstaff).

When idling, the air velocity of the gas turbine intake made horrendous noise at the front of the vehicle but there was no time to work on silencers so out it went. The vehicle was interesting to drive because it needed no clutch. Compared to Maxidyne engines it was not very impressive and I had many good conversations on the subject with Win Pellizzoni the Maxidyne concept inventor.

The fuel economy was poor (it was a prototype), the engine management was buggy and black art stuff, plus the engine costs were enormous. It was reasoned that 500 hp and the costs would not be successful so the idea was dropped.

I might be able to find my photos of the project and post them.

Tom, thank you so much for adding to this discussion and correcting my memory where necessary.

Once upon a time, I found myself at the Mack Trucks distributor in Phoenix. As you recall, the distributor was leasing to Mack Trucks a building across the yard from their shop, for turbine truck work (owing to Garrett AiResearch being in Phoenix). I spent the day watching Mack engineers going about the installation of a turbine into a Hayward-production Value-Liner. And yet, I've never read any mention about that truck?

When you say that Win Pellizzoni was the developer of the game-changing Maxidyne high-torque rise engine, then would you describe Walter May as the project manager?

Tom, the work that was done by you and your colleagues at the Mack Engineering, Development and Test Center (R&D center) in Allentown put the global truck industry on notice time and time again that Mack Truck engineering was second to none. Thank you for your many years of dedication to the greatest name in trucks. What Volvo has done, reduce a global icon to a mere shell of its former self, should be a crime.

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Thank you for the kind welcome. I really enjoyed working for Mack Trucks but things went downhill when AirResearch bought the company...development investment was drastically scaled back. RVI was purchased, and the rest is sad history. After Mack I enjoyed positions at Mercedes-Benz, Britax Child Safety, and lastly BMW where I retired as VP of Engineering.

Walter May eventually became Chief Engineer and then retired, followed by Bob Zalokar and then Steve Homcha, Win was the father of the Maxidyne concept...Walter May was the father of the "Walter May" test. That was, for anything mounted on the truck with a bracket, smack it with your hand and if it moves it's not robust enough. A seat of the pants method that all young engineers could understand, and it forced hands-on development. He also helped establish the fuel tank "bump test" (with Dr. Bill Geiger) where a filled tank and brackets on a frame were lifted and dropped at least 1 million times. I think if Mr. May stayed on the company would have continued to flourish.

I remember the big development projects for UPS trucks since they always got special features like mirrors and steps, etc. The head guy at UPS had worked for Mack at the Test Center so he was a big supporter of Mack. Eventually, some bean counters tightened the belt and UPS moved on.

There were a lot of very talented people that left Mack. The strikes and "us vs. them" mentality were devastating. During one strike I was warned not to look at strikers while driving into work, or risk getting my tires slashed. I was pelted with grommets from line workers on break at the Macungie plant when I was there to fix leaning fire trucks. Engineers could not pick up a screw driver and use it even once or there would be a grievance filed. Sadly, management was also to blame. As a Senior Test Engineer in 1979 with about 7 big projects at once, I was paid the same as a plant floor sweeper. When engineers met with management and showed them the numbers their response was "you don't have a union." I left shortly thereafter.

I still have the actual bulldog from the prototype MA model cabover build that I supervised. Nice memories.

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Thank you for the kind welcome. I really enjoyed working for Mack Trucks but things went downhill when AirResearch bought the company...development investment was drastically scaled back. RVI was purchased, and the rest is sad history.

I still have the actual bulldog from the prototype MA model cabover build that I supervised. Nice memories.

Just so there's no confusion, Mack Trucks was never owned by Garrett AiResearch (Garrett Corporation).

In 1964, Garrett allowed itself to become a subsidiary of The Signal Companies, the nation's largest west coast oil company, in order to avoid a hostile takeover by Curtiss-Wright Corporation.

In 1967, in order to raise capital to support Mack's rapid growth, Mack Trucks agreed to become a subsidiary of The Signal Companies on the condition that that Mack was guaranteed complete autonomy (a requirement demanded by legendary Mack president and CEO Zenon C.R. Hansen).

Thus, both Mack Trucks and Garrett AiResearch were subsidiaries of the Signal Companies.

Signal purchased Mack Trucks in 1967, sold 40 percent to Renault in July 1983 and sold 50 percent in a public offering in August 1983. The remaining 10 percent (3.1 million shares) was sold in July 1986 by the Henley Group, a corporate spin-off resulting from the Signal-Allied merger.

In 1985, Signal merged with Allied Corp. and became Allied-Signal. The company bought Honeywell in 1999 and adopted the Honeywell name.

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It sounds like a book should be written. I'm fascinated. Being an engineer and a truck guy this is cool to read. Thanks for the info and consider writing down your experiences. It might be worth the effort and these days digital makes publishing easier...food for thought.

I know many of us would read it all.


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to bad mack didnt stay independent . if they hadnt gone in with signal they never would of ben sold to renault and later volvo. renault allowed mack to do its own thing but still got gobbled up by volvo. didnt paccar almost buy mack in the late 80s or early 90s ?that would of been a better end result . mack could of been paccars east coast heavy vocational and regional brand and with paccars cash could have kept improving mack engines and transmissions . maybe even mack e9 v8s would be powering peterbilt and kw long haul trucks today. oh well i guess we will never know.

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to bad mack didnt stay independent . if they hadnt gone in with signal they never would of ben sold to renault and later volvo. renault allowed mack to do its own thing but still got gobbled up by volvo. didnt paccar almost buy mack in the late 80s or early 90s ?that would of been a better end result . mack could of been paccars east coast heavy vocational and regional brand and with paccars cash could have kept improving mack engines and transmissions . maybe even mack e9 v8s would be powering peterbilt and kw long haul trucks today. oh well i guess we will never know.

That's not exactly what happened. Signal was very good to Mack, providing substantial capital to the company while allowing Zenon C.R. Hansen to run his own ship.

Aside from when Signal purchased Universal Oil in 1975, Signal was heading down the road to being an aerospace and technology company from the moment they acquired Garrett in 1964. So it should come as no surprise that by the early 1980s, Signal was deciding that trucks was not on the same radar screen as aerospace and technology.

The original reason that Mack and Renault began doing business together was solely to market a medium truck in the U.S. market. And the Mid-Liner was terrific.

When Signal offered a 40 percent of its Mack stake to Renault in 1983, it made perfect sense. Like Signal, Renault allowed Mack to operate with a tremendous degree of autonomy. But unlike Signal, Renault immediately became a major customer for Mack engines and engineering. It was a good fit with attractive synergies.

Signal's public sale of 50 percent of its remaining Mack shares demonstrated Signal's decision to focus its investments in technology.


Year 1990 - http://articles.mcall.com/1990-07-20/news/2761289_1_renault-vehicules-industriels-mack-trucks-rvi

Year 2000 - http://www.thefreelibrary.com/Navistar+Draws+Takeover+Offer+From+Truck+Competitor+PACCAR,+Stark's...-a065633850

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