• Optimizer 6500

    Optimizer 6500
    Diesel Power for AM General's HMMWV

    Written by Jim Bigley
    Photography by the author & AM General
    All Rights Reserved

    This article first appeared here in TheDieselPage.com in 2007.

    Since 1984, AM General's High Mobility, Multi-purpose Wheeled Vehicle (HMMWV) has been powered by the Detroit Diesel designed GM 6.2L & 6.5L diesel engines. GM's production capacity, overall low cost and adequate performance made the original GM engines a natural choice for AMG's front-line military rig. Many evolutionary changes were made to this engine family through the years, but perhaps the most significant enhancements have appeared since November 2001. AM General assumed control of engine production in 2000, and immediately began making plans to improve the durability and performance of the 6.5L Turbo Diesel engine - now called the Optimizer 6500.

    In mid-2006 The Diesel Page's Jim Bigley visited AM General's HMMWV assembly plant in Mishawaka, Indiana, to bring you the latest news and information about both the new engine and the vehicles they power. Every photo you see here was either taken by the author or supplied, with permission, to The Diesel Page. At the time, the Optimizer 6500 was produced in Franklin, Ohio by GEP (General Engine Products), which was a subsidiary of AM General.

    Once assuming 6.5L engine production in mid 2000, GEP initiated a bold engine program designed to end the cylinder block & head cracking problem that had nagged the GM manufactured 6.5L engines throughout the late 1990s. Solving the cracking problem involved a serious approach to both the design of the castings and to the metallurgical mix. To achieve the high level of expectations placed on these combat veteran diesels, design and casting duties were handed off to International Casting Corporation in Indiana - the foundry that produces the castings used in the Ford Powerstroke diesel. As a result, the grey iron used in the cylinder block saw the addition of molybdenum, which produced a 20-25% increase in tensile strength. In addition, the block design received taller and wider main bearing webs and caps, and the head bolt bosses in the block deck were strengthened, which improves cylinder head gasket durability. The cast-iron cylinder heads used in the 6.2L and the 6.5L diesels produced by GM could develop hairline cracks between the valves. AM General & International redesigned the head castings and added chromium to the cast-iron alloy. All of these design improvements add durability and greatly reduces the potential for cracking. As a result, the new AM General 6500 has become the best and most durable 6.5L diesel yet produced.

    The civilian H1 Hummer program received the new Optimizer 6500 in late 2001, which continued in production through early 2005 - before being replaced by the Duramax 6600. This photo was taken June 2006 while I was in Michigan. Tom Bridgewater, from GEP, is shown here with a fairly recent 6500 powered H1 Hummer. Sadly, there will be no more civilian H1 Hummers. A total of 711 Duramax powered Alpha models were produced before shutting down the assembly lines. I had the privilege of seeing the last three H1's roll off the assembly line in June of 2006. AMG is adamant in saying there will be no more H1 Hummers.

    Armor and air-conditioning are two features that have become essential in HMMWV development. The aluminum skinned and light armor used by the first vehicles to see combat in Afghanistan and Iraq proved to be inadequate. The current model-1151 rolling off the assembly lines are saving soldiers lives and allowing them to effectively complete their mission. Air conditioning allows them to overcome the withering summer heat of the desert even while wearing full combat gear. The doors have significant weight, feeling more like those used on a quality gun safe. The side and front windows are a special multi-layer 1" thick polycarbonate ballistic laminate capable of defeating small-arms fire. In addition to what is shown here, the roof, cab floor and cab corners all receive armor. Dual air-conditioning is available in models capable of carrying more than two Soldiers or Marines.

    HMMWV armor, as well as a long option list have increased max GVW to a portly 12,000-lb. The weight increases are compensated for by increasing rated power. Now producing 205 horsepower, the Optimizer 6500 power/torque rating has also improved through the years to deal with the increasing demands on the powertrain. Engine development is continuing however, and I'd expect even that number to improve in the near term. The engine development program benefits all of us here at home as well, for those driving 6.5 powered pickups and Suburbans. The new Optimizer 6500 is available through any GM dealer as well as a few selected vendors, as either a brand new or remanufactured engine (see source listing below).

    While touring the manufacturing facility, I asked why the H1 cost upwards of $140,000. My tour guide responded by pointing to the beefy suspension components used by the HMMWV chassis, then said the A-arms, for example, are easily twice as strong as those by an HD pickup truck, and were designed to allow the HMMWV to be dropped via parachute out of a C-130. No pickup could do all that the HMMWV can do. The civilian H1 incorporated nearly all of the very same components used in the military spec vehicles, which made them nearly as capable - and as expensive to produce.

    The A-arms, coil springs, differentials, steering knuckles and brakes are all interchangeable front to rear. The rear hubs and steering knuckles are simply anchored with fixed tie-rods to prevent turning. I couldn't help but wonder about a hydraulic rear-steer mod...

    Many different versions of the HMMWV are being produced. Some with armor and some without, some to haul troops & supplies, some to serve as either an ambulance or vehicle repair station, and some to provide mobility for a turreted 50 caliber machine gun or guided rocket launcher (see lead-in photo). The highly flexible platform and the new Optimizer 6500 allow the HMMWV to excel in just about any role the military chooses. TDP

    Comments 2 Comments
    1. arveetek's Avatar
      arveetek -
      Thank you for posting the article, Jim!

      FYI: Some of the links at the end of the article are no longer working. Optimizer6500.com and Peninsular Diesel are no longer available.

      Thanks, Casey
    1. More Power's Avatar
      More Power -
      Thanks. I removed those links. Stay tuned for more HMMWV and Hummer stories returning to The Diesel Page. Stories worth telling! Jim