2005 Chevrolet Tahoe Police Package

[x635 4,066]

Good to see Chevrolet is reintroducing the Tahoe in a Police Package. It's definetly needed IMO....sometimes a regular stock Tahoe just doesn't cut it.

Chevrolet's 2005 Police Package Tahoe 

 

  By John Bellah 

http://www.pfmmag.com/

For the first time in five years, a pursuit-capable package will be available on the Chevrolet Tahoe. The police package Tahoe, code PPV, will be available in the third quarter of 2004 as a 2005 model. The pursuit-capable Tahoe comes only with the 285 hp, 5.3L Vortec V8, the M30 4-speed automatic, the 3.73 rear gear ratio and only in 2 Wheel Drive. The 4WD layout was looked at but GM Fleet decided not to do it due to the side loads and torque exerted on the 4WD components. The L59 5.3L V8 is flexible fuel rated. It can operate on 87 octane gasoline or an E85 (85 percent) ethanol as an alternate fuel. 

The pursuit-rated Tahoe was only available in the 1999 model year. The Special Service package was available in 2000 on both 2WD and 4WD versions. After the introduction of the 2005 PPV Tahoe (in 2WD), the Special Service Tahoe will only be available in 4WD.

The PPV Tahoe, like the Special Service package, Tahoe is based on the 1ST Commercial package, which is essentially a de-contented retail Tahoe. The police versions use an argent painted grille, while chrome is available as an option. These vehicles come with the “lift gate” rear door, as opposed to the “twin barn door” style. A 140-MPH certified police speedometer, divided into 1-MPH increments replaces the standard 120-MPH speedo. Front and rear heaters and front and rear A/C is standard on the PPV Tahoe, which should keep the K9 happy. The wheels are vented, heavy-duty 16-inch steel, painted black, with a chrome center cap.

In the overall development of the pursuit-capable Tahoe, GM Fleet looked at five basic areas: ride and handling; braking; cooling system; performance; and adequate electrical system capability.

Stability

Ride and handling is the top priority. These areas cover the overall stability of the Tahoe platform under pursuit conditions. In general terms, changes from the retail vehicle involved lowering the center of gravity, reducing body roll, and altering the jounce bumpers.

The center of gravity was lowered by the selection of lower profile, 70-series tires, instead of the taller 75-series tires mounted on special 16” wheels. The vehicle was also lowered by an adjustment in the front torsion bars and the use of shorter but stiffer rear coil springs. 

Lowering the vehicle is an engineering balance between better handling (stability) under aggressive driving and suitability for the intended police purposes. The vehicle can only be lowered so far. First, lowering the vehicle reduces the ground clearance, an important feature of any police SUV. 

Second, lowering the vehicle limits the suspension travel. If a vehicle is always into the jounce bumpers, stress will be exerted on the frame or sub-structures. This may eventually lead to fatigue cracks, so the police vehicle is suspended to avoid using up all the suspension travel except in extreme conditions. 

The body roll was reduced, and the transient response was improved, by a selection of stiffer springs, larger diameter sway bars and shock absorbers. The anti-sway bars, spring and torsion bar rates and shock valving are specifically developed for the PPV Tahoe.

The suspension of the PPV Tahoe will be developed around a typical police payload. This accounts for a lightbar, communications gear, prisoner partition and front pusher bars. It also includes weapons, scales, ammo, dive tanks and other specialized gear in the cargo compartment.

Braking

Braking is a close second in the priority of development. This covers the entire spectrum of components and systems including front and rear rotor sizes and designs, front and rear pad compounds, wheel material and vent design, and ABS calibration or logic. The ABS on the PPV Tahoe, however, will not have the traction control features available on the retail Tahoe. During aggressive driving on many road surfaces, traction control may actually impede vehicle performance.

The PPV Tahoe uses Akebono brake calipers and pads. The brake rotors are the same as used on the Special Service Tahoe, as is the front to rear brake proportioning. As complex and inter-related as those components are, the real challenge with the 2005 Tahoe is the hydro-boost braking system.

The 2005 PPV Tahoe will be the first GM police vehicle to use hydro-boost brakes. Hydro-boost is not really new; it has been used on medium-duty trucks since the 1970s, and Chevrolet has recently adapted this technology in pick-up trucks within the last few years. So-called “power brakes” introduced on police cars in the mid-1960s used engine vacuum to assist the pedal pressure. While automotive braking systems have advanced dramatically over the past 40 years, all 2003 police vehicles use vacuum-boosted brakes. The GM hydro-boost system uses the hydraulic assist from the power steering pump. The result is the maximum stopping power with the minimal pedal effort and with the least delay in boost.

With vacuum-assist brakes, the first part of the pedal travel compresses air. Power steering fluid is incompressible making the braking action on a hydro-boost start at the instant the brake pedal begins its travel. The downside to vacuum-boosted power brakes is the lack of vacuum at wide-open-throttle. While vacuum power brakes do have a reserve reservoir that will allow for about two stops, this reserve can be depleted in a pursuit situation under urban conditions where rapid acceleration and stopping is required. With the lack of engine vacuum, the officer is faced with a “hard” pedal—and longer stopping distances.

The power steering pump produces hydraulic pressure for the system. As the braking continues, an “accumulator” is needed to keep the line pressure high for times of extended, extreme braking. The power steering pump feeds line pressure through a T-fitting to both the steering system and the braking system. The hydraulic proportioning is set up to give priority to steering first, then brakes. 

This is not the priority conflict that it may appear. Maximum braking is usually done in a straight line, when little pressure is needed for steering. Maximum assist for steering is usually needed at lower speeds, when little pressure is needed for braking. The call for maximum braking and maximum steering at low speeds is rare. Even still, the pressure accumulator dampens out this peak need.

Hydro-boost brakes are clearly more responsive than vacuum-boost brakes, and they are more predictable for the same pedal travel. The accumulator allows the vehicle to make multiple, closely spaced, full-pedal stops, for example, a 120 mph to 60 mph stop followed within seconds later by a 60 mph to zero stop.

Just like the ABS brakes of the early-1990s, a vehicle equipped with hydro-boost has a unique pedal fell and pedal travel. The pedal has a different feel from maximum assist to normal assist to no assist due to sequential valving. According to the MSP test drivers, this sensation is extremely easy to adapt to...once you realize that it is supposed to feel that way...just like ABS pedal modulation. 

Cooling

Changes to the cooling system are, in comparison to the brakes and suspension, quite simple. Chevrolet learned lessons from the development of the Caprice, and later the Impala police cars. The pursuit-capable Tahoe has auxiliary coolers on nearly every fluid that absorbs heat! In the development of the pursuit-capable Tahoe, cooling system upgrades were much lower on the priority list.

The Special Service Tahoe already has a power steering fluid cooler. To this, the police version has the transmission oil cooler, optional on the Special Service package, as standard equipment. An engine oil cooler from the Z71 package is added to the pursuit vehicle. Finally, a larger radiator from the 6.0L V-8 is used on the pursuit Tahoe. Chevrolet engineers intend for the PPV Tahoe to be able to sit at an extended idle period for up to four hours.

Drivetrain

The current engine for the pursuit-capable Tahoe is the 285 hp, 5.3L V-8. This is a relatively new engine that shares little in common with the old “small-block” engine of Chevys past. In the era of Over Head Camshafts, the 5.3L engine is a pushrod engine, as was the old “small-block.” Chevrolet engineers feel that a pushrod engine produces more bottom-end torque and gives added reliability. An engine under unofficial consideration for future years is the 345 hp, 6.0L V-8 from the Chevrolet Silverado SS.

The pursuit drive train has a performance calibration. The timing is allowed to be more advanced, but still controlled by the detonation (ping) sensor. The shift points on the transmission are increased by 500 rpm. This allows the engine to be at or near peak horsepower for longer periods, improving acceleration. Finally, the top speed limiter has been bumped from 98 mph to 127 mph. Fuel economy is estimated to be a tad higher than the retail Tahoe, due to the higher shift points.

In terms of performance, the 3.73 rear gear ratio, optional on the 2WD special service Tahoe, is standard on the pursuit-rated Tahoe. After extensive testing, Chevrolet engineers feel that this ration offers the best compromise between acceleration and top speed. The 3.42 and 4.10 ratios are also used on the Special Service Tahoes, depending on driveline. As of this writing, Chevrolet is considering the G80 limited-slip differential as an option. Chevrolet engineers indicate the G80 limited slip differential is good for getting unstuck from mud and snow. It has no limited-slip capability at speeds above 25 mph.

Chevrolet worked extensively with General Tire on the tire situation. General came up with a variation of an export tire for the PPV Tahoe. This tire was designed for use in Saudi Arabia where road conditions are different from the U.S., due to the different pavement construction. This is compounded by the addition of sand, gravel and the extreme temperatures. 

The General Ameritrac design and tread are utilized; however, a different rubber compound is used for the PPV Tahoe, which has held up well under police testing. Using an existing tire design also helps to keep costs down and with various rubber compounds, the tire can be tailored for different conditions. This tire is designed with somewhat less “grip” than other police tires, and is designed under extreme conditions to slide, rather than grip so much to cause a stability problem. 

This is a police-specific tire, and will be the only tire that will be offered by GM Fleet as a police tire for this vehicle. While other tires in this size may be available, none has the critical load rating and tailored tread compound. This is the only tire recommended by GM Fleet for the Police Tahoe. 

Electrical Capacity

The PPV Tahoe is fitted with a 160-Amp alternator and will have a police-specific wiring harness which will have strategically placed power connectors, outlets as well as ground straps so that the police equipment can be easily installed. Borrowing from Cadillac technology, which has filtered through the Police Impala, the idle speed will automatically increase if voltage drops in order to keep the alternator charging. With this system, as with the Impala, it is imperative to follow factory recommendations when installing police equipment, and is why the police version Tahoe wiring harness offers plug-in connectors, because to splice in to the system at the wrong location can cause serious electrical problems.

As part of their extended idle testing, Chevrolet engineers have designed the electrical system to also function for up to four hours with a 100-Amp electrical load.

Hot Laps

We were given a 32-lap tour of Grattan Raceway at the hand of a Michigan State Police trooper. Grattan is a 2.0-mile, 13-turn road racing course with a number of tight and off-camber turns and a 3,200-foot straightaway. On some parts of the track, cars can actually get airborne while on other sections the suspension may be completely bottomed out.

The PPV Tahoe, at perhaps the middle stage of development, took it all in stride. A couple of turns leading to the front straight have bumps and dips that tax the suspension travel but the Tahoe cornered hard in spite of the wavy pavement. 

The vehicle, at this stage of development, was described as having neutral steering. In fact, it showed little sign of understeer and wheelspin kept it from any oversteer. The vehicle was equipped with ABS, but even during aggressive driving around the course, the ABS was seldom activated, indicating good proportioning and ABS logic.

At the end of the front straight the PPV Tahoe reached 105 mph, compared to 110 mph for the Ford CVPI. The Tahoe had plenty of power, enough to spin the inside rear tire during heavy acceleration exiting many of the corners even at higher speeds.

The PPV Tahoe was also tested under the Los Angeles County Sheriff’s Department Vehicle Test Protocol. This testing consisted of three tests. The 1.57-mile Preliminary Handling Course is a high-speed course that tests how the vehicle behaves at high speeds. While top speeds are not measured, during this course, speeds in the 100 mph range are possible during the straights. Numerous curves in this course wring out brake and suspension components. The Pursuit Course simulates a vehicular pursuit in an urban area. The vehicles run both courses for time. The brake testing involves several high-speed stops to test stopping distances, stability and fade. 

Los Angeles County Sheriff’s deputies conduct these tests. Various sensors are attached to the vehicle to measure component strain and temperatures. The amount of lateral loads generated during the testing are also measured. All of this information is downloaded to an on-board computer and is analyzed by the engineering staff at the end of each phase.

Deputy reaction has been favorable during the testing. They noted some body lean, which is expected with a high-profile vehicle. The deputies also gave high ratings to the brakes, vital components of any police vehicle. All in all, the deputies feel that it will make a good police car.

John Bellah has been involved in setting up maintenance, selection and purchasing programs for the agencies for which he had been employed. Currently he holds the rank of Corporal with the California State University, Long Beach Police Department. He has written numerous articles for law enforcement and automotive publications and regularly attends the annual Michigan State Police and Los Angeles Sheriff’s police vehicle tests. He can be reached at jbellah@csulb.edu.

 

[Guest VFDJrSqd02]

any one got any pictures?

[Guest rreimund]

Sounds pretty hot.. even hotter if they drop the SS engine in there..

I've been consideirng picking up a 1999 Pursuit capbale Tahoe from Key Motors in Albany to build on as a project to build a nice sport truck.

I'm still a few years away from starting anything, so I might wait until these guys are retired in a few years, preferably with the hotter engine.

I would need a real limited slip in it though, since it's 2WD only.

Even so, the 2WD Special Services package are nice too.. a buddy of mine who's on the job in Greenburgh bought one through the state's fleet purchasing program. He's modifying that nicely with suspension and some other stuff (this is a new model with the 4WD though, non pursuit capable.)

-rick