Volume 1 Issue 3 - Diesel Articles

The GM Solution

The LBZ intake was looking more and more like an attractive option. I returned to the GM bulletin and put together the parts I needed to upgrade to the GM LBZ air intake. In the process, I discovered a few other parts that GM wanted installed to ensure the effectiveness of their intake system: there were three extra baffles and a duct to install on a Chevy truck in addition to the intake system itself. On a GMC truck, even more was required: seven seals to install around the headlights and hood as well as a foam baffle. That led me to believe that there was more to this cold-air intake than meets the eye. GM engineers were obviously trying to manage airflow into the air inlet of the filter assembly. It seemed logical to me, based on the efforts of the GM engineers, that this system would prove much more effective than the LLY air intake.

Another component of the LBZ intake caught my eye as well; one that is not provided for in the service bulletin. The air duct that clamps onto the front of the turbocharger itself is completely different between the LBZ and the LLY. I had an opportunity to compare both ducts and discovered that the LBZ duct looks like it will allow far more air than the LLY duct. In fact, the LLY duct looks terribly restrictive. At the elbow – where it bends into the turbo inlet – there is a sharp, 90º corner on the inside radius. I’ve ported enough engines to know that a sharp, 90º inside corner is nothing but trouble. At the air velocities this air intake sees, there should be tremendous turbulence at that 90º corner and through most of the bend. The result of this design is that the turbo must work even harder to draw air for boost. This means less efficiency and more heat. It made me wonder why GM did not provide the LBZ turbo inlet duct in their service bulletin. But I had seen enough to know that I wanted to try the new part on my truck. (The redesigned LBZ intake (left) is much larger and more efficiently designed than its LLY predecessor (right). The restricting design of the LLY intake contributes strongly to the vehicle’s overheating issue.)

Testing: “One, Two, Three, Four”

In order to measure how efficiently the new intake would provide cold air while the cooling fan was engaged – the Achilles Heal scenario for the stock LLY intake – all I really needed to measure was the intake air temperature. That is a simple task with the scan tool equipment provided by GM. We were looking at more than just the intake air temperature, however, so we needed a way to determine if the LBZ upgrade actually mitigated or, better yet, prevented the runaway overheating. By comparing the engine temperature rise between test runs, we could paint a reasonably accurate picture of how much less heat the intercooler was sending on to the radiator right behind it. Another parameter that would be good to watch was the turbocharger vane position. With the variable-vane turbocharger on the LLY, it would be easy to monitor how efficiently it was working. The variable-vane control system closes the vanes to provide more boost and opens the vanes to provide less boost. This boost control system is advantageous because it is more efficient in using the exhaust gases to drive the turbo. It also can be set up to reduce the spool-up time. If the turbocharger is working more efficiently, it takes less vane angle to generate the same amount of boost, generating less heat in the process. This means less heat for the intercooler which also means less heated air sent to the radiator. The turbocharger vane position parameter can also be monitored by the scan tool. Intake air temperature, engine coolant temperature and turbocharger vane position data would give a pretty accurate picture of just how well the new LBZ air intake worked compared to the LLY version.

I set up the truck with the same tow tuning and fifth-wheel trailer that I used during my initial overheating experience on Killer Hill. Each run would start at roughly the same temperature and be carried out at the same speed, 65 MPH. To gather the data, I used EFI-Live Flashscan V2, which allowed me to log multiple engine parameters at the same time and store them on my laptop.

Four test runs were required to provide good test data – one for each modification:

The stock LLY intake. The truck was returned to stock cooling condition: the fender holes were covered back up. Torture for my truck and for me, but necessary to provide a baseline for the testing.

Simulating an aftermarket cold-air intake. The LBZ airbox would be installed without any additional baffles. The fender holes would be opened back up. The LBZ airbox gets close to the fender and draws air from the fender and behind the headlight. But it is not perfectly sealed without the extra baffles. Without the extra sealing, it would simulate most aftermarket cold-air intakes I have experienced.

Testing the intake installed to GM bulletin specification. Following GM’s instructions to the letter by installing the extra baffles and hardware, this test would be able to clearly show the effectiveness of GM’s solution.

Adding the LBZ turbocharger inlet duct. This part was not included in the GM service bulletin, but it looked like it would make a difference in turbocharger efficiency. One final run with this part installed would be able to determine if it nets an improvement GM’s solution as posted in the service bulletin.

With the fifth-wheel trailer hitched and the truck loaded up with my laptop, some tools, and all the new parts, I set off in search of a good test hill, one that was long enough to get the fan to engage and still have at least 60 seconds of pulling in order to demonstrate the overheating effect. As I remembered, the cooling fan would normally come on after I pulled the hill, while on level ground. Sure enough, every time the fan came on, the intake temperature shot up 20ºF rather quickly. That proved conclusively that the stock air intake was getting flooded with warm air coming off the radiator whenever the cooling fan clutch engaged. The engine temperature remained between 206ºF and 212ºF when this happened: nothing to get alarmed about (maximum engine temperature specification is 250ºF). Interestingly, the GM diagnostic test for the cooling fan clutch lists an approximate cooling fan engagement range of 185 to 205ºF engine coolant temperature. This number has a wide range because the cooling fan clutch itself engages based on the air temperature that is coming off the cooling stack, which depends on the A/C condenser, the intercooler, and the radiator. There is also a hysteresis – simply put, an unknown – in the engagement of the clutch. For instance, if the engine temperature is climbing quickly enough, clutch engagement will lag behind while the temperature rises quite high. These variables render engine temperature a poor indicator of exactly when the cooling fan will engage. Cooling fan clutches have been replaced due to perceived inconsistent operation when, in reality, they were working fine. After some driving, it became apparent that none of the hills around my hometown would provide a definitive test. There was only one hill within 60 miles that would even turn the fan on while the truck was still climbing, and that only allowed about 30 seconds of fan operation; not enough to drive the engine into an overheat. There are two factors that contribute to the runaway overheat condition: temperature and altitude. Local temperature was only 62ºF and the altitude was around 2,500 feet; not a good testing environment for this particular problem. I could not do much about the air temperature so I needed a considerably higher altitude. I only knew one place within range of a single day’s trip that fit that description. I had to return to Killer Hill.