OTR Cold Air Intakes for VT-VF

OTR Cold Air Intakes

The LS engines in Commodore and HSV models, from VT to VF, have airboxes that hold back their power. Since the VT model came out, owners have created better intake systems for these engines. At first, many of these were simple pod intakes. The best designs include shielded pods, like the well-known Growler systems.

Later, some people found a way to collect air from the car’s front grille. They aimed to direct the air over the radiator and into the throttle body. Some of these systems were made at home and did not have air filters. These homemade intakes worked well at drag races.

In 2004, we tested one of these DIY intakes made for racing. It also did not have an air filter.

Our LS1 car improved by a solid 0.5 seconds at the track compared to the stock airbox with a K&N filter. This showed us that an intake like this, especially with a good filter, would be very effective.

Engines produce more power when they have enough oxygen in the air into the intake valve and cylinders. A naturally aspirated engine relies on the local air pressure to bring in air. In contrast, forced induction pushes air into the intake valve. At high altitudes, the air pressure is lower. This means there is less air and oxygen for the engine. As a result, the engine produces less power because it cannot burn fuel as efficiently.

Air pressure can change with the weather, even at the same altitude. This means an engine might work better on certain days. The standard air pressure at sea level is 101.325 kPa. It decreases by about 1.2 kPa for every 100 meters you go up. On some days, air pressure at sea level can be higher than 104.0 kPa, while during storms, it can drop below 99.0 kPa.

When an engine is under heavy load and high RPM, increasing the air pressure that reaches it is important. This depends on the design of the cold air intake system. A well-designed intake can direct air better to the throttle body. It can also gather air from a larger area, which improves overall pressure.

Science of Induction

What Happens Regarding Air Pressure On VT-VF Commodores And HSV?

In a naturally aspirated engine, the pressure at full throttle cannot be higher than the air pressure around it. The engine relies on the atmospheric pressure to draw in air. The engine cannot create more pressure than what is available in the environment. The only way this would ever be possible is if the air intake can provide a “ram” effect on the airflow. A ram effect will never happen in the real world when an air filter is used in the intake.

A pressure sensor in the intake manifold is called a “Manifold Absolute Pressure” (MAP) sensor. This sensor is essential for accurate tuning. At idle, the map sensor can show as low as 30 kPa. However, it measures the air pressure at full throttle and low RPM. At that time, it may show 101 kPa.

However, with the stock airbox and filter, this may fade to as low as 89Kpa. This would be evidence of 12kpa restrictions in the intake system and is a significant loss of potential power. With a sound OTR system that uses a high-tech filter, this drop can be as small as 0.5 kPa. This means the MAP sensor reading may drop to only 100.5 kPa daily, that is, Barometer = 101.0 kPa. Usually, an air filter, even a good one like a K&N design, will cause a drop of around 1.0Kpa at very high rpm.

Regarding power, a drop of 1 kPa may only mean a loss of about two rear-wheel kilowatts (rwkw). However, a drop of 12 kPa could result in a loss of around 24 rwkw using the same calculation method. The main aim is to retain as much air pressure as possible.

What Are The Benefits Of A Cold Air Intake?

Cold air is denser than warm air.

This means that for every degree change in air temperature at the intake valve, you gain or lose about one rwkw.

Unshielded pod filters do not work. They bring in air that is warmed by the exhaust manifolds. This air can be 10 to 20 degrees hotter than the outside air. The extra heat in the air could easily cause a loss of power of 10-20 rwkw. The ideal temperature at the intake valve is the same as the ambient (outside) temperature. Still, this goal is unrealistic since the air temperature will increase as it enters the intake manifold. However, variations in ambient temperature are matched by a very similar amount inside the intake manifold. The Intake Air Temperature (IAT) sensor is essential in modern EFI engines. It helps maintain the correct air-fuel ratios. This is crucial, especially when the weather changes. On a hot day, the air is less dense and less fuel must be injected to create the same ideal air-fuel ratio.

On a cold day, the air is denser. This means more fuel is injected to match the higher oxygen levels. A more powerful engine is the result of these conditions. You may have noticed that your car feels faster on a cold night. A proper OTR Cold Air Intake can always give you this type of benefit.

What About Heat Soak?

Hot objects near the intake and its piping have a minimal effect on the temperature of the flowing air. This is because a hot object takes more time to transfer its heat to fast-moving air molecules. This heat then affects the air temperature of the molecules that reach the intake valve. However, heat soak can significantly affect the temperature reported by the intake air temperature sensors. This change can hurt the vehicle’s performance. Positioning the Intake Air Temperature (IAT) sensor correctly is crucial. This ensures it can accurately measure the air temperature in the intake. Proper placement is key for optimal engine performance. This is crucial because fast incoming air temperature closely matches the outside ambient air temperature. The best place to mount the IAT sensor is outside the engine bay. This allows it to measure the ambient temperature accurately. Make sure to keep it dry and away from water.

Water can cause the sensor to rust, eventually leading to its failure. If your OTR (Over The Radiator) intake has a mass airflow (MAF) sensor, it is probably found in a newer car model. This setup usually includes an intake air temperature (IAT) sensor within the MAF. This setup is acceptable, but it often shows a much higher temperature than the actual ambient temperature. This is especially true after the car has been parked for a while.

This isn’t a significant issue if it is taken into consideration.

If you are racing at the drag strip, you want the best performance right after idling in the staging lanes. The position of the IAT sensor can affect your car’s performance.

Additionally, heavy traffic can cause the sensor to overheat, reducing performance. These reporting errors can be fixed in the tune if the tuner knows the normal temperature range. This helps reduce any adverse effects.

What Are Average Gains From A Good OTR?

Combined with a tune to suit, we have consistently seen 30 rwkw or more from HSV LS3 using factory exhaust, similar to L77/L76/L98/LS2. LS1s are identical but vary in performance much more with the different models.

What Does The OTR Sound Like?

They produce a great sound when the throttle is wide open. The car stays quiet when it’s driving at a steady speed.

For many people, a custom tune and an OTR cold air intake, are their only vehicle modifications. They are pleased with the increase in performance and the sound quality.

What Difference Does Having A Maf In The OTR Make To Performance?

It makes no difference in maximum power compared to a mafless tune. However, there are benefits to tuning a car without using a mass airflow (MAF) sensor, as long as it is done correctly. This process is much more complex and requires more effort from the tuner. The advantage is that fuelling can be more accurately setup at all rpm and load. This gives better fuel economy and can reduce popping during deceleration if you want less of it. Many say power delivery is smoother without a mass airflow (MAF) sensor. This is because mafless tuning allows for smoother timing advance transitions.

In contrast, the MAF sensor can create turbulence that affects performance. Tuning an engine without using the mass air flow (MAF) sensor can still be effective, even if the MAF is in place. The benefits of this approach are clear. Removing the MAF does not provide additional gains as long as the screen is taken out of the MAF.

What OTRs Do You Recommend?

We recommend OTR Cold Air Intakes that easily remove filters for cleaning and ones that last well. Many brands are available, including Duspeed, Ramjet, X-air and others.

We currently recommend :