NGK/NTK L2H2 Lambda Backpressure Calculator

Accurate and Durable

We use NGK/NTK L2H2 wideband sensors on our Cosworth Pectel SQ6M engine controllers. Pectel SQ6 and SQ6M controllers are designed for these sensors as they are the most accurate available. These are five wire sensors. We use Deutsch DTM six pin connectors with the 6th pin filled by a dummy wire/contact.


The NGK/NTK sensor should be located near or about 12" from the exhaust valve(s) of the engine on motorcycles and no futher than 48" on cars. A location further from the engine may be used as long as it is at least ten times the exhaust pipe diameter upstream of the end of the exhaust system. For example, with a 2" diameter exhaust pipe, the sensor should be at least 25" upstream of the end of the exhaust.

The problem with locations less than ten diameters upstream is that reversion air may be trapped in the exhaust giving leaner than actual readings. This especially occurs at low exhaust flowrates (i.e. idle). Locating the wideband (UEGO) sensor far from the engine exposes the sensor to more liquid water during both start-up and normal operation and is not recommended.

Short turbo exit dump tubes on race vehicles like our Bonneville Bullet preclude mounting a Lambda sensor so close to atmospheric air. Placing the sensors in each of the Bullett's primary tubes (V-Twin) allows us to trim each cylinder.

Backpressure OEM

OEM vehicles with multiple catalytic converters and mufflers are all subject to backpressure which is figured into the million plus lines of code in a modern ECM which may contain 8000+ modifiers. For most of its engines, GM recommends no more than 8.62 kPa (1.25 psi) at idle, and no more than 20.68 kPa (3 psi) at 2,000 rpm.


NGK/NTK L2H2 Wideband lambda sensors can be installed pre-turbo unlike the Bosch LSU-4.2/4.9 lambda sensors.  The NGK NTK wideband sensors are tolerant of leaded and methanol fuels and are rated at higher temperatures than are the Bosch wideband sensors. The operating range is up to 950 Degrees Celsius C or 1742 Degrees Farenheit. Backpressure in the turbo manifold will skew the readings of engine controllers and displays unless compensation tables are built in.

Closed Loop Considerations

Closed loop Lambda operation should be considered as a "trim function" and not an overall control strategy. With the SQ6M we tune in Open Loop but we monitor each cylinder on our V-Twins with the NGK/NTK wideband sensors. The base fuel map (or maps) have to be correct in Open Loop. In boosted operation we do not use Closed Loop wide band control beyond very low boost figures.  Logging engine backpressure and monitoring EGT's are all part of the development process.

For tuning you have to figure in backpressure compensation as the Lambda readings are skewed under boost.

Backpressure Air Fuel Correction Calculator
Input Answer
Boost Pressure: Positive numbers in PSI up to 10.00

Air Fuel Ratio (AFR) Displayed: This number is skewed by the exhaust backpressure. Enter numbers from 8.00 to 18.0

AFR less than 14.7 (rich side) are displayed richer than they really are.

AFR greater than 14.7 (lean side) are displayed leaner than they actually are.

Actual Air Fuel Ratio: Corrected for Exhaust Backpressure