Engine Dyno Basic Test Measurements and an Explanation of What Each One Does

The data gathered with a modern engine dyno is invaluable for those looking to make bigger, better modifications. When you’re working with such complex machinery it’s important that your knowledge reaches beyond just temperature and pressure readings – here are some key bits of information from the sheet itself as well as why they matter!

Airflow SCFM

The airflow SCFM is a measurement of the amount and volume of air that flows into your engine. This number should be monitored closely because it can tell you how powerful or efficient this machine will run, meaning its performance under different conditions may change accordingly!

Brake Mean Effective Pressure (BMEP)

The average pressure required to achieve recorded torque is shown by this calculation. High cylinder pressures show that the engine is generating enough force, and therefore has a high BMEP.

Brake Specific Air Consumption (BSAC)

The value of this measurement is derived from the quantity of air ingested by your engine and power output, given in pounds per horsepower-hour.

Brake Specific Fuel Consumption (BSFC)

This is a calculation of an engine’s efficiency derived from the horsepower and fuel flow rate. This figure can give the dyno operator an indication as to whether the air/fuel ratio is within the zone. At near peak torque, BSFC will be low with numbers in the low 0.4s or high 0.3s showing excellent power production alongside with good air-to-fuel ratios.

Corrected Horsepower 

This calculation is derived using the equation HP=(TQ x RPM)/5,252. It simply means that corrected torque was used in the calculation.

Corrected Torque 

This is a measurement given in pound-feet and refers to the twisting force applied by the engine. The corrected number result arrives at the raw torque meter reading to the test results reading had it been administered using a set standard atmospheric pressure, humidity, and temperature. Atmospheric conditions tend to create variables and using a corrected number eliminates these variables.

Correction Factor 

This is the correction factor that is applied to the raw or measured torque data to ascertain the corrected numbers. STP and SAE are the two most common correction factors used. Ambient conditions will affect the correction factor, for example, on a day with 110-degree temperatures, steaming humidity and very low barometer readings, the correction will be higher to correct the power numbers back to standard conditions.

Exhaust Gas Temperature (EGT)

The EGT can indicate if there are dangerously high temperatures present, which can point to mixture distribution issues and cause engine damage. However, some dyno installations have thermocouples that can read the exhaust gas temperature. 

There are several factors that can impact the EGT, such as valve timing, and it may take experience to be able to interpret results. Although in saying this, sometimes it can give an indication of air/fuel ratio. Advanced Lambda sensor systems have made tuning the mixture obsolete. 

Fuel Flow (lb/hr) 

The fuel flow meter measures in pounds of fuel flow per hour, and most dyno installations include this for measuring the amount of fuel that is entering the engine. 

Lambda A/F Ratio

One of the top developments to happen to the dyno world since the strain gauge, the wideband Lambda – or O2 sensor – provided a real-time, very accurate reading of the air/fuel ratio. Prior to the Lambda, a super-tune required lots of trial and error, guesswork, and skill to arrive at an acceptable result. Now, this instrument removes all that guesswork.

Observed or Measured Torque 

This is the strain gauge or load cell measurement and is the actual torque reading delivered to the dyno. This can vary widely – even on the same engine – when variants in temperature, humidity and atmospheric pressure occur. The observed or measured torque is a raw, uncorrected number.

RPM 

You will always find the RPM in the dyno sheet’s first column, probably because this is the reading that everyone already knows.  Like the tach on a truck, it will give you the engine speed measured the number of revolutions per minute the crank is turning.

Volumetric Efficiency (VE)

This is generally a calculation that is given as a percentage and determines the percentage of air ingested, compared to the displacement volume of the engine. For example, a VE of 100% means the engine is pumping at 100% of its displacement volume regarding the given RPM point referenced. Very trick race engines can easily reach levels of well over 100%. 

There are many different models of flowbenches available at SuperFlow. For example, The SuperFlow SF-750 is a great bench that is ideal even for a big engine shop.

SuperFlow calls its SF-750 the new standard in digital flow testing, with increased accuracy with digital measurements, and more capacity than its predecessor, the SF-600.  

FlowCom™ automatically measures test pressure and temperature, ensuring accurate digital airflow measurement and control. It then presents corrected flow data on the easy-to-read, precision display. In contrast to standard manometer type benches, this saves users considerable time when making calculations to achieve corrected flow numbers. The heat generated during operation is greatly reduced, which in turn extends motor life, by using an automatic motor controller that also maintains constant test pressure; all without the use of knobs and valves. With the reduction of heat, operators can run the SF-750 for longer periods than they can with benches that lack motor control features.

When SuperFlow launched its first flowbench in the beginning part of the ’70s, most of the cylinder heads were very rough in port design and constructed in cast-iron, however the market for flowbenches is now transitioning and expanding.

Because CNC heads consist of a proprietary design, more engine builders are using flowbenches to validate flow numbers and to make internal comparisons to help determine things like cam timing and other engine adjustments. Further, they also flow each port to ensure the cylinders display consistency.

When calibrating a flowbench for a test program, consistency is crucial. Engine builders are recommended to maintain accurate records and establish a reliable A-B-A process.