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Race Car Engine Analysis Using Running Compression

By Lee Hearnden - LMH Engineering Services

This Case Study is based upon the Running Compression waveform that is produced when using the PicoScope Automotive Oscilloscope and the WPS500X Pressure Transducer.

It is strongly recommended that if you are not familiar with the Running Compression Waveform and how to identify the events that take place within the waveform, you should read the Technical Article we wrote to help you understand. Simply click on the image to be re-directed to our article.

Click here to View Running Compression Technical Article

Ridgeback Automotive Engineering

At LMH Engineering Services we were recently contacted by Mr Barber at Ridgeback Automotive Engineering who had just completed a re-design of their A - Series Race Engine and were interested if we could identify with the PicoScope and the WPS500X Pressure Transducer the overall condition and balance of the engine.

Race Car Specification

Technical Information

  • Engine– 1275cc 'A' Series Engine
  • Ported Intake and Exhaust Ports
  • Custom Built Inlet and Exhaust Manifolds (Designed and Built by Ridgeback Automotive Engineering)
  • Twin R1 Carburettors
  • Upgraded FORD EDIS DIS Wasted Spark Ignition System Powered by a MEGAJOLT LITE JR with Mapping and Data Logging capabilities



Image Sourced and Copyright protected from Autosport Labs

  • Lambda Sensor with Digital Computer

Some of the work detailed by Ridgeback Automotive Engineering was porting the engine’s intake and exhaust ports however this was not able to be gas flowed so there was some uncertainty to the balance of the porting and as a result, and if this had an effect on the balance of the engine and the overall power output of the engine.

High Performance Camshaft

Work carried out on their engine also involved a Kent CAM High Performance Camshaft which the specification is detailed as follows:-

Information sourced from Kent CAMS Website:

Mini Engine Configuration

For us to be able to understand what we are seeing, we need to understand the construction, configuration and characteristics of the 'A' Series engine.

Volumetric Efficiency

Volumetric Efficiency is a key factor when deciding how to modify any automotive engine, as this is the key element in the overall power output achieved from the engine.

When the engine is on the 'Intake Stroke', a fresh mass of air is charged into the cylinder. This is induced through the Intake Port, Past the Intake Valve and into the Cylinder from Atmosphere.

The Intake system can be designed in the following 4 ways:-

Naturally Aspirated - Engine allowed to Induce Air through the depression created via the Intake Stroke

Ram Charging - Often Race cars are fitted with larger Air Intakes strategically positioned at the front of the car to allow air to be forced at a higher rate into the Plenum Chamber whilst driving at high speeds.

Turbo Charging - A turbine is driven via the kinetic energy created within the blow-down process once the exhaust gas is expelled from the cylinder. The turbine directly drives an impeller which draws air into the compressor housing and forced into the Plenum chamber at high pressure.

Super Charging - A compressor is directly driven via the engine by using either a geared system or via a belt driven from the crankshaft. The Compressor draws air into the compressor housing and its then forced into the Plenum chamber at high pressure.

The air induced into the cylinder is often referred to as 'mass of air supplied'. The atmospheric conditions of air pressure and air temperature are typically known as 'Ambient Conditions'.

The Volumetric Efficiency therefore defines the actual state of which the mass of air supplied into the engine during the valve 'open' period in comparison to a mass of air that would perfectly fill the swept volume of the engine under the perfect Ambient Conditions.

To assist in reaching the perfect Volumetric Efficiency, Race cars often have manifolds and intake ports 'ported and polished'. Forced Induction Systems are generally fitted with an Intercooler to reduce the temperature of the air to increase the air density.

Ridgeback Engineering redesigned the Intake Manifold for their Race car engine to be able to not only allow the strategic positioning and fitment of the Twin R1 Carburettors but to allow them to be ported with the Cylinder Head to try and increase the overall volumetric efficiency.

This is what we measured with the PicoScope and the WPS500X Pressure Transducer. 

In order to complete the Running Compression Waveform we needed the following equipment:-

  • PicoScope Automotive Oscilloscope
  • WPS500X Pressure Transducer
  • BNC to BNC test lead (Supplied with the WPS500X)
  • Compression Hose

Setting up the PicoScope Hardware

Channel A - Running Compression

Connect the WPS500X Pressure Transducer to Channel A of the PicoScope as shown in the illustration below using the BNC to BNC test lead.

Connection Diagram

Ensure that the WPS500X has performed the self-calibration process and is set to 'Range 1' for the test.

Remove the 'HT lead' from the Spark Plug and then remove the Spark Plug from the cylinder which is to be tested. Using the 14mm WPS Compression Hose, Connect the WPS500X to the engine accordingly.

 Example Running Compression Waveform

This is an example Running Compression waveform taken from a Conventional 4 Cylinder Engine.

Cylinder Test Results

The results we obtained from all 4 Cylinders are as follows:-

Cylinder 1 Results

  • Idle Speed Running Compression Waveform
  • PMAX 6.606 BAR

  • Wide Open Throttle Running Compression Waveform
  • PMAX 18.12 BAR

Cylinder 2 Results

  • Idle Speed Running Compression Waveform
  • PMAX 12.08 BAR

  • Wide Open Throttle Running Compression Waveform
  • PMAX 17.63 BAR

Cylinder 3 Results

  • Idle Speed Running Compression Waveform
  • PMAX 11.29 BAR

  • Wide Open Throttle Running Compression Waveform
  • PMAX 17.46 BAR

Cylinder 4 Results

  • Idle Speed Running Compression Waveform
  • PMAX 7.367 BAR

  • Wide Open Throttle Running Compression Waveform
  • PMAX 18.5 BAR

Cylinder Test Results Comparison

We then used the PicoScope Software to create a reference waveform of all the cylinders so we could overlay them to see a direct comparison of all 4 cylinders.

  • Comparison of Idle Speed Tests

  • Comparison of Wide Open Throttle Speed Tests

Now we had all our results from the Cylinders we were able to produce our analysis and report our findings back to Ridgeback Engineering.

Cylinder Analysis

When Looking at the Running Compression Waveform is just as important to look at the detail within the waveform as well as the pressures obtained from the cylinder. This gives you some good insight into how the cylinder is performing mechanically as well as effectively.

Cylinder Sealing

One Important aspect to check is Mechanical Sealing, this identifies to us if we have a leaky Inlet or Exhaust Valves or worn Compression Rings which would give us some Power Loss from that cylinder.

We can identify this quite easily from the Running Compression Waveform by looking at the 2 areas highlighted on the waveform below.

We should expect to see on an engine that has good Mechanical Sealing, the same pressure at the points shown above with the blue arrows. These points are indicated as BDC (Start of Compression) and BDC (Start of Exhaust)

If the pressure is the same then this tells us that the Valves are correctly seated and providing an effective seal and it also tells us that the Compression Rings on the Piston are also providing a good Mechanical Seal within the Cylinder/Liner.

If we saw a pressure which was lower (More Vacuum) after the Compression phase this would indicate that the cylinder had leaked air through either one of the Valves or through the Compression Rings indicating our cylinder wasn't providing an effective Mechanical Seal.

We would expect to see a very minor loss as the Engine will not hold a perfect seal however any major loss would initiate a Cylinder Leakage Test to identify where the Compression is being lost and by what amount. 

This Technical Article is included in our WPS500 Training booklet which is

supplied FREE with the purchase of the WPS500 Full Kit.

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