Turbo Rallye project – the plan

It helps to be clear what you want to achieve with these types of builds or they tend to spend years half completed languishing in a garage surrounded by expensive parts that were bought on a whim.
So with that in mind the ethos will be:
- Quality – use proven parts, measure twice, cut once
- Low cost – good use of second hand and essential parts only
- Reliability – no chasing figures at the expense of reliability
The approach for this project will be to turbocharge the 16V 1600cc TU5J4 engine from the 106 GTi. I will not be lowering the compression, or using forged steel components to keep the cost down. The TUJ4 is a relatively high compression engine at 10.8:1 so I will be looking at running low boost – probably 7.5psi or half a bar of boost depending on how much air the turbo can flow. Any more than this and cylinder pressures rise and the risk of detonation and a melted engine goes up.
Benefits of a low boost standard engine approach
- Cost – Tu engines are plentiful and cheap. Should the engine let go, replacing it will be easy and cheap. Small turbos are cheaper.
- Less heat – Having to run relatively low boost should mean less heat management issues to contend with (generally speaking)
- Responsiveness – high static compression means good drivability off boost and should give good turbo spool
- Kinder to the transmission – Less boost, less power, less torque through the drivetrain.
Drawbacks
- Risk of pre-ignition – A bad batch of fuel, or hot intake temperatures could pre-ignite the fuel and melt the engine
- Limited boost means limited power before knock occurs.
- Increased wear – Running over 50% more power than the engine was designed for, will increase stress and fatigue
- High cylinder pressures – risk of head lift and head gasket blowing
So given our clear objectives, next time we will delve into the black art of choosing a turbo.
Remember to put your nerd specs on and bring a calculator.