Turbo Rallye project – the plan

PlanSpeccing a turbo conversion for a naturally aspirated motor is not an easy task. Every man and his dog has an opinion, and everybody knows best. My approach is to find a reliable manufacturer that produces a turbo which is well matched to the high revving 1600cc engine. I’ll be doing this by analysing turbo compressor maps to find an efficient turbo that is also available at a low price. I’ll also be using empirical data gathered by the 106 community – first hand experiences can be invaluable and save a lot of time and effort. The aim will be a fast road car that is equally at home on trackdays.
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:
  1. Quality – use proven parts, measure twice, cut once
  2. Low cost – good use of second hand and essential parts only
  3. 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.
  • 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.

Losing power, jerky, no acceleration

More problems with the Pug! This time the car started hesistating badly under load, and felt very much down on power. Pulling out of a junction, it felt like the exhaust was blocked as the car would barely accelerate up to road speed. It was also ‘kangarooing down the road, one minute it had a little more power, then the next it was gutless again. I nursed it to work and back and set about taking a look at he possible causes. I started with inspecting the coil pack. Typically symptoms like this are down to fuelling or ignition problems. The coil pack can be a possible failure point when experiencing a misfire and relatively cheap to replace. I observed a large crack in the coilpack, with could be causing the lack of spark on one cylinder and hence absence of power. Since I had a spare coil pack I set about replacing it which was fine until I realised that Peugeot obviously have two types of coilpack. They look almost identical with the same product numbers but the loom plug is slightly different. Fail. So I managed to get hold of the correct coil pack, started the engine and… …same problem.

I booked the car into the garage to get sorted quickly and the diagnostics indicated a faulty injector on cylinder 1 and a intermittent fault on number two injector. Two replacements and the car was up and running. The garage cleaned the throttle body and inlet manifold while they were replacing the injectors.

If you’re car has the same symptoms (misfiring, down on power) you can usually narrow it down to one of the following areas (in ascending cost order):

  • Spark plugs
  • Fuel filter – blocked or dirty
  • Coil pack – cracked or faulty
  • Blocked exhaust – cat internals may have dislodged and blocked the exhaust
  • Injectors – dirty or faulty – ultrasonic cleaning can sometimes fix this
  • Lambda sensor – faulty sensor affects engine fuelling
  • Fuel pump – failed or unable to provide adequate fuel pressure
  • Camshaft timing out – backfiring
  • ECU fault

If you don’t have access to a diagnostic machine you could investigate the fault in the above order, however diagnostic checks can be worthwhile (as in my case) and tell you exactly what the problem is, for not much cash.

Another costly month! Though nice of the garage to fit an auxiliary belt, tensioner and spark plugs for free. It can pay to go to a decent reputable garage.

106 GTi Turbo

I stumbled across this video on YouTube – quite nippy for a little French tin can!

Track n Road rolling road

Track ‘N’ Road are a well respected tuner, offering engine mapping services on their 1200bhp rolling road. Renowned for no-nonsense advice and none of the usual pub-talk figures put out by other rolling roads, their premesis just off the A13 in Rainham, Essex is often frequented by powerful road cars right up to powerful Le Mans prototype track only motors.

I decided to take the 106 along to see how many of it’s horses had been lost over the years! Currently on 125,000 miles, the engine in the 106 still feels strong and healthy to be fair, and it was only a fraction slower on the straights than a 220bhp Mini Cooper S, at the last trackday. Therefore I was intrigued to know what it would make.

Several Rotrex-powered supercharged 306 Gti-6s made good power at 240bhp and upward. A standard GTi-6 made bang on the factory output with a very nice stock power and torque curve.

Then it was the 106’s turn. The little pug decided it didn’t like the rolling road operator and proceeded to shock him as he was trying to find an RPM signal. Turns out the coilpack has a crack in it, hence the shock.
When the car was finally hooked up and strapped down, the run started. Up came the result: 127.3bhp, 7.3bhp up on standard. Now usually I wouldn’t read anything into a 7bhp difference on a rolling road as there are so many variables. But because we had other cars to compare to rather than it being an isolated run, and the good reputation of this rolling road, meant I was very impressed, especially for a motor on 125,000 miles.

BHP graph here