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.

106 GTi Turbo

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

Oil Change time

Probably one of the important, yet easiest jobs to carry out on your car. With just a basic set of tools you can ensure your engine is running on clean oil, lubricating all the moving parts. Given the 106 gets tracked regularly, I like to change the oil every 6 months or 6-8000 miles at least.

Having used a washing up bowl for years, I decided to go upmarket and buy a proper oil drain pan with spout to stop the annoyance of spilling the used oil when trying to get it back into a bottle. I found a pan on ebay for £13.95 delivered.

I used:

Oil filter Part no. 1109.N2

10W40 semi synth oil

Copper crush washer

24mm socket

Oil drain pan

Start by ensuring the engine is warm (not hot you dont want to burn yourself on the oil). Jack up the nearside of the car and getting an axle stand under the chassis to ensure you can get underneath safely.

Place the oil pan underneath the sump and undo the sump plug. I use a 24mm socket to start it off, and carefully unscrew it.

Withdraw the plug, and let the oil drain into the pan.

If your oil pan is big enough like mine, move it forward so it is both under the sump plug and under the oil filter. You can now unscrew the oil filter and let any oil drain into the oil pan. I use a reliable set of Halfords oil filter pliers I bought years ago, far easier to use than any chain tool.

Replace the filter with a new one, careful not to overtighten it.

Replace the sump plug with a new copper crush washer.

Clean up the sump with newspaper or cloth.

Oil and filter

Refill the engine with new oil, checking the dipstick regularly.

Start the engine, let it warm up and check the oil level again. Top up if necessary.

Job done 🙂

Shake baby shake…

I noticed at , how much the engine moved on it’s mounts when the operator came on and off the throttle. This is usually a sign of worn engine mounts, so I placed an order at 106parts.com for 2 new mounts. Other symptoms of worn mounts include a ‘shunt’ when coming off and on the throttle, often accompanied by a clunk from the engine bay. You can also often feel shaking inside the cabin when the engine is idling.

I decided against choosing group N harder rubber mounts as I’m not a fan of the increased vibrations they transmit into the cabin. It was also slight overkill for a road and occasional track car. So armed with the new mounts to fit I set about swapping them over. This job is very often overlooked as part of maintenance, as garages don’t often recommend to owners to change the mounts and, if you’re not au fait with cars, are hard to identify as a problem. This is not as daunting job as it sounds and with a few simple tools is very easy to do yourself.

I’ve written a guide to changing the mounts .

The gearbox mount was visibly worn, having ovalled the rubber, however the lower mount looked in good condition when compared with the new one.

Having successfully swapped over the gearbox and lower mounts, I took the GTi for a spirited drive down one of my favourite roads, throwing it into corners coming on and off the throttle abruptly and braking hard. The difference was noticable but there was still some driveline shunt present as you came on and off the throttle. So next on the list is a wishbone and top engine mount change, hopefully one of which will cure the problem. I’m pleased to report however the in-car shaking seems much reduced, so at least there was some benefit from the change!

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