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Turbocharge Your MG Midget

How To Do It

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Troubleshooting page 2
Neil's (mine) 1098cc
Simon's 1275cc
Paul's 1275cc
Arno's 1275cc
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How To Do It
 
OK a brief HOW TO turbo charge your midget

Lets start with the Head.

A standard cylinder head is OK for the job and if you have a gas flowed one so much the better. Try to find a head that has not had too much skimmed of it as this will push up the target compression ratio. Make sure that the valve seats are cut nice and wide to give a good contact area to help dissipate some of the heat .

The compression ratio has to be kept fairly low so Simon Atherton used Marina van dished pistons which gives a compression ratio of 7.44:1 (8.5:1 being the norm). 

Good results can be had from the standard pistons and compression ratios as long as you do not use more than about 0.5 to 1 bar of boost. You could get away with more boost if you had an inter cooler fitted.

The standard oil pump does not need up rating. There are various versions of the standard oil pump around.  Both I and Simon have around 20 psi idle and 40+ psi while driving and engine being hot

The Metro Turbo oil pump will not fit.

The turbo needs its own oil feed for lubrication and to some extent for cooling, this feed can be taken off the oil pressure gauge line using a T piece or from some other convenient point.  (In this case both me and Simon have taken it from the same place but using slighlty differrent ways, I have taken the oil from the big screw that holds the banjo connection pipe that goes into the oil filter and have placed a fuel filter into this line to create an inline oil filter.  Simon's is also taken at the same place but as can be seen by the photo on the photo's page is where his oil filter actually is.

The oil has to return to the engine some how. Some but not all A series engines have a hole cut in the block for this (it's sometimes blanked off). It used to be for the petrol pump drive on early engines. This may need breaking through and a couple of studs fitting. Or some other way found to return the oil from the Turbo to the sump.  In my case I used a pluming attachment in the sump to allow my oil to return to the sump from the turbo.

 An Oil cooler might be needed, you will have to run and see.  Mine hasnt got an oil cooler, but does have a kenlow fan and appears to be fine

The standard camshaft is good enough; (it is retained by the Metro Turbo cars). You can fit 1.5:1 ratio high lift rockers to give you that extra valve lift, but this may lead to a little extra turbo lag. You should be aiming to lift the valves about 400 thou.

The standard water pump is OK but you may need to play around with the drive pulley size to help cooling. Simon used a 3 1/2" dia pulley combined with a 6-blade fan which has proved adequate for UK weather conditions. You could fit an electric fan like me instead of playing with the static fan. 

 The thermostat should be a summer one as it opens a couple of degrees lower than the winter one. Or you could use the special tuning blanking sleeve. Part number (AJJ4012) and the bypass hose blanking kit part number (AJJ4013).  But again mine is a standard one

Standard bearings and rods are good for about 7500 rpm so you do not need to worry too much about this. It may be a good idea to have the crank and Clutch dynamically balanced to reduce vibration.

Use good synthetic oil Mobil one is what I recommend. Although it is a little expensive.

The breather system for the block needs to be improved; adding an extra breather pipe in the Rocker cover can do this. The 3 way (red) crankcase breather valve from a Metro Turbo is a must if you are using a servo on the brakes. It allows a vacuum to be formed in the crankcase regardless of boost conditions. Essential if you do not want your dipstick shooting out due to high internal engine pressures caused by the rings passing little.  I have on mine taken this pipe from the rocker cover and fitted it to the air intake to the turbo pipe by placing the a T piece connection into the pipe and bonding it in.

A high pressure fuel pump, a return line into the tank and boost sensitive fuel pressure regulator are needed to supply the Correct volume and pressure of fuel and dump the rest back to the tank.

As can be seen by one of the photos both me and Simon have a standard fuel tank, and on the fuel filler line have placed a small piece of piping into the filler pipe to return the fuel straight back into the tank.

A good air filter for easy breathing is needed, K and N or similar.

 A 1 7/8" to 2" single box free flow exhaust (twin box if you like very quiet).  You may find it a bit tricky creating the inital downpipe mine took about a day of cutting and welding to create an S shape to get it out the car in the usual place.  Where as Paul Dorner has taken a different route and cut through the passenger footwell and sill and routed the exhaust cobra style down the side.

 One of Simons additions is the Inertial cut out switch from a Montego. This cuts off the fuel pump and ignition if all goes Wrong.

Do away with the Metros Boost modulation device, this was a gearbox protection device for the Metro. This device limits the amount of useable boost to 4 psi at around 4000 rpm and we do not want any restrictions.

The Three way fish tank valve fits in the signal pipe from the waste gate actuator and is used to bleed air off the waste-gate and fool it into thinking that there is less boost than there actually is. This is because the standard waste-gate is set for a max boost pressure of 7 psi. You could always change the Waste gate actuator spring for one that is stronger to get higher boost pressures as many have.

The Distributor is standard just set to give about 20 deg advance. You need loads of advance with low compression engine to get the fuel burning early enough when the motor is off boost.

So whats the performance like now

Ok on my 1098 I use only 7psi but as I have a very standard engine and no intercooler im not going to go mad with boost.

I would have to guesstimate around 90 bhp, but more inportantly when the turbo kicks in at around 2000rpm I have a massive torque increase especially in 3, 4 and 5 (Toyota gearbox) as my clutch slips slightly in 1st and 2nd

Ok and here is what Simons 1275 has ended Up With Rolling road tests showing 103 bhp at the flywheel about 80 at the rear wheels and that was using only 4 psi boost. Not much in the way of a horsepower boost, but the increase in torque is massive. The more torque that you have the faster the car will accelerate.

Simon has run the car totally unregulated and it is Stupidly quick (something silly like 21psi). Even using 10 psi it is Amazing (I couldnt stop laughing every time he floored it), you just can not change gear fast enough, even with a Toyota 5 speed gearbox kit fitted.

Fit a good rev counter or a rev limiter because once it starts to boost the revs pile on very very quickly. Simon has done about 60000 miles and has had NO real problems.

 

Problems I encounted


Oil pressure, I first took the oil pressure from the oil pressure gauge line and my oil pressure was none existant ie 5 psi idle and 10-20 driving, but as soon as I changed the location to the big screw on the bango pipe going to the filter the oil pressure was fine again, but as this is IIRC the most unfilted section of oil on mine as my filter is in the normal place ie bottom right I also added a fuel filter into the plastic pipe going to the turbos oil inlet (the filter cost 2.50 and gives me a visual indication oil is going there, its held up to both the pressure and temp of the oil, and when checking the pressure both sides of the filter it matched that indicated on the oil pressure gauge).

Second problem as I made a plenum chamber I didnt appreciate what all the holes going into the carb did, so when starting the car it wouldnt do anything other than tick over, this is because as you look at the car from plenum chamber there is a an extra hole on the righthand side that increases pressure to the float chamber thus allowing fuel to be sucked up, and not blown down like in my case.

Problems Simon encounted

Don't do what I did and slap on the first Turbo that comes to hand as that is a recipe for disaster. The oil seal in the Turbo went after about 1000 miles. The experience is hard to describe, Immaculate car bellowing great clouds of smoke, a Bat mobile could not have produced a better dense blue cloud. It cost 150 to put right.

Link to Simon Athertons web pages