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MG Midget and Sprite Technical - Gone Turbo!

Thinking of options, other than rebuilding the 'big valve' 12G 940 head after the dropped valve at Silverstone earlier this year, there seem to be 3:

BMW 16V head

KAD 16V head

Metro turbo set-up

As it's in a heavier car, the Minor, and I want good mid-range 5th gear road performance, have decided to go 'turbo' and bought and collected the whole set-up from an eBay auction yesterday. It looks complete, in good condition and includes head, turbo, manifolds, oil feed/drain, wiring etc. I do not have the turbo dizzy.

I would like to get the magic 138bhp to go with the 1380 capacity and have heard about a number of things to do to get up to this, such as the air bleed to fool the wastegate control. Does anyone have experience of developing the Metro turbo? Bob, what arrangement have you got?

The plan at the moment is to flow the head, reduce the CR to ~8.0:1 to allow more boost, clean up the internals of the inlet manifold, retain the 1.5 roller tipped rockers, change the 276 to a 266 (I already have one, but is it a good turbo cam?) - anything else?

Currently I have an Aldon 'Yellow' dizzy with vacuum and Aldon Ignitor, so will have to replace that. Was thinking MegaJolt, but does this have the capability to respond to boost pressure, and is it necessary? Or would I need to fit the MeagSquirt to get this function?

Obviously the bottom end will get all new shells etc., and already has a centre main strap; hopefully this will be enough?

I have heard the the Metro turbo oil pump will not fit an in-line engine, not sure why not (clearance behind the flywheel?), but was planning to use the MiniSpares high capacity one that I have used up until now?

For the rest of the drivetrain, it already has a Toyota 5-spd box, Tran-X LSD with twin pin diff, Peter May's EN24 halfshafts and double bearing hubs - so ahould be in reasonable shape to cope with the additional torque that will (hopefully!) be generated by the turbo.

The last item is the clutch, which is a standard 1275 6.5" diaphragm cover plate, with a special AP Racing driven plate with the Toyota spline. Does anyone know the torque capacity of this cover plate?

Looking forward to an interesting project I think??

Richard

Richard Wale

What about intercooling/charge cooling - you'll need this to raise the power. The simplest way is to obtain the Montego/Maestro plenum or modifying one as Bob has done.

I'd have thought you can stay with the 276 cam.

I'd have also thought you can keep your existing distributor and simply add a boost retard function to it - Microdynamics do one.

Simon Page is probably one of the most experienced people in developing the in-line turbo A-series and hangs out here occasionally. I think he also holds the record for the most power out of an A-series engined Spridget. He had a special turbo built but also had a lot more than 138bhp.

Working with Simon with the big improvements to power output came with getting the engine coolant temperature well under control. You do have an uprated radiator on the Minor?
Daniel Thirteen-Twelve

and brakes I hope!
Cheers John
JOHN HALL & JULIE ROBERTS

"Currently I have an Aldon 'Yellow' dizzy with vacuum and Aldon Ignitor, so will have to replace that."

Any plans for that? I may have a good home for those.
S.A. Jones

http://turbocharged-midget.tripod.com/index.html
Toni Kavcic

Thanks for the replies:

"obtain the Montego/Maestro plenum" - ah, wondered if I would need to intercool, sounds like I will do.

"You do have an uprated radiator on the Minor?" - yes, one has been fitted all the time with the 1380 engine (last 11 years), so think it should be ok?

"and brakes I hope!" - Yes, think so; Metro vented discs, Metro 4-pot calipers, Mintex 1155 pads and M20 equivalent rear linings, DOT 5.1 fluid and a 2.2:1 ratio servo to make it all 'feel' nice!

"Aldon 'Yellow' dizzy - I may have a good home for those." - Sorry, not yet!!

Daniel, do you have a contact for Simon Page?

Richard
Richard Wale

Toni,

Apologies, thanks for the link, very useful information there.

Richard
Richard Wale

Hi Richard I am afraid I am a mere MGCC member and therefore apparently we are not very technical :-)) but I will let you know where I am and hopefully it will help a bit.

First to state are the difficulties of installation.

The major problem is getting fuel to the carb at the right pressure. You need a supply of fuel at a couple of psi above your boost pressure. So if you plan on having maybe 20psi boost then you will need a fuel supply of about 22 psi.

The Metro and I do this by having an injector fuel pump, (fitted to thousands of F.I. cars) that is reduced by resistors and then regulated by the fuel pressure reg. I use a couple of 1 ohm high power resistors to help reduce pressure. The fuel pressure regulator is one from a Montego turbo and is simple to operate. The only difficulty I had was with the fuel return line (The regulator sends excess pressure back to the tank) I made it in 6mm pipe to start with back to the filler pipe at the tank, but found this caused too much back pressure and thus pressure at the carb was too high and flooded the carb. Fitting a 10mm return pipe seems to have cured this problem.

Fitting an intercooler I think goes without saying but what it gives me I can not say. I modified a Metro plenum chamber to suit my intercooler but in a moggy I think fitting the angled Montego/Maestro plenum would make it straght forward.

I decided simply to have a basic engine to start with and see what power I would get before doing serious modifications (cam, Standard turbo head 8.5/1cr. You saw my basic set up last year at our rolling road session and I was very pleased to find that even a basic set up was a good match for all but the most advanced ultra high revving N.A. Mine was 112 at a mere 5400 revs where as he best was 119 at about 8000 RPM so plenty to be pleased about.

At that time I had 8.5/1 CR and my boost was only restricted at about 15psi which coincided with 5400 RPM Thus I felt that I needed more CR to make use of the boost pressure in the lower rev band.

About 10 years ago I was trying my best to get as much as possible out of a normally aspirated engine and thus I was working with very high CR values. I was just about to make a big step forward when I lost some income and my development had to cease, in favour of building my MGA which had been in my garage as a pile of bits for a good few years. What I wanted to do was fit programmable ignition so that I could run 12.5/1 CR and be able to program a retarded ignition setting at medium revs to prevent detonation. Alas I did not have the coin to develop this properly so I had to abandon it.

I tell this story so you can undertand where I am going with my engine.

First I will fit a flowed head to monitor what improvement that will bring, I already have fitted programable ignition so then I will up the CR to make better use of the boost and use the programable ignition to supress detonation as I had planned to do years ago to my best N.A. engine.

My clutch is the same as you have fitted because I also have the toyota gearbox. It is no problem at all.

Unfortunately apart from getting mey programable ignition up and running I have not had time to sort any further engine mods out as I have been working on the rear axle. I needed to shorten this to get 185/60 tyres inside square arches and have also designed and fitted rear disc to my Midget. This is almost finished now so hopefully if the economic climate picks up I can start on developing my engine. 140 should be a breeze. :-)
Robert (Bob) Midget Turbo

Hi Bob,

Thanks very much, some very good information there. I will look for a Montego plenum as a starter for the intercooler - which intercooler do you use?

I think I will also use a programmable ignition, which one are you using?

Richard
Richard Wale

This thread was discussed on 31/05/2009

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