Engine mod help needed please
Turbo Mini Forums

Hi all

Just joined up as i'm looking to start a turbo mini project. I'm not new to minis, owned a 93 spi and a 71 clubman, but not owned one for about 3 years now and the itch of missing owning one really needs scratching now...

I'm also not new to forums so i've spent the last couple of days trawling through this forum looking for advise etc using searches, a few general google searches and asking my brother who's an engineer and did a full rebuild with performance modifications all round on his mpi Sport 5.

The two most useful threads i've found is one by Tom, and one by Paul. In Tom's he suggest the following work is needed:
"Therefore, the main changes that concern us as potential Mini Turbo owners within the engine itself are thus-

1) The pistons are the main difference, and are a thicker crowned dished piston, to withstand the increased forces in the combustion cycle due to the boost pressure.
2) Some of the early cars were fitted with a toughened crankshaft. However, this was not continued throughout the life of the Metro Turbo, and so is considered unneccesary by many people.
3) The cylinder block itself is the exact same casting as all the other A+ 1275cc blocks. There is no difference in any of them, meaning a donor block to build an engine from is easily located.
4) The cylinder head casting itself is essentially the same as the other 1275cc A+ head castings. Where the turbo head stands apart is that it is fitted with exhaust valves with a larger stem diameter. This was done to increase the contact area between the valve stem and guide, to allow superior heat conduction away from the valve head. These exhaust valves are also sodium filled. This makes a "genuine" turbo head easy to identify, as the size difference between inlet and exhaust valves is visible with the naked eye.
5) The turbo engine uses a higher capacity oil pump, as it has to also supply the turbocharger itself with lubricating oil. These pumps are still available as reproduction parts, and are interchangable on all of the A+ blocks.
6) The nose support bearing on the end of the first motion shaft is different (larger) on the Turbo engines. The reason this was done is not clear. The bearing in the larger Turbo size is still available."

But then Paul kindly did this little table which suggest for lower boost the engine can remain quite standard:
http://www.turbominis.co.uk/forums/attachments/348364-1.pdf

The mini i'm thinking of making isn't to produce masses of power for hillclimbs etc, I've got a Maestro Turbo that's been fettled a little and a motorbike if i want to go racing about. I only want a turbo strapped to the mini to make it a little quicker and therefore that little more fun, plus it'd make it a bit different.

From the other reading i've done i believe that the T3 used on the metro runs at 4psi normally, which can be tweaked up to around 6 or 7psi by playing with the actuator. That's all i'm looking at making with it bolted to a 1275.

So the questions i have are as follows:
With a standard A series engine would 4psi achieve 100ish bhp or would i need to tweak it up to nearer 6 or 7?
Going off Pauls table if i were to fit a T3 running no more than 7psi to an Aseries i wouldnt need to change the pistons as Tom suggested, is that true?
Would i still need to replace the exhaust valves?
From searching on here i don't think i need to do anything with the cylinder head, because standard compression shouldnt be too high for the low boost im after?
And i don't think i need an intercooler from the searching ive done either?

Apologies for the essay, and for the potential repost of questions - but i have done a fair bit of searching 8).

All help is greatly appreciated

You'll need 7 psi to make the std 93 hp as the metro turbo limited the boost to 4 psi in the mid range to protect the gearbox.... then let it build to 7psi after 4500rpm.



it depends what engine you have to start with as to weather you can boost itsucessfully ... ie there are some low compression engines ( think they were in vans) which have really shit pistons.... also the non turbo MG engine will be to gigh compression ( the pistons are different to get different compression ratios.)

essentially a standard non turbo head will be ok, the exhaust valves should not be an issue at the power your looking for,

really with any turbo motor... the forst thing I would do is fit an intercooler... it is litterally the easiest thing you can do, and gives good gains, and gives that bit more margin on det for hot days.. crap fuel etc.... 25quid or so for an intercooler form ebay... and some hose... its a no brainer in my book.

Cheers for the reply Joe.

I didnt realise intercoolers were that cheap tbh. I'd be happy with 93bhp, having run standard minis an extra 20-30bhp will do me fine. Turbo + stage 1 kit should be 90-100 i'd think?

Is there a particular one that would be more suitable? Obviously the smaller the better, would love to find another clubby shell for the extra room if possible.

But according to Paul S and his table for 100bhp i wouldnt need to play with the pistons and could use just standard ones?

I'm not trying to suggest i know more than you by any means btw, just showing the contrasting thoughts :)

RS turbo or reno 5 intercoolers are popular, also the 2wd cossie one, but thats a bit bigger and good for a 200 hp build.


I think by standard pistons Paul means standard turbo pistons, but I think you would be ok with standard non metro pistons, but its worth checking the part number on them incase they are the ones that are made of cheese.

I can never remember what all the production pistons are... just that the turbo ones are good for 200hp or thereabouts.

a slightly warmed head like a stage 1 will definatly help, but you need to watch the compression ratio, often the heads are skimmed for NA use, you want to keep the Cr to 9:1 or a bit below.

the other problem... is that you always want more... and the temtation is to up the boost... so its often an idea to build with this in mind... ie if you want 100, build for 150... LOL

Haha yeah i understand its a dangerous game to play, and could get highly tempting. But my maestro turbos up at around 180bhp and is a 2 litre Oseries so has plenty of torque so thats my quick car 8)