Info on 998 turbo
Turbo Mini Forums

Hi all my first post of probably many.
I bought an Austin mini city e 998 1989 for wich I had identical one 20yrs ago.
Iv just started my mini rebuild and Iv started with the engine and decided to go down the metro turbo route.
Iv stripped down block head etc and started getting bits together.
Iv got
Standard 998 block think it’s aPlus block
12g940 head (block will be pocketed)
Iv rebuilt the metro t3 turbo an actuator
Hiff44 carb (will be turbo modified)
Manifolds
Fuel regulator and hoses
Still trying to get a plenum
Firewall box for turbo
Now my question:
I have flat top pistons in my block and standard cam
From what Iv been reading I’m worried the compression will be to high for the turbo can anyone shed some light on this?
Also should I change cam for a metro cam?
Cheers guys.

The metro T3 won't be any good for the 998, its way too big.

If your going for a more suitable turbo for the 998 then they'll likely not to have the T3 flange that is std fare for the metro manifold, a better investment would be a Fusion fabrications manifold which accommodates the T2/T25/GT1752's flange pattern etc and allows fitment without the need to modify the bulkhead.

Before we can determine if the compression ratio is too high you'd need to know some fundamentals of the proposed engine;
Bore size eg std +020" etc
CC's of the cylinder head your proposing to use.
Crank/stroke, either 998 or 1100.
If it's an A-plus then likely to be flat top pistons, are you intending to retain or sourcing others / dished like the ones from Calver ST?
How far are the pistons down the bore.
Depths and diameter of the pockets to ascertain CC's (this will be dependant on valve size and cam lift/rocker ratio).
Proposed head gasket used, suggest BK450 if using the 12g940 head.
As for camshaft, good gains can be had from some original fitment cams and common off the shelf items.

A good bit of searching the 998 section will turn up half the info you require.

Shane

Edited by shane on 16th Dec, 2020.

You don’t necessarily need to pocket the block, depending on valve lift. There are also other options to pocketing. Have a watch of this: https://youtu.be/rE9K1xspc68

Regarding the compression ratio it’s simple enough to work out as long as you know the engine cc and a few other things. This video shows how easy it is: https://youtu.be/9Lp-1Rbb4Yo

Phil.

WWW.TURBO-MINI.COM

Thanks for the reply’s
I have and will keep reading through the archives can never have to much information
I’m not new to Resto’s but i am new to turbos and retro fitting turbos etc.
I’m using a 1275 copper gasket for aplus block
Before I pocket the block I will measure and make sure it needs it first.
Iv watched a few vids in how to work out the compression so will give it a go tomorrow.
What would be the ideal compression to look for and what is considered to much?
Also is the t3 completely out the question?
I’m going to cut the bulkhead and install the box from minisport,
Do you mean to big in size for the bay or to big for the engine to cope with?
Thanks again

Would prefer to keep pistons but open to options.

Would prefer to keep pistons but open to options.

Both, the T3 installed with the metro manifold is a substantial size unit that necessitates cutting of the bulkhead.

If your bothered about weight saving the metro assembly weighs a hefty 12.450 kg, the mirage manifold with a hybrid T2 I weighed at 6.950kg, 5.5 kgs less, it doesnt sound alot but in the bigger picture........

The T3 is a large turbo which takes a fair bit to spool up, fitting it to a 998 with its lower displacement of exhaust gasses would make it laggier and a pig to drive.

The T3 is also an old hat technology turbo, there are more efficient and more compact turbos that can be fitted and give better drivability and power and as mentioned above if fitted with a Fusion Fabrications manifold or if you can find a used one a Mirage manifold can be installed without cutting the bulkhead.

I believe there was a historic thread which covered using the T3 on a small bore unit in the 998 section, several well invested hours with the search button will yield a lot of the answers to your questions and lessons learnt by others mistakes.

Shane

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=223253

I had a moment of deja vu with this.

Shane

Thanks Shane
Looks like il have to re think my build.
Gutted as i got most of the parts for the t3 cleaned rebuilt etc😭
Iv got a while as the body work is going to take quite a bit of work
Is there no way of using the t3 Manifold for the t2 as that’s the only thing I can see being an expensive problem.
I’m not to fussed about modifying the bulkhead.
Iv seen some really small turbos for small block engines the one Iv been researching gt1238sz
Only good for 50-150hp wich I don’t really wanna go above the 100 mark anyway.
Appreciate the reply’s.

There is an old thread on here (waaaaaaay back) where there are some images of the metro manifold modified to take a smaller turbo (runs off to use the search button ...........http://www.turbominis.co.uk/forums/index.php?p=vt&tid=9465.

With the photo bucket debacle a lot of the historic threads have lost their images.

Theres no reason that you couldn't make a manifold to be similar to this mentioned above if you have basic fabrication and welding skills, materials are reasonably inexpensive, for me this would be more favourable then cutting the bulkhead (personal preference only)

Shane.

Thanks Shane
Looks like il have to re think my build.
Gutted as i got most of the parts for the t3 cleaned rebuilt etc😭
Iv got a while as the body work is going to take quite a bit of work
Is there no way of using the t3 Manifold for the t2 as that’s the only thing I can see being an expensive problem.
I’m not to fussed about modifying the bulkhead.
Iv seen some really small turbos for small block engines the one Iv been researching gt1238

That’s what I needed, cheers Shane technically could do this mani mod with a 3 flange turbo or any orientation?
Suppose I need to word my searches better🙈
Delving into the 998 turbo conversion having never tackled anything turbo before is definitely a head scratcher sometimes

If you’re not bothered about cutting the bulkhead it’s simple enough to adapt the Metro manifold to accept a GT17 or T2 etc

Phil.

WWW.TURBO-MINI.COM

Theoretically yes, but attention will need to be paid to good installation practice regarding to oil feed and drain positions and the core being level.

I can't remember who's car it was but I recall someone on here having a remote set up with the core/ shaft positioned off horizontal and they had issues with minor oil ingress in to the exhaust housing.
For what you are proposing to achieve with the metro manifold only the points re oil feed and drain should (unless you make a total fu@@ing balls up of it) be relevant.
Don't forget to pay thought to fastening positions, don't make a rod for your own back for assembly/disassembly.

I am running a stock metro t3 on a 998 , (temporary engine) and the turbo brings nothing, not even noise!! It just about makes 4psi if ragged until valve bounce!
I have a small turbo from a renault kangoo. I just got some flanges from the laser cutters and hopefully when fitted it will give the 998 a little bit of get up and go . No science has been used in spec, turbo is cheap and kangoo makes around 60hp at lowish revs.

Think I’m swaying towards gt17 the one I’m looking at is for a Saab 9.5 wich looks a lot smaller than the t3
Suppose il sell the t3 and other bits.
The t3 needed a plenum is this also the case for the gt17?
cheers for info.

So the one I’m going for is the gt1752s please tell me if its wrong
Cheers guys

From doing a lot of reading on here gt 1752s good for 1275 but not 998 T2 is about perfect but old Hat
Gt 1548 would be a good modern T2 but no longer made. There are some old threads about fiat 500 abarth turbochargers maybe being ideal but can't find if anyone has tried them. Hope this is some help

Edited by Pete B on 17th Dec, 2020.

Gt1544?

The Metro plenum, fuel pressure regulator, carb, and inlet manifold can be retained, the only thing you'd need to sell is the T3 turbo itself.

I'd consider a T2 or T2 Hybrid like those fitted to a Renault 5Gtt which have been used with good feedback. As they are an old hat turbo and not so desirable these days they may be a cheaper option.
I know the GT1752 has been used by one particular forum member on a 998 but his build is EFI and far more advanced than what your contemplating.

Managed to get a gt5 turbo last night, hopefully can start getting my head round it now