Which pistons for 998 turbo?
Turbo Mini Forums

Update,

According to Des Hammill's book on 998 tuning, the gudgeon pins are a different diameter between the A and A Plus engines.

So I'm going to need some 998 A Series rods if I want to use the 20773 pistons.

Can anyone confirm this?

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Yes, the A and A+ pistons only fit the correct rods. So A rods for A pistons, A+ rods for A+ pistons.

If you use the A pistons, be sure to invest in a set of PTFE buttons to retain the circlips. I once had one get out and wreck an engine.

Interestingly, I use the 20773 pistons on rods that came from an A+ engine which had 20600 flat top, circlip fitted pistons.

So, A+ 998s were fitted with these pistons. I've never checked, but I would assume that the gudgon pin diameters are still different though.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

Apparently, the 998 A Plus pistons changed from circlip to press fit in the late 80s.

So, logically, as long as the engine is not late 80s it should be possible to use the 20773.

Sods law is that the 998 A Plus engine I have just aquired is late 80s. It has a 99HE20 number which is the same as the engine fitted to my lads Mini 30 (1989)

I'm starting to think that for now I should stick with flap top slipper pistons and limit the boost.

I've also aquired an unleaded standard 12G295 head (megabucks but worth it) This should give me a compression ratio of approx 8.8:1 with flat top pistons.

I'm looking for about 120 bananas and 100 ft lbs which should be achievable with 10 psi boost.

But will it be possible to run 10 psi on an 8.8:1 compression ratio and a low overlap cam such as the SW5?

Problem is, I can see that I will soon want to up the boost but with limited piston options this will not be possible.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

This is the latest spiel from the Minispares website for the new Mega pistons for the 998:

"This modern piston from Hypatech are flat top with oil holes rather than slots behind the rings and are suitable for up to 12-1cr. The flat top design will yield a compression of about 9.6:1 when used with a Cooper cylinder head. This pistons replaces the original Hepolite pistons 18516KR and P20950 used on the original Coopers. Owing to non availability of 998cc pistons these have been re-introduced in Mega type material for use in any engine whether road or race at a very competitive price. non slipper type and you only use 2 of the 3 rings from the ring set. On later press fit con rods you just discard the use of circlips or alternatively hone out the small end of the con rods"

I'm thinking of using these in my 998 turbo with an original 12g295 head which should give me about 8.7:1 static compression ratio.

My engine is currently fitted with the press fit slipper pistons.

Anyone like to comment on the last sentence of the above?? Do you think that you can you just discard the circlips and use these pistons as press fit?

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

Yeh, but we know how the suppliers will tell us anything to get a sale!

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

indeed, Im gonna stick with the std flat tops now and use head similar to yours to get the compression down on the first 998 build, after that ill use the +20 dished pistons that minispares sell (same as what wil_h is running i think).

With the flat tops and 28.3cc head, the 8.8(ish):1 cr well get will (according to the graphs benross posted up a while back)...

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=7872

...we should be able to get away with around 10psi if we use decent pump fuel.

"Turbo's make torque, and torque makes fun"

"did you know you can toast potato waffles?"

the 12G295 head is from a 998 Cooper and a MG1100, if I understand well.
On which models was this head and does it fit straigth to the cilinderblock off the mini??

Just to add, it fits straight on 850/998/1098cc engines (small bore)

It won't fit onto 1275 large bore engines.

it will fit, but will not work:)

hi all. I know this is an old thread but their are many unanswered questions!

i was looking at the dates on the posts and most are from 2005! So any updates on the P20773 piston? has it worked? survived?
Reason im asking is that my blocks now at the machine shop and they want to know what im puttin in it.
best regards
matt.

The 20773s appear to be an ok piston. But I went through two sets last season. Mainly I think because of high inlet temps.

This year I am trying the Mega pistons, so we'll se how it goes.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

Water injection is for use when you have the wrong turbo. turning the boost down is easier and has the same effect.

Yes we have an intercooler see www.twin-turbo.co.uk

A new turbo is the answer.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

PISTON SINGLE MINI 1000cc +020 P20773-20 how much can be milled out of these any idea? thanks

I'm stupid Ive A fiesta with most of the bits to make my megajolt thingy. Thick or what!!!! OHHHHH and ive got a metro for free !!!!! Metros have become rare over here!!!!!!!!!
http://s216.photobucket.com/albums/cc273/weewheels_2007/

Not sure how much you'd need milled out. they have a 6cc dish as standard.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

just read this thread, and it has helped me with my future build, which alas will be 850 or 998 turbo pending on what needs to be done :)

Yet again TM provides answers to the many Turbo realted questions......and other shit too !

Edited by Richie on 10th May, 2007.

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mcalvert39
water injection is a band aid for not doing the job right in the first place buddy (nothing else)
quote:- CORK Bell

how true!

what would happen with a 295 head & 20773s+20's i think the C/R is getting very low?

SKYLINES ARE LIKE CLITS, EVERY FLANGE SEEMS TO HAVE ONE: see this sticker on my silvia

the Search-section on this forum is blummin superb & simple to use, unlike some other forums, without the search-section & the help of this bunch of chaps on here i'll never be able to !!!Start the day with a 998cc turbo!!! :) i'm getting closer though!

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