Which pistons for 998 turbo?
Turbo Mini Forums

Which pistons would be best for my 998 turbo? the block is going to be bored out +20 just to make sure, so can I use normal pistons and then sort out the compression with head mods?

Mod Edit: Moved to correct section

Edited by AlexB on 7th Nov, 2005.

Watch this space.

Currently Mini1071 is building a 998 turbo and planning on using the later 'slipper' type pistons. But I used these and they didn't last very long (which surprised me as they are amazingly reliable usually).

I now use these http://www.minispares.com/SearchResults.aspx?s=1&ss=p20773

Cheap too.

Wil

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

www.twin-turbo.co.uk

what sort of compression would these give? would i have to do a lot of head work or would the only way of telling be to fit them and find out

998's have verydeep combustion chambers in the head to start with

Metro turbo weekend driver,Mini turbo in the making again!

Should be easy to calculate what size head chambers you'll need, as you know everything else.

Standard 12G295 head is 28cc this will be more than enough with a dished piston. In fact probably too much.

Wil

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

www.twin-turbo.co.uk

thats great, ill stick them the pistons on the list along with every thing else to get

So a decent 295 will be fine with a few tweaks to get the right compression

I don't know for sure if anyone has got a running engine (998 with a 12G295) of that spec.

However, on paper from basic assumptions it should work well. The 295 head as standard flows well and has decent sized valves for the swept capacity of the engine. In addition due to the original configuration of the engine it was designed for, it also has large combustion chambers, which go a good way towards getting the desired low compression ratio.

The only thing you need to make sure of is that you get an "unmolested" 295 head, as many of them have been skimmed to the maximum extent possible for use on normally aspirated small bore engines with dished pistons, in an effort to get the high compression ratio desired for a performance normally aspirated engine.

So a decent 295 is a must then. If i cant get one how different would the 940 head be compared with the 295?

will the 940 head release a lot more power than the 295?

im going to try and get a decent 295 as i cant be bothered to get the block pocketed and its going to be too hard to get it done back home. what size valves should i go for or just leave them standard? Will said to just remove the guide bosses and leave it at that

"Will said to just remove the guide bosses and leave it at that"

well I said that that was all I was doing as I'm not sure any more than that will be worth while, as I don't want to spoil the off boost power.

Also, if I can make 140bananas on a standard head, why spend money you don't need to.

wil

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

www.twin-turbo.co.uk

The real reason we went 940 wat that we had been moding NA 998s for years and in out experiance the 940 gave much more power than the 295, and they are cheeper and more available.

I think a 295 head will work very well though and it the way I plan to go with my road mini when I get round to putting a turbo on that.

I think it is Graham Harvey that has a 998 turbo with injection running a 295 and he has seen very good power (110+ I seem to remember)

http://www.twin-turbo.co.uk
http://www.hillclimbandsprint.co.uk/default.asp

A man without a project is like a like a woman without a shopping list.

I suppose I should quantify that we have used 276 cams to good effect with the 940. And have friends running 286 cams in a NA that manahed 15.5 sec 1/4 male at avon this year.

http://www.twin-turbo.co.uk
http://www.hillclimbandsprint.co.uk/default.asp

A man without a project is like a like a woman without a shopping list.

I'll try and get a decent 295 otherwise ill go for the 940 instead as there are plenty of non-modified around.

Most of the people that runied it have left or very rarely post so its much better now

Yeah theres so much on the site, its taken me a while to find everything out. When do you reckon you're car will be done? im aiming for the riv run at the latest, prefer to get it done before that though, maybe over xmas

what about using the ones that wil posted above?

So many people have recommended morspeed i wilol get any work done by Simon, so many good things must mean he;s excellent

sorry to dig up an old thread, got nothing better to do!

just a few questions..

1 ) Above when you refer to "they don't recommend the slipper pistons either" are you refering to the std 998 pistons?

2 ) is it just the piston dish that denote the 8.6, 9.3 and 10.1 cr's of std 998's?

3 ) if so, what cc is the std A+ 998 head?


basically im trying to plot a graph of chamber size vs CR on a std (10.1 piston'd) 998.

thanks in advance

Edited by joeybaby83 on 8th Mar, 2006.

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

"did you know you can toast potato waffles?"

1) the slipper pistons ar the later no skirt pistons with the press fit gudgon pin.

2) Yes I think it must be piston dish, the 10.1s are flat tops.

3) Can't remember but 24cc rings a bell (and works in the clculations)

The pistons I use have a 5.9cc dish

Wil

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

www.twin-turbo.co.uk

Hey, im looking at pistons now for my 998cc turbo project.

the block is going off to morspeed to get cleaned and the bores checked (so i dont know the bore yet)

But the link for pistons at the start of this thread dont show any anymore! :(
I asked morspeed and they said that their hard to get hold of at the minute!
so can you lot suggest the best (on a budget) ones to use that are out there at the minute!

thanks martin

ill give them a ring just i cant seem to find the 998cc ones on the internet,
do i want flat or dished?
its a 12g295 head! but i spose ill need to know the bore first right?

just phone minispares and they dont have any!!
theyve all dried up!!!
They have some standard ones which are flat top, so i just dont know!!!!!

well i phoned northern branch and he said theyve never been any!which i have seen some on here linked before!so im trying to phone the london branch!

London branch have found them now, but no stock so hes seeing when theyll be in.
a month to two month till there in!!
there flat top will this be ok?

Cam will be a mg metro one,
intercooler is the cosworth 4x4,
boost no more than 10 probably 8psi
12g295 head
is this enough? thanks by the way!

Question,

It is possible to use the earlier A Series 20773 dished pistons with the later A Plus con-rods currently fitted with the flat top slipper pistons?

The 20773s use circlips and presumably in the earlier A Series engine, the gudgeon pin is loose in the little end.

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."