ive put sti pistons in a block and wondered what size headgaskets to get to mate up the v3/4 sti heads. what is the standered head gasket size of a v3/4 sti ?. then wondered does it matter if its getting mapped anyway. the pistons come to the top of the block but they dont have much of a bowl compared to the old ones. any help would be great. phil

 

Of coarse , it will determine how much igntion advance you can use when mapped

 

but surly the mapper will work around this, no 2 engines can have the same cr surly..

 

The correct static CR is vital - get it wrong and the engine could be flat 'off boost' or det limited when it comes to mapping.

What STi pistons did you fit ? if they are flush or slightly below deck, then it sounds like they are STi V5~6 with a small bowl to match the larger chambered heads on the Phase 2 engines.
STi V3~4 pistons sit above deck with a larger bowl to match the smaller chambered heads on the V3~4 heads.

Standard MLS head gasket thickness for the STi V3~4 is 1.6mm (approx. 1.4mm compressed).


Mick

 

thanks merlin, you no your onions buddy. i was told they are v3/4 sti pistons. they are defo flush with the block at tdc and the bowls are half as deep as the old ones. and the new ones was not as long and dont have skirts. im thinking 1.6mm but standered v1sti gaskets are also 1.6mm and have the larger bowl and also finished flush with the block, how can they have the same cr, im confused again, lol. phil

 

Got any pictures of your old and new pistons to help identify them ?
The only standard STi pistons i know of which sit flush/slightly below deck are the STi V5~6.
Are you using standard length rods ?

Mick

 

here are the old ones.


these are the new ones ive tryed to show the size of the top crown bowl.

and the depth, note ive done the centre and the edge,


and a over all view. note the depth of the old pistons to the new. thanks buddy phil

 

 

Is that arrow on the piston not ment to be point towards the front of the engine mate?

 

yep lol as merlin sain 3-1 are in backwards. cheers baz..

 

So head gasket thinkness is the least of your worries lol Have you the ring end gap in the correct position?......

If you are using the original heads and correct thickness gasket for the Version 3/4 heads I doubt the cr will be much different. But if you want it perfect you need to calculate it with the parts you are using

http://www.importcarparts.co.uk/part...en=&searchKey=

 

baz i did the ring gap as instructions said to. not too much of a problem to turn the pistons around. im thinking 1.6. but i may sell this refurbed block and go with a newage sti block. thanks for your help buddy. phil

 

They are not sti pistons, not unless someone has machined the valve cutouts in them and machined the height? What markings are on the underside of them? If they are sti pistons they will have HF and a number 1,2,3,4. V2 sti pistons are the same shape as the dog bone type pistons in your first picture, they use 1.6mm headgaskets as they protrude from the block. V3/4 are flush, they have a 14cc bowl and use 1.2mm gaskets, V5/6 sti are the same pistons as 3/4 but use 0.6mm headgaskets to compensate for the extra 2cc in the cylinder heads in the v5 and later heads.
From just looking at the pics they really dont look like they have enough combustion volume in them and will give too high cr.

 

They look like legacy pistons and not sti versions.

All engines to V3/4 crown height are above deck, V5/6 are different to deck (crown height same as deck) OEM headgaskets are 1.35mm and 0.75mm.

If you take sometime you can work out the cr ratio easily, as stated above plenty of sites to help you along the way.

Or you can fit the thicker standard headgasket for v3/4 heads and away you go, however are you saying the pistons you fitted are not above deck now?

All the best with it.

 

I thought they were early Leggy pistons too but did some checking today and they are Version 3~4 2.0L SOHC N/A pistons.
Bowl volume came in at 7cc and combined with being flush with the deck, the Static CR is going to be sky high - dont use them in a turbo engine Phil.

Mick