Before going any further with my engine I was considering a set of upgraded rods for it, however I've got this 79mm stroke crank sitting on the bench which is crying out to be fitted It would be rude not to whilst it was apart

Pauter will do custom length rods for around $600 so I was thinking about retaining my Sti4 pistons but joining them to the crank with a 2mm shorter rod (1.5mm shorter actually to improve the squish and CR)
I realise that I will compromise my stroke / rod ratio but it is still decent in comparison to Fords revvy little x-flow for example

My concern is whether there is enough room for them to go 3.5mm further down in the bore without hitting anything ?? (2mm stroke + 1.5mm rod)

Andy

That plan to tune no further lasted almost a whole day

[Edited by Andy.F - 6/4/2003 3:32:37 PM]

 

 

lmao! I was just about to say i thought you were giving up tuning. Lasted long! lmao

 

I was going to do the same, it should work fine. Lower Oil ring will cross the gudgeon pin hole in liner, but this is the same for all strokers pretty much.

Only other thing to watch out for is big end hitting block, but this is easily fixed with chisel, although the pauter rods are rather slimmer than mine.

Go for it.

Paul

 

Andy,

IIRC, EJ25 pistons differ from EJ20 ones in height as well as bore... I would check this out before risking oil control ring to gudgeon pin access hole issues etc. This might not be the case, but now would be the time to find out.

Moray

 

THe EJ25 uses longer rods and makes up the difference in stroke and rod length pin height. The phase 1 EJ25 uses a thickish 1.5mm gasket and the pistons sit slightly proud of the deck, phase 2 is, I think a 1.1mm gasket and the pistons are nominally flush.

The only thing I can't be sure of is if the lower compression ring sits much lower on the EJ20 piston. I don't think there will be a problem though. The std EJ25 has the lower oil ring passing the top of the gudgeon pin hole anyway.

Paul

 

Is that the case Paul ? I can't remember. Comparing my N/A 2.5 pistons with my old WRX ones, the rings on the 2.5 are approx 4mm nearer the crown. The skirts are also much shorter on the 2.5, is this in order to miss the crank ?
My concern was similar to Morays regarding the oil ring coming below the pin hole. I thought that the scraper ring may not function properly if there was oil in the pin hole which could get to the wrong side of it ?

 

I can assure you the oil ring goes past the pin hole.

Compression ring would be a no go though as it's under much greater load (load pushing it outwards).

The Sti pistons are much more like the 2.5 N/A pistons in there skirt length etc.

Paul