hi guys i have a P1 with a 2.5 fitted the front right piston has broke the pieces off between the rings i need to have it bored my question is does anyone know what may have caused this also what pistons are good to use its my first scooby it was running 350 bhp would i need to upgrade rods crank injectors (running yellow) turbo (td05 20g)etc to get more power ? the car has been stood 8 months before it blew Thanks Neil.

 

Fairly common fault if it was a standard EJ257 piston.

If you have to get it bored then you may as well get it pinned at the same time.
Crank and rods should be fine and good for 400bhp I suggest some Wiseco or Cosworth pistons but get the bores honed to suit which ever ones you choose.

If you have aspirations of going over 400 then now would be the time to swap the rods too.

Here's a pic of my block which has been pinned but other than the pins and a 14mm stud conversion is as it came out of the factory.

 

JDM or uk?

 

I've knacked a lot of pistons through the years with faulty/worn sparkplugs

 

As mentioned above Neil - det damage to the ring lands is quite common on the EJ257 fitted with the standard Hyperthuretic pistons - these cast pistons do not tolerate det at all and results in the ring land breaking up and damaging the bore in the process. Seems to be No.2+4 cylinders which suffer the most from detted pistons on the EJ257.


Mick

 

thanks for the advice not sure what pinned is ? is it pinning of the liners ?thanks Neil

 

Mick, what is a Hyperthuretic piston? Is it a casting type or a brand name. Cant find anything good info on Google.

 

hi mick what would cause det faults could it be stale fuel or maybe an injetor fault thanks Neil

 

You are right, pinning is the pinning of the liners, i have edited the pic above to highlight the pins in RED.

these are NOT standard and will strengthen the block.


I have a EJ257 in my RA, done under 2500 miles and i have lost compression on No2 Cylinder. I suspect broken Ring Gland.

Car has been off the road nearly 12 months now due to it.

 

thanks for that i have tried to get a standad piston today but when i spoke to subaru i was told they needed vin no when i explained the car had a different engine they said they could not help me ? how crap is that ?

 

Subaru part's Dept's Suck lol. they have always demanded a Chassis No. before sorting parts.

Give Ashburton Motorworks in Torquay a Call 013646 52302, I deal with these Guy's all the Time now, and they Sort me parts without the Chassis No.

 

get yourself a set of uprated pistons and rods.
lateral performance are very good and not to expensive for what you get. as in parts are very good.

cheers mickyboy

 

cashyn: if I were you, running 350 or so, I'd not even be tHINKING standard pistons.

AFAIK, they are called hypereutectic pistons, and are made from an alloy which is MEANT to not expand as much, so has lower clearances.

However, in an engine running above the standard hp, they CAN expand enough to "pick up", or melt in the bore due to insufficient clearance, so less oil, plus the skirts below the ring lands are brittle, and break off if the engine dets at all.

When I went 2.5 after cooking my 2 litre, I was told be TWO respected engine builders to find a short engine at a price that would allow me to split it and fit AT LEAST forged pistons. I was lucky enough to get one that was unused, still in it's crate, at a price that allowed me to afford forged rods too.

 

hi the more i have read into this the more i agree with going forged i have looked at mahle pistons at £400 per set but not sure if there any good ?

 

Hi im not sure i dont know what to look for ?

 

anything that will raise temperatures in the cylinder will help promote detonation. This rise in temperature could occur many different ways: very lean air/fuel ratios, heating of the charge air prior to entering the combustion chamber, compression of the air molecules from forced induction, or poor heat dissipation through the cooling system. Increase of cylinder pressure will also prompt detonation. Camshaft profile, compression ratio and quench area all come into play. Design criteria as to combustion chamber shape and mixture motion, spark plug location and piston design can all make an engine more or less inherently prone to abnormal combustion. Naturally, spark timing and fuel quality round off the list.

 

JDM= Japanese Domestic Market, ie: an imported car.
UK= obvious, but since you have a 2.5, the question is moot: the Japs are still using the stronger 2 litre engines.

 

Mahle Piston are excellent you'll not go far wrong with them. Due to your damage I'd go for an over size piston (99.75mm) and get the bore honed to suit these pistons. For your aim of 400 you'll be fine with the standard block but anything above 400 and I would advise getting the block pinned. It's not very expensive but its very effective.

 

dazdavies..........just out of curiosity is that the Mahle Powerpak series you mentioned above?

Shaun

 

Mahle do a piston in the powerpak range that is 99.6 which is enough oversize to rectify most bore minor bore faults, including broken ringland marks.
Part No WRX209921P22
If you must put OE pistons back in i have dozens off them all ready to weigh in for scrap, some new.

 

thanks for the info ill try and get a price tomorrow cheers

 

hi i looked at some cp pistons today but they are shaped different to mine they had a square hole cut into them where mine look like the ones in your picture would they be ok to use or should i stick to what was in it thanks Neil.

 

The pictures of the CP ones were probably the 2.0L ones as they had the square cut in them.

This is a CP 2.0L piston


This is a CP EJ257 Piston


Hope that helps

Daz

 

hi mate thanks for the info im now struggling with head gasket size im told it has standard sti heads on it ?

 

Hi ive been told to get some 100mm pistons by engine company and they will bore to suit im not sure if this is correct as the bore was not that bad in my opinion anyway im not sure which head gasket to be im told it has standard sti heads i have measured the dia of the round part in the head and it measures 91.5mm ? hope you can help thanks

 

To go straight to 100mm is a bit overkill, if you say the bores are'nt bad, there's 99.75 pistons available first, when at 100mm there's not many options if the same happens again in the future.

 

hi whats the cost and who does this pinning im trying to source some parts for rebuild and seen some 100mm pistons and rods in usa for £500 ? i dont know which road to go down divorce or quick scooby ? thanks neil

 

hi am i right in thinking theres a ej25 and a ej257 engine ? i was just about to order some pistons and noticed there were 2 different part numbers on the block mine says ej25 so are they the ones for me ? i have also been offered a 09 short motor but not sure if this would be suitable ? please advise thanks Neil