If I put the pistons from a V3 Sti into my 1995 Wrx block, will it affect compression?
Also, would it make a difference if I used the full V3 Sti short block and put my heads on?
Thanks.

 

Anyone?

 

You will be fine swapping either the HF forged pistons from the STi V3 for your cast dogbone pistons in your '95 WRX or fitting the STi V3 short motor.

The static CR will be near enough the same due to:
The combustion chamber volume's are the same between the EJ20G and EJ20K heads.
The compressed thickness of the WRX graphite composite head gasket and the STi V3~4 MLS head gasket are the same.
The piston volume of the WRX dogbone piston and the STi V3~4 HF forged piston are within 1~2 cc of each other IIRC.

Your only limiting factor tuning wise are your WRX Hydraulic heads - STi heads would be a far better option.

Hope this helps

Mick

 

Thanks for the usual detailed reply mate, much appreciated.

 

One more thing, I've read that pistons have a and b sizes. Does that mean that there is a possibility that the sti pistons will not match my wrx bores?

 

standard pistons are classafied into two grades, "A" and "B" these grades should be used as a guide line to selcting the standard sized piston
A = 92.005 -92.015 mm
B = 91.995 - 92.005 mm

this is what is says in my manuel, not quite sure what it means but its a start. i have the whole manuel i can send via a email if u want

 

Have a look on your 2 blocks to see what size bores you have if you plan on just swapping the pistons :





You will quite often find 'A' + 'B' on each side of the block halfs - picture above shows all 'B' sized bores.


Mick

 

Thanks guys.