I have a good 99 EJ25D and a spare set of 251 pistons. Curious if the Rods from the 52mm Ej25D will work with the 251 pistons. Or if the stroke is different?

 

So pretty much 99 EJ25D block, crank, rods w/ Ej251 Pistons. 

The stroke is the same, 79mm, but the actual A and B piston diameters are different. Attached are spec sheets.

 

O.

general description.pdf

Specifications Engine.pdf

????

From the specs you gave, the pistons are the same?

 

If 251 pistons don't fit, why not?

Not saying they won't fit, but you have to check the diameter of the ones you have versus your actual bore diameter.

This will insure that you will get the best fit. An A piston in a B bore will leave more room for the piston to wiggle, accentuating the possible of getting piston slap. On the other side, a B piston in an A bore with std rings will lead to undue wear of the rings.

 

O.

They'll fit just fine as long as you match a to a and b to b, I've actually done this with a 25d block.

 

btw, "a" is bigger than "b" you've got it backwards above

Edited December 13, 201312 yr by 86BRATMAN

Were you able to use the 25D rods?

 

99 EJ25D block, crank, rods ?

 

first, is it in fact a 99 ej25d block? (count the engine to trans bolts)

if yes, then  it is in fact already a phase 2 block, ej251 .

 

the 99 forester was / is a phase 2,  ej251 SOHC engine. (maybe ej253 depending on the trans, but the same block)

the 99 outback and GT were / are a hybrid engine from the factory,

ej251 phase 2 block with ej25d DOHC heads and intake.

 

i'm not sure what the internals are,

except to say the phase 2 blocks must have the phase 2 crank with the thrust bearing in the 5th position.

Edited December 13, 201312 yr by johnceggleston

8 bolt's on the bell housing. 

 

So essentially I can use the 251 pistons to up the compression for my frakenmotor build and run an STI HG on the Phase 2 EJ25D just like I would with a 251?

there is some concern that the 251 block and pistons may interfere with the valves of the ej25d heads.

and it is recommended that a thicker head gasket is used to eliminate that possibility.

and i don't know if this concern is based on experience or speculation.

but i do know you can use an ej251 block, 00 - 04 as a replacement for an ej25D, 96 - 98 block.

 

but if the turbo head gasket is thicker, i would use that just in case.

of course, the thicker gasket may offset any gain in compression from using the 251 block and pistons.

 

what heads are you planning on using?

You already have a 251 short block.

Pull the heads and check the pistons. They're probably the same as the spares set you have.

Yes we used the 25d rods, it was a 97 shortblock and they went in no problem. No protrusion from the cyl like the 25d normally does.

 

The 99 25d uses the same pistons as the 97/98, as long as you're sure the pistons are 251 then you are good. Use some STi head gaskets and 25d heads and enjoy high compression.