EJ25D to EJ251 swap-need info please

[scar13]

I have a 98 OBW that's developed a rod knock. I got a ej251 long block at the pull it yourself yard. I could use 95 2.2 heads or the 25D heads. I'm leaning towards using the 2.5 heads as I already have them. I'm not sure which head gasket to use though. There are different part numbers for 251 and 25D. I have heard this combination will raise the Compression. Does anyone know how high? On that same topic what would the compression be elevated to if I used the 95 EJ22 heads? The 251 engine came out of a 2000 model legacy. Thanks in advance for any info.

[johnceggleston]

the 251 block should work with the ej25d heads.

but tyou need to double check the gasket.

there is a head  / block combination where a thicker gasket is required.

 

but generally speaking,

the head gasket MUST match the block.

if the fire ring? on the gasket does not fit the block,

it will not seal.

[wtdash]

HI,

The Ej22 heads/EJ251 block will be a 'franken engine" and raise comp to over 10:1. You'll want to run Premium.

 

I think you can run the STi 2.5 HG w/the Ej25D/EJ251 combo....read up on NASIOC.

 

GL,

TD

[logic23]

if you are using a 2.5 dohc block then you need to use the 2.5 dohc headgasket. The pistons come above deck height at TDC. if you use a thinner gasket it wont work.

[wtdash]

^- He's using a SOHC EJ251....heads are the issue - not the block.