cynner wrote:What about with a pre-2009 ej255 engine?
I'm a complete n00b when it comes to engine builds. With Kris's custom engines here:
http://risingsunsubaru.com.au/2-5L-Option-1.php - what is actually re-used from the stock engine? Both the block and the heads? Or does he take the stock block and build new heads?
bigBADbenny wrote:They're short blocks afaik.
Yes all short blocks, no oil or water pump though AFAIK.
As for pre-09, you don't want as a factory short; early 2.5L pistons are the worst I'm told. Subaru separated the rings a bit for later ones but not enough apparently.
As a platform for a light build (forged pistons only), they are good if you can find a really cheap, low use one. But, for the price, new or near-new is a better bet IMO.
The later years (09+) come with a hardened crank. Subaru firstly nitrided them, then for some reason (some time in 2010) switched to heat treating for a short while, then went back to nitriding. Hardened crank obviously has advantages
Rods are no different from what I can find from my research.
Kris tends to use brand new short blocks for his Option 1 motors: CP 257 forged pistons with stock crank, rods, bearings, etc.
Re-use your peripherals and heads.
If you supply him with your old. Short block he uses these for Option 2 and custom build (option 2 include aftermarket rods and ACL race bearings instead of Subaru ones.
What I was planning for my old Foz (2011 S-Edition):
- Option 1 short from Kris ($3,000)
- Timing Belt kit ($550 from memory)
- Gasket/seal kit ($330)
- ARP 260-4701 head studs ($250 new or thereabouts)
- 11mm Oil pump ($275 from memory, could be wrong)
- Heads hot washed and "decked" ($350)
I was going to do the work myself saving a few dollars
My research showed this setup would be perfect for up to about 275, through a manual, or about 250 through an auto.
You could probably run a lot more with this setup (PCXT had his2006 Forester at 283kW with a Dom 2.5XT-R on 98RON running basically this plus ACL bearings for nearly 2 years or something...), but it would be more than adequately solid for sub-250.
As for the increase in comp ratio with 257 block and 255 heads, it's because:
255:
- piston dish 22 mm
- head combustion chamber 49cm
257:
- piston dish 19mm
- head combustion chamber 55cm
(Sizes are cubic)
Because of the piston dome size in relation to combustion chamber size, any decrease in the piston size will be exponentially greater than a change in the combustion chamber size...not something I'd personally do with stock pistons and head studs.
This is all just info I gathered from my research last year before offloading my Foz.
HTH
Sean..