[spshultz]

Eventually this car (99 2.5RS) is going to be paid off. I've always wanted to build up an engine in a car or truck that I enjoy driving. I'm currently working on a 350 for my '83 Chevy C-10 (top end rebuild only) but building up a Subaru engine really intrigues me.

Most, when going forced induction, will go with 8.5/8.0:1 forged pistons, forged rods and forged crank. Drop the comp ratio, up the boost and you've got longevity (somewhat).

What I'd like to do is the following but I just don't know enough to know if this will have major problems.

Stroke the 2.5 to 2.7
Use 9.5:1 forged pistons with nice set of rings
Use forged rods
Stock crank (unless new crank needed with stroking)
Cobb turbo cams or similar
Keep block open deck (just a basic cleanup)
Clean up heads (stock valves and springs)
Clean up intake manifold
Link engine management system
Templars S/C kit running 8 - 10psi
New torque converter from ProTorque

And...be able to use only 91 octane here in the Denver area without popping a rod or piston or over heating problems.

I know that it will be a lot but spread out over a period of time will help psychologically (especially with my wife).

Any and all criticisms are welcome. Even if I am a dumbass for wanting to do something like this. :biggest:

 

[5252]

leave the stroke alone. subaru's have robust cranks. so just go rods and pistons. and go either hi comp all motor or low comp forced. remember, you got to run on pump gas.

...truck that I enjoy driving....

and get some suspension. you will enjoy driving your rs alot more than a truck. i like my truck, but for work.

 

[spshultz]

If I only had the specs on the stock cams I might be able to figure out the Dynamic Compression Ratio from various Static Compression Ratios. I know that running a DCR of 8.5:1 and you are going to need racing gas. Somewhere around 7.9:1 is where you can get away with running 93 octane (sea level) or 91 octane (5000 feet above sea level).

Doesn't the Rally Knight (sp?) team run a turbo'd and stroked 2.5? Someone is doing it and it's where I got my idea from.

I guess if I went all motor then I could only take it so far before I hit an HP plateau. With a low SCR and high boost I will hit a much higher HP plateau.

Decisions, decisions!

 

[szm426]

whats the difference between open and closed deck blocks? Thanks

 

[spshultz]

Someone please correct me if I'm wrong but I believe that our 2.5 blocks are open deck meaning that there are large cooling holes around the piston walls. A closed deck means these large holes have been partially filled to reduce stress on the cylinder walls during hi-boost applications. It doesn't seem to affect cooling.

Is this atleast somewhat close? I'm sure someone can better explain it.

 

[Safir]

open deck:

closed deck:

closed deck block are able to hold more pressure with some loss of cooling capability.. everything is a trade off.

I wish i had examples from hondas... they really get the poitn across, the sleeves (cylinder walls) on a honda block don't touch the outside of the case at all, they will fill those gaps at the top of the sleeve until ther are only a few holes for teh coolant to pass through for added strength

 

[szm426]

thaanks so which one is better for 20-25 psi?

 

[spshultz]

Closed deck for your high boost applications.

Anybody on here running 20 - 25psi open deck with no problems?

 

[Safir]

20+ PSI open deck without problems... i dont even know of anyone running that kind of pressure in anything open deck... at the very least you will need to be re-sleeved i would think...

oh yeah and thanks to cobb tuning for the pictures in my last post

 

[Tall J]

I was wondering if you guys ever run into cooling problems having the water jackets bridged like that on the closed deck blocks? It looks like the heat the pistons generated against the cylinder wall can radiate to the rest of the block pretty easily.

 

[HOK]

no heat problems what so ever... i think the cooling arguement is overrated... guys in AUS run these things to the ground and no problem.. but some also say that closed deck is overrates... who knows...