Just a few lame questions from a noobie, whats the deal with a 'Semi Closed Block' whats it mean, and as for pre-02 model sti engines? They have forged Pistons and 'Semi Closed Block's too?

open<semi closed<closed

less cylinder movement. more strength.

pictures will be good and explains things clearly, but i dont have any

Hi Guys,

If you look at this pic posted on pg1, there are small parts highlighted in blue, these are what is added to make the block "semi closed", all it does is stop the bores moving back and forth.



cheers
Michael

so closed would have a filling all the way around the bore? Why not do this always, does it have a disadvantage?

I think getting adequate cooling is the main issue with fully closed decks.

yep, so its better to get a semi closed to retain oil lines and then sleeve the block to increase bore strength and decrease movement. but costs start getting quite high after u've spent ur money on everything else

Just another question on this *sorry for the bump* pre 02 STi engines, are they semi closed? They have Forged Pistons or is there a diff deal with them.

The V5 and V6 STi blocks I have seen are basically the same as the vanilla model WRX...open deck. Basically the V5/6 STI have Forged pistons, better heads and cams, same rods, similar crank and block over the Vanilla model WRX...and a poofy red inlet manifold running higher water system pressure to boot. Hence some of the earlier fully closed liberty rs blocks had become more desirable for that HIPO rebuild.

Not sure what the specs are for the earlier models but please start your own thread if interested.
Guys can we lock this one in for future reference as the comments and pictures from Michael South are Gold!

some more info from an American accociate regarding V7 sti and Spec-C engines.

Sort of relevent.

Ausie heads are small port. The Spec C engine has large port heads. It also has higher duration cams. The factory redline is 8300 depending on Rom code. Could be 7800 as well.. The Spec C ran a smaller VF35 turbo and did not run more boost. It has more Cam timing, less fuel and more ignition timing. Later Spec C's had the VF34 turbo which is Ceramic bearing. They make about 30hp more then the standard motor. Mainly due to the cams and the ECU tuning. AVCS is shut off earlier which makes a bit more top end. Spec C engines also had Sodium filled exhaust valves and they had hollow Manifold Risers. No TGV and no Plate devide like your Aussie motor or Standard V7 motor. They also ran a higher pressure FPR which was marked STI. Early ones had the older Acc belt cover of the V6 engine. Later ones have the plastic cover that the current cars do. Spec C engines also had a Dual Oil Galley crank. V7 engines used Forged pistons. Very strong. They ran tight bore clearances. 10-12 ten thousands. Some had issues with high hp and or track events with the pistons expanding and running tight in the bore causing wear and piston slap/scuffing. If a V7 Engine is going to be run at several hundred hp higher then stock or if it is a race engine the engine should be bored out slightly to increase clearance. Fit and oil cooler at least. Spec C engines also had an addition intake air temp sensor under the manifold. This sensor fed the 970-972 code or S202 code ecu to run the Auto IC spray system. S202 code ecu will permit more power. It has a very smooth mapping and lots of advance. You must use high octane fuel however. V8 versions of the Spec C and V9's use Hyper cast pistons. They also seem smoother in operation and most but not all are twin scroll VF36 or VF37 turbos. The V8 and V9 engines have higher static compression. Fit heat range 8 plugs to these motors if pump gas is used. All will take 27 to 30 psi out of the box with proper tuning. Valves seem to float past this. Standard V8 and V9 motors got V7 spec C cams. A V8 standard motor is about the same as the V7 Spec C in terms of power. Maybe bit more. Its a toss up to which one is stronger. The v8 hyper cast pistons never scuff or run tight as they have more clearance and I never hear of them failing like the 2.5 pistons do. I ran a v7 Spec C motor for a year with a 30R. Its rod bearings finaly let out. I had the rev limit set to 8650 rpm and hit that just about every day. I did run it to 9000 maybe 20 times but later backed it down. It was an incredible motor and very much more refined then the 2.5. The V8's that I have tuned have been so smooth that you could run down the expressway at 6k rpm and not even know it. If you did that with a 2.5 you would be wincing...

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K.E.R.S!!!1

I had a rebuild lately. This was my brand new 2.0L '02 STi short block, ordered diretly from Subaru Australia:



This was my original 2.0L Forester short block:



Side by side, open vs. semi closed: