Can someone please tell me what a closed deck block is? I'm looking at buying a wrx and some say they've got one and some don't?

 

The pre 1996 engines tend to be CDB, but not all, though the higher output 'red top' engines do have the stronger CDB. (RA's Sti's etc)

The CDB is simply stronger at the cylinder head face where the bock casting is solid, later engines are 'open' around the cylinder linings.

There are pleanty of 400bhp engines running the 'weaker' open blocks.
I wouldn't worry about it; Subaru didn't after all as the Sti /RA's had open blocks after 1996 (Version 3) as a general rule.

 

But the STI and RAs have forged internals, right?

 

Did any pre 1996 WRX's have closed deck blocks then?

 

Yes, I have one sat in my garage now from a 94 wrx and hopefully the one in my car is as well

 

CDB can be identified by the square hatching markings on the outside of the block. IIRC all heads have this but only CDB's have it on the block.

Not sure about semi CDB's however, which apparently all the latest 2.5 turbo uk engines have..!

Out of interest, what compromises a semi CDB..?

 

Can you do anything with a 2l closed deck block to increase displacement? What are the options, I've heard about the 2.2l CDB's that can be increased to 2.33/2.35 but not the 2l. Any advantage of a 2l/2.2l CDB over a 2.5l on a 500/500 build?

 

You can get it machined to take the later 2.5 crank and then get a stroker kit of rods and pistons and this'll make it a 2.15.

 

What kind of markings are you talking about?

 

On the oil ways that run under the turbo inlet and alternator that go to the heads you'll see hatching over them, whereas its plain on open decks, plus it'll be on the section above the oil filter.

 

like an extended noughts and crosses board around the oil filter area as Jim says

 

This should help you out>>>>>>
Subaru Block

 

A real one:

 

It took me a while to understand what is a noughts and crosses board . In Spain that's called "3 in line"

Anyway, using the picture that 911 has posted, the hatching you talk about is what we can see where the cylinder is, right?

 

Yes.
I'm not sure that this is THE reliable way to be sure of a CDB though.
The only way is with the heads off of course.

Incidentally, that block when I had it had oil squirters in it to cool the pistom crowns. Not sure if all CDB had them!

They are not rare. API engines and Lateral have them on the shelf, some modified for the STi V9 cranks too.

 

The only definite way to tell is that ALL CDB's have the cross hatch squares on the casting immediately above the oil filter location. None others are absolutely definite.

David APi

PS We have stock all the time and can make 2.1, 2.2 , 2.35 from that casting with ease.

 

Here's a close up of the cross hatching on the oil filter casting




All the CDB came with Bore Squirters

 

It's all clear now

 

It is possible to have an early centre thrust block that is open deck AND have bore squirters. They are really rare and it is just as well that it is not a block that is in demand. But yet again bore squirters are not a definite for cdb identification.

However, we have never seen a block with the hatch marks by the oil filter that is anything other than cdb.

We are quite happy when we get the open ones as it gives us extra bore squirters for our stocks - but just as equally p1ssed off as we didn't get the CDB.

David APi

 

How did I do that?