61 replies to this topic

[WillC]

Hi Guy, Been wondering what was really under the hood a bit of googling didn't help at all, does anyone actually know what is inside the EJ20TT ? i'm trying to find out if its got forged internals? any info would be sweet

[Xon]

Believe the B4 is "semi forged". I don't know what is and what isn't forged though

[Evil_VZ-T]

Yes, They do have "Factory forged pistons".. These are better than standard WRX ones, But not as good as aftermarket ones. They are also Open deck blocks

[Hypnotic]

Forgive my ignorance yet again and apologise for the slight hyjack of thread (as im slightly intoxicated) however "open deck blocks"? please elaborate as im still trying to grasp lingo of certain things

[DukeNik'em]

Forgive my ignorance yet again and apologise for the slight hyjack of thread (as im slightly intoxicated) however "open deck blocks"? please elaborate as im still trying to grasp lingo of certain things

Just picture a veranda for your engine.

"closed deck: the cylinders are bored out of the block, the cylinder may have a liner of a hard/low friction metal

open deck: the cylinder is a seperate piece; its walls are freestanding, located by th block at the base, and the cylinder head at the top. Coolant thus circulates the entire cylinder (most hondas use this design)"

EJ20TT is schmick though, not as good as EJ25T, .

[Dylan]

Forgive my ignorance yet again and apologise for the slight hyjack of thread (as im slightly intoxicated) however "open deck blocks"? please elaborate as im still trying to grasp lingo of certain things

Perfectly welcomed question.


http://www.cgperform...ubaru_block.htm should help you. Has a good description of it.

Closed Deck:


Semi-Closed (think STi):


Open Deck:

[WillC]

I see, it seems as the full closed deck vs open deck might have its pros and cons. Although it looks stronger and how does it work for cooling ?

[B4TT]

Molybdenum coated Forged pistons are the ones in the B4.. and your right they are not as good as after-market forgies...which I now have. The Exhaust valves are sodium filled.

[Soop]

Should have filled them with rainbows and leprechauns.

[Jeff]

Should have filled them with rainbows and leprechauns.

Mine are Soop..... thats where all my power comes from..... the leprechauns at the end of the rainbows

[DukeNik'em]

I see, it seems as the full closed deck vs open deck might have its pros and cons.

Although it looks stronger and how does it work for cooling ?

The open deck allows for coolant between the cylinder walls and the block, where as the closed deck uses a liner to ease the friction and assist movement. Closed decks are thought to be more stable as they are bored out of the block, not having there own free standing walls. But of course cooling is a lot easier for your open deck.

Nick

[Soop]

It'll make little to no difference in the cooling ability. Engines have been closed deck since the time of the dinosaurs.

[DukeNik'em]

It'll make little to no difference in the cooling ability.

Engines have been closed deck since the time of the dinosaurs.

Really I've never seen anyone want to change from one to the other, or complain that they'd rather the other, it's just a boring engineering detail. 4 out of 5 people wouldn't know the difference, nor care anyway. The internals, now thats another story.

Nick

[Soop]

Closed deck will suit a high performance far more. For a starter the bores wont split under high loads. Close decking and sleeving an engine is the way to go if you're looking for high performance and durability.

[DukeNik'em]

Closed deck will suit a high performance far more. For a starter the bores wont split under high loads.
Close decking and sleeving an engine is the way to go if you're looking for high performance and durability.

My understanding was that closed deck was the norm, and open deck was a later development, with the added cooling ability. I agree that closed is definitely stronger and being sleeved is an obvious advantage, but I guess open doesn't require a sleeve if it's walls are full of coolant.

Hey B4's are DOHC aren't they?

Nick

[Jeff]

Hey B4's are DOHC aren't they?

Nick

Yes

[Soop]

IIRC the only Subaru block that was CD'd as standard was the RS block and the USDM EJ22-t. The closed deck makes exactly d**k difference to cooling. (Higher power levels acheived with the added ability to run higher levels of boost will obviously result in higher engine temps, and therefore a higher need for a better performing cooling system.) The sleeves have nothing to do with cooling. The essentially reinforce the bore walls, to avoid "ovaling" and cracking.

[DukeNik'em]

IIRC the only Subaru block that was CD'd as standard was the RS block and the USDM EJ22-t.

The closed deck makes exactly d**k difference to cooling. (Higher power levels acheived with the added ability to run higher levels of boost will obviously result in higher engine temps, and therefore a higher need for a better performing cooling system.)

The sleeves have nothing to do with cooling. The essentially reinforce the bore walls, to avoid "ovaling" and cracking.

But sleeves also lower the friction,which in turn lowers the amount of heat put out by the movement of the pistons. I see that the new STi short block is semi-open like Dylan posted above, I'm guessing this would allow for ample cooling but still give the stability of a closed deck.

Nick

[Soop]

Sleeves don't lower the friction. How the hell did you come to that conclusion? They act exactly the same was as the original bore walls do! If you have polished bores the rings wont seal. Which is generally pretty ordinary for performance.

[Xon]

Nik.... The bores on a closed deck block are not bored out of a solid block of metal. They are cast using a mould. Could you imagine the cost of getting one big solid piece of metal and CNC'ing the entire thing in to an engine? Not to mention the MASSIVE amount of metal that would be wasted...