Is closed deck more important for high RPMs or High Boost?

[douglas vincent]

Discuss.....

[dzx]

Both?

[dscoobydoo]

I would think the closed deck would be better able to withstand the pressures of higher boost. I think the DOHC/SOHC/ pushrod issue would be the discussion for higher rpms. ( as the heads would be the deciding force)

[def09]

Both. Closed deck keeps the cylinder walls in place for much needed strength for both applications. Less likely to have a block failure at least. It would be more prone to blow at the headgasket. If I had a choice I would go closed deck or (semi-closed deck like USDM Sti) for turbo (or dont go turbo at all) and open for a "budget" high compression.

[Legacy777]

I'd say it's more important for higher boost, then higher rpm.

[-K-]

I believe it's biggest advantage is for high boost.

[93forestpearl]

I would have to agree that it is more beneficial for high boost. There are open deck honda motors spinning at 9 grand no problem, but then you throw some boost at it and you've got trouble.

[professor]

the goals of a turbo engine and a high rpm engine are very much at odds.

I would go as far as to say that the open deck might be better for a high rpm engine, due to better coolant flow to prevent heat build-up. Along with light weight pistons, conrods and of course serious mods to the valve train (no hla)

for turbo, closed deck, and bulletproof pistons and conrods that can withstand a little detonation without breaking, favoring that over weight. Subaru's open deck is REALLY open, which I suspect is behind the 2.5L head gasket disaster. cylinder wall flexing just wears away the head gasket eventually, even without boost.

there are other cars where the older, cruder castings are preferred for turbos, a good example being BMW scouring the earth for used 2.0 liter iron stock blocks, with which to build 1400hp formula one motors. By the time they did this they could have chosen from two further updates to that block, but went for the heavier 1960's design, incredibly liking to start with used motors from junk yards initially, then learning how to "run them in" from new, to relieve metal casting stresses

[free5ty1e]

OK... I'm gonna have to ask the stupid question, being the ignorant constantly-learning fool that I am:

What are the basic differences between a closed-deck engine and open-deck engine? Are the differences in head design only? This also has to do with whether or not the engine is an interference engine or not...?

I'm getting that closed-deck designs provide additional reinforcement for the cylinder walls to avoid their flexing under high overall compression. The EJ22T is ... open deck? Why or why not?

Please educate me.

[Legacy777]

The open/close deck refers to the block itself and how it is cast.

Look at the multitude of pictures I have of the EJ22T
http://www.main.experiencetherave.com:8 ... ges/ej22t/

It has coolant passages around the cylinders. The extra "meat" around the cylinders provides more strength and rigidity.

Now look at pics of the open deck design
http://www.main.experiencetherave.com:8 ... endeck.jpg

There is much less "meat" around the cylinders

As for head design and interference/non interference.....that has nothing to do with it being open or closed deck.

[rallysam]

Agree with most posts above - it seems closed deck mostly helps with high boost. The closed deck molding technique really affects what the engineer can do with the shape and features of the block. The technique allows them to design block shapes (and gasket shapes) that better stand up to the higher pressures. But, the block doesn't really know or care what SPEED things are moving, it mostly addresses a static issues (to oversimplify a bunch!)

Instead, for high RPM, you normally worry about upgrading the MOVING parts (making everything lighter, better balanced, and stronger, so they don't fall apart at high speeds).

This is a huge oversimplification that people will shoot holes in, but I think the gist is right.

[free5ty1e]

I see - thanks again Josh

So the EJ22t is a closed-deck block. I like that.

Seeing how well the coolant system works, why would anyone want an open-deck block? It also looks more difficult to produce - what benefits does it have over the closed-deck design?

[Legacy777]

Open deck blocks are going to have better cooling then the closed deck designs. More coolant suface area around the cylinders.

The closed deck engines are more complex to build. They are built via sand casting. The cast must have the coolant passageways and such cast into them. The open deck engines are less complex to cast. The biggest advantage over the closed deck motor is quite a bit reduced costs on casting as well as casting time.

[rallysam]

Agreed with L777. On top of that, I think I heard that open deck is actually better quality in terms of how good the castings come out. Closed deck is only "better quality" in the sense that the technology allows the engineer the freedom to design some unique shapes with it (allowing him to design some features that are more resilient). But, it's reliatively shoddy in terms of the resolution and repeatability of the casting process. So, in that sense it's actually kind of old school and ghetto.

So, if you are just making a cookie cutter generic car with no exotic performance requirements, why not go for the open deck process that's cheaper and better?

Some of this is from me reading between the lines, so correct me if I'm wrong.

[evolutionmovement]

I thought I read (SAE papers?) that the closed deck engine is actually a combination of sand casting and die casting which makes it so expensive to build while the open deck design is die cast only.

I think a stable platform is better for everything, but definitely more so for boost. With the speed of parts at high rpm in the N/A application I don't think the cylinders would walk that much and less so with the 2.2 than the 2.5 with its bigger heavier pistons.

Steve

[THAWA]

To the original question, neither. Subaru first started closing the deck to prevent head gasket/overheating problems. Over the years they figured out how to make an open deck that wasn't prone to overheating/blowing a hg, starting with the EJ series. All from the EA71 I believe were closed, someone else should double check that though.

[93forestpearl]

My professor explained to me how die casting is actually more expensive initially for the setup of making dies and what not, but is much less expensive in the long run do to quicker production time. The ej20 has been around for quite a while and is a relatively high volume engine for subaru. I can see from a production and cost standpoint that die casting is the way to go when you can make it good enough to get the job done but don't need to go the extra mile.

I read somewhere (I can't remember) that the medium pressure used in the sand casting is better than the high pressure in die casting due to tiny air bubbles that form when the molten aluminum rushes into the die. Don't quote me on it though.

Josh- I don't see how an open deck block would have that much better cooling capacity since the main difference between the two is right a the deck. The coolant passages from the block are quite a bit bigger than the ones going into the head. I wouldn't think flow would be much different. Unless there is something I'm missing. I dunno.

Dan

[rallysam]

...Over the years they figured out how to make an open deck that wasn't prone to overheating/blowing a hg, starting with the EJ series...

Ha! (from an EJ25 owner)

[Legacy777]

Josh- I don't see how an open deck block would have that much better cooling capacity since the main difference between the two is right a the deck. The coolant passages from the block are quite a bit bigger than the ones going into the head. I wouldn't think flow would be much different. Unless there is something I'm missing. I dunno.

Dan

You're probably right.

[THAWA]

...Over the years they figured out how to make an open deck that wasn't prone to overheating/blowing a hg, starting with the EJ series...

Ha! (from an EJ25 owner)

From what I've heard of the pre-EA71, (again someone check that) EJ25's are nothing compared to that. Don't get me wrong, EJ25's still suck.

[rallysam]

...Over the years they figured out how to make an open deck that wasn't prone to overheating/blowing a hg, starting with the EJ series...

Ha! (from an EJ25 owner)

From what I've heard of the pre-EA71, (again someone check that) EJ25's are nothing compared to that. Don't get me wrong, EJ25's still suck.

Gotcha.

[Impregacy]

Open deck honda engines run very reliably at high rpms. The real kicker is that they do it with a dangerously low rod ratio at the same time 1.57 for a type R integra. The type r's b18c5 actaully has ludacris pistons velocity and force exertion on the cylinder walls -more than any honda race engine. It seems like they can do whatever the want with the right materials selection. Are they just trying to cut costs?

[Matt Monson]

...Over the years they figured out how to make an open deck that wasn't prone to overheating/blowing a hg, starting with the EJ series...

Ha! (from an EJ25 owner)

From what I've heard of the pre-EA71, (again someone check that) EJ25's are nothing compared to that. Don't get me wrong, EJ25's still suck.

I am going to have to beg to differ here. The problem on the first gen EJ25 was not the open deck, but the crank girdle and the center thrust bearing. On the phase II engines they beefed it up and moved the bearing to the end. The Ej25 is an excellent engine. In fact, I have come to the conclusion that the whole closed/semi closed thing doesn't matter very much, and am selling my Ej257 STi block and rebuilding my stock Ej251 bottom end for my 12.5:1 CR monster.

Furthermore, the SOHC heads on the EJ251 are the best heads Subaru has ever designed. I think in production they continue to use the DOHC on the turbos strictly from a marketing standpoint. If you look up the Rigolis, down in Australia, you will see they have come to the same conclusion. For those not familiar with the Rigolis, they are pretty much the originator of the EJ22T high power formula using DOHC heads in 9 second drag cars. They have gone to the SOHC heads because the roller rocker design opens and closes the valves more quickly and have less valvetrain weight and lower inertia. On some of their builds they are even using stock valves and springs with 20+psi of boost and 8000rpm redlines

[tris91ricer]

Ha! (from an EJ25 owner)

From what I've heard of the pre-EA71, (again someone check that) EJ25's are nothing compared to that. Don't get me wrong, EJ25's still suck.

I am going to have to beg to differ here. The problem on the first gen EJ25 was not the open deck, but the crank girdle and the center thrust bearing. On the phase II engines they beefed it up and moved the bearing to the end. The Ej25 is an excellent engine. In fact, I have come to the conclusion that the whole closed/semi closed thing doesn't matter very much, and am selling my Ej257 STi block and rebuilding my stock Ej251 bottom end for my 12.5:1 CR monster.

Furthermore, the SOHC heads on the EJ251 are the best heads Subaru has ever designed. I think in production they continue to use the DOHC on the turbos strictly from a marketing standpoint. If you look up the Rigolis, down in Australia, you will see they have come to the same conclusion. For those not familiar with the Rigolis, they are pretty much the originator of the EJ22T high power formula using DOHC heads in 9 second drag cars. They have gone to the SOHC heads because the roller rocker design opens and closes the valves more quickly and have less valvetrain weight and lower inertia. On some of their builds they are even using stock valves and springs with 20+psi of boost and 8000rpm redlines

So 0wn3d.

I want a CR monster. . .

[rallysam]

Ha! (from an EJ25 owner)

From what I've heard of the pre-EA71, (again someone check that) EJ25's are nothing compared to that. Don't get me wrong, EJ25's still suck.

I am going to have to beg to differ here. The problem on the first gen EJ25 was not the open deck, but the crank girdle and the center thrust bearing. On the phase II engines they beefed it up and moved the bearing to the end. The Ej25 is an excellent engine. In fact, I have come to the conclusion that the whole closed/semi closed thing doesn't matter very much, and am selling my Ej257 STi block and rebuilding my stock Ej251 bottom end for my 12.5:1 CR monster.

Furthermore, the SOHC heads on the EJ251 are the best heads Subaru has ever designed. I think in production they continue to use the DOHC on the turbos strictly from a marketing standpoint. If you look up the Rigolis, down in Australia, you will see they have come to the same conclusion. For those not familiar with the Rigolis, they are pretty much the originator of the EJ22T high power formula using DOHC heads in 9 second drag cars. They have gone to the SOHC heads because the roller rocker design opens and closes the valves more quickly and have less valvetrain weight and lower inertia. On some of their builds they are even using stock valves and springs with 20+psi of boost and 8000rpm redlines

Well, I would agree that EJ25's dont "suck", but I think our concern with the EJ25 head gaskets relates to a) factory recalls to address head gasket failures - even on stock engines b) head gaskets blowing like swiss chees on most RS's with aftermarket turbos - even on very moderate boost levels