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

[THAWA]

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.

umm, not quite

Matt, I wasn't saying the reason the EJ25's overheat is because of the open deck block style. I was saying that pre-EA71(confirm?) the open deck engines were supposedly really bad at overheating/hg, and when the EJ series was introduced they could make open decks that weren't so bad at overheating/hg. We've all seen EJ22's blow HG's, I'm not saying it is a bullet proof design, but the chances are much less. And we've all seen EJ25's blow HG's, again, not saying it's a bullet proof design, but the chances are less. It seems as though you're trying to defend that the EJ25's don't blow the HG's because they're open deck. That's fine. I can't proove one way or another, but you can't say that EJ25's don't blow a lot of HG's (which to me qualifies as a sucky engine). I don't think we're disagreeing on anything, just that we're stating two different bits of information.

[Matt Monson]

Well, lets start with the example of the blown head gaskets on boosted Ej25's. Many of those have happened on phase I engines. These engines had the weak bottom end and coupled with the open deck design, the cylinder bores are subject to walking. I see far fewer instances of this problem on phase II engines, especially with guys who have put in forged pistons with lower compression ratio. But regardless, to say that the engine is weak because an engine (and head gasket) designed for 165 normally aspirated horsepower and running stock compression cannot handle 250 boosted horsepower for very long just isn't a fair comparison. I know of a handful of guys with 9:1 CR EJ25's who run 12-15psi very reliably on phase II engines.

I am absolutely nor trying to defend that Ej25's do not blow head gaskets because they are open deck. I don't know where I ever said that. All I said that was the Ej25 engine does not suck, and gave some very good reasons to back that up...

[entirelyturbo]

Just to throw a twist into the argument, I heard from a source I don't remember that the Phase I EJ25's were blowing HG's because of improper head-bolt tightening procedures at the factory. I have no source for that info though, so that info is at your disposal.

[Matt Monson]

Just to throw a twist into the argument, I heard from a source I don't remember that the Phase I EJ25's were blowing HG's because of improper head-bolt tightening procedures at the factory. I have no source for that info though, so that info is at your disposal.

That is part of the problem to my understanding. I concur that the phase I Ej25's are crap for anything over 200hp. But so much of what was wrong with the first gen was fixed in the second gen. And since Subaru changed the head gasket for the phase II's the problem has gone down significantly...

[scottzg]

so its not because there isnt enough clearance between the cyls due to the stretched engine design? Learn something new every day.

I don't understand how the sohc can be more rev friendly than the dohc. Rockers have to change direction every rotation via the spring, a considerable load on the spring and cam. Do all dohc heads have hydraulic lash adjusters?

[THAWA]

Well, lets start with the example of the blown head gaskets on boosted Ej25's. Many of those have happened on phase I engines. These engines had the weak bottom end and coupled with the open deck design, the cylinder bores are subject to walking. I see far fewer instances of this problem on phase II engines, especially with guys who have put in forged pistons with lower compression ratio. But regardless, to say that the engine is weak because an engine (and head gasket) designed for 165 normally aspirated horsepower and running stock compression cannot handle 250 boosted horsepower for very long just isn't a fair comparison. I know of a handful of guys with 9:1 CR EJ25's who run 12-15psi very reliably on phase II engines.

I am absolutely nor trying to defend that Ej25's do not blow head gaskets because they are open deck. I don't know where I ever said that. All I said that was the Ej25 engine does not suck, and gave some very good reasons to back that up...

Okay, you're adding another variable into the equation. That up above doesn't matter, none of this matters. I'm simply stating that engines before a certain time had hg/overheating problems, and through R&D subaru could make open deck engines that didn't have as many hg/overheating problems. That's it. Someone noted that EJ25's blow headgaskets, that's true. Now where the fault lies with the EJ25 blowing hg doesn't matter to me, at all. I don't care if you can get 400 hp out of an EJ25, it just doesn't matter to the arguement I'm trying to make. Which is, that with the EJ-series subaru could make open deck engines that didnt blow hg's/overheat as much as before. Your example up above means nothing because I never once mention modified engines, so I dont even know why you'd bring it up. Anyway, I personally feel that EJ25's suck. You don't have to think that way, noone else does, it doesn't matter if you feel completely opposite, it's just my opinion.

[Matt Monson]

Thawa,
Look at the title of this thread. My points absolutely matter to the discussion at hand. The topic here is does the closed deck matter for high rpms or boost. I guess you are making an off topic point about the evolution of the engines, that I didn't realize was out of the context of the larger question, which I was trying to address.

Just because I quote you and disagree with your opinions doesn't make it personal. But you seem to want to argue that you are right and that I am somehow challenging you on a personal level even though you claim that we are both entitled to our opinions. Lighten up man...