[brusso]

One thing I know is that open deck on a boosted motor becomes a problem especially at higher rpms ... aka 7K and above. You actually get wobble on an open deck under high hp and high rpms.

Just my .02 from past turbo and high rpm days.....

[Turkishexpress]

I think the head is more of a factor for high rpm applications... Forged internals and DFI should really help with keeping the block safe...

[A418t81]

Originally Posted by Ninji

What a crock of shit. That "information" is a bunch of nonsense and there is no way to relate block design to how much boost pressure an engine can handle.

Detonation is what cracks sleeve, esp. lean detonation which smashes the thrust surface of the pistons into the cylinder sidewalls. As long as you aren't detonating, you can run 40+psi of boost on an open deck motor with thick enough sleeves.

And if you have a problem with cylinder walk blowing head gaskets, the standard fix is to upgrade the head bolts to high strength aftermarkets (e.g. ARP studs) to increase the clamping force between the head and the sleeves.

Thanks for saving me the time typing.

Also, the EJ205, or standard WRX engine is a weak design in the first place. Anything over 300 whp is on borrowed time. This is NOT inherently because the block is open deck. When I have more time I'll go more into why this is but suffice it to say that an open deck means basically jack when it comes to power production these days.

[Motor She Wrote]

What kind of decks do the 996/997 Turbo and GTR have?

[NM_BMW]

good info.

[SfValley335i]

Originally Posted by Ninji

What a crock of shit. That "information" is a bunch of nonsense and there is no way to relate block design to how much boost pressure an engine can handle....

Crock of shit or not... Thats the word in the "public"
You may or may not know more than those that stated open deck is a weaker than a closed deck block...


Are there any other members here that agree or disagree with Ninji?

[Ilma]

If you define Detonation as an uneven and uncontrolled explosion which is lopsided against one side of the piston, then it makes sense the forces produced would smash the other side of the piston skirt against the cylinder wall and have the potential to fracture it just like in the photos.

So yes......I agree with Ninji.

Most of the research I have read indicates that engine manufacturers tune the combustion chamber to produce an evenly propagating flame front which burns evenly across the entire cylinder.

Doesn't that make sense?

[Dr_Dirt]

The block on my 3000GT VR4 was a closed deck, but that didn't do anything to prevent knock. It wasn't recommended to go over 14psi unless we used race gas or had other supporting hardware. Mine was tuned for 16psi on 93 oct and there was still some knock. There were alot of people who blew their VR4 motors and without using excessive boost.

The closed deck type motors don't seem to be a proper method of determining boost limits.

[Ilma]

Originally Posted by Dr_Dirt

The block on my 3000GT VR4 was a closed deck, but that didn't do anything to prevent knock. It wasn't recommended to go over 14psi unless we used race gas or had other supporting hardware. Mine was tuned for 16psi on 93 oct and there was still some knock. There were alot of people who blew their VR4 motors and without using excessive boost.

The closed deck type motors don't seem to be a proper method of determining boost limits.

Was the knock audible to you?

[Ninji]

Originally Posted by SfValley335i

Crock of shit or not... Thats the word in the "public"
You may or may not know more than those that stated open deck is a weaker than a closed deck block...


Are there any other members here that agree or disagree with Ninji?

The original post is just the kind of blanket statement that's meant for automotive noobs. At the basic level, yes - an open deck is weaker and generally less preferable than a closed deck for high hp motors. But "weaker" doesn't really mean anything. Is a lead bullet weaker than a steel bullet? Well yeah, but what difference does it make - they both do their job.

It's very clear on this forum which members come from automotive backgrounds and which members just went out and bought a BMW one day and decided to join a forum. Once you've been building and tuning engines for about a decade, you'll start to see "information" like this as pure nonsense that only serves to confuse and worry people who still view engines as magically complex mysteries.

[ar design]

Originally Posted by Dr_Dirt

The block on my 3000GT VR4 was a closed deck, but that didn't do anything to prevent knock. It wasn't recommended to go over 14psi unless we used race gas or had other supporting hardware. Mine was tuned for 16psi on 93 oct and there was still some knock. There were alot of people who blew their VR4 motors and without using excessive boost.

The closed deck type motors don't seem to be a proper method of determining boost limits.

Closed or open deck isn't going to do crap for knock. Sounds like your tune sucked. End of story.

[SfValley335i]

Originally Posted by Ninji

The original post is just the kind of blanket statement that's meant for automotive noobs. At the basic level, yes - an open deck is weaker and generally less preferable than a closed deck for high hp motors. But "weaker" doesn't really mean anything. Is a lead bullet weaker than a steel bullet? Well yeah, but what difference does it make - they both do their job.

It's very clear on this forum which members come from automotive backgrounds and which members just went out and bought a BMW one day and decided to join a forum. Once you've been building and tuning engines for about a decade, you'll start to see "information" like this as pure nonsense that only serves to confuse and worry people who still view engines as magically complex mysteries.

Very true.... I know which group I'd fall into.

[Ninji]

Lol. Further proof of the n00bery in here is the way people talk about boost pressure as an absolute measure of hp. FYI, psi means nothing; what matters is the mass air flow rate, which you can painstakingly determine from the turbo compressor maps. And since cfm is the determining factor, you can easily have a car running 8psi that makes much more power than another car at 16psi.

And as far as cylinder walk - perhaps a more important variable would be the engine's r/s ratio. If if has short rods, there's going to be much greater sidewall loading which will distort the sleeves and potentially pop the head gasket.

The N54 stroke is 84mm. I wish I knew the rod length so I could calculate the r/s.

[scollins]

Originally Posted by Ninji

Lol. Further proof of the n00bery in here is the way people talk about boost pressure as an absolute measure of hp. FYI, psi means nothing; what matters is the mass air flow rate, which you can painstakingly determine from the turbo compressor maps. And since cfm is the determining factor, you can easily have a car running 8psi that makes much more power than another car at 16psi.

And as far as cylinder walk - perhaps a more important variable would be the engine's r/s ratio. If if has short rods, there's going to be much greater sidewall loading which will distort the sleeves and potentially pop the head gasket.

The N54 stroke is 84mm. I wish I knew the rod length so I could calculate the r/s.

Does this help at all? Found it on another forum...

[Ninji]

Whoa, nice! Looks like the rods are ~130mm, so the r/s is ~1.55:1.

That's actually lower that I would have hoped...

[McLuVan]

Originally Posted by Motor She Wrote

What kind of decks do the 996/997 Turbo and GTR have?

gtr is closed

and a 996tt S, closed

[BavarianBullet]

Originally Posted by Ninji

Lol. Further proof of the n00bery in here is the way people talk about boost pressure as an absolute measure of hp. FYI, psi means nothing; what matters is the mass air flow rate, which you can painstakingly determine from the turbo compressor maps. And since cfm is the determining factor, you can easily have a car running 8psi that makes much more power than another car at 16psi.

And as far as cylinder walk - perhaps a more important variable would be the engine's r/s ratio. If if has short rods, there's going to be much greater sidewall loading which will distort the sleeves and potentially pop the head gasket.

The N54 stroke is 84mm. I wish I knew the rod length so I could calculate the r/s.

My 2c is that if you have issues with the tune or the engine itself that cause detonation on an engine making serious power, you're going to have parts breakage. If it doesn't split a cylinder wall as some seem to be concerned about here re open deck, you'll hole a piston or melt the head. Something has to give and one always hopes it would be the head gasket first.

Detonation does not release substantially higher cylinder pressures (2x, 3x etc) but rather makes a lot of heat and that is what destroys things. The speed the metal parts are moving at and inertia are what tends to break things in spectacular fashion.

Because piston to wall clearance, piston to head clearance (quench), etc are pretty tight on modern engines and a lot of parts are aluminium, it doesn't take much to blow something up. Piston crown expansion from detonation is a big problem.

There is no lubrication above the top combustion ring of the piston and carbon tends to build up there as well. So what is a small piston-to-wall clearance gets smaller with carbon and if you heat the piston crown severely from detonation it'll expand enough to "grab" the unlubricated cylinder wall and the crown won't stand a chance vs the connecting rod ripping it downwards- it'll snap parts of the crown right off with ease.

I wouldn't be surprised if this might be what splits a cylinder wall on an open-deck engine but I've no experience with them. I find it unlikely that maybe ~ 1300psi combustion pressure could split an iron sleeve cylinder wall by itself (without detonation etc).

BB

[bdkevoIX]

Originally Posted by Dr_Dirt

The block on my 3000GT VR4 was a closed deck, but that didn't do anything to prevent knock. It wasn't recommended to go over 14psi unless we used race gas or had other supporting hardware. Mine was tuned for 16psi on 93 oct and there was still some knock. There were alot of people who blew their VR4 motors and without using excessive boost. The closed deck type motors don't seem to be a proper method of determining boost limits.

It's called poor tune and idiot tuners who called themselves tuners and even more idiots who run their cars with apparent knocks.
Deck design has nothing to do with prevention of knock.
You could blow a supra motor just as easy with a poor tune.

And its not for determining boost limits. It's more like how much power the motor can hold. Take 2jz-gte, rb26dett, and 4g63 for example, these closed deck engines make more than 250whp PER cylinder or 500whp PER liter of displacement when built right. Just think of the extreme cylinder pressure when one cylinder is making excess of 250whp. It's obvious to me closed deck will be more sturdy to this kind of "extreme" pressure than an open deck.

This doesn't apply to most guys who are pushing ~400whp. And frankly I wouldn't worry about deck design until I'm past 500whp mark on 3.0L motor.

[scheherazade]

This is all moot.

If you have persistent detonation in any engine, you will destroy it. The end.

Closed deck WILL take greater combustion pressures than semi closed.
Semi closed deck WILL take greater combustion pressures than open.
The end.



The only reason anyone cares is because people are pulling out imaginary numbers from their butts and saying things like :
"engine needs new internals if you go over 500 hp!"
(you can replace the 500 with any other number greater than the current low 400s ish tunes)

Only when the N54 is nicely aged and there is some tuning history to look back upon will anyone be able to say "X was the limit for this deck".

-scheherazade

[bdkevoIX]

Originally Posted by scheherazade

This is all moot.

If you have persistent detonation in any engine, you will destroy it. The end.

Closed deck WILL take greater combustion pressures than semi closed.
Semi closed deck WILL take greater combustion pressures than open.
The end.



The only reason anyone cares is because people are pulling out imaginary numbers from their butts and saying things like :
"engine needs new internals if you go over 500 hp!"
(you can replace the 500 with any other number greater than the current low 400s ish tunes)

Only when the N54 is nicely aged and there is some tuning history to look back upon will anyone be able to say "X was the limit for this deck".

-scheherazade

What I said. +1

[BaLLzZz]

Whell the s54 is reaching limits of 1100 hp HPfed and supercharged. I know some internals are changed but not the block itself and that's an open deck. Im defiantly a newbie on the details but like many have said until a block or few get blown the real limits are still limitless!

[bdkevoIX]

Originally Posted by BaLLzZz

Whell the s54 is reaching limits of 1100 hp HPfed and supercharged. I know some internals are changed but not the block itself and that's an open deck. Im defiantly a newbie on the details but like many have said until a block or few get blown the real limits are still limitless!

huh? if you're talking about e46 s54 inline-6, it is a closed deck cast iron block with aluminum head.