ENGINE BLOCK DECKS: Open vs Closed vs Semi Open
171,032
Published 2020-04-26
D4A merch: teespring.com/en-GB/d4a-merch
Patreon: www.patreon.com/d4a
The key difference between open, closed and semi closed engine block decks is the structural reinforcement in the coolant passage area at the top of the cylinders, that is the engine deck area. Open deck engines will have the entire coolant passage are around the top of the cylinders free and open. Semi-closed decks will also be mostly open, but will have structural reinforcements in the form of little "stems" or "pillars" between the cylinders and engine block walls. The name of the closed deck engine is somewhat misleading because the area around the top of the cylinders isn't really fully closed of course, but there are opening left for the coolant to pass through. Subaru is an interesting brand here because they made virtually the same blocks in all three versions of the deck design.
Now if you look up the differences between open deck vs closed deck vs semi closed deck engine blocks online you will likely run into an over-generalization of how closed deck blocks are the strongest because they have the most structural reinforcement and how open deck engines are the weakest because they lack structural reinforcements, but how they have the best cooling because of the largest cooling passages. You'll also likely read how if you're interested in a performance forced induction build you should stick to a closed deck block or reinforce an open or semi open deck block. This information does make sense but it's really outdated and comes from the early days of turboing engines. Closed deck engines are stronger than open and semi open deck ones, but it's not that simple and open decks are not as weak as the internet might try to convince you.
Here's an example. The BMW N54 is BMW's first turbo engine in a pretty long time. Some call the N54 the modern day RB26 or the modern day 2JZ. Just like the 2JZ, the N54 is an inline six cylinder, 3.0 liter twin turbo engine, but unlike the 2jz, which is a cast iron closed deck engine, the N54 has an open deck aluminum block, so it stands at the opposite end of the perceived block strength scale. That means it should be weak right? It should fall apart when boost is increased? But today capable tuners and enthusiasts take the bone stock N54 block to beyond 700 whp. And the N54 is just one example there are plenty more modern open deck designs (k20c, ford ecoboost, volvo t5 and many others) where you can increase the boost without the blocks or the cylinder sleeves complaining at all.
So how come, why are open deck designs so popular today, and why aren't they falling apart under increased boost. They're popular because they're cheaper and easier to manufacture compared to closed deck designs. Open deck engines can be made using high pressure die casting (hpdc) which is cheaper and simpler compared to methods needed for closed deck engine blocks. But the other side of the coin is that casting technology has come a long way, and is far better and more accurate then decades ago, which enables manufacturers to make much stronger and better open deck blocks. On top of that manufactures have access to sophisticated CAD and simulation software that enables a better and more complex block and deck design.
But there's something else that plays an important part as well, and that is tuning technology. ECUs and sensors are much better, much more sensitive and capable than they were decades ago. They are able to sense knock better and react faster to prevent it. The open deck design of the Honda B16 was blamed for the cylinders cracking under boost of these engines in the late 90s. Today we know that the B16 block is good and can sustain well over 400hp on the stock block. What happened in the 90s is that knock happened but the sensors and ECUs did not sense it and react fast enough to preven it. In most cases knock cracks cylinder sleeves, not boost. Just look at the Honda K20 today, capable tuners are taking it well beyond twice it's power level on the stock block. Something that was impossible a few decades ago without significantly shortening the lifespan of the engine. So the key takeaway is that the open deck and semi open deck engines aren't weaker, they actually have a smaller margin of error for knock, but good tuning and modern electrinics are capable of keeping the engine safe, even within a smaller margin for error.
A very special thank you to my Patron:
Daniel
driving 4 answers is part of the Amazon Associates program.
#d4a #enginebootcamp #engine
All Comments (21)
-
Support d4a: driving-4-answers-shop.fourthwall.com/ Rebuilt GM crate engine: amzn.to/3cIpmfG POR-15 Engine block paint: amzn.to/3eIKOCY Red Line engine assembly lube: amzn.to/2XYHkWV Engine degreaser: amzn.to/3cLjqCF D4A merch: teespring.com/en-GB/d4a-merch Patreon: www.patreon.com/d4a
-
This channel is so underrated!
-
I love mechanical history, this video is great. Showing how a misconception started. Explaining the reasons for it existing. And describing how the misconception is being countered by new technologies. I love this type of info. Your goal to inform is honest and it staggers me to see how much effort is put into these videos. There are a lot of youtubers out there that can talk about nothing for ten minutes and it shows in their quality. You love this field and want to share it with others. I respect and appreciate your work immensely.
-
Love the nuanced information on this channel. No bro-science here! Might we be getting an EJ video soon?
-
Awesome video D4A! I assumed sleeving was required on open deck engines but you make a good point about ECU tuning. 20 years ago, most tuning was done using "piggy-back" ECU's or rising rate FPRs which had zero knock control. I remember tuning my JR supercharged Miata and the instructions were to advance timing until there was audible detonation and then pull back 2 degrees. On hot days I could still hear it ping once in a while which was absolutely nerve racking. Again, awesome video and I love the editing :D
-
Also, it's not just tuning technology that has come a long way, we've made heart stopping discoveries in the world of materials science. There are VERY strong Al alloys.
-
Awesome video! This is becoming one of the best car channels on youtube. Very informative, thank you. Greetings from Czech Republic!
-
Crazy good info on this engine boot camp. This channel is different from the others that just scratch the surface or give a 'mechanics' point of view (no offence to mechanics, you guys are great at what you do) which doesn't really explore the fundamentals or is more based off of experience. You communicate information in such a clear way and with such in depth explanations that I would give you 3 likes if I could. Amazing content, keep up the good work and I will be sure to follow the channel closely!
-
open deck crank cases are traditionally a much more demanding job for the cylinder head gasked. The modern MLS gaskets also helped the open block design a lot. Open deck can be casted as dye casting (without water cores) which is very cost effective, this is the main driving force behind it (and better cooling).
-
As beginner i've been trying to learn more about the engine rather than bolt on mods or other mods and your channel has taught me a lot about what I wanna know. Hope you hit a million+ followers one day you deserve it bro.
-
This is amazing. Could you do the same on modern ZF auto transmissions / modern ones? Edit: i know this is an engine bootcamp series but your dispelling fiction is amazing. People need to to know how strong and fast modern transmissions are becoming.
-
I love the way you say engine "Blaahck"! Really enjoying your content and style of explanation. Hope you get more subs. Excellent channel.
-
Love your videos! Just technical enough without being boring. Funny but not surprising that no EJ engines were featured 🤣 It seems to be the consensus that you need to go closed deck for anything over +100-150hp for us STi owners. Looking forward to seeing that video! 👍😊
-
air cooled vs liquid cooled engines, also: great content
-
This channel has everything! I can understand everything easy af, his voice is somehow relaxing, and this channel has videos for every single bolt of a car! After watching all the videos uploaded here you can build a car your self from the beginning!! Love you so much!!!!
-
I laughed at FordEcoBlownGasket being capable of high boost.
-
Absolutely phenomenal explanation. Never stop making these videos!
-
Such good information I love the green screen very helpful with the background information Great video keep it coming
-
Really good stuff man! These videos are killin' it.
-
There is also the issue of long term reliability. Dealing with a lot of open deck engines (Mostly Volvo Modular N and RN series) the main killer long term is cylinder oscillation, even with a MLS head gasket, they vibrate during opperation due to the latteral forces caused by rod-angle. So they fatigue. Typically inserting and welding in small supports to make it semi-closed makes a big difference, and inserting a block guard makes them hold up ALOT. For more extreme cases we use the "D5" block (Diesel variant of the "T5" block) and insert and weld a deck guard, then the block is good for 200Nm per cylinder.
