Open Deck Engine???
03-05-2005, 06:02 PM
#1
Race Director
Thread Starter
Open Deck Engine???
Okay I am not by any means an engine design expert.
Heres my question, in some of the other posts there is talk about an "open deck" vs a "closed deck" or similar type of head/engine. Apparantly the 928 design is an open deck design that is inherently weaker than the closed design? Why is a closed deck better and what makes it stronger?
There was also talk about stronger engine blocks made of iron instead of aluminum (even I know iron is stronger) in some other commonly modified engines (supra, lexus V8, Ford 4.6), besides being made of iron, what makes these blocks "stronger" than a 928? For being a "weak" engine design, 928 engines seem to last a very long time in stock/near stock form....often longer than "stronger" designs?
Thanks in advance
Heres my question, in some of the other posts there is talk about an "open deck" vs a "closed deck" or similar type of head/engine. Apparantly the 928 design is an open deck design that is inherently weaker than the closed design? Why is a closed deck better and what makes it stronger?
There was also talk about stronger engine blocks made of iron instead of aluminum (even I know iron is stronger) in some other commonly modified engines (supra, lexus V8, Ford 4.6), besides being made of iron, what makes these blocks "stronger" than a 928? For being a "weak" engine design, 928 engines seem to last a very long time in stock/near stock form....often longer than "stronger" designs?
Thanks in advance
03-05-2005, 08:01 PM
#2
Addict
Rennlist Member
Rennlist Member
This is normal 928 block with open deck:
Cylinder walls don't have any side support on their top 4 to 5 inches. This is much weaker design than closed deck where there is just small water passages worth of material missing. Check 928 SG page for how similar block looks like when there is deck plate added to it. http://www.928sg.com/block.htm 928 blocks will last long time as long as piston rings are good and water can't get to combustion chamber, and there isn't too much boost applied.
When any of the above happen block can be destroyed in matter of seconds. Reason why Porsche used open deck was that it's easier to manufacture yet strong enough to last on well maintained stock engine.
Cylinder walls don't have any side support on their top 4 to 5 inches. This is much weaker design than closed deck where there is just small water passages worth of material missing. Check 928 SG page for how similar block looks like when there is deck plate added to it. http://www.928sg.com/block.htm 928 blocks will last long time as long as piston rings are good and water can't get to combustion chamber, and there isn't too much boost applied.
When any of the above happen block can be destroyed in matter of seconds. Reason why Porsche used open deck was that it's easier to manufacture yet strong enough to last on well maintained stock engine.
03-05-2005, 09:42 PM
#4
Race Director
Thread Starter
Vilhuer
Great pictures to a great link! It makes sense that the "closed" deck is stronger. My old Turbo Starion had a closed deck (which didn't help me from blowing the head gasket!). So a closed deck engine would not leak coolant under a blown head gasket then?
Bill
The open deck design does look like it would cool better than a closed?
Great pictures to a great link! It makes sense that the "closed" deck is stronger. My old Turbo Starion had a closed deck (which didn't help me from blowing the head gasket!). So a closed deck engine would not leak coolant under a blown head gasket then?
Bill
The open deck design does look like it would cool better than a closed?
03-05-2005, 10:52 PM
#5
Nordschleife Master
As far as closed decks leaking coolent, maybe maybe not.
I belive some cars, expecaly turbocharged cars, have coolent passages for the exaust valve. By cooling the head around the exaust valve, they can keep the detonation away. To do this pretty much requires passages to be drilled through the deck. So a leak is possible.
I belive some cars, expecaly turbocharged cars, have coolent passages for the exaust valve. By cooling the head around the exaust valve, they can keep the detonation away. To do this pretty much requires passages to be drilled through the deck. So a leak is possible.
03-06-2005, 06:50 AM
#6
Rennlist Member
A closed deck will have water passages through the top face to join up with head passages, so there is still scope for water leakage if you blow the gasket. Water passages to help cool exhaust valves are all in the head, and not really related to whether or not the deck is closed or open. Closing the deck, as indicated by Erkka, assists in keeping the top edge of the cylinder in place (ie stops it from moving and weakening the gasket seal) under extreme loads, which in 928s really only occur when blown or stroked, IMHO.
jp 83 Euro S AT 49k
jp 83 Euro S AT 49k
