Closed vs. open deck
12-07-2003, 11:47 PM
#2
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Join Date: Dec 2002
Location: Sacramento CA
Posts: 10,029
Car Info: 02 Impreza WRX sedan
The deck surface of the block, which is the mating surface for the cylinder head, will be either solid across the deck around the cylinders or have different degrees of areas around each cylinder open to the water jacket (where the coolant flows around the cylinders).
The closed deck surface of a block translates to more rigidity and ultimately more potential for a modified engine to put out more power without the cylinders moving around under high output and load. Any vibration or shift in the cylinder walls under load causes piston rings to lose some sealing ability, allowing combustion pressure and gasses to be leaked to the crankcase, with a subsequent drop in power.
This is why V8 engines often have cylinder bores that are honed with a deck plate or torque plate bolted to the deck, simulating the distortion of the cylinder bores being pulled slightly out of round when the heads are bolted down.
--
0==WW==0
"…axles of evil…" - george w. bush
The closed deck surface of a block translates to more rigidity and ultimately more potential for a modified engine to put out more power without the cylinders moving around under high output and load. Any vibration or shift in the cylinder walls under load causes piston rings to lose some sealing ability, allowing combustion pressure and gasses to be leaked to the crankcase, with a subsequent drop in power.
This is why V8 engines often have cylinder bores that are honed with a deck plate or torque plate bolted to the deck, simulating the distortion of the cylinder bores being pulled slightly out of round when the heads are bolted down.
--
0==WW==0
"…axles of evil…" - george w. bush
02-25-2004, 06:41 PM
#7
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Join Date: Jun 2003
Location: my home is Portland but I'm @ School in Seattle
Posts: 2,801
Car Info: 1998 Subaru Legacy L 5-speed
Originally posted by ch0g
sorry to bump an old topic, but which subaru engines are closed, etc..?
for example, i have a my97 ej22 impreza brighton..which type of deck would this be?
sorry to bump an old topic, but which subaru engines are closed, etc..?
for example, i have a my97 ej22 impreza brighton..which type of deck would this be?
02-26-2004, 11:51 AM
#12
Registered User
Join Date: Feb 2004
Posts: 23
taken from here...
Originally posted by Joel Gat
Hello,
Using Subaru blocks as an example:
Open:
Semi-Closed:
Note the extra metal around the outside of the cylinders at the 12 and 6 o'clock positions.
Closed:
Note the extra metal around the outside of the cylinders at the 12, 1:30, 4:30, 6, 7:30, and 10:30 o'clock positions, pretty much surrounding the bore.
All pics taken from Cobb Tuning's webpage. They offer semi and fully closed deck blocks for WRXs and 2.5RSs.
Semi or Fully closing the bore is most important to allow higher RPMs safely. At higher RPMs, the cylinders will tend to move around and the pistons can crash into them. By closing the deck, you reduce the amount the cylinders can move or deform from cylinder pressure.
Fully closing also offers significantly more gasket mating area and can make the gasket much less likely to blow, a good thing only if you've got strong pistons and a strong head.
Joel
Hello,
Using Subaru blocks as an example:
Open:
Semi-Closed:
Note the extra metal around the outside of the cylinders at the 12 and 6 o'clock positions.
Closed:
Note the extra metal around the outside of the cylinders at the 12, 1:30, 4:30, 6, 7:30, and 10:30 o'clock positions, pretty much surrounding the bore.
All pics taken from Cobb Tuning's webpage. They offer semi and fully closed deck blocks for WRXs and 2.5RSs.
Semi or Fully closing the bore is most important to allow higher RPMs safely. At higher RPMs, the cylinders will tend to move around and the pistons can crash into them. By closing the deck, you reduce the amount the cylinders can move or deform from cylinder pressure.
Fully closing also offers significantly more gasket mating area and can make the gasket much less likely to blow, a good thing only if you've got strong pistons and a strong head.
Joel
