0 Deck ?
Race Director
Joined: Feb 2004
Posts: 12,517
Likes: 19
When you build or freshen a motor you should deck the block. When building a performance motor 0 deck will equal approx .025 removed from deck height. This will improve efficiency and make the motor less octane sensitive at a given compression ratio. All parts block, pistons heads etc should be on hand before the deck height is set. Engine builder should determine "actual" compression ratio and deck accordingly. If ,for example, actual compression ratio is 11.0 to 1 with an .025 deck you may want to minimize cut on deck. The opposite would be true if actual compression ratio was on the low side. Then you would deck the heck out of it and select the desired thickness head gasket to further tune your compression ratio. Whew, simple answer is maybe yes, maybe no, it all depends.
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
Decking the block is definitely a good idea as it accomplishes several things at the same time:
It assures that the deck surface is flat front to rear and side to side
It assures that both deck heights are the same
It creates a new surface condition for best head gasket sealing
It allows a certain degree of compression ratio fudging
The decision as to whether or not to zero deck the block is best left to a competent machinist who has experience in dealing with performance engines and the parts you'll be running.
One consideration is the effect the piston to wall clearance will have at TDC rockover. Using forged pistons (with the greater piston to wall clearance they call for) can cause the piston deck to actually extend above the block deck surface at TDC.
Depending on head gasket thickness, etc., this may or may not cause a problem when running a zero deck.
Be careful here! Someone on the Forum had such a problem last year; it's not uncommon when you begin pushing the envelope.
Jake
It assures that the deck surface is flat front to rear and side to side
It assures that both deck heights are the same
It creates a new surface condition for best head gasket sealing
It allows a certain degree of compression ratio fudging
The decision as to whether or not to zero deck the block is best left to a competent machinist who has experience in dealing with performance engines and the parts you'll be running.
One consideration is the effect the piston to wall clearance will have at TDC rockover. Using forged pistons (with the greater piston to wall clearance they call for) can cause the piston deck to actually extend above the block deck surface at TDC.
Depending on head gasket thickness, etc., this may or may not cause a problem when running a zero deck.
Be careful here! Someone on the Forum had such a problem last year; it's not uncommon when you begin pushing the envelope.
Jake
Instructor
Joined: Jan 2003
Posts: 182
Likes: 0
From: Newberry SC
also take the quench distance into consideration, i'm running a quench of .040 with flattop keith black hyper pistons at 12:1 compression ratio. i'm able to get by with 93 octane with no problems at all, but i feel the setup has to be right to do that.
i don't put much faith in the piston rocking theory, say a piston set up at .003 cylinder wall clearance rocks at the the top of the stroke, the edge that rocks up the highest is probably only gonna come up around .005(depending on skirt lengths, and i dont think he is gonna be running ultralites here), and unless you are running TIGHT clearances with the flat of the head, i don't think its even gonna come close to hitting.
eh, just my $0.02, take it for what its worth
i don't put much faith in the piston rocking theory, say a piston set up at .003 cylinder wall clearance rocks at the the top of the stroke, the edge that rocks up the highest is probably only gonna come up around .005(depending on skirt lengths, and i dont think he is gonna be running ultralites here), and unless you are running TIGHT clearances with the flat of the head, i don't think its even gonna come close to hitting.
eh, just my $0.02, take it for what its worth
Pro
Joined: Apr 2003
Posts: 552
Likes: 13
From: Oz
Ideal quench is 0.040" to 0.060". I like to leave 0.005" on the decks and use a 0.039" or 0.041" gasket to give 0.044" - 0.046" quench. This also leaves 0.005" on the decks for next time you want to square up the block.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Originally Posted by ben73
Ideal quench is 0.040" to 0.060". I like to leave 0.005" on the decks and use a 0.039" or 0.041" gasket to give 0.044" - 0.046" quench. This also leaves 0.005" on the decks for next time you want to square up the block.
RACE ON!!!
