Is Deck Height the same as....
Thread Starter
Senior Member since 1492
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From: Just because I'm paranoid doesn't mean people aren't out to get me...
St. Jude Donor '09
Is Deck Height the same as....
Piston clearance? Can't find in my manual a spec for "deck height". It does have a listing for piston clearance (0.0007-0.0017)though. Is this the same? It's for an '89 GM-350.
[Modified by 1970 Stingray, 9:37 AM 3/5/2002]
[Modified by 1970 Stingray, 9:37 AM 3/5/2002]
Drifting
Joined: Sep 1999
Posts: 1,908
Likes: 0
From: Manassas, VA, USA
Re: Is Deck Height the same as.... (1970 Stingray)
Deck height is the distance from the top of your pistons (assuming you don't have domed pistons) to the top of the cylinder bore at TDC. To measure it, move the piston to TDC, put a machinist's straightedge across the cylinder bore, and use a feeler guage to measure the deck height. Most fall in the 0 - 0.03" range.
There's no particular spec for deck height; it will be smaller if your block has been decked. It's just additional combustion "dead space" that affects your compression ratio: more deck height = lower compression.
There's no particular spec for deck height; it will be smaller if your block has been decked. It's just additional combustion "dead space" that affects your compression ratio: more deck height = lower compression.
Burning Brakes
Joined: Dec 2000
Posts: 1,183
Likes: 2
From: Des Moines Iowa
Re: Is Deck Height the same as.... (lyonsh)
Quote: "Most fall in the 0 - 0.03" range."
I disagree. Believe that you're more likely to find deck height of unmolested 350 in a C3 to be around .018" to .025" or higher. Believe when rebuilding an engine, some machinists will try to reduce this, especially if on the high side, but as I recall, most specs call for some minimum to be retained for rod and piston stretch during high rpm operation, so I don't believe .000" is ever recommended.
I disagree. Believe that you're more likely to find deck height of unmolested 350 in a C3 to be around .018" to .025" or higher. Believe when rebuilding an engine, some machinists will try to reduce this, especially if on the high side, but as I recall, most specs call for some minimum to be retained for rod and piston stretch during high rpm operation, so I don't believe .000" is ever recommended.
Instructor
Joined: Feb 2002
Posts: 154
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From: hersey mi
Re: Is Deck Height the same as.... (john's '81 mouse)
my 383 is zero decked. this was done to increase cr. to 10:1 . 76cc heads. the new trick flow heads i just got are 64cc which should increase the cr to 11.2:1 this is the max i would go and still expect to drive it around town. Just my .02 i guess i should add the piston clearence to valves need a min of .080, however many have got away with .041-.044. hope this helps. Rick :cheers: :cheers:
[Modified by faster69, 1:02 PM 3/5/2002]
[Modified by faster69, 1:02 PM 3/5/2002]
Le Mans Master
Joined: Sep 2001
Posts: 7,739
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From: Unreconstructed, South Carolina
Re: Is Deck Height the same as.... (1970 Stingray)
Len: Deck height & clearance not the same at all. From factory the 350 block designed to have 9.025" deck height (from centerline of crank main to top of deck). Measure half of crank stroke (3.48/2 = 1.74") PLUS length of rod from center to center (stock = 5.7") PLUS compression distance of piston (from centerline of pin hole to top) this number ranges but for a TRW cast H345NP flat top w/4 VR's the CD is 1.560". So... 1.74 + 5.7 + 1.56 = 9.000" ... with that combo on an uncut deck the top of piston will be about 0.025" "down in the hole."
Race Director
Joined: Nov 2000
Posts: 11,872
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From: Waterloo ontario Canada
Re: Is Deck Height the same as.... (1970 Stingray)
My pistons were down the hole by .030 on one side and .032 on the other so I decked the block .030 and .032 to arrive at zero deck height. The gasket becomes my clearance. I have read that too much deck and the motor is lazy.
Melting Slicks
Joined: Oct 2000
Posts: 2,268
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From: Roanoke Virginia
Re: Is Deck Height the same as.... (faster69)
my 383 is zero decked. this was done to increase cr. to 10:1 . 76cc heads. the new trick flow heads i just got are 64cc which should increase the cr to 11.2:1 this is the max i would go and still expect to drive it around town. Just my .02 i guess i should add the piston clearence to valves need a min of .080, however many have got away with .041-.044. hope this helps. Rick :cheers: :cheers:
[Modified by faster69, 1:02 PM 3/5/2002]
[Modified by faster69, 1:02 PM 3/5/2002]
somebody zero decked my 406 and put 64cc heads on. CR was 11.5+ and there was no way it could run on the street, even with retarded timing. I now have 76cc heads, and I still have the total timing set back to 32* to eliminate detonation.
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Drifting
Joined: Sep 1999
Posts: 1,908
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From: Manassas, VA, USA
Re: Is Deck Height the same as.... (jackson)
Len: Deck height & clearance not the same at all. From factory the 350 block designed to have 9.025" deck height (from centerline of crank main to top of deck). Measure half of crank stroke (3.48/2 = 1.74") PLUS length of rod from center to center (stock = 5.7") PLUS compression distance of piston (from centerline of pin hole to top) this number ranges but for a TRW cast H345NP flat top w/4 VR's the CD is 1.560". So... 1.74 + 5.7 + 1.56 = 9.000" ... with that combo on an uncut deck the top of piston will be about 0.025" "down in the hole."
(No, I'm not a engine genius. We just had this exact same argument in the class I'm taking as an excuse to use all the cool machining machines at the local community college.) :cheers:
Melting Slicks
Joined: Oct 2000
Posts: 2,268
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From: Roanoke Virginia
Re: Is Deck Height the same as.... (faster69)
they were cast iron head, casting #041. Somebody had spent a lot of time and money to have them professionally ported and polished. i sold the pair to a guy who has a 302 in a 1957 Corvette. Funny thing was, whoever built my 406 (some previous owner I guess) had steam holes drilled in the 041 heads, but used non-steam hole head gaskets :crazy: :smash:
Yes, I heard you can push the CR higher with aluminum heads. Lars was kind enough to rebuild me a set of 400 SBC heads for my 406. I'm theoretically at 9.7 CR now, and I'm just at the point of detonation if I go over 34* total mechanical advance. For me, the only thing that was cool about the higher compression ratio was the exhaust note. Sounded like a WWII era fighter :D
Yes, I heard you can push the CR higher with aluminum heads. Lars was kind enough to rebuild me a set of 400 SBC heads for my 406. I'm theoretically at 9.7 CR now, and I'm just at the point of detonation if I go over 34* total mechanical advance. For me, the only thing that was cool about the higher compression ratio was the exhaust note. Sounded like a WWII era fighter :D
Instructor
Joined: Feb 2002
Posts: 154
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From: hersey mi
Re: Is Deck Height the same as.... (thejaf)
thejaf, he must of had the heads on a 400 ci that would be the reason for the steam hole. by the way, i had a set of 041 heads that were ported and polished on a 355 in a S-10 and it would scream :D :D :cheers: Rick
Le Mans Master
Joined: Sep 2001
Posts: 7,739
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From: Unreconstructed, South Carolina
Re: Is Deck Height the same as.... (lyonsh)
I hate to get all technical and stuff, but you're talking about what's called BLOCK height.
(No, I'm not a engine genius. We just had this exact same argument in the class I'm taking as an excuse to use all the cool machining machines at the local community college.)
lyonsh:
I'm no genius either ... and Len, I stand corrected ... 9.025" refers to block height ... "down in the hole" refers to deck height. Sorry, ya get the picture though, right?
Jack
(No, I'm not a engine genius. We just had this exact same argument in the class I'm taking as an excuse to use all the cool machining machines at the local community college.)
lyonsh:
I'm no genius either ... and Len, I stand corrected ... 9.025" refers to block height ... "down in the hole" refers to deck height. Sorry, ya get the picture though, right?
Jack
