Head gasket

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, and can be detected with certain techniques. Left unfixed, a blown head gasket could cause severe engine damage. Many symptoms of a bad head gasket are not apparent until the problem is very bad, including the ones listed later in this article.  
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==Overview==
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The '''cylinder head gasket''' provides the critical seal between the engine block and the cylinder head. They seal the combustion in the combustion chambers and keep coolant contained to the cooling ports in the heads and block.
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Blown head gaskets can be caused by various engine problems, and can be detected with certain techniques. Left unfixed, a blown head gasket could cause severe engine damage. Many symptoms of a bad head gasket are not apparent until the problem is very bad, including the ones listed later in this article.  
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Various different types of head gaskets exist today, for different applications. Care must be taken in removal of the old gasket, selection of a new gasket and proper installation of the new gasket.  
 
Various different types of head gaskets exist today, for different applications. Care must be taken in removal of the old gasket, selection of a new gasket and proper installation of the new gasket.  
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====MLS head gaskets====
 
====MLS head gaskets====
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[[File:Mls felpro hg.jpg|thumb|400px|Felpro MLS head gasket showing the layers]]
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Be sure to consult the manufacturer's recommendations concerning surface preparation, sealers, and application.
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Sealant use may be required when retrofitting MLS (multi-layer steel) head gaskets to engines which were not originally produced with MLS head gaskets, or when using MLS head gaskets on engines that have not been properly prepared. For proper coolant, oil, and combustion sealing, MLS head gaskets require surface finishes of 30 RA (Roughness Average) or finer, this is because the elastomeric coating on the sealing surfaces of MLS head gaskets is approximately .001" thick which is too thin to seal leak paths in the peaks and valleys of rougher (RA30+) finishes.
 
Sealant use may be required when retrofitting MLS (multi-layer steel) head gaskets to engines which were not originally produced with MLS head gaskets, or when using MLS head gaskets on engines that have not been properly prepared. For proper coolant, oil, and combustion sealing, MLS head gaskets require surface finishes of 30 RA (Roughness Average) or finer, this is because the elastomeric coating on the sealing surfaces of MLS head gaskets is approximately .001" thick which is too thin to seal leak paths in the peaks and valleys of rougher (RA30+) finishes.
  
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Cometic has a 'Phuzion' head gasket that "combines MLS tech with a gas-filled, aerospace-alloy O-ring for ultimate head sealing" without special block mods.
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Cometic has a 'Phuzion' head gasket that "combines MLS tech with a gas-filled, aerospace-alloy O-ring for ultimate head sealing" without special block mods. <br style="clear:both"/>
  
 
====Graphite head gasket====
 
====Graphite head gasket====
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Graphite head gaskets can be used on aluminum heads with an iron block (they work equally well with iron heads on an iron block). Graphite is excellent in handling high temperatures and is anisotropic (draws heat away from hot spots). It also seals very well too. Some drawbacks to using graphite is that it cannot withstand exposure to oil over a over a long period of time, can be crushed and extruded, and it also leaves a coating on the block and heads that is harder to remove than traditional head gaskets.
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Graphite head gaskets can be used on aluminum heads with an iron block (they work equally well with iron heads on an iron block). Graphite is excellent in handling high temperatures and is anisotropic (draws heat away from hot spots). It also seals very well too. Some drawbacks to using graphite is that it cannot withstand exposure to oil over a long period of time, can be crushed and extruded, and it also leaves a coating on the block and heads that is harder to remove than traditional head gaskets.
  
 
An article that mentions graphite gasket technology is '''[http://www.enginebuildermag.com/Article/2585/gasket_technology_the_science_of_sealing.aspx here]'''.
 
An article that mentions graphite gasket technology is '''[http://www.enginebuildermag.com/Article/2585/gasket_technology_the_science_of_sealing.aspx here]'''.
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The turbulence caused by the piston coming in close proximity of the underside of the cylinder head will "squish" the unburned mixture out of the area and jet it towards the spark plug, thus fully mixing the mixture. This action contributes to a more complete combustion, more power, less emissions and suppresses detonation.  
 
The turbulence caused by the piston coming in close proximity of the underside of the cylinder head will "squish" the unburned mixture out of the area and jet it towards the spark plug, thus fully mixing the mixture. This action contributes to a more complete combustion, more power, less emissions and suppresses detonation.  
  
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[[File:Round dish sbc piston.jpg|thumb|left|340px|This stock type SBC piston is the least desireable design as far as quench action is concerned]][[File:KB P-N 135 SBC 383 PISTON.jpg|thumb|330px|The D-cup design is much better for quench action if a dish is required]]
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[[File:Round dish sbc piston.jpg|thumb|left|340px|This stock type SBC piston is the least desirable design as far as quench action is concerned]][[File:KB P-N 135 SBC 383 PISTON.jpg|thumb|330px|The D-cup design is much better for quench action if a dish is required]]
  
 
The best piston design to use for this is one which has a dead flat area where it will meet the cylinder head. Stock Chevy pistons, for instance, have only a thin band around the perimeter of the piston to accomplish squish. Flat top pistons having minimal valve reliefs will work best. The D-cup pistons offered by various manufacturers also work well (better than a round dish) when a dish is needed.  <br style="clear:both"/>
 
The best piston design to use for this is one which has a dead flat area where it will meet the cylinder head. Stock Chevy pistons, for instance, have only a thin band around the perimeter of the piston to accomplish squish. Flat top pistons having minimal valve reliefs will work best. The D-cup pistons offered by various manufacturers also work well (better than a round dish) when a dish is needed.  <br style="clear:both"/>
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Any "leak stopper" or head gasket "repair additive" should be avoided. Use of such products leads to further engine damage, such as seized or leaking water pumps, clogged water or oil passages, or clogged radiators and thermostats. If you use these products, be aware of possible problems caused by them.  
 
Any "leak stopper" or head gasket "repair additive" should be avoided. Use of such products leads to further engine damage, such as seized or leaking water pumps, clogged water or oil passages, or clogged radiators and thermostats. If you use these products, be aware of possible problems caused by them.  
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==Head gasket torquing==
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Follow the sequence for the engine being worked on. If no sequence can be found, start from the inner fasteners and work outward.
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Use at least three steps, i.e. if the torque is 65 ft/lb, torque the first step to 20 ft/lb, second step to 40 ft/lb and the last step to 65 ft/lb.
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[[File:80632permatex.jpg|right]]
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If using OEM fasteners, most times the recommendation is for the clean threads to be lubricated with motor oil before torquing. Threaded holes can be cleaned with a thread chaser. Do not use a tap for this, it can enlarge the hole and/or thin the threads by removing metal, increasing the chance of pulling the threads.
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Fasteners that enter the cooling jackets have to be sealed. Various sealants can be used depending on personal preference. Some sealers are:
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*Hylomar
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*Permatex #2
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*Permatex High Temp Thread Sealant
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*Permatex High Performance Thread Sealant 56521
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*Permatex 80632 with teflon
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*[http://www.summitracing.com/parts/ARP-100-9904/ ARP thread sealer]
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*Locktite thread sealant
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Follow the factory torque specs unless aftermarket fasteners are used. In that case, follow the fastener manufacturer's directions for what type of lube to use and what torque to use- this will often differ from the factory specs. 
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{{Note1}} Do not use RTV or any type of sealant or adhesive that hardens or sets up. The sealant needs to be pliant, not hardened or brittle.
  
 
===Head gasket re-torquing===
 
===Head gasket re-torquing===
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*Retracing the original torque pattern one fastener at a time, slightly loosen the bolt or nut (to overcome the friction set), then re-torque to the specified torque setting
 
*Retracing the original torque pattern one fastener at a time, slightly loosen the bolt or nut (to overcome the friction set), then re-torque to the specified torque setting
  
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It is suggested by some to retorque cast iron heads/blocks while still warm (not hot). This should NOT be done with aluminum blocks or heads.
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{{!}}It is suggested by some to retorque cast iron heads/blocks while still warm (not hot). Whether or not to do this when using iron castings  is up to the builder (''research this beforehand''). But this should NOT be done with aluminum blocks or heads.
  
 
===When replacing a blown head gasket===
 
===When replacing a blown head gasket===
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*Sometimes a sealant will need to be used on the head bolts, as they may intersect the water jackets, and be exposed to engine coolant. Use a non-hardening sealer.
 
*Sometimes a sealant will need to be used on the head bolts, as they may intersect the water jackets, and be exposed to engine coolant. Use a non-hardening sealer.
 
*Change the oil and oil filter too -- they're likely contaminated with coolant.
 
*Change the oil and oil filter too -- they're likely contaminated with coolant.
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*Don't be surprised if some of the water ports are "blocked off" on your gasket. Various gaskets are made to differently meter the coolant and direct its flow. Gaskets are also made differently for street and race applications. 400 small block Chevys are a special case. There are steam holes drilled in the block that release steam pockets which are formed in the block as a result of the cylinders being siamezed, with no water passage between the cylinders. You must use 400 gaskets on this motor that have the holes in the gasket which coincide with the holes in the block deck. If using heads other than 400 heads (which are also drilled with corresponding holes), you must drill steam holes into the deck of the heads to allow the steam to escape from the block and up into the heads to be dispersed.  
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*Don't be surprised if some of the water ports are "blocked off" on your gasket. Various gaskets are made to differently meter the coolant and direct its flow. Gaskets are also made differently for street and race applications. 400 small block Chevys are a special case. There are steam holes drilled in the block that release steam pockets which are formed in the block as a result of the cylinders being siamesed, with no water passage between the cylinders. You must use 400 gaskets on this motor that have the holes in the gasket which coincide with the holes in the block deck. If using heads other than 400 heads (which are also drilled with corresponding holes), you must drill steam holes into the deck of the heads to allow the steam to escape from the block and up into the heads to be dispersed.  
  
 
===Re-using head gaskets===
 
===Re-using head gaskets===
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Some head gaskets are re-usable several times and others should never be re-used. Steel shim head gaskets are designed for one use only. Composite or graphite head gaskets are most often not re-usable because of [[rust]] damage to the steel core, disintegration of the surface material or damage or loss of the sealant material. MLS gaskets are most often not re-usable because the elastomeric coating is scubbed off of the combustion and coolant seals by abrasion from temperature induced expansion and contraction. Traditional copper head gaskets are re-usable, Titan and ICS Titan copper head gaskets from SCE are also re-usable. Even if a head gasket is re-usable, many people prefer to use a new one. The labor involved in replacing a head gasket, and the potential for engine damage from a blown gasket are too great to risk.
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Some head gaskets are reusable several times over, while others should never be reused. Most head gaskets are designed for one use only. Composite or graphite head gaskets are most often not reusable because of rust damage to the steel core, disintegration/delamination/peeling of the surface material or damage to or loss of factory-applied sealant material.  
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*MLS gaskets are most often not reusable because the elastomeric coating is scrubbed off of the combustion and coolant seals by abrasion from temperature induced expansion and contraction.  
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*Copper head gaskets are often reusable. Examples are Titan and ICS Titan copper head gaskets from SCE.  
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*Even if a head gasket may be reusable, many prefer to use a new one; the labor involved in replacing a head gasket and the potential for engine damage from a blown gasket are too great to risk.
  
 
==How to differentiate the top and bottom of a head gasket==
 
==How to differentiate the top and bottom of a head gasket==
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==SBC head gasket applications==  
 
==SBC head gasket applications==  
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Many SBC head gaskets are going to have at least a 4.090" gasket bore diameter, so are usable on a 0.060" over 4" block.
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Many SBC head gaskets are going to have a 4.090"-4.100" gasket bore diameter, so are usable on a 0.060" over 4" block.
  
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There are a large selection of head gasket types and thicknesses for the SBC engine. Many composite head gaskets are right at 0.041" compressed thickness. Suffice to say ALL manufacturers of SBC head gaskets will have one or more that compress to 0.040"-0.041".
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There are a large selection of head gasket types and thicknesses for the SBC engine. Many composite head gaskets are right at 0.041" compressed thickness. Suffice to say ALL manufacturers of SBC head gaskets will have one or more that compress to 0.038"-0.041".
  
 
===SBC head gaskets having less than 0.040" compressed thickness===
 
===SBC head gaskets having less than 0.040" compressed thickness===
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*FelPro's FEL 1094 is a steel shim with a 4.1" gasket bore diameter and 0.015" compressed thickness, if you've got super flat surfaces on the deck and head, this is a great gasket. It does not tolerate the engine being overheated.
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*GM p/n 3830711 is also a steel shim with a 4.1" gasket bore diameter, and is 0.026" thick. Good flat surfaces are required, same rules apply as the Fel-Pro above. This is the GM production gasket for '''non''' 400 bore SBCs. Simple and low cost.  
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*GM 3830711 is also a steel shim with a 4.1" gasket bore diameter, and is 0.026" thick. Good flat surfaces are required, same rules apply as the Fel Pro above. This is the GM production gasket for '''non''' 400 bore SBCs. Simple and low cost.  
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*GM p/n 10105117, this head gasket is a multi-layered stainless steel gasket with a 4.1" gasket bore diameter, is 0.028" thick, works with iron or aluminum heads, good for holding back high compression, and tolerates some surface irregularities in the deck and head surfaces. This is the “revised” gasket, see [http://www.thirdgen.org/techboard/tech-general-engine/269378-head-gasket-thickness-gm.html post #23].  
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*GM 10105117, this head gasket is a multi-layered stainless steel gasket with a 4.1" gasket bore diameter, is 0.028" thick, works with iron or aluminum heads, good for holding back high compression, and tolerates some surface irregularities in the deck and head surfaces. This is the “revised” gasket, see [http://www.thirdgen.org/techboard/tech-general-engine/269378-head-gasket-thickness-gm.html post #23].  
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*GM p/n 14096405, it has stainless faces over a graphite core, 4.1" gasket bore diameter and 0.028" compressed thickness. This thing hangs tough on uneven surfaces and puts up with high compression ratios. Good for iron or aluminum, this makes a good race engine gasket as it's very tolerant of engines running very hot. It lets the block and head move around to adjust for their temperature differences without breaking its seal.   
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*GM 14096405, it has stainless faces over a graphite core, 4.1" gasket bore diameter and 0.028" compressed thickness. This thing hangs tough on uneven surfaces and puts up with high compression ratios. Good for iron or aluminum, this makes a good race engine gasket as it's very tolerant of engines running very hot. It lets the block and head move around to adjust for their temperature differences without breaking its seal.   
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*Victor Reinz Nitroseal p/n 5746, has a compressed thickness is 0.025", 4.1” gasket bore diameter. NAPA carries Victor.
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==Other possibilities (nowhere near a complete list):==
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===Composite type===
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Victor Reinz Nitroseal p/n 5746, has a compressed thickness is 0.025", 4.1” gasket bore diameter. NAPA carries Victor.
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===Shim type===
 
===Shim type===
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*Jegs p/n 210044- Embossed Shim w/ Rubber Coating. Bore 4.150", compressed thickness is 0.024".
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*FelPro's p/n Q1094 is a steel shim with a 4.1" gasket bore diameter and 0.015" compressed thickness. Used in some sportsman drag race and flat top oval track categories. Rubber coated steel shim, 4.100 in. gasket bore diameter, 0.015" compressed thickness.
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*SCE #511101 Specialty Component Engineering
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**Bore: 4.100"
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**Gasket Material: Graphite coated steel core laminate
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**Compressed Thickness: 0.015"
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**Compressed Volume: 3.245cc
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**Lock Wire: No
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**Coolant sealing '''not''' compatible with GM lightweight head castings used on 305-350 from 1987-95.
 
*Mr. Gasket p/n 1130 0.018”- 0.020” compressed thickness, steel embossed w/coating.  
 
*Mr. Gasket p/n 1130 0.018”- 0.020” compressed thickness, steel embossed w/coating.  
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*Jegs p/n 210044- embossed shim w/rubber coating. Bore 4.150", compressed thickness is 0.024".
  
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There are several thinner coated shim type gaskets like:
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===400 SBC===
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*Fel-Pro Q1094- SBC 307 327 350 283 #1094. Used in some sportsman drag race and flat top oval track categories. Rubber coated steel shim, 4.100 in. gasket bore diameter, 0.015" compressed thickness.
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*[http://www.summitracing.com/parts/CGT-C5248-027/ 400 SBC 0.027” head gasket]
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*Felpro p/n's #1004, #1034, #1044
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===SBC by displacement===
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From [http://www.amotion.com/csb.html amotion.com]
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*262  Solid steel core 3.850              McCord 7039M
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*262  Embossed Steel 3.850                McCord 6908
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*267  Solid steel core 3.850              McCord 7039M
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*267  Embossed Steel 3.850                McCord 6908
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*283  Graphite 4.090                      McCord 7104G
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*283  Performance Graphite 4.140          McCord 94-2025
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*283  Solid steel core 4.090              McCord 6631M
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*283  Embossed Steel 4.100                McCord 6910
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*302  Graphite 4.090                      McCord 7104G
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*302  Performance Graphite 4.140          McCord 94-2025
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*302  Solid steel core 4.090              McCord 6631M
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*302  Embossed Steel 4.100                McCord 6910
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*305  Solid steel core 3.850              McCord 7039M
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*305  Embossed Steel 3.850                McCord 6908
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*307 Graphite 4.090                      McCord 7104G
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*307  Performance Graphite 4.140          McCord 94-2025
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*307  Solid steel core 4.090              McCord 6631M
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*307  Embossed Steel 4.100                McCord 6910
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*327 Graphite 4.090                      McCord 7104G
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*327  Performance Graphite 4.140          McCord 94-2025
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*327  Solid steel core 4.090              McCord 6631M
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*327  Embossed Steel 4.100               McCord 6910
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*350  Graphite 4.090                      McCord 7104G
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*350  Performance Graphite 4.140          McCord 94-2025
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*350  Solid steel core 4.090              McCord 6631M
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*350  Embossed Steel 4.100                McCord 6910
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*400  Graphite 4.180                      McCord 6837M
  
 
==Suppliers and manufacturers of head gaskets==
 
==Suppliers and manufacturers of head gaskets==
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==References==
 
==References==
 
===Compression calculators===
 
===Compression calculators===
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====Static CR====
 
*[http://www.wheelspin.net/calc/calc2.html Static compression ratio]
 
*[http://www.wheelspin.net/calc/calc2.html Static compression ratio]
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*[http://www.empirenet.com/pkelley2/DynamicCR.html Dynamic compression calculator] by Kelly
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*[http://www.kb-silvolite.com/calc.php?action=comp2 Dynamic compression calculator] by KB
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====Dynamic CR====
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*[http://www.wallaceracing.com/dynamic-cr.php Wallace Racing DCR calculator]
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*[http://www.empirenet.com/pkelley2/DynamicCR.html Kelly DCR calculator]
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*[http://www.uempistons.com/calc.php?action=comp2 KB/Silvolite DCR calculator]
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*[http://www.rbracing-rsr.com/comprAdvHD.htm RSR DCR calculator]
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{{Note1}} Some dynamic compression rtatio calculators (like KBs) ask for an additional 15 degrees of duration be added to the IVC @ 0.050" lift point figure. This works OK on older, slower ramped cam lobes, but the faster lobe profiles may need to have 25 degrees or more added to be accurate.
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{{Note1}}If the intake valve closing (IVC) point isn't known, it can be calculated:
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# Divide the intake duration by 2
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# Add the results to the lobe separation angle (LSA)
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# Subtract any ground-in advance
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# Subtract 180
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This result does not need to have any amount added to the IVC point, like the KB calculator calls for.
  
 
===Forum discussions===
 
===Forum discussions===
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[[Category:Engine]]
 
[[Category:Engine]]
 
[[Category:Good articles]]
 
[[Category:Good articles]]
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{{Develop1}}
 
 
[[Category:Cylinder head]]
 
[[Category:Cylinder head]]

Latest revision as of 12:48, 7 September 2023

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