Quench
m (→Parts stack height) |
(Add text, images; minor clean up) |
||
| Line 13: | Line 13: | ||
;From [http://www.corvetteonline.com/tech-stories/engine/ultimate-guide-to-budget-bbc-cylinder-heads-under-2000/ corvetteonline.com]: | ;From [http://www.corvetteonline.com/tech-stories/engine/ultimate-guide-to-budget-bbc-cylinder-heads-under-2000/ corvetteonline.com]: | ||
<blockquote> | <blockquote> | ||
| − | While the terms “quench” and “squish” are often used interchangeably by many manufacturers, quench and squish are not the same thing, nor are they produced by the same set of conditions. The [http://www.sae.org/ Society of Automotive Engineers] (SAE) has defined squish as the gases trapped between the piston dome and head that are ejected across the combustion chamber at high speed by the near-collision of the piston dome and head, causing turbulence and mixture homogenization. For our purposes, if the squish area is too close, there is a pumping loss and if the area is too far apart there will be lower squish velocity and less turbulence. | + | While the terms “quench” and “squish” are often used interchangeably by many manufacturers, quench and squish are not the same thing, nor are they produced by the same set of conditions. The [http://www.sae.org/ Society of Automotive Engineers] (SAE) has defined squish as the gases trapped between the piston dome and head that are ejected across the combustion chamber at high speed by the near-collision of the piston dome and head, causing turbulence and mixture homogenization. For our purposes, if the squish area is too close, there is a pumping loss and if the area is too far apart there will be lower squish velocity and less turbulence.<br><br> |
Quench on the other hand, is the ability to lower temperature of the end gases trapped between the piston dome and head by conduction. This prevents a second flame front from igniting the air/fuel mix prematurely. Members of the SAE acknowledge that for motors with 3.5” to 4.5” cylinder bores, a quench distance of 0.035” to 0.040” work well and result in near zero clearance due to thermal expansion, rod stretch and piston rock-over. | Quench on the other hand, is the ability to lower temperature of the end gases trapped between the piston dome and head by conduction. This prevents a second flame front from igniting the air/fuel mix prematurely. Members of the SAE acknowledge that for motors with 3.5” to 4.5” cylinder bores, a quench distance of 0.035” to 0.040” work well and result in near zero clearance due to thermal expansion, rod stretch and piston rock-over. | ||
</blockquote> | </blockquote> | ||
| Line 20: | Line 20: | ||
One way to arrive at a ~0.040" quench distance is to cut the block decks to zero piston deck height and to use a head gasket that compresses to around 0.040". This allows a quench (or squish, or "squench") measurement of 0.040". | One way to arrive at a ~0.040" quench distance is to cut the block decks to zero piston deck height and to use a head gasket that compresses to around 0.040". This allows a quench (or squish, or "squench") measurement of 0.040". | ||
| − | While that is a straight forward way to go about it, there are | + | While that is a straight forward way to go about it, there are other ways: Use a thinner head gasket and cut the deck only enough to get a flat surface with the correct finish for the head gasket to seal against. By doing it that way, more deck thickness is maintained, resulting in a potentially better head gasket seal due to the deck being thicker. |
==Parts stack height== | ==Parts stack height== | ||
| Line 30: | Line 30: | ||
The bottom line to all this is it's best to maintain an adequate quench figure of 0.040". There's nothing to be gained by going tighter, and a 0.040" quench distance will avoid unseen problems for the most part. If the quench is less than 0.040", be sure to double check clearances to be sure there is no contact between the piston and head- for obvious reasons. | The bottom line to all this is it's best to maintain an adequate quench figure of 0.040". There's nothing to be gained by going tighter, and a 0.040" quench distance will avoid unseen problems for the most part. If the quench is less than 0.040", be sure to double check clearances to be sure there is no contact between the piston and head- for obvious reasons. | ||
| + | |||
| + | ==Piston design== | ||
| + | For a wedge shaped combustion chamber like used in many engines, a flat top piston is the best design for promoting the quench effect. However there are times when a dish has to be used. In those cases a reverse dome, also called inverted dome, or D-cup piston (below left), will be the best compromise. | ||
| + | |||
| + | {| | ||
| + | |[[File:KB P-N 135 SBC 383 PISTON.jpg]] | ||
| + | |[[File:H423NP.jpg|300px|center]] | ||
| + | |} | ||
| + | |||
| + | Next to a D-cup piston would be a wide quench band ''round'' dish piston as seen above right. This isn't as good as a D-cup, but it is better than a stock-type SBC piston seen below. The stock piston has a too-narrow quench band due to the large dish plus the 45 degree large chamfer around the piston OD. | ||
| + | |||
| + | [[File:Round dish sbc piston.jpg|500px]] | ||
==Some excerpts from posts by Hotrodders forum member, oldbogie== | ==Some excerpts from posts by Hotrodders forum member, oldbogie== | ||
*From Hotrodders forum thread [http://www.hotrodders.com/forum/350-290-help-170440.html 350/290 Help]: | *From Hotrodders forum thread [http://www.hotrodders.com/forum/350-290-help-170440.html 350/290 Help]: | ||
| − | <Blockquote> | + | <Blockquote>“Squish/quench is a method of building mechanical octane into the engine. These two functions are provided for by the closing of the piston's flat crown surface to that of a similar surface of the combustion chamber opposite the valve and spark plug pocket. The closing distance should be 0.040 minimum to 0.060 maximum for best effect. This is hard to achieve with the factory's round dish being under the quench pad area of the head. The round dish's depth is added to the gasket and piston deck clearance stack up. </Blockquote> |
<Blockquote> “The squish happens as the piston closes to the top of the chamber. This ejects the mixture toward the spark plug. This does two things. First is it mixes the fuel and air providing a smooth and complete burn; better mileage and power result. Second, it puts nearly all the mixture in front of the spark plug which increases its density, making it easier to light off and causing it to burn faster; fewer miss and late fires and more early pressure with less ignition advance is the result. End product is better fuel economy and more power as well as lower emissions. </Blockquote> | <Blockquote> “The squish happens as the piston closes to the top of the chamber. This ejects the mixture toward the spark plug. This does two things. First is it mixes the fuel and air providing a smooth and complete burn; better mileage and power result. Second, it puts nearly all the mixture in front of the spark plug which increases its density, making it easier to light off and causing it to burn faster; fewer miss and late fires and more early pressure with less ignition advance is the result. End product is better fuel economy and more power as well as lower emissions. </Blockquote> | ||
<Blockquote> “The last function is quench, like it sounds it dampens the end burn. The end burn is where detonation occurs, the last mixture furthest from the plug is subjected to high pressures and temperatures that cause it to self ignite ahead of the burn, its explosion is the ping you hear when the pressure wave slams into the metal parts. The quench is an area of little volume and a lot of surface area, so it sinks the heat of the late burn, delaying the point where the unburnt mixture explodes. This lets you push the engine harder, at cruise you can operate at higher temps which increase thermal efficiency, and at WOT it holds off detonation which raises the RPM operating limit, assuming the cam will sustain more RPM and bottom end is strong enough.”</Blockquote> | <Blockquote> “The last function is quench, like it sounds it dampens the end burn. The end burn is where detonation occurs, the last mixture furthest from the plug is subjected to high pressures and temperatures that cause it to self ignite ahead of the burn, its explosion is the ping you hear when the pressure wave slams into the metal parts. The quench is an area of little volume and a lot of surface area, so it sinks the heat of the late burn, delaying the point where the unburnt mixture explodes. This lets you push the engine harder, at cruise you can operate at higher temps which increase thermal efficiency, and at WOT it holds off detonation which raises the RPM operating limit, assuming the cam will sustain more RPM and bottom end is strong enough.”</Blockquote> | ||
| − | |||
*From Hotrodders forum thread [http://www.hotrodders.com/forum/another-hp-torque-estimate-350-a-170908.html Another HP/torque estimate on a 350??] | *From Hotrodders forum thread [http://www.hotrodders.com/forum/another-hp-torque-estimate-350-a-170908.html Another HP/torque estimate on a 350??] | ||
<Blockquote>“OEM pistons are as usual a bone of contention. Even with the Vortec head, GM just couldn't let go of the circular dish in the crown. This does a lousy job of squish and quench forcing you to buy fuel with more octane content to keep from blowing the heads off with detonation. To the rescue is the D-shape dish of the aftermarket. These function like a flat top for squish and quench while putting all the dish under the valve pocket where you select the dish volume to dial in the compression ratio for the fuel you want to use. A commonly used source is Keith Black, it's on the web.”</Blockquote> | <Blockquote>“OEM pistons are as usual a bone of contention. Even with the Vortec head, GM just couldn't let go of the circular dish in the crown. This does a lousy job of squish and quench forcing you to buy fuel with more octane content to keep from blowing the heads off with detonation. To the rescue is the D-shape dish of the aftermarket. These function like a flat top for squish and quench while putting all the dish under the valve pocket where you select the dish volume to dial in the compression ratio for the fuel you want to use. A commonly used source is Keith Black, it's on the web.”</Blockquote> | ||
| − | |||
*From Hotrodders forum thread [http://www.hotrodders.com/forum/l-31-compression-ratio-piston-type-170262.html L-31 compression ratio and piston type?] | *From Hotrodders forum thread [http://www.hotrodders.com/forum/l-31-compression-ratio-piston-type-170262.html L-31 compression ratio and piston type?] | ||
[[File:L31 PISTON DISH DEPTH .080 002.jpg|thumb|right|350px|L31 OEM round dish piston design]] | [[File:L31 PISTON DISH DEPTH .080 002.jpg|thumb|right|350px|L31 OEM round dish piston design]] | ||
| − | <Blockquote>“With aluminum heads you can up the compression by at least a full point, maybe a point and a half. But the factory L-31 piston follows GM's keep-it-cheap-as-possible format by using a circular dish. These pistons are the bane of performance as they lead to a less-than-ideal compression ratio for the fuel being used because of their lack of adequate squish and quench. As you can see from the picture on the right, the dish is 0.080 inch deep. Add to the dish's depth the typical production head gasket of about 0.020 inch crushed and the typical Chevy having another 0.025 inch between the top most part of the piston and the block's head deck. All told that adds up to 0.125 (1/8) inch between the bottom of the piston cup and the head's squish/quench deck! The optimum squish/quench is achieved at 0.040 inch from the pistons head surface to the heads squish/quench deck. That's a long way from the 0.125 (at best) the factory lets you live with. You make up the difference in squish/quench function with the amount of octane you buy at the pump. Now, ''some'' part of the OEM piston (the rim around the outer edge) does get close to the head, but it is too small to be of much value.”</Blockquote> | + | <Blockquote>“With aluminum heads you can up the compression by at least a full point, maybe a point and a half. But the factory L-31 piston follows GM's keep-it-cheap-as-possible format by using a circular dish. These pistons are the bane of performance as they lead to a less-than-ideal compression ratio for the fuel being used because of their lack of adequate squish and quench. As you can see from the picture on the right, the dish is 0.080 inch deep. Add to the dish's depth the typical production head gasket of about 0.020 inch crushed and the typical Chevy having another 0.025 inch between the top most part of the piston and the block's head deck. All told that adds up to 0.125 (1/8) inch between the bottom of the piston cup and the head's squish/quench deck! The optimum squish/quench is achieved at 0.040 inch from the pistons head surface to the heads squish/quench deck. That's a long way from the 0.125 inch (at best) the factory lets you live with. You make up the difference in squish/quench function with the amount of octane you buy at the pump. Now, ''some'' part of the OEM piston (the rim around the outer edge) does get close to the head, but it is too small to be of much value.”</Blockquote> |
<Blockquote>“Squish and quench are functions that build what's called mechanical octane into the engine, they also improve off idle and high axle ratio cruise performance as well as optimizing performance against the available octane fuels. The same parts perform both functions, which are merely separated in cycle time. Squish happens first, as the piston closes to TDC the mixture on the far side of the chamber is ejected by the close closing of the piston and head decks toward the spark plug. This stirs the mixture and increases its density before the spark-plug making it easier to light off and faster to burn.</Blockquote> | <Blockquote>“Squish and quench are functions that build what's called mechanical octane into the engine, they also improve off idle and high axle ratio cruise performance as well as optimizing performance against the available octane fuels. The same parts perform both functions, which are merely separated in cycle time. Squish happens first, as the piston closes to TDC the mixture on the far side of the chamber is ejected by the close closing of the piston and head decks toward the spark plug. This stirs the mixture and increases its density before the spark-plug making it easier to light off and faster to burn.</Blockquote> | ||
| Line 54: | Line 64: | ||
<Blockquote>“A digression to squish and quench. All engines, be they hemi, pent, or wedge use this in some design form. It is an area where the piston and head close very closely together. With hemi and pent heads. it's located around the outside diameter of the bore, pushing the mixture toward the middle where the sparkplug is usually located. On a wedge chamber it is found on the side opposite the sparkplug and valve pocket, pushing the mixture toward the sparkplug. These parts, or features of parts, perform two functions; one is squish the other is quench. They are separated by time in the cycle of compression to power. Squish happens first on compression as the flat surface of the piston closes toward the matching surface of the head. This ejects the mixture toward the sparkplug with great force both stirring the fuel and air together and increasing the density of the mixture directly in front of the spark plug. This both improves the chance of the plug lighting a burn (reduces miss and late fires), and it speeds the burn so cylinder pressure is optimized for piston position to press on the crankshaft with the greatest force possible (best power and use of the energy you pay for). At what is called the "late burn" part of the cycle is where detonation is like to occur.</Blockquote> | <Blockquote>“A digression to squish and quench. All engines, be they hemi, pent, or wedge use this in some design form. It is an area where the piston and head close very closely together. With hemi and pent heads. it's located around the outside diameter of the bore, pushing the mixture toward the middle where the sparkplug is usually located. On a wedge chamber it is found on the side opposite the sparkplug and valve pocket, pushing the mixture toward the sparkplug. These parts, or features of parts, perform two functions; one is squish the other is quench. They are separated by time in the cycle of compression to power. Squish happens first on compression as the flat surface of the piston closes toward the matching surface of the head. This ejects the mixture toward the sparkplug with great force both stirring the fuel and air together and increasing the density of the mixture directly in front of the spark plug. This both improves the chance of the plug lighting a burn (reduces miss and late fires), and it speeds the burn so cylinder pressure is optimized for piston position to press on the crankshaft with the greatest force possible (best power and use of the energy you pay for). At what is called the "late burn" part of the cycle is where detonation is like to occur.</Blockquote> | ||
<Blockquote>"The temperatures and pressures ahead of the flame front are getting very high to where the remaining mixture is entering the "diesel" zone where it's happy to just blow up. To counteract this tendency is now the quench function of the close fitting parts of the combustion chamber. This is now a zone with a lot of surface area to volume, so it acts as a heat sink, delaying the point where the temperatures and pressures become so great that the mixture explodes instead of burns. These days of restricted octane fuels has made this feature very important as you can no longer just throw more Tetra-Ethyl-Lead at the problem.”</Blockquote> | <Blockquote>"The temperatures and pressures ahead of the flame front are getting very high to where the remaining mixture is entering the "diesel" zone where it's happy to just blow up. To counteract this tendency is now the quench function of the close fitting parts of the combustion chamber. This is now a zone with a lot of surface area to volume, so it acts as a heat sink, delaying the point where the temperatures and pressures become so great that the mixture explodes instead of burns. These days of restricted octane fuels has made this feature very important as you can no longer just throw more Tetra-Ethyl-Lead at the problem.”</Blockquote> | ||
| + | |||
| + | ==Compression ratio calculators== | ||
| + | ===Dynamic compression ratio=== | ||
| + | *[http://www.wallaceracing.com/dynamic-cr.php Wallace Racing DCR calculator] | ||
| + | *[http://www.empirenet.com/pkelley2/DynamicCR.html Kelly DCR calculator] | ||
| + | *[http://www.kb-silvolite.com/calc.php?action=comp2 KB/Silvolite DCR calculator] | ||
| + | *[http://www.rbracing-rsr.com/comprAdvHD.htm RSR DCR calculator] | ||
| + | |||
| + | ===Static compression ratio=== | ||
| + | *[http://www.wheelspin.net/calc/calc2.html Static compression ratio] | ||
==Resources== | ==Resources== | ||
*[[Valve train points to check]] | *[[Valve train points to check]] | ||
| + | *[[Pistons and rings]] | ||
*[[Head gasket]] | *[[Head gasket]] | ||
*[[Dynamic compression ratio]] | *[[Dynamic compression ratio]] | ||
Your Privacy Choices