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Original Message
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| RE: Quench Clearance |
| By Martin Edridge - 04/19/2002 2:45:02 PM; IP 195.194.51.129 |
It is the distance between the top of the piston (flat part) and the corresponding area of the cylinder head when it is bolted to the block. Keeping this distance to about .040" is generally accepted as being ideal for steel-rod street and mild race engines with a limit of about 6000-6500 rpm. Higher rpm engines or those with aluminum rods need more to allow for the 'growth' and to avoid contact. The idea is that as the piston rises on the comp stroke it gets very close to the head and the air/fuel mix from that area is 'squished' out across the chamber, helping the combustion process by inducing swirl and evacuating end gasses from the area furthest away from the spark plug (ignition initiation point) The upshot of all this in case you are wondering is that you can usually build an engine with slightly higher compression than normal and avoid detonation. It is said that if an engine is just tipping into detonation at, say, 10:1 with good quench (.040") then putting thicker gaskets in to drop the compression will actually make things worse due to the loss of good quench clearance. Try to think of it as having a custard slice in your palm and slapping it with your other hand. The custard flies out! Hope this explains a bit for you.
Cheers, Martin. |
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