Join Date: Apr 2000
Location: Whittier, California
Quench distance being right will make an engine, off will kill it.
Years ago, engineers foound the proper distances for steel rod engines were the aforestated .040/.045. If yiou look at most performance engines fromk the musclecar era, you will find the pistons down in the hole about .022/.025, not a bad thing or wrong, considering the head gaskets were .020 compressed steel, giving the proper .042/.045 quench neded.
Only problem with quench arose from later pack type head gaskets. They seal well, are nicer to use, don't require a dead straight deck/ head surface, as Galen pointed out, but wrecked havoc on proper quench distance. In the beginniing of the quench/pack gasket times, gas was much better, and power loss from incorrect quench wasn't as noticable as is today.
Only time quench rules are altered is for aluminum rods/very high rpm engines, 12,000 rpms and above (steel rod Indy and Formula 1 engines). And, even then, the quench comes back to the same level as a .040/.045 engine after the added stretch is developed.
In motorcyle engines, both 2 and 4 stroke design, quench distance is called squish clearance, and is as vitally important as it is in our engines.
Even today, companies like Silvolite have pistons for regular replacement they call "de-stroked". These pistons are not altered in the stroke, which is determined solely by the rod throw distance on the crank, but have altered compression heights. Compression height is the distance from the flat deck of the piston to the center of the wrist pin. Normally, the average 265 thru 350 small block Chevrolet engine will have a 1.560 comp hgt, "destroked" will have 1.540 distance, for a .020 lower deck as measured in the same block.
If we look at the average 1.560 piston, down .025 and with a pack type .040 compressed thickness head gasket, we get .065 quench distance. With a "destroked" piston of 1.540 c/h and the same .040 pack gasket, the qusench goes to .085.
It is easy to see that quench can make or break performance in an engine, even in a stocker too.
[This message has been edited by IgnitionMan (edited 10-09-2000).]