Quench

[dirty dan]

How much is enough? How much is to litlle ? How much is to much? Inquiering minds want to know.

[cuda367]

Keith Black study this when coming with his piston line. My memory is a short as my ----, but I beleive he felt that .055 to.060 was about max to receive good results. Which also happens to be about what most builders want for piston to head clearence, which answers your second Question. The minimum is what you can run and not have the piston hit the head.

[Jims451]

The idea is to get a near collision between the head and piston with the engine running, which has to account for main/rod/pin clearances, piston rod stretch at RPM, thermal expansion, even how much the piston rocks in the bore.
So it depends alot on the engine and application.
For example a low RPM engine with steel rods may be fine with very little clearance of 0.030" or less. A high winding engine with aluminum rods may need over 0.060"+.
For many general purpose performance engines with steel rods 0.040" to 0.050" sems to be considered "safe".
If the clearance is too large, you loose the benifit of the "quench" effect.