Clearance

joe boom

New member
What is the minimum piston to head and valve to head clearance for an open turning between 8500 and 9000 rpm
 

flattop1

Dawg 89
The obvious.
i can see that as piston hitting the head will beat the rod bearing up and may stick the ring .

Valve too head clearance
Considering the stockers float the valve till it kisses the head , its free to drop back into the free space . Where as the high lift cam is in constant contact with the lobe .
Collision here will bend the valve .

Have you all tried less ?
 
^ Yep. Less that .035" quench seems to hurt performance (upper power band) in my experience. That's why I settled on that.
For valves, it's as long as they don't hit. If it's a big lift cam, you had better not be kissing the head. We routinely valve pocket the heads for big lift cams so that they do not hit. Actual clearance above the valve doesn't seem to matter, as long as it doesn't hit. Another thing to consider is if you have any valve float at all and how heat affects the clearance. Better to be safe than sorry.
 

flattop1

Dawg 89
:) In all honesty you would need to be pretty good to get it too .035 .
Real good to get it closer !
 

Freezeman

Premium User
I have gone a bit less than .030 on limited mod flatheads and that is when problems start. I have some old heads that are inprinted with the type of piston that was slamming against them.
 

fatjet87

Member
Do the limited modifieds float the valves when their spinning 9000 rpm. Do you want the valves floating like a stocker or no? I would think not
 
Do the limited modifieds float the valves when their spinning 9000 rpm. Do you want the valves floating like a stocker or no? I would think not

Definitely not.
Replace springs, rod bolts, and bearings every race (or two) if you're going to spin them up to 10g's.
They'll live a lot longer @ 88-9200, trust me...but man, do they sound (and run) good in the 10s. :)
 
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