piston to valve clearance

whats minimum clearance for a hemi? Im using bae fuel heads, with 2.40 intake and 1.94 exhaust. both valves are titanium. brooks aluminum rods. this is blown alcohol, should see 9200 rpm. If memory serves me I think I need about .080 on the exhaust? thanks for the input. side note; I will keep the springs at 300lbs min.

 

Valve To Piston Clearance

Intake Should Have A Min Of .090 To 0.100
And Exh Min Of 0.100 To 0.110

 

That sounds a little low to me. I run .125 clearance on the intake, any less and it puts a shiny mark on the piston. Exhaust is more critical, as the piston and valve are moving opposite directions. I run .150 minimum, but I like to have .200 if I can.

 

I have found that .070 piston to head is about minimum, for small motors it works great because it gives you a bit of "squish" that seems to build a bit more power. For funny car motors with a large stroke, we're usually around .090 or .100.

 

we never use less than .085 on intake .120 on exhaust piston to head .080 valve seat pressure never less than 480 on seat worked for us shifting at 10200rpm hope this helps ralph p

 

cut out clearance

thanks for the input. second part is how much can you safely cut away on the piston for clearance? I know I can adjust with different length rods, but there comes a time to flycut the piston for final clearance. .125 to much?

 

If you have to cut .125, more than likely you have the wrong pistons or rod, or you have the cam in wrong.

 

i agree, and if you had to cut to get .125 on the exhaust, how much do you have on the intake valve.?

 

somethings wrong

thanks for the input, I must have done something wrong, including not claying the new heads. time to take it apart. at least I didnt start it. just when I thought I knew something...

 

You didn't ask,....but I would sure bump that pressure up a lot more.

Blessings.......Ron.

 

Mark,
I bought a couple of light springs from a hardward store and replaced a intake and exhaust valve spring with them. Then I put my dial indicator on the retainer and measured clearances at 5 degree increments of crankshaft rotation. You can push the valves down until they contact the pistons and measure clearances. Then I rotate the motor another 5 degrees and do it again. You should only have to do it when the piston nears the tops of the cylinders. I was once told by the builder of my last Walt motor (the one that blew itself to bits) that he loosened rod bolts to push pistons up into head to measure piston to head clearance. He used a dial indicator to measure from the head of a rod bolt. I suppose you could take the cap off completely and measure off the parting surface of the rod. I have tried the clay thing and it didn't seem real accurate. Dave Germain

 

cam timing off

Hi dave, I checked the cam timing. it was at 15degrees btdc when lifter is at +.050. it was supposed tobe 38 degrees at .050 lift. hmm... Back to work. I will still have to recheck valve-piston clearance.