[DeTomaso] Camshaft selection

[JDeRyke at aol.com]

10-1/2:1 should be fine with the hi-octane gas you mention and the aluminum 
CHI cylinder heads, but I wouldn't go higher or you could wind up being forced 
to run aviation fuel or expensive racing gas, or severely retarded ignition 
timing.   If a std lift roller cam and notched lifters is put into a 351-C, 
you'll get 16 massive oil leaks each time the cam revolves! So, some retrofit 
roller cams use cut down cam cores to keep the roller wheels from protruding into 
the huge oil galleries behind the tappet bosses. The thinner camshaft will 
then be a little weaker than normal and will twist under heavy valve spring 
loads, which unfortunately must be used with the 351-C's   big valves and heavy 
hydraulic roller lifters. Running such a cam at high revs might cause camshaft 
breakage or at least give flexible camshaft timing to confuse your tuning 
efforts.

What seems to work better for street cars is shrouded-roller hydraulic 
lifters that use slightly smaller rollers with a lifter body that is cylindrical all 
the way down past the roller wheel. So normal cam lift doesn't cause an oil 
leak and a stronger normal-thickness camshaft can be used. Crane uses such 
lifters on some retrofit roller cams. As always, for a specific cam for an engine, 
I recommend calling a few cam grinders on their Tech Lines and asking the 
people who build the things for advice. 

A last note- my Ford-SVO A-3 aluminum cylinder heads specify no more than 175 
lbs closed valve spring pressure. Any heavier and the hard valve seats will 
begin to sink into the soft aluminum. Open pressure is not a problem. Good luck 
with your build- J DeRyke


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