The Stovebolt Site Forums The Shop Area The HiPo Shop cam coice

hi, new to the site and just bought a new project. i'm not a total novice but, i'm no seasoned pro so please keep that in mind.

i'm working on a 1951, 3100 chevy panel with a 235 in it from 1957. its a 4 spd, 420 transmission (i think).

i am doing a rebuild on the motor and want to "hop it up a bit" but it will be a daily driver so dependability is important.

based on almost everything i've read, it seems the best way to do this is with a dual carb set up, headers, dual exhaust, and a "mild" cam.
i found a vintage NOS ebelbrock mainifold with 2 zenith 228s which i purchased. i also have a new set of fenton headers and a local shop to build the exhaust. my question is in regards to the cam. can anyone make a suggestion as to what cam would be a good choice?

also, any other ideas or suggestion would be welcome.

thanks!

Elgin E-293S as previously suggested. I don’t know if the Zenith 228s have changeable jets or not. If they do, jet them down as small as possible or block one off and run on 1 using the other as eye candy. No one will know but you.

One can usually gain a few HP by milling the head. Always first want to measure valve to head clearance. I milled the head on my GMC 302 .060" with plenty of clearance, GMC 503 .090" with plenty of clearance(similar engines.)

If not want to waste a head gasket in the process, roll some pieces of modeling clay small enough to fit loosely in spark plug hole, one could wrap the clay around a piece of welding rod for increased rigidity, slip it in the spark plug hole, being careful to find the valves. Turn the engine over several times, by hand, to get your clearance. Of course might want to make sure valves are in spec. first.

Ed

The intake valve is the only one that can possibly contact the piston. The exhaust valve is deeply recessed in the head, and at an angle that makes it impossible for it to touch the piston. With the head snugged down against the head gasket, not necessarily torqued, use a weak spring on the intake valve and lever it down against the piston top while measuring the valve travel with a dial indicator. Start doing this when the crankshaft is around 20 degrees before top dead center, and measure the valve-to-piston clearance every 5 degrees until you get to about 20 degrees after top dead center.

With those dimensions in hand (or on your computer memory) you can figure out what cam lift/head milling you can get away with. Don't let the valve get closer to the piston than .060" to allow for valve float, head gasket compression, etc. On one of the round track small block V8's we ran, the closest piston/valve clearance came at 20 degrees AFTER top dead center. The valve was outrunning the piston for the first few degrees of the intake stroke!
Jerry

What Jerry said.... my smallest intake clearance came in at .063 with a mild cam and a head that a PO had milled an unknown amount. I’ll be watching my intake valve clearances very closely.

Be sure to check the valve springs. They weaken with age and with valve getting closer to the piston you want to avoid valve float at higher rpm.

I've seen the valves float on a stovebolt engine occasionally- - - - -but only if it was installed in a boat. Getting a street engine up to valve-floating RPM might be possible, wide open in granny gear on a SM-420. Otherwise it's pretty unlikely. Stretching or breaking one of those limp spaghetti connecting rods would probably happen first.
Jerry