Thread: 350 / 305 head combo (what am I leaving on the table)

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Originally Posted by techinspector1

Understand this: YOU CANNOT INTELLIGENTLY CHOOSE ANY CAMSHAFT FOR ANY MOTOR UNTIL YOU ABSOLUTELY, POSITIVELY KNOW THE STATIC COMPRESSION RATIO BY MEASURING COMPONENTS YOURSELF OR HAVING SOMEONE ELSE MEASURE THEM FOR YOU.
You need 5 values:
1. Cylinder volume in cc's
2. Combustion chamber volume in cc's
3. Piston deck height volume in cc's (the volume between the piston crown and the deck of the block with the piston at top dead center)
4. Piston crown volume in cc's (a true flat top piston will have about 6-7 cc's in the eyebrows that are cut into the crown for valve clearance. Otherwise, for a dished or domed piston, the mfg will usually publish the volume). Most of the stock-type 350 pistons have a recess that isn't actually called a dish, but it is a depression across the crown, with a very thin ring of material sitting up a little higher around the bore. That little thin ring of material is insufficient for generating a good squish and you should be very careful with compression ratio and cam if you use that type of piston. The very best type to use in a street/strip build in my opinion is a D-cup dished piston. These provide a generous shelf of material that comes up against the underside of the cylinder head to generate a very good squish. If you build any kind of reasonable static compression ratio into the motor without using a good squish, there is a good possibility that the motor will detonate on pump gas.
5. Head gasket volume in cc's
If you want me to go through the entire routine and teach you how to find the exact SCR, just ask.
The camshaft will normally be the last component chosen, after everything else is nailed down for the build.

If you do end up using L31 heads, don't let anyone talk you into increasing the valve sizes. Stock, they are 1.94"/1.50" and will do a fine job on a 350. Any cutting done on an already thin-wall casting is just asking for trouble.

I found this great info from techinspector and wanted to add it to my post. I will ned this info to find my SCR.