Cubic inch Questions...

First, let me preface this by saying that I'm not an engine builder, nor do I claim to be an expert in any sense of the word, but here are my thoughts:


A 306 is achieved by taking a stock 302 block with a 4 inch bore and boring it 30-thousandths over (.030 over) to 4.030. The reason most people bore their block larger than factory specifications is because they did a rebuild and the cylinder walls had scratches or something (that was the case with mine). A .030 bore will give them "new" cylinder surfaces, but they also must buy new pistons to accommodate the larger bore (4.030 pistons) and then new rings to match the pistons. Increasing the bore really isn't an attempt to create horsepower as much as to just give a fresh cylinder wall.

Stroking an engine is done by purchasing a crank and rods to provide a larger stroke. I'm not sure how a stroker crank ranks relative to a stock crank as far as strength goes, but you can purchase a forged crank if you're worried about strength issues.

You can also stroke and bore to a 331 or 347, but I can't tell you the details off of the top of my head.

Others who know a lot more about this than me will chime in, but this should wet your whistle for now

Rick91GT on stangnet builds engines and many have gotten engines built by him. He's in Pennsylvania if I remember correctly.

My 306's are always .030" overbore and a .010" polished crank

331 and 347 are the same animal with more clearencing and a 5.4" rod and matching crank.

Good question!
Unstable Performance

User is correct about boreing, only done for rebuilds, not power. 331's and 347's are .030 over bore too. a 302 has a 3" stroke, 331--3.25" stroke, and 347--3.4" stroke. 331/347 usually utilize a 5.4" rod where 302 use a 5.095 I believe. The stroke does not effect the crank stregth. However, with a longer stroke the rod comes in at a sharper angle when pushing the piston up the bore...creating a heavier lateral load on the piston/cylinder wall.

because you can run better cam profiles

No. Because the lifters have a roller bearing that rides on the cam.

Hydraulic Rollers in a sense are more tolerable on the streets...

A 331 consist of a 4.030" bore (piston) and a 5.315" rod and a 3.25" stroke. A 347 can consist of a 4.030" bore with either a 5.315" rod (street) or 5.4" rod (strip) with a 3.4" stroke.

Stock 302 rods are 5.09 I believe...

A 306 is cheaper and provides a fresh bottomend, as do the strokers for some more dough and more power.

The 5.315 rod keeps the piston pin out of the oil ring grooves. Helps to keep from using oil.