Cubic inch Questions...

[Georgie]

As some of u may know i blew my engine..so time for a new one.. i got some Q's abut Cubic inches... All of our stock 5.0's r 302 cubic inches right?? I see some guys on here with 306's...How is that achieved, and why? If its stroked, why not stroke it to more cubic inches and if its bored, why go threw all that hassle for 4 more cubic inches? Now also, the two ways to increase displacement : Stroking and Boring...which is better? If you bore ur block, the cylinder walls get thinner, which isn't good. And if you stroke it, the distance from the center of the crank to the center of the part where the connection rod rests get longer,..wouldnt that make ur crank weaker?

Any comments would be appreciated! Thanks!

 

[TheUser]

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.

 

[donsbad68]

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

 

[tylerrocks]

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.

 

[Georgie]

and why do ppl refer their engins as a Roller??

 

[88mouse]

because you can run better cam profiles

 

[tylerrocks]

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

 

[5spd GT]

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.

 

[tylerrocks]

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