What are the benefits of increasing/ decreasing the size of these in an engine. If someone can fill me in or point me in the right direction.

Thanks Mike

 

Anytime you increase bore or stroke, you're increasing the displacement. That's always good for power, but not always good for MPG.

The easiest way to find the displacement of an engine is this formula.

Bore X bore X stroke X .7856 X number of cylinders = cid

Rod ratio is the length of the rod divided by the stroke. The higher the number the "better". I say "better" because what's better isn't always practical.

 

Oh...... go to www.Mortec.com and look at the Bore and Stroke list. That will help you figure out what engine has what combo.

 

So what if I was to replace the 5.7 rods with 6.0 rods in a 350 what would the out come be. Does adding larger rods make a difference when selecting cranks or pistons?

Keep it coming guys

 

ttt

 

The 6" rods would give you a bit more power by slowing piston speed at TDC and BDC and also increases the rod/stroke ratio in a favorable direction. The longer rod gives the piston slightly better leverage on the crank, giving it a bit better torque ratio.

Is it worth tearing down an engine for? Probably not, but when building a new engine, I would say yes, it is worth the extra effort.

With the existing 350 crank, you would need to add pistons with the pin moved up to accept the longer rods, or you would stick the pistons right out the heads. You could use a shorter stroke crank, but then you decrese your engine size...

 

A 350 with 6" rods is still a 350. Changing the rod length doesn't change the displacement of the engine. You'd need pistons with the appropriate wrist-pin location for that length of rod.

 

Your question is very broad and encompasses so much, you could literally write books about it and people have! The beauty of the Small Block Chevy (SBC) is that there is so much interchangeability with regards to crankshafts, rods, heads, and camshafts that this question still hasn't been answered. Here is a nice link to get you started.

http://www.chevyhiperformance.com/techarticles/71298/

You have to ask yourself what you want from the motor you want to build, then make a plan to get there. Be aware that there will be compromises. The trick is to limit them and still attain your goal.

From an engineering stand point, IMHO, the best place to begin is the fact that the standard factory SBC has a crank centerline to deck height of 9.025" and armed with that knowledge you can play around with combinations. Though the factory production crank strokes you would probably be interested in are 3.00", 3.125",
3.48", and 3.75", the aftermarket can accomodate anything.

Give us some goals and there is enough brilliant minds on this site to steer you in the right direction.

 

Thanks for all the info. Im going to play around with rod ratio stoke and bore #'s and see what I combos I can come up with.

 

OK. There were 5 different strokes that were stock from GM in a Gen I SBC.

3.0", 3.1", 3.25", 3.48", 3.75"

There were 7 different bores, not including the overbores (.030", .040", .060") when rebuilding a SBC.

3.5", 3.671", 3.735", 3.75", 3.875", 4.00", 4.125"

And I don't even wanna guess how many different aftermarket strokes are out there.

We'll see you in a few weeks when you're done figuring them all.