liveforphysics
You guys frequently make reference to 'safe psi' on XXX sleeve. Get a clue guys, there is no relationship between these things. Peak cylinder pressure can be higher on a NA than on an engine with 30psi. Also, peak cylinder pressure is not even as much of a factor as the rod angularity at the point this pressure occurs. If your RS was something like a b16b with a moved up wrist pin and longer rod, your sleeve loading at 30psi might be something like a stock LS engine with the timing adjusted slightly.

Think about this guys, rod angle, crank angle that peak cylinder pressure occurs(directly related to compression and spark timing), chamber shape and quench (greatly effect burn rate). These things have effects on sleeve loading so great that they can make a low comp NA be more likely to break its sleeves than a high comp high boost engine.


This has just been a little pet-peeve I have been seeing frequently on this site.

liveforphysics
overblown- i will try to interpret what BH intended to say. Due to great temp differences inhearent in turbos of different flow capicities for a given PSI, the O2 density available to react with fuel and create cylinder pressure will also be radically different.

boosted hybrid
I'll take a quick stab at this:

Here is a ghetto picture to help you understand:



As you can see from the picture, the r/s ratio is the rato of the rod to the stroke of the engine. The "long rod" is merely the rod length in comparision to the stroke of the engine. The b16a rod is physically shorter by 3mm than the b18a/b18b/b20b rods, but in comparision to the stroke of the engines its a long rod. You can see the angle is much less with the shorter rod, this gives the rod in motion up and down the bore a faster speed than the greater angle of the b16a engine. It comes down to a dynamical analysis of the piston, but with the angle of the b16a engine the piston dwells at top dead center longer thus slowing the overall speed of the piston down in comparision to the b18a/b18b/b20a engines.

On another note, by the picture I have drawn you can see why the higher r/s ratio places less stress on the sidewall of the cylinder wall. With the increased angle of the b16a engine, there is more force in the y-direction (up) and less force in the x-direction (cylinder wall).

If you change the location of the wrist pin journal you can actually increase or decrease the r/s ratio depending on which direction you move the wrist pin location.

Now in relation to ignition timing. The longer rod engine has the piston dwell at TDC longer than a shorter rod engine. The longer duration allows for less timing to be used to ignition the fuel mixture (igniting the mixture closer to TDC) and therefore less overall cylinder pressure from doing so. The goal is to have peak cylinder pressure meet the piston when traveling about 15-20 degrees ATDC (after top dead center). By being able to not run as much ignition timing, and having less cylinder pressure the tendency for knock to occur is much less. With the longer dwell time for the longer rod engine at TDC, you also get a longer burn rate available burn rate which translates into being able to use less octane fuel to sustain knock.

liveforphysics
as the R/S get numerically higher, the graph of piston height VS time becomes a perfect sin wave. As the number gets smaller, imagine the corners of that hill on top getting shaved off and pasted to the sides of the hill on the bottom. This is how the BDC dwell gets fatter, and the TDC dwell gets skinnier. Visualize it. Now, visualize that you have a smaller window of time to change direction of the piston when its a TDC. TDC right after fireing the exaust pulse making a low pressure area on top of the piston is also the point of peak rod stress.

The angularity thing, look at Jeffs diagrams. Now imagine putting a weight on top of each piston. The closer the rod is to vertical, the smaller portion of the weight is directed towards the walls. Now, someone said somethign about pressure being equal in there. Yes, gas pressure is essentially equal in there. But that equal gas pressure gets multiplied by the surface area of the piston, then the pressure of all the gas on the piston is split between pushing down on the crank and pushing out of the sleeve. The gas pressure alone has essentially zero effect on the sleeves. Stock sleeves could handle 10times the pressure we can ever make them see, even with tripple digit boost builds and nitro. Its always the piston pushing into the side of them that causes the failier.