Can we do a poll on people with built engines on what their builds are vs how high they rev their engines and take borescope photos of their walls (front and back)?
I think certain oils and piston skirts will resist wear better than others.

 

Update: theoretical max piston speed already takes into account the crank angles.

 

this

 

Sorry guys, I'm eating at a restaurant and drawing my pictures on my son's coloring paper and my napkin to imaging this
Are you guys seeing what I'm seeing?

 

and you too
Actually, you before 2winscroll.

 

Did you know that when crank is horizontal (90°) the piston isn't 1/2 way down? It's actually 54.55mm down, not 47mm like we intuitively think.

So pistons speed up on way down and max it's speed out at 58% of the way down! Then it has to stop at BDC from max speed to zero with remaining 42% (or 39.45mm)!!
So that means I need to recalculate the forces from revving since I assumed (incorrectly) that everything was 1/2 way.

 

I'm sure the engineers at English Racing with their custom Wiseco pistons and ER spec Carillo rods have it plenty well figured out.

2006EvoIXer is over here trying reinvent the wheel on stuff that has already been mathed out and proven reliable.

 

I did some reading and found out that these theoretical 24 to 32 m/s are average piston speeds so crank angle are already accounted for. I'll go back and clean up above.

 

I've never been someone to blindly accept someone else's work. I've been burned too many times. I would like to see the calculations for myself before accepting. If not, then I'd like to go through my own calculations and do my own due diligence since these are not small change going into these builds and I want to understand how much each option helps for the difference in price. I enjoy going through the understanding of options and I learn a lot of things to treat my engine better.

 

Of course, these theoretical stuff varies depending on who you talk to. Formula 1 cars have piston speeds of 24 m/s. Integra Type R & S2000 gers up to maybe 26 m/s, but normally aspirated doesn't see the pressures that we have. So what makes sense to me?
My stock evo 9 has signs of being overrevved. I hit between 8300 and 8500 rpm at the drag track when my clutch gave up in 4th. (For those that don't know, the smaller valve relief cuts on piston is exhaust side and the larger cuts are the intake side.)

 

When I took these photos, I rotated the pistons to BDC. What's interesting is that the wear is slightly below the midpoint. Of course my head is already installed so I can't measure it without taking everything off again. (DARN!!!)

 

What I see from the wear is that engine was overrevved. But noticed that the intake aide has more wear. This shows me that combustion + overrevving = compounded wear. Also, notice that the wear is only in the center. That tells me I overrevved slightly when my pistons exceeded the max piston speed slightly.
Let's be conservative here and assume this damage was caused by 8300 RPM rev. Then I would be confident that 8200 would be at oem bottom end limit.

 

My disclaimer: This is what I imagine happened. I have not done any research.

How exactly does overrevving wore my cylinder walls?

As we (sort of) know, the weight and forces of piston and rods push and pull the pistons at different angles. The skirt resist the pivoting forces. Looks like skirts are starting to give at the pistons fastest speed. (I won't include too much details since that will be too lengthy )

 

You see accelerated wear like that from having too loose PWC. Also, the majority of your wear will come from when the engine is cold or if you're fluttering the rings.

You can do all the math you want, you still won't get real world results on paper. There's so many variables that people don't even think about, like cross hatch angle on the cylinder wall, piston design (offset gudgeon pins, ringland thickness, gas porting, skirt width), ring material and how thick they are, was the cylinder plateau honed or not, was the bore machined with a taper to even out with future wear?, are the pistons being cooled by squirters or splashed oil, what about piston material (4032 or 2618, or something exotic like DW-215).

And they all play a part in how things wear as well as influence power output. Point is, there are so many variables, some of them that you can't control either, that the only good you can get from math is a very, very, very rough ballpark estimate, which sometimes still isn't even right.

 

I agree that there are a million variables. I want something more realistic. That's why I'm starting with my car's actual results. At 8300 rpm, I started to see wall wear. I plan on calculating the piston speed limit from there. But that's not the only variable. I will calculate the equivalent lateral load experienced by my engine and stay right below that on new build.
I understand it will be a shot in the dark, but it's a educated shot in the dark by knowing the direction.
I truly believe I will end up close enough on the conservative side to prevent accelerated wear on walls (or at least reduce dramatically), which is my goal anyway (to help my engine live long and prosper ). I plan to adjust my calculations for each of the items you listed above as I select the piston on my build. I truly believe I have the best rods for my needs (althought I decided on 150mm to save a few hundred $ because the performance difference was minimal according to my calculations).
Thanks for your practical insights because it is great knowledge learned from experience.