OK, I'm working on the calculus of piston acceleration.

In the meantime, about valve and spring problems. The F20C runs into problems when revved substantially over 9000 rpm, as in mechanical overrev. What billman is talking about here is revving to 9000 rpm. Unless its valves are heavier (possible) or cam profiles steeper (possible), the F22C upper end should be able to withstand the same revs as the F20C.

Jet designer dude

 

dhayner, I agree with everything you've said but might offer one additional point of discussion. Max acceleration of the piston would be overiding factor assuming the F20C and the F22C have identical pistons. Even marginally more mass in the piston at the same max G load would have a pretty dramic effect as well (assuming similar piston contruction - i.e. cast vs cast).

Can anyone speak to how/if the F20C and F22C pistons differ?

 

Ok, here's what I'm talking about:



In this crude, out of scale diagram, A is the length of the stroke. C is the rod (which is a constant in our discussion) and B is the horizontal force exerted on the side of the cylinder wall.

As you can see, when A gets longer the resultant force B gets stonger. This is bad for revs ummkay?

F1 cars have tiny strokes and super nice R/S ratios. They make up for this short stroke with a wide piston that revs to the sky.

 

And the wider bore allows room for a longer con rod, thus minimizing the side load stresses he's talking about.

As far as I've been able to determine, the only internal differences between the F20 and the F22 is the crankshaft and con rod. Pistons, supposedly, are the same. In the head, the valves are supposedly the same because they didn't change the bore so there's not room for larger valves. It has been determined that the valve springs are different on the F22 than they are on the F20. At least the part numbers that Honda lists for the two engines are different. Whether or not there are any significant difference in the valve spring specs, I haven't seen data to indicate that.

FWIW!
Drive Safe,
Steve R.

 

I thought they only lengthened the stroke by changing the crank circumference. I doubt they would lengthen the connecting rod since all that would do is up the compression and eliminate the added displacment of the engine.

 

They didn't lengthen the con rod, they shortened it. The F20 and the F22 use the same engine block. They had room in the crankcase to increase the stroke with a different crankshaft and then shortened the con rod to keep from pushing the piston through the cylinder head. The end result being a slight increase in the compression ratio, 11.0:1 for the F20 vs 11.1:1 for the F22.

That's what a lot of this conversation has been concentrating on. With a shorter con rod and longer stroke, everything else being equal, the F22 should see slightly higher side loads on the pistons than the F20. The speculation and/or opinions stated is that this increase in piston side loading is more responsible for the decrease in redline rpms than the increase in piston speeds generated by the longer stroke.

I'm not qualified to state which parameter is more significant but the conversation's been interesting!

Drive Safe,
Steve R.

 

Thank you for your eloquence. That's what I've been trying to say and frankly, I'm not qualified either, but if you survey the redlines of various motors you'll usually find that the poorer the R/S the lower the redline.

 

Thanks for that great summary, and glagola1, thanks for your clear display of piston/cylinder side loading.

Just so you both know I clearly understand the fact that the F22C may have more side loading than the F20C. There are two factors: 1) shorter rod with greater angle, and greater piston force down that translates to greater side force through that angle (I am assuming greater force from the greater displacement). So at the same RPM there are two factors that make piston side loading increase in the F22C than in the F20C.

But still I ask, is that truly the limiting factor in maximum RPM? (I ask not to be a prick, but to increase my knowledge and keep this interesting discussion going.)

Also, if we truly know the limiting factors we will know where there is room for improvement and where there is only danger when it comes to tweaking.

What else could it be? Can the valving and intake system keep up the necessary breathing with the greater displacement of the F22C?
-probably: to fill an F20C "lung" requires 499.3 cc of air/fuel, and to fill an F22C "lung" it takes 539.3 cc (8%) more. That's 4500 liters/min for the F20C and 4857 liters/min for the F22C for the entire engine. You would think an 8% greater air/fuel requirement would not be enough to force a lower redline. Would it?


As I said in a previous post the most common S2000 engine failure mode has always been mechanical overrev. (I have only read of a few instances of thrown rods, etc.) Obviously the source of the "load" is different on a mechanical overrev vs. a power stroke.

But maybe the new weakest link in the F22C (when it comes to high RPMs) is indeed the R/S ratio.

 

Eh, I just don't think this discussion is in our "theorist" realm. I leave that stuff to the egineers... and guess what they did? Yep, 1000 less rpm baby.

And the discussion goes full circle.

 

[QUOTE=LATEOTT,Jan 26 2005, 07:33 PM] Thanks for that great summary, and glagola1, thanks for your clear display of piston/cylinder side loading.

Just so you both know I clearly understand the fact that the F22C may have more side loading than the F20C. There are two factors: