Quote:
Originally Posted by serialk11r
Yeah, but it has 139mm connecting rods (from google) rather than 133 (what I calculated for the FA20, using the "same dimensions as FB20" + increased compression ratio), giving a rod:stroke ratio of 1.616 instead of 1.547.
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That 0.069 rod ratio change isn't that great of an effect on the peak piston accelerations nor the instantaneous peak piston speeds. Side loading changes aren't that great either. I will however say it isn't to be ignored. A quick crank-slider model will show you that.
Quote:
Originally Posted by old greg
Uh, so what? Even with a lower rod/stroke ratio the 133mm rod FA20 has ~4% lower peak piston acceleration than the FA22C which revs to 8200rpm just fine.
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Exactly. I don't think the FA20 is going to be a 9k+ screamer engine but I'll be trying to prove myself wrong. However if I find the engine hitting a brick wall, I'll go down the other shortblock avenues that I've been looking into. I'll be chasing area under the curve, not a high redline.
Quote:
Originally Posted by Dimman
It's not simply the rpm vs stroke and rod:stroke. These affect the force on the rods, pins and bolts. It's also the materials and manufacturing of these that are resisting the forces.
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Exactly and there is always lots to change
I keep my 9.5:1, 4" pistons to 405-410 grams (fluctuates with batches) in 2618. Newer things in the works, which I'll be starting with on the FA20 engine.
Basically, for now I'm working on everything in the shortblock, as it's the only part that I have absolutes on. I'm going to see what the shortblock and manifolds can bring to the table and by that time, their should be some aftermarket camshaft support
I start with shortblock geometry (confinements and limitations), from there I have calculated loads and start with modeling/FEA work. Then it's off to prototype testing...same as always.
Cylinder heads, I have a few potential points of interest and I really hope that the TGV and plates that extend into the heads don't carry over from the FB!!
-Micah