Ok...sorry regal and old fart, I couldn't resist. I do believe you are both agreeing to some degree....but just saying it in different ways.
How about we think about the subject of stroked motors like this?
Strictly speaking, a "stroked" motor is one where the distance from BDC to TDC has been altered in some way...be it "de-stroked" like a sbc 377 (350 crank in a 400 block, OR "stroked" like a 383 (400 crank in a 350 block)..let's suspend for the sake of this discussion the fact that my numbers are abstract since it's probably more like a 406 or a 388---depending on final bore size....anyway.
NOW, having said that, when you decide on "stroke," the one thing you cannot ignore is rod length since it is a "component" in the whole system.
From what I can understand, the biggest effect rod length has on a motor is the acceleration/decelleration of the piston at the BDC and TDC. There is no doubt that stroke+rod length+piston compression height (function of wristpin location)+piston head shape all relate and have to work together to keep the piston where you want it (.0025 in the hole, "zero decked" or whatever).
If the stroke is fixed say at 3.75," the connecting rod could be 2 feet long and the small end of the rod (at the piston) will only move a total distance of 3.75" So, we know that connecting rod length in a 4 stroke does not control the static compression ratio since the rod is basically along for the ride and only does what the crankshaft tells it to do.
What else do we have to effect the static compression ratio?
1. Piston head shape (i.e. flat top, dome dish)
2. Combustion chamber volume (usually measured in cc's)
3. Ratio of volume at BDC to cylinder volume at TDC.
I use the word volume in #3 because it accounts for combustion chamber size as well as bore and stroke.
In this rambling thread, I have chosen to ignore the effects of thermal expansion and high load connecting rod stretch and their effects on compression ratio because:
a. I don't know if they really matter much
b. I don't understand them anyway.
Now, please discuss!
How about we think about the subject of stroked motors like this?
Strictly speaking, a "stroked" motor is one where the distance from BDC to TDC has been altered in some way...be it "de-stroked" like a sbc 377 (350 crank in a 400 block, OR "stroked" like a 383 (400 crank in a 350 block)..let's suspend for the sake of this discussion the fact that my numbers are abstract since it's probably more like a 406 or a 388---depending on final bore size....anyway.
NOW, having said that, when you decide on "stroke," the one thing you cannot ignore is rod length since it is a "component" in the whole system.
From what I can understand, the biggest effect rod length has on a motor is the acceleration/decelleration of the piston at the BDC and TDC. There is no doubt that stroke+rod length+piston compression height (function of wristpin location)+piston head shape all relate and have to work together to keep the piston where you want it (.0025 in the hole, "zero decked" or whatever).
If the stroke is fixed say at 3.75," the connecting rod could be 2 feet long and the small end of the rod (at the piston) will only move a total distance of 3.75" So, we know that connecting rod length in a 4 stroke does not control the static compression ratio since the rod is basically along for the ride and only does what the crankshaft tells it to do.
What else do we have to effect the static compression ratio?
1. Piston head shape (i.e. flat top, dome dish)
2. Combustion chamber volume (usually measured in cc's)
3. Ratio of volume at BDC to cylinder volume at TDC.
I use the word volume in #3 because it accounts for combustion chamber size as well as bore and stroke.
In this rambling thread, I have chosen to ignore the effects of thermal expansion and high load connecting rod stretch and their effects on compression ratio because:
a. I don't know if they really matter much
b. I don't understand them anyway.
Now, please discuss!
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