what are the pros/cons of fly cut pistons?
06-19-2006, 12:20 PM
#1
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what are the pros/cons of fly cut pistons? what are the pros/cons of fly cut pistons on long rod high rpm engines besides being able to fit a bigger cam in? i would also like to know how flycut pistons effect piston velocity
06-19-2006, 12:37 PM
#2
The point of flycutting pistons is to gain piston to valve clearance on cams with lots of duration and low LSA, i.e. Overlap. That is one of the problems with a LS1 design is that it limits piston to valve clearance with the stock slugs in the motor. Installing aftermarket pistons does the same thing as fly cutting because you have valve reliefs in the tops of the pistons.
The flycutting of the pistons can do three bad things....
1. weakens the piston because the design of the piston wasn't made to have valve reliefs cut into them.
2. if the reliefs are not radiused the sharp edges of the cuts can cause knock due to hot spots.
3. the other bad thing about the reliefs is that they cause the compression ratio to drop since they add volume. Now most times you have a milled cylinder head that has a lower volume in the chamber anyways to cause this so when everything is all teamed up the compression ratio will be higher.
Flycutting does not change the piston velocity, that is all due to RPM, rod length and stroke. It usually does lower the mass of the piston some, that will lower the forces the pin, rod and crank see at the same R and piston g's. (F=ma) Either way it's not going to be a lot and if you really wanted to improve that getting rid of that king kong stock piston pin would help more.
Bret
The flycutting of the pistons can do three bad things....
1. weakens the piston because the design of the piston wasn't made to have valve reliefs cut into them.
2. if the reliefs are not radiused the sharp edges of the cuts can cause knock due to hot spots.
3. the other bad thing about the reliefs is that they cause the compression ratio to drop since they add volume. Now most times you have a milled cylinder head that has a lower volume in the chamber anyways to cause this so when everything is all teamed up the compression ratio will be higher.
Flycutting does not change the piston velocity, that is all due to RPM, rod length and stroke. It usually does lower the mass of the piston some, that will lower the forces the pin, rod and crank see at the same R and piston g's. (F=ma) Either way it's not going to be a lot and if you really wanted to improve that getting rid of that king kong stock piston pin would help more.
Bret
06-19-2006, 01:33 PM
#4
Originally Posted by bowtieman81
Agreed.
One main reason I did not flycut on my car was I was too worried about all the metal shavings. I don't see how you can get all those out.
One main reason I did not flycut on my car was I was too worried about all the metal shavings. I don't see how you can get all those out.
You will likely want to keep your flycut depth between .075 and .100 on a stock piston. For both strength and balance reasons.
