Flycutting Pistons

TruckYou

TruckYou

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Originally intended in running a 188/220, but plans evoloved and now putting the 207/220 in the engine on my stand. Hamilton just says .100 flycuts, but doesn't say "if piston protrusion=X and valve face depth=X

Stock sized valves in the head (1.77 and 1.65)
.020 piston protrusion
.025 valve face depth
.020 head gasket will be used
Cam- Hamiltons 207/220( .360/.360)
Hamilton recommends a .100 flycuts

How much larger than the valve are flycuts typically cut?

.100 deep enough? Little extra for insurance?
 

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You can't have .020 protrusion and .020 HG Thickness. I never let piston get closer than .030 to the head. And never let valve get closer than .050 to piston on high rev motors. Also can't determine relief depth without knowing cam lift at TDC on both intake and exhaust. Also we assume factory rocker ratio?
 
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Assuming this is a 12v engine? If so, piston protrusion sounds right, usually .0195". A standard thickness gasket can be used with that. If you were to cut .006" off of the deck, increasing the protrusion, you'll want at least .010" over gasket. However, that spec is tailored to a stock engine. An aftermarket cam most of the time throws all of that out the window.

Valve face depth (recession) sounds a little low to me though unless this head has had some custom work done to it. A stock 12v head will have a minimum valve recession of about .035", if I recall correctly.

Most fly cuts I've read about usually end up around .250" but as mentioned above, many other bits of info are needed first in order to determine the depth of the reliefs.

If you've run all of this info by the guys at Hamilton, they should be able to give good recommendations specific to your application.
 
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jimbo486 said:
Assuming this is a 12v engine? If so, piston protrusion sounds right, usually .0195". A standard thickness gasket can be used with that. If you were to cut .006" off of the deck, increasing the protrusion, you'll want at least .010" over gasket. However, that spec is tailored to a stock engine. An aftermarket cam most of the time throws all of that out the window.

Valve face depth (recession) sounds a little low to me though unless this head has had some custom work done to it. A stock 12v head will have a minimum valve recession of about .035", if I recall correctly.

Most fly cuts I've read about usually end up around .250" but as mentioned above, many other bits of info are needed first in order to determine the depth of the reliefs.

If you've run all of this info by the guys at Hamilton, they should be able to give good recommendations specific to your application.
Click to expand...

Thanks for the information. In fact, i stated the incorrect Valve face depth. When I had the valve job done, I had then cut from .025 to .055, which at the time was planning on using the 188/220, which was the reason for the .055 vfd. And yes, this is a 12v p7100 build

188/220 is a great cam, I'm not knocking the longevity of the equipment, Iv run this cam shaft in my other truck, but this engines going in a truck I'll be using for drag racing, running higher rpm and large compound s400s , and was looking for a cam shaft for that rpm range. The .020+ HG has been the plan just to lower compression a smig due to the large turbos, and my cylinder heads fire ring grooves are cut to the .020" HG ring depth requirements currently... cut/drilled/tapped intake, and drilled for 14mm studs, p&p...

Now that I think about it, I could set the head on the block, slide the cam in and take a measurement with the depth gauge, I just figured the comp section would be a good place to ask. All my machine work was done to meet the criteria of Hamilton's "drop in" 188/220 (no more than .025 PP and at least .055 vfd) so it seems my measurements are fairly standard,
 
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I’m running a 188/220 and if I remember correctly with .030 flycuts I was .070-.085” clearance with std gasket, .025 pp and .045-.055 vfd. Zach told me I wouldn’t need fly cuts but I ordered pistons with them anyway to be sure.
 
You should check for your self but i think .050"-.060" on exhaust and .100" on intake should give you plenty of room. Also I think the 207/220 will work well for you just check for coil bind that cam gives some serious lift.
 
188/220 made more peak power below 4000 rpm on the dyno , but if you desire power above 4K then 207 might be better
 
I have no back to back dyno info I have just seen that 207 work well for a few friends maybe the 188 is better id like to hear if any one else has done dyno testing and would be willing to share what they learned. Thanks for sharing Rich most people won't give up dyno results and its expensive to do so most don't.
 
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