custom pistons: valve pocket depth

[ChargerST]

I need to order custom pistons and need to provide the depth for the valve pockets. I know this is not a straight forward calculations as P/V clearance is not measured at TDC and full lift. My idea was to provide a general depth figure which would be on the safe side to allow a cam change later. I think that 440 source pistons for example allow cams up to .680" lift.
Which is a somehow valve pocket depth figure?
btw I use Trick Flow 240 heads - is the valve to deck distance the same as on production heads (e.g. 906s)?

 

[Lefty71]

Ross does .200 on the exhaust. .220 on the intake. Any closer of an answer would make my brain bleed lol. It takes a lot of calculations to hit this right on, and how close do you really need to be, depends on whether you are building the most thought out, on the edge racecar, or just a hot street cruiser!? If i were you, I'd look at everyones on the shelf pistons and see what they specify the best lift, compression, etc. that they offer, and start jotting that info down for comparison to what you want to build. What is your build info and why do you need custom pistons? If possible, you may want to buy the most closely on-the-shelf spec'ed piston, and mock it up with that to get your exact answer. BTW, there are probably people here with that math "in their heads" and may be able to supply a more detailed answer. Documentation for the TF 240's does say longer pushrods may be requiered, so they seem to be saying, you'll need to measure everything, although the port locations are stock. HTH, Lefty71

 

[Challenger340]

You need to know the duration @ .050,(seat to seat is nice as well), and the Tappet Lift TDC on overlap with the Cam Intake Centerline installed at a set point ie: 106* or 110* ATDC etc.
The above should allow any Piston Manufacturer to provide Valve Pockets sufficient for what you doing.
Also,
the TF240's use a 2.19" Intake and smaller 1.76" Exhaust but BOTH still on the same stock V/Guide location.... so IMO make sure they have that information as well to enlarge the Intake relief accordingly as best practice when getting into the bigger shafts.

 

[ChargerST]

Great info, thanks! But how to get the lift at TDC without measuring it? Most cam manufacturers don't really publish any lift points other than base, @.050?

 

[451Mopar]

Sounds like you already know that peak lift doesn't matter in P-V Clearance, it is Duration, and installed centerline, and also Lobe separation.
I did not measure the depth of the 440 source (KB ICON pistons), but though about having the valve pockets cut deeper, until I measured the thickness of the piston where the valve reliefs are, I think it was already only about 0.100" thick, so I just used a slightly smaller duration (274 @ 0.050") cam.

A guesstimate for the cam lift at TDC may be to estimate the lobe ramp speed from 0.050" to 0.200" (how many 0.0xx" rise of the lobe per degree), using the difference in duration to estimate the lobe lift at TDC for whatever the installed cam position is?