I've been searching this and other sites all morning, looking for an answer to this question:

How much can I mill a P75 (B20/B18b) head going onto a B20b block (stock) with an OEM headgasket, and maintain P2V clearance for use with Crower 403 cams?

-I realize this is not the proper way to gain compression, but I have a spare head and they are cheap anyways, I don't want to build the bottom end at this time
-I realize I will need adj. cam gears to compensate for the milling of the head
-I realize that claying the engine is the proper way to do this, but I don't currently have the cams, I may never get the cams, I just want to plan for these cams

Any other considerations that I may not have thought of are welcome as well, but I'm really looking for some numbers or a method of doing this mathematically. I'm looking to have the head milled as much as .050 which would bring compression to the 9.8-10:1 range from the stock 8.8:1.

try this link http://www.honda-tech.com/showthread.ph ... ad+milling
i wouldn't mill the head unless i had to if u do use a 3 layer head gasket if you don't mill the head use a 2 layer gasket and u should be fine but that is my 2 cents

There's some good info in there, but they are searching for compression ratio not piston to valve clearance. I'd actually come across that thread when I was searching earlier.

Can I clay the engine stock, and calculate with accuracy the clearance after milling and with the larger cams, or is there some reason I'm not thinking of that it wouldn't work, to many unknowns, etc?

Do you have a factory service manual for a CRV?

I'm sure I can find the PDF for it. It wouldn't have piston to valve specs though would it?

Not sure if you've stumbled upon this or not..

http://www.c-speedracing.com/howto/claymotor/clay.php

you can always clay the motor.

I've found that how to and browsed through it, but I don't have the 403 cams yet, I actually may never get the 403's, but I'm planning for the future, so I can't clay it in the condition that I am asking about.

Am I able to calculate from claying the stock engine and using the published cam specs accurately enough to ensure that I won't have issues down the road if I DO get those cams?

I'm getting the impression that you really need to have all the pieces of the puzzle and see if they fit together to figure this out. I realize this is not a conventional recipe for these engines, but I was hoping there was more info available, or some experience I could draw from. Thanks for all the replies so far!

Update:
-Honda recommends tossing the head out after .045 has been milled off the head, this = service life
-from this I would assume that you will be fine running a head milled .045 with stock cams, and no adj. cam gears with no P2V concerns
-if you plan on running big cams, I'd clay the motor and use adj. cam gears
-this will raise compression on a B20b from 8.8:1 up to 9.7:1, almost a full point!