Hi guys when a cams is rated lets say 9.0 to 9.5 am I right to assume this is calculated on corrected compression?  Also when a set of heads is CNC ported will that change the compression in the motor, if you know what the cc's are.  I have a set of heads that are 84 cc's if I have them ported will the related compression change? and will it be much if it does?

Cam makers usually suggest a calculated compression ratio to aim for. Any work on the head chambers, (sink valves, polish chambers etc) will alter the compression ratio. If you need to reduce chambers after head work, from memory every 0.007" off the deck surface = 1cc reduction. I do have a compression ratio calculator in xls format, but I don't know how to add it to this post. It was down loaded off this site some years ago, if your will to look for it.

Thanks guys, I have been checking out the big boyz site, and I have put in all the values using 3.885 4.6cc Wiseco forged pistons, Andrews 37g cams and 84 cc heads which should give me a static compression of around 10.1 - 1 and a corrected compression of  about 9.36 - 1, the corrected is in the optimum range for the cams but not sure how that is affected by the static compression, that's what's got me unsure. The heads are flowed already.  Any extra advice would help me, as I am not far off getting this done. Similarly if you think this mix may not be quite right could you give me some advice around that, I went with the 4.6cc, because I didn't want to raise the compression too much, but wanted a little more than flat tops.  Hope this makes sense

Here's a more indepth calculator that I downloaded off this forum some time ago. Click on the link & download it as an exel file.

docs.google.com/spreadsheet/ccc

Thanks mate