Formula for CC displacement

Doug Domm · 01-18-2009, 07:31 PM

I'm looking for a formula to measure CC displacement. I need to replace valve seats as some of my valves are sunk more than I would like them to be. These heads have seen a number of valve jobs over the years and I have no record of chamber volumes before and after each valve job. They are sbc 291 castings with 1.94 and 1.50 valves. My chambers are average 3 cc's larger than they should be. How many cc are gained for any given amount that I raise the valve. I realize that any formula used would only give a theoretical volume and I still need to measure but I would like some idea how much I can gain raising the valve. And yes I realize raising the valve should open up the runner volume as well but I do have lots of room there. Also on a chamber volume how much margin are most leaving for tech? Thanks for any help. Doug

Rich Biebel · 01-18-2009, 08:22 PM

I CC'ed many heads in my engine shop days. I had no formula but obviously the bigger the head diameter of the valve the more you will change the CC's by moving the valve up or down in the chamber. It took a considerable amount of grinding of a 1.94 valve to change the CC's much. It was a slow process of grind and recheck. It was common to make heads 1.0 CC over the minimum. I did them down to .5 if requested. That was back in the days of using a hand ginder to do seats. The seat heights would not have been all the same unless it was a real virgin pair of heads and installing seats was not the norm either. Todays Serdi type machines would make the equalized seat heights easy to do.....If your heads were 3 CCs over......you can mill them .010" and should still be about 1 cc over......the factor for milling those heads is between .005" and .006" per/CC I don't recall the exact figure. We had a file for all the common heads.

Chad E532 · 01-18-2009, 09:14 PM

Would it work to take the area of the valve face (in square centimeters) and then multiply it by the height change of the valve in cm to get a close approximation of the cc change in the chamber?
You would have to assume that the valve face is flat and that it basically creates a 3D cylinder of volume as you move the seat.

Travis Miller · 01-18-2009, 09:25 PM

Doug, The formula for figuring CC's can be found in the 2009 NHRA rulebook on page 288.
Hope this helps.

bore x bore x 12.87 x depth

Travis

Doug Domm · 01-18-2009, 10:26 PM

Thank you very much. That is exactly what I was looking for. Doug

01-18-2009, 07:31 PM	#1
Doug Domm Member Join Date: Apr 2006 Location: canada Posts: 251 Likes: 28 Liked 84 Times in 21 Posts	Formula for CC displacement I'm looking for a formula to measure CC displacement. I need to replace valve seats as some of my valves are sunk more than I would like them to be. These heads have seen a number of valve jobs over the years and I have no record of chamber volumes before and after each valve job. They are sbc 291 castings with 1.94 and 1.50 valves. My chambers are average 3 cc's larger than they should be. How many cc are gained for any given amount that I raise the valve. I realize that any formula used would only give a theoretical volume and I still need to measure but I would like some idea how much I can gain raising the valve. And yes I realize raising the valve should open up the runner volume as well but I do have lots of room there. Also on a chamber volume how much margin are most leaving for tech? Thanks for any help. Doug

01-18-2009, 08:22 PM	#2
Rich Biebel VIP Member Join Date: Jun 2007 Location: Northern New Jersey suburbs Posts: 2,314 Likes: 25 Liked 544 Times in 213 Posts	Re: Formula for CC displacement I CC'ed many heads in my engine shop days. I had no formula but obviously the bigger the head diameter of the valve the more you will change the CC's by moving the valve up or down in the chamber. It took a considerable amount of grinding of a 1.94 valve to change the CC's much. It was a slow process of grind and recheck. It was common to make heads 1.0 CC over the minimum. I did them down to .5 if requested. That was back in the days of using a hand ginder to do seats. The seat heights would not have been all the same unless it was a real virgin pair of heads and installing seats was not the norm either. Todays Serdi type machines would make the equalized seat heights easy to do.....If your heads were 3 CCs over......you can mill them .010" and should still be about 1 cc over......the factor for milling those heads is between .005" and .006" per/CC I don't recall the exact figure. We had a file for all the common heads. __________________ Rich Biebel S/C 1479 Stock 147R Last edited by Rich Biebel; 01-18-2009 at 09:08 PM.

01-18-2009, 09:14 PM	#3
Chad E532 Member Join Date: Jul 2008 Location: Lindstrom MN Posts: 156 Likes: 7 Liked 54 Times in 7 Posts	Re: Formula for CC displacement Would it work to take the area of the valve face (in square centimeters) and then multiply it by the height change of the valve in cm to get a close approximation of the cc change in the chamber? You would have to assume that the valve face is flat and that it basically creates a 3D cylinder of volume as you move the seat.

01-18-2009, 09:25 PM	#4
Travis Miller Member Join Date: Jun 2007 Posts: 478 Likes: 1 Liked 276 Times in 27 Posts	Re: Formula for CC displacement Doug, The formula for figuring CC's can be found in the 2009 NHRA rulebook on page 288. Hope this helps. bore x bore x 12.87 x depth Travis

01-18-2009, 10:26 PM	#5
Doug Domm Member Join Date: Apr 2006 Location: canada Posts: 251 Likes: 28 Liked 84 Times in 21 Posts	Re: Formula for CC displacement Thank you very much. That is exactly what I was looking for. Doug

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