Jarrid,
No, it's a virgin head. Here's how I estimated at first. I used two methods. In first estimate, looking at the Vizard Excel sheet I have, printed full size using the valve centerlines as a guide. You can estimate or appproximate that the added area (just the area, at the surface) is equal to adding 0.4 in dia or 0.2 in rad to about 37% of the "large circle" that represents the chamber area around the Intake valve. That calculates out to about 3.4 Sq cm area. I also took a cc scale and divided the added area into ten 1 cm long segments, measured each segment width, and totalled up all the pieces. It showed abot 3.5 sq cm area. So i am pretty confident that the area of the Vizard- at the surface- is about 3.5 sq cm. Now the total depth of the chamber - to the casting, not the valve, is a mean depth of about 0.5 in. And less deep on the side where the largest mods are made. IF the mods were then cut with straight vertical walls down from the indications noted above, the volume would be the area (3.5 Sq cm) times the depth (0.5 in or 1.3 cm). That would make 4.5 cc volume. BUT the Vizard drawings I have show the side wall mods all tapering linearly as they move into the casting. This would yield a volume exactly half as much as if you made the mods to the walls straight sided. So that makes it about 2.2 C. And if you take into account that the larger mods, in the edge opposite the plug holes, are the shallower part of the Combustion Chamber, it seems that 2.1 or 2.0 is more likely.
And when I actually made these mods I was careful to maintain as close as possible to a smooth, linear, not curved, taper. I actually achieved about a 1.8 cc increase. I could take some more material out and still maintain the right shape. I'll do that on final pass after I get the #4 chamber welded and fixed from the ring damage.
I assume a Holbay head has similar mods but I thought I saw that the mods had steeper sides to them, rather than the linear taper sides of the Vizard.
One more thing. In looking at the Vizard drawings I have it shows the changes at the surface and then two cross sections showing the taper. Actually only one of the cross sections show the depths of the mods, the other cross section shows the unchanged exhaust valve area. BUT, in looking closely at the cross section with the mod depth, it seems to show the larger changes are on the deeper side of the chamber. But this is wrong. The big changes are on the shallow side .
Thanks for all the thoughts.
Tom