head cc

[badsix]

I need so input here. I had my heads fly cut just to clean up were the cylinders fit, he said he took .005 off. anyway i'm rechecking the volumes and come up with this
no. 1 head
58cc
57.3
no. 2 head
57
57.2
I checked the depth with a depth mic and they are all the same or within .001. with the cylinders set in the head they fit perfect with a straight edge across the end that go's in the block. so how do I make all the volums the same? i'm thinking I need to make them all 58cc
thanks Jay D.

[Jack Staggs]

Ok, I'll bite again, even though my previous suggestions may not have been well received. First of all, depth measurements mean nothing. A variation of even .100" there could be fine. All we want there is for the step of the barrel to clear the fin on the head by a small amount, (even .006") so the very top of the barrel fits squarely in the spigot of the head without interference to the head. In certian competitions, where compression ratios can not be exceeded, much more needs to be considered in regards to head cc 's. Changes can include the following. If the cases were retrieved to standard, or align bore done, the bore could be slightly offset beyond spec. Decking of the cyl base could be needed to achieve perfect uniformity. Conrods could differ in length. Crankshafts can have strokes that are not exactly equal. Piston domes/wrist pin locations/valve pockets as well. Add it all up, and differences can easily exceed 1cc in the combustion chamber. Of course, Porsche (as well as most manufacturers) allowed some deviation from blueprint. They were pretty close, but not perfect, at least for production. How many times have you performed a compression test on an engine, with exact matching numbers? As a side note, a friend of mine that builds VW engines for Baja type racing was close to being DQ 'd for to high compression on a single cylinder. He removed the carbon build-up, proving to the judges compliance, and received the 1st place trophy. Bottom line, I don't sweat 1cc.

[badsix]

THANKS Jack, and I mean that. I've had some problems putting this engine together and I still have some things to work out so stay tuned.
thanks Jay D.