cobraguy":19d50uwk said:
I ysed a 10ml syringe and got 47ml/cc for the chamber and 7ml/cc for the dish in the stock piston. Deck height .145 Head gasket .045. Bore 3.700 at .020 over and 3.910 stroke equals 8.87:1 if all I do is bore .020 over and new pistons are just .020 bigger. Decking .020 gets me to 9.2:1 as long as new pistons....... So it looks like I get my rebuild kit first and measure the dish and piston height and recalculate. Thanks for the help In the past I've always just threw the parts together and hoped for the best. This time I feel like I will know exactly what I want the machine shop to do. I would like to get the CR close to the upper limit for 87 octane. Where would that be?
The quick and safe way is to just put a desmal point in the middle so 87 Fuel = an 8.7 C.R. the upper limit though all depends on your tuning skills 9.2 to maybe as much as 9.5. But because of the 250's excessive deck height, you will need everything to be just right to push it to the high end of the limit including getting the distributor's (you need to at least use a DS II) advance curve set up correctly there are a couple of site members that are good with that if you need help. If your on a real tight budget and your stock cam is still in good useable condition then you could advance it to 4 degrees. That would help low end power some at the slight expense of some lost top end but with your light weight car it could work out very good, this is what I will be doing on my 250. On your engine kit if you could get them to customize it by including 255 V8 pistons in place of the 250 stock type that would help get the compression up without the need to deck the block beyond a light cleanup cut if it even needs to be trued. Other items I ask or look for in Master Kits are Felpro gaskets, Clevite bearings, Melling oil pump, and Molly Rings. One other way to get the pistons up higher in the bore is to use the 300 rods with a set of custom pistons if your budget allows. Your are getting lots of good suggestions from everyone for your build. Good luck