> Date: Wed, 05 Apr 2006 23:55:18 -0700 > From: [EMAIL PROTECTED] > Subject: Re: Pistons, CR's and overbores > > > I've found a guy with a set of .040 overbore 350 pistons > (used w/5k miles) with a 10cc dish for $65. > > What happened to the engine? Catastrophic failure? Are the > pistons okay for sure? Before you put them in, go over them > with a fine tooth comb! Especially the ring lands need to be > in spec, or you'll be rebuilding again soon. > > >If, in the future, I need another overbore, how much farther > >can you go before you have to scrap the block? > > You can go 60, generally. You still do not have to scrap the > block if you want to pay for sleeving. I would doubt that you > are that interested in keeping the original block in an 86 supreme > though. > > >Will the 9.1:1 CR netted by the 10cc pistons affect the > >workings of the Computer Carb on my '86 Supreme? > > No. We are not talking sophisticated computer systems here. > > >And...Is it worth $65 for an additional 9hp? I suppose it > >might be worth it for the happiness of knowing I have a TRUE > >9.1:1 CR engine... > > The only way to know what you have truly is to CC your heads and your > chambers at TDC (with your new pistons installed). Likely you > will find that your true compression will be even lower. I.e. my #7 > heads on the 71 Cutlass I used to own had 64 cc after I had several > tens of thousands (I think 30 ?) taken off the heads. And your head > gasket from felpro will be thicker than the stock one too. What I am > saying is that you should go ahead and not worry about going to high > in compression, as it will likely be under 9 after you are done. Some > stock engines of that era would have less than 8:1, if you'd measure. > The head cc numbers on the FAQ are very optimistic. > > I think I shall get an 80s Cutlass, sounds like fun! > > George
I agree with George that you will not have 9.1:1 compression ratio with those pistons. Remember that the heads are in the 68-70 cc range, the block deck is .020"-.030" too tall due to machining tolerances, and aftermarket cast pistons are .015"-.030" short on compression height. My calculations show that you are likely to get about 8.5:1 with that setup and have around .080" quench. If you insist on using aftermarket cast pistons then either get flat tops (there is so much extra unswept volume in your combustion area due to large tolerances that adding to it with a dished piston is just silly) or be sure to deck the block and mill the heads. I think it's just a lot easier to use the pistons with the correct dimensions. Kenneth 1971 Cutlass Supreme convertible Phoenix, AZ
