Did you read the Dynamic Compression article I linked in post #18? I need you to understand that subject.
I really appreciate all the info, I've read through it all and I have a good understanding of the difference between SCR and DCR, I need to read up on the effects of different cam specs, as im not familiar with performance correlations with different lifts, durations, ect. I do have one question I know you said keep the DCR at 8.0 or a bit below. What are the effects of lower ratio like 7:1
From the DCR article, "Why it matters: A 355 engine with a 9:1 static CR using a 252 cam (110 LSA, 106 ICL) has an intake closing point of 52º ABDC and produces a running CR (DCR) of 7.93. The same 9:1 355 engine with a 292 cam (having an intake closing point of 72º ABDC) has a DCR of 6.87, over a full ratio lower. It appears that most gas engines make the best power with a DCR between 7.5 and 8.5 on 91 or better octane. The larger cam's DCR falls outside this range. It would have markedly less torque at lower RPM primarily due to low cylinder pressures, and a substantial amount of reversion back into the intake track. Higher RPM power would be down also since the engine would not be able to fully utilize the extra A/F mixture provided by the ramming effect of the late intake closing. To bring the 292 cam's DCR up to the 7.5 to 8.5:1 desirable for a street engine, the static CR needs to be raised to around 10:1 to 11.25:1. Race engines, using high octane race gas, can tolerate higher DCR's with 8.8:1 to 9:1 a good DCR to shoot for. The static CR needed to reach 9:1 DCR, for the 292 cam mentioned above, is around 12:1. This lowering of the compression ratio, due to the late closing of the intake valve, is the primary reason cam manufactures specify a higher static compression ratio for their larger cams: to get the running or dynamic CR into the proper range." Caveats: Running an engine at the upper limit of the DCR range requires that the engine be well built, with the correct quench distance, and kept cool (170º). Hot intake air and hot coolant are an inducement to detonation. If you anticipate hot conditions, pulling some timing out might be needed. A good cooling system is wise. Staying below 8.25 DCR is probably best for trouble free motoring. >>Unless you have actually measured the engine (CCed the chambers and pistons in the bores), these calculations are estimations, at best. Treat them as such. The published volumes for heads and pistons can, and do, vary (crankshafts and rods, too). It is best to err on the low side. When contemplating an engine of around 8.4 DCR or higher, measurments are essential, or you could be building another motor.<< The pistons you have will produce an SCR of 11.1:1. If you run a cam like the TA 290-08H, https://www.taperformance.com/proddetail.asp?prod=TA_290-08H The DCR will be around 8.22. That's below 8.4, but that cam may be more than you want on the street. It needs gears and converter to be all it can be. Not sure what your preferences are for street manners. Also, your quench distance will be .072" because those pistons will be .032" in the hole to begin with. Using the right pistons will allow you to run 0 deck which is better for detonation resistance and efficiency.
Thank you larry I apologize for my ignorance, this is a new world to me and a lot of information at once. I really appreciate the help.
I'm with you and learning a lot from this forum. Lots of experience from these guys! Looking forward to seeing your build come alive.
Read post #4 in this thread, https://v8buick.com/index.php?threads/your-new-diamond-pistons.181425/ It is not uncommon to have to mill .050 off the block to get to 0 deck. The right way is to buy the correct custom pistons. That gets you to zero deck and allows you to tailor your compression ratio with the piston dish/valve relief cc's.
If you opt for Cometic MLS head gaskets they make them in different thicknesses to control compression and quench. .027" all the way to .100" or more. The extra thickness compromises the quench but its not a big deal for your setup. If you get the .051"you'll be dropping static compression about .25. So you will be under 11 to 1.They are about $200 a set but reusable.
With the quench already at .072 if I go thicker and take it to .083, isn't that too large? What is optimal?
optimal is .038 to .050. you're already outside that so a little more wont affect what you currently have very much.
I'm looking into pistons that will give me 0 deck height, I'd love to be able to sell mine. But if I can't at least there are options
If you're going to change pistons to get close to 0 deck, personally I like between .005 to .10", in case a further decking is needed sometime, you'll need probably around a 20 cc dish in the piston to stay under 11 to 1. Calculate it out before ordering pistons. With the strokers we build our pistons are between 20 to 23cc.
