It seems to me
that if you get the Q into the ballpark with off-the-shelf-pistons and
closed chamber heads, the rest you can do by manipulating the ICA. I'd rather spend my money on heads than a few thou of compression distance.
The target for Q is about .028 to .050. With .028 gaskets, the acceptable deck clearance thus, is zero to .022 in the holes. The tight-Q will allow the running of about 5 psi higher than not having any Q at all..... which allows one of; a little shorter Ica, or the running of one grade lower fuel,or operating at ~1000ft lower if the need arises, while staying out of detonation, or even just running a hotter minimum coolant temperature.
Quench, actually, in this case a misnomer for Squish, is a very useful thing to have, simply because it allows a great deal of flexibility to maximize performance on a small engine. Combined with alloy heads, a great deal of pressure can be run.
Pressure is NOT Static compression ratio. Pressure is what Scr and Ica combine to make. Pressure is the thing to keep your eye on. At WOT, excessive pressure leads to heat,which leads to detonation, which leads to broken parts and destroyed engines.
But when NOT at WOT, the high pressure makes for a stout bottom end, and leads to the potential of making great fuel economy. A high pressure engine makes for fun Part Throttle operation.
If it weren't so, then there would have never been developed a small displacement VVT engine. The 2.5 DI-VVT in my alloy 2014 Orlando pumps 220 psi, and is advertised to make 167hp at 6700IIRC. That's a lot of pressure and a lot of power in a pretty small package. And at 3600 pounds it never feels under-powered.The VVT doesn't kick in until 4500, and I rarely feel the need to go that high. When I do, it is usually just for kicks,lol.
If I had to build a 318, that is what I would do; namely get the Q into line and pump up the pressure, even if it meant sacrificing power at 5500, where I never go; cuz with 3.23s, 5500 is; 119 mph in direct, 82 in Second, and 49 in First; with an 85" roll-out. So since in Manitoba where I live, the speed limit is typically 100kph/62mph, 5500 means nothing to me.
From empiracle data posted here on FABO, and by personal experimentation, I have found the following to be true;
1) Pressure with closed chamber alloy heads, can approach;
190psi with 91Gas; 185 with 89 gas; 180 with 87 gas. A tight Q can easily push this 5 psi higher to as much as 10 psi higher. Some guys here claim 200psi with full timing.
2) With open chamber IRON heads you gotta drop at least 25 psi. And tightening up the Q is good for 5 more psi, but I won't say 10psi.
@yellow rose might tho, cuz he is sure that he can run 170/175 with iron, but is a little tight-lipped about it..... and who can blame him, that is quite an edge on most of us..
So, if you have to run open chamber iron heads and want to run 87 gas, you better stick to not more than 155psi until YR (or somebody in-the-know) spills the beans.
But,
I will tell you a secret. You can build a 165psi closed chamber iron headed beast, and run 87 in it for like maybe 90% of the time. But at WOT, and full timing, she better have 91 or better in the carb. I'll leave you to figure out how to make that possible. But, IMO, that would be the best of all worlds. I'm leaning towards a dual inlet spreadbore carb, and a dash-mounted dial-back timing-retard ignition box .......lol.
It's just too bad nobody makes a 5-bbl carb. Or a 3bbl would be OK too. Or a cheap 6-pack. Or plain old meth injection.....
