Hastings Ring Gap?
i, of course found out the hard way.
Hyup; as did I. I fought what I thought was an overheating issue, for months. Finally I took the engine out and apart and opened up that top gap; and presto! the engine got a whole new personality.
To the OP:
Here's a tip for you;
The ring gap changes by .0031416 inch per .0010 bore change.
You can use this tidbit of information to measure all your bores, using the same ring, to find the hole-size variation. Mark the holes from smallest to largest. Then, in the smallest hole fit each top ring to find the tightest or loosest rings by the size of the gaps. Then match-fit each ring to each hole, so that your ring-gaps are all the same and you don't have one or two cylinders with tighter gaps.
This is especially useful if you are file-fitting your rings.
By starting in the smallest cylinder, if you file too big a gap, just move the ring to a bigger hole.
What? you think 20-over means something?
Well, around here it doesn't seem to. My 40-over holes varied enough to, by using the same ring, the gaps varied over .003 inch. After I had a different machine-shop straighten and equalize the bores, what was originally supposed to be a 4.040 bore, they ended up mostly at 4.045.... and my KB107s were did nuts all the same to about 4 decimal places. For my street application, KB listed the skirt clearance at .0015 to .0020;
Yeah so the pistons ended up being a lil baggy, which really disappointed me. As it turns out tho, after some experimentation with the minimum running temperature (I ended up at 207*F in compensation), that is just what this combo needed; she turned into a wicked sweet engine.
OP I wish you all the best.
Now; as to your 9.4 Scr; you said;
Basically it's just going to be a mild street/strip motor, I don't want to baby the thing, but it's only getting 9.4:1 compression and is essentially destined for a lot of street driving.
I googled Skaget and get elevations ranging from zero to 5740 ft. but typically 3400ft.
If this is correct;
then you are gonna have to be careful with cam selection, so as to get an altitude-compatible cylinder pressure, at 9.4Scr.
That is to say, the stock 318 cam has an Ica of about 50*, and is predicted to make around 152psi@3400ft which is great. But; If you take that car down to sealevel, the pressure is predicted to rise to over 170, but at 5700ft is just 140. That 170psi in an open chamber iron head design, is usually iffy to operate even with 91 octane gas.
The smallest performance cam that you might consider is likely to be around 262 advertised, which you might install at an Ica of say 59*. This is predicted to drop your pressure to 140psi@3400, 158psi@sealevel, but just 128@5700
So keep those things in mind. Or maybe you already have......... IDK.
You can mitigate some of that gross pressure difference by
1) not taking the car too far from it's home base, or
2) using a solid-lifter cam-design with fast ramps. Also,
3) alloy heads will like more pressure.
