Checking for warpage:

Measure the short way across the head, between the cylinders and at each end. Use a straight edge and feeler gauges. The maximum distortion specified in the Volvo manuals is 0.25mm (0.01").

Measure diag. across the length of the head. From the right rear, to the left front, and vice-a-versa. Measure with straight edge and feeler. Max. distortion here is 0.5mm (0.02").

If the distortion or warp short way across head is 0.5mm (0.02") or more, or diag. long way is 1mm (.04") or more, the head must be replaced, not machined and reused.

I have no idea whether or not Volvo wants to imply that you don't need to machine the head if the warpage is less than or equal to the first two figures given or what. But I prefer a head to be flat, with a capital "F" so . . . if it will meet minimum height spec (see next paragraph) after machining, it gets machined.

Check the height of the head: measure at the front of the head, from the machined part at the bottom of the head, near the thermostat hole, and below it, to the top of the valve cover gasket (machined area). A new, never machined head should be 146.1mm in height (5.7563"), and the minimum **after machining** is 145.6mm (5.7366").

If the head is off of the car already, you have to get it machined anyway, unless a very careful and accurate check shows that it is perfectly flat, and there is no damage to the surface finish. Take it to a good, reliable, reputable machine shop, after you do a rough check on it. Give them the minimum height spec, and ask them to flatten it, but not to take it below min. height. Some mechanics will take these heads considerably below that, but I have found problems with that.

Turbo and non-turbo heads are identical, known as a "530" casting, from the casting number, which I think is 1000530. The only differences are in what is installed in the heads: the "T" cam and sodium filled exhaust valves in the turbo heads (B230FT), vs. a different cam (I think it is the "M", but not sure) and solid exhaust valves in the non-turbo B230F.
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Scott Cook - 1991 745T, 1985 RX-7 GSL-SE, 1986 Toyota Tercel (Don't laugh, it is reliable, faithful AND gets 41 mpg!)