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I have to say this doesn't make much sense to me. For sure Paul's idea about tightening the valve lash will blow down the compression, and yes, that will reduce the chance of pinging. It's just that the cure for the symptom neglects the cause.
Admittedly Volvo used some huge lash specs - and they varied for reasons known only to them from .016- .022 over the years of the B20. Good shop mechanics set lash to whatever - it is no big burden for them to set to .020 or .016. I can't imagine that it had anything to do with expediency. I set them all at .018 for noise, and I find that is the tightest setting that won't disturb idle quality. Some, like the R cam are speced to .016 on the intake, and I set them to that. I set the cylinder two along in the order from the one on overlap.
Tightening the lash will dramatically increase overlap, for sure. It won't do much for lift at all. It may also put the lifter outside the clearance ramp, and for a better discussion of that than I can provide I advise reading John Passini's book on carburetion. Tightening lash won't change the fuel requirements except at idle, and then only because the overlap has changed enough to vary exhaust gas dilution. Above idle, no change.
The original problem, pinging, needs to be addressed as a separate issue. A K cam in a high comp. B20E engine is going to be on the edge, but the K-jet system is still more forgiving than carbs if all is right with it. In Canada all carb B20's were to get premium, and all B20E high comp engines were spec'd regular, right in the owner's manual. Mixture formation is everything I suppose.
Perhaps the primary advance spring is loose. Total advance seems fine, but how you get there is important. If the head has been on the engine for years, and especially if it saw leaded fuel, then perhaps it is hugely carboned up, and that can cause pinging. I just feel that the pinging should be corrected by identifying the problem, rather than adjusting around it.
All of the preceding is my opinion, formed by experience, and offerred in the best tradition of this board.
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