What would "normal" psi per cylinder be for this high mileage engine? The problem: Around town at regular speed all is fine. It runs great w/no apparent oil burn. However, if I drive the car at or over 60-70mph (3500rpm) for around 10 minutes when I decelerate AND/OR take off after a stop I often get a slightly detectable "machine-gun rattle" followed by a blanket of exhaust smoke so thick cars behind me disappear. Once I'm back to speed everything is fine again... til next repeat. It never smokes - nor smells -- while cruising.
Friends have told me it's everything from "piston slap" to a faulty (Midas) muffler that's backing up. I thought a compression check would be good for starters but I need some good, sane, advice on how to pursue. Thanks, Ray.

 

piston slap is usually most noticeable on cold start up and a medium[ 3000rpm] revving of the engine. Does the PVC valve still have the plunger and spring in it?
Check the bottom of the air filter area for oil/blowby
A compression test will tell you the pistons are going up and down, but will not show if the oil wiper rings are collapsed. I've seen several of those engines, that had bad vacum advance diaphrams that allowed the engine to run out of time[pinging/machine gun rattle??] far enough to crack the piston lands between the rings, but as long as the compression rings are contacting the cylinder walls, the compression will read okay. Because I don't know the mileage of the engine I'd just throw out a guess that the compression will be around 115-120 psi.
unplug the injectors before running compression check so you don't 'wash' the pistons with gas.