440 low cranking pressure on one cylinder

hi guys
i have a 440 that i am bulding up the top end for more power. i dicided before pulling the heads t0 do a compression test. i have 170 psi in all cylinders except #3. that one only has 140. i put a tablespoon of gear oil in and still had the same reading. i then pulled the valve cover and loosend the rockers. i put shop air to all the clyinders and there is a lot of air sound in the crankcase from any cylinder. i just want to be shure the rings are good before putting the big power#'s to it. its currently mostly stock engine. plese help me figure out the condition of this thing. was rebult 40,000 miles ago and beat on alot and has had very frequent oil chages
thanks nick

GET some engine fogging oil ... then do the test.

If it does the same thing .. sounds like to me you have some leaky valves.

W the eng in the car I'd pull the pan/heads/intake and ridge ream/rering it w a ~$150 moly ring/bearing kit & do your intended head upgrade and read "breakin secrets" at www.mototuneusa.com (a 5 minute read)or easier/quicker just swap the heads & go & be up & running in no time

so whats the best way to figure out if it needs rings. ill try the foging oil tommoro

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so whats the best way to figure out if it needs rings.

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compression test (which you've done) leakdown test, oil consumption and general performance/power. A good rering & it'll last a long time and you'll gain alot of addt'l sealing but as you know it'll take more down time as opposed to a head swap but me I'd do it as it's cheap and you're already opening it up then your set and wont have to go inside it again for a long time. Due to bore taper/out of round/piston land/groove/skirt wear it wont be perfect but it'll be damn good. EDIT your #'s are very good/EVEN & I'd say one cyls valves are leaking slightly skewing the readings so with a bit of thought I'd swap the heads and go