In my experience, and also that of every opiate/opioid user I know, smoked diacetylmorphine(heroin) beats the hell out of orally administered oxycodone. In fact, smoking heroin is better than ANY type of orally ingested opiate/opioid. The reason for this is the rapidity of onset of effects, which is usually only a couple of seconds. This method of administration allows large amounts of the drug to enter the system in a shorter period of time. Orally ingesting a drug means that the drug must first be disolved in the stomach before it can slowly begin to enter the bloodstream and eventually end up in the brain. Smoking heroin produces a faster and much more intense high than oral oxycodone. However, as the first reply states, the effects of orally ingested opiates last much longer than any other method of administration.
Now, your question about a conversion ratio: comparing oxycodone to heroin "pound for pound" so to speak would be next to impossible because the actual diacetylmorphine content of heroin (and 6-monoacetylmorphine, in the case of black tar heroin) is never consistent. Unless, of course, you're talking about pharmaceutical-grade diacetylmorphine. So, even if you were to determine the actual opiate content of your heroin, you would never be able have an accurate ratio because of the inconsitensy of street heroin.
Of course this is not possible with all oxycodone pills, but have you tried to smoke or insufflate your oxycodone? Or do you just prefer to eat them? Nothing at all wrong with the latter, everybody is different. I hope I was able to offer some sort of help.
A.P.