If all you want is a good pump and bloodflow then what you need to look into are vasodilators.
Penis Enlargement pills contain all kinds of crap in addition to vasodilators to supposedly "stimulate" testosterone production and enhance libido.
The most common OTC vasodilator is NO2 or specifically Arginine. Arginine is converted by the body into Nitrous Oxide (NO2). The most effective form of Arginine is Arginine Alpha Ketogluterate (AAKG). I have tried AAKG and love it. I'm currently testing out a relatively new Arginine molecule called DiArginine Malate.
Yohimbe is also a mild vasodilator as is Niacin and Tetrahydrocannabinol (THC), the major active chem in Marijuana. Smoke pot to get a boner... a win/win situation.