Just swapped a performance radiator brand heater core into my LJ and wanted to provide some info.
I first (ignorantly) bought a spectra brand heater core on Amazon because I was already doing the AC evaporator, so figured if I was doing one of them, I should do both. In hindsight, I probably should've tried to keep the Mopar core somehow.
Either way, I put the spectra heater core in and instantly noticed my heat not getting anywhere near as hot. So, I replaced the water pump, thermostat, and factory radiator. Again limited heat. I left the radiator cap off, hoping air was just in the system. After getting fed up, and reading the above threads, I ordered the performance radiator heater core. When it came, it was in a box branded as a generic Chinese brand - so I was under the impression it was identical to the Spectra brand core I took out. I was very hesitant to go through the all the work of replacing the core if it was in fact the same thing.
I did further research and discovered that some brands of heater cores weigh 1.8 pounds (crown and OCS) and other brands weigh 1.4 pounds (Spectra, omix-ada, and my current Performance Radiator brand). It is my assumption that the 1.8 models have the metal turbulators, while the 1.4 models have plastic turbulators.
Regardless, given that colder weather will soon be upon us in Ohio, and given the absence of other in stock brands, I decided to bite the bullet today and swap my Spectra Heater Core for the Performance Radiator Heater Core. After having replaced the core initially a few months ago, the process went much faster (but was still a pain the ass). Lo and behold, my heater is back to burning my feet. So I'm not sure if perhaps Performance Radiator is just buying a higher grade heater core from the Chinese factories, if the Spectra core was just broken, or something else, but despite appearing identical and weighing the same, the Performance Radiator core is a night and day difference..so if you find yourself in a similar situation, here's one vote for biting the bullet.