While I agree with Brownbrown that refilling a KR808D-1 carto with VG based liquid will increase the vapor production... I've never been able to get them to perform as well as the 510 (or especially a mod). And it's not for lack of trying!
If using VG won't get you where you need to go, then the KR may not be the model for you.
If using VG won't get you where you need to go, then the KR may not be the model for you.