I think everyone on BITOG has at some stage seen the Calcium & Magnesium numbers on a VOA.
I've been doing a bit of Google-fu & come up with a little rule of thumb to translate VOA metals into TBN which someone might find useful.
If you see 1000 ppm of Calcium in an oil, it will be roughly equivalent to putting 2.6 TBN into the oil. This will be true regardless of whether the over based Calcium detergent is based on Sulphonate, Phenate or Salicylate chemistry. This rule holds because regardless of what chemistry you employ, you will essentially have the same Calcium Carbonate (and to a lesser extent, Calcium Hydroxide) in colloidal suspension.
If you see 1000 ppm of Magnesium in an oil, it's roughly equivalent to putting 4.2 TBN into the oil. Likewise this applies to most chemistries. Please note that for the same amount of metal, you get more TBN bang for the buck from Mg.
If you take something like Amazon's Basic 5W20 which (according to PQIA) contains 1,927 ppm of Ca & 18 ppm of Mg, you can simply estimate their respective TBN contributions as 5.01 & negligible. The oil has a measured TBN of 6.68 so you know 1.67 TBN is coming from non-detergent sources such as ashless dispersant, diphenylamine AO or whatever.
Do bear in mind that bum results happen all the time so if things don't stack up, don't blame me!
I've been doing a bit of Google-fu & come up with a little rule of thumb to translate VOA metals into TBN which someone might find useful.
If you see 1000 ppm of Calcium in an oil, it will be roughly equivalent to putting 2.6 TBN into the oil. This will be true regardless of whether the over based Calcium detergent is based on Sulphonate, Phenate or Salicylate chemistry. This rule holds because regardless of what chemistry you employ, you will essentially have the same Calcium Carbonate (and to a lesser extent, Calcium Hydroxide) in colloidal suspension.
If you see 1000 ppm of Magnesium in an oil, it's roughly equivalent to putting 4.2 TBN into the oil. Likewise this applies to most chemistries. Please note that for the same amount of metal, you get more TBN bang for the buck from Mg.
If you take something like Amazon's Basic 5W20 which (according to PQIA) contains 1,927 ppm of Ca & 18 ppm of Mg, you can simply estimate their respective TBN contributions as 5.01 & negligible. The oil has a measured TBN of 6.68 so you know 1.67 TBN is coming from non-detergent sources such as ashless dispersant, diphenylamine AO or whatever.
Do bear in mind that bum results happen all the time so if things don't stack up, don't blame me!