I was thinking about 10W20's in the bath. This is what I came up with...
You start off with Chevron 220R Group II base oil. According to what I see on Google, this stuff has the following properties...
KV100 6.6 cst
KV40 43.7 cst
CCS-25 5600 cP
VI 105
Noack 10%
So straight away I see a base oil which almost meets the basic KV100 (>6.9) and CCS-25 (2.6 HTHS though).
At 10%, the Noack isn't especially low but when you consider that Chevron 100R, the next lightest base oil, has a Noack of 26%, then 220R looks a very good starting point to build a 10W20. Also note you have 1400 cP worth of CCS 'headroom' to play with.
Okay so as a very minimum you will need to add about 0.9% of ZDDP to the oil to give you 800 ppm of Phos (for wear control). You also need to add 2% of 400 TBN Mg Sulphonate to put 8 TBN into the oil (for rust & acid control). I would also put say 0.1% of PPD in the oil (for MRV control) as this 10W oil will be borderline in winter.
Now the thing about ZDDP, detergent and PPD, is that whilst they're all thicker than 220R, and will push up the oil's KV100 & CCS-25, the effect will be modest with say the KV100 hitting 7.0 cst and the CCS-25 say 6100 cP.
The oil will clearly need some VII polymer. A typical high SSI OCP might have a Thickening Power of 10 (1% of neat rubber gives a 10 cst uplift in KV100). We might need an uplift of 1.5 cst (from 7.0 to 8.5 cst) so we might need 0.15% of solid rubber (or 2% of liquid VII). I'm guessing this might get you to 2.6 HTHS.
I'm not sure where everything would end up property-wise but I suspect with a bit of playing about, maybe with a splosh of Chevron 110RLV Group II+ and 600R Group II you could keep the oil's Noack the right side of 10%.
The one thing that this oil DOESN'T contain yet is any Ashless Dispersant (a typical US oil might contain 5-6%). The reason why I hesitate to add it is for say a 5k OCI, I'm not overly convinced it does anything. If the oil doesn't massively oxidise, then you don't dump sludge and if you aren't reaching that point, then why put ashless in the oil in the first place? On the other hand, if you do add ashless, as well as adding cost, Noack takes a huge jump upwards which is the one thing you're wanting to avoid in a 10W20.
Okay, so in short you have a 10W20 with (possibly) a Noack of 10%, a 2.6 HTHS, a combined DI/Liquid VII/PPD treat of 5% (vs say 17% for a GF-5 5W30), it's based on cheap Group II/II+ and it's probably good for 5k miles of everyday driving. It wouldn't be everyone's cup of tea but it does have a certain appeal...
PS - this is for gasoline engines only. Diesels dance to a different tune entirely.
