For modern day petrol, except 1275cc.
We have found nearly all vac units are not to be the originals, but with the change of added oxygenates to petrol in the 1980's and then ethanol in 2003 all previous economy and timing figure applications became incorrect. Nearly every after market vac unit checked appear to be similar to 37H8225 / 37H8226 without any distinguishing marks for identification.
We have a range of distributors to work with correct simplified vac units as ethanol leans off petrol making engines run weak.
The new vac units are designed for our distributors they are not worse than anything else being sold on the market to match old distributors as well.
Very few 850 / 998cc owners get their ignition and vac poundage checked out so many people are not aware of the power or economy loss.
For 850 / 998 / 1098cc, we use 37H8414MS for 45D and 59D.
For 1275cc, we use 37H8379MS for 45D and 59D.