i think you'll find that you are both wrong on this.
There is no plural of Volvo as it is a brand. Therefore you would have to insert an objective complement. An objective complement is a noun that aids the description of another noun to make sense. So if you say "volvo" on its own, it only really means a brand or company name. it does not actually mean car. To signify this you would add the word "car" which would then itself becomes pluralised to form "Volvo cars".
I hope this makes sense dumb asses!
Also never heared of BSR, to be honest i would stay with experts on your car, not another brand