Recognise members making good contributions with titles that reflect that contribution.
If a member is answering most questions about car engines, give him a role of car engine chief, or expert and allow him to add (CEC) next to his member name.
You can also invite him to take responsibility for answering questions about the topic, moderating discussions about the topic and even drafting advice columns. He is also well positioned to interview experts (manufacturers, top modders and representing your community on the topic elsewhere.
If he ever leaves the community, you can start a search for a replacement to take the role. You turn a contribution one member was making into a meaningful role that members want to have.
There are no shortage of titles you can use, chiefs, champions, ambassadors to recognise individual effort in a personal manner. Be creative and go beyond admins, volunteers or moderators.