contrails are caused by water vapour condensing in the lift vortex.
you could increase the moisture in the atmosphere (race on rainy days) or have a really big sprinkler/mister set-up; or you could add a smoke generator (like aerobatic planes do).
Possible, though I don't see it being allowed in any sort of race circumstance.
Drivers are taxed enough that I don't think they would appreciate having the guy in front of them churning out vapor that would either impair visibility or make track conditions worse. Just something to consider.
If you mean a vortex not a contrail, then very possible and useful. Look into vortex generators and such.
