PLT OF AN SMA SEL ON IFR FLT HAS CLOSE ENCOUNTER WITH AN AT-6 DOING AEROBATICS AFTER EXITING SOME CLOUDS.

Narrative

AFTER DEPARTING FROM PONTIAC ARPT (PTK) ON AN IFR FLT TO KA20 VIA LAN; I ENTERED A CLOUD AT MY CRUISING ALT OF 4000 FT. UPON EXITING THE CLOUD I CAME INTO AN OPEN AREA WHERE A SINGLE ENG WARBIRD; APPEARED TO BE AN AT-6; WAS DOING AEROBATICS. THE PLT WAS DOING LOOPS; VERT CLBS ALONG WITH INVERTED FLT. EVASIVE ACTION WAS TAKEN BY ME TO AVOID THE AT-6 BY DOING SEVERAL TURNS AND CHANGES IN ALT. DTW APCH WAS INFORMED WHY I WAS DOING THIS AND THE CTLR RESPONDED WITH; DEV AS NECESSARY AND RESUME COURSE TO LAN VOR. WHEN THE ACFT WAS NO LONGER IN THE AREA I CONTINUED TO LAN. THIS ACFT APPARENTLY DID NOT HAVE MODE C OR JUST HAD IT TURNED OFF BECAUSE THE TFC (AT-6) WAS NOT CALLED OUT TO ME NOR DID THE CTLR SEEM TOO CONCERNED WITH THE EVENT OR TO MY FLT. I THEN CONTINUED TO LAN WHEN I CALLED THE CTLR TO SEE WHEN I WOULD BE HANDED OVER TO LAN APCH BECAUSE I WAS GETTING CLOSE. HE RESPONDED WITH 'WHAT IS YOUR LOCATION?' I WAS 12 MI TO THE E OF LAN VOR WHEN HE TOLD ME TO CONTACT LAN APCH. THE CTLR AT DTW MENTIONED THAT HE JUST GOT ON DUTY. I THINK PLTS DOING AEROBATICS SHOULD GET A BLOCK OF AIRSPACE ASSIGNED TO THEM OR AT LEAST DO CLRING TURNS BEFORE EVERY MANEUVER. AS WITH THE CTLR THEY SHOULD BE BRIEFED AS TO WHAT IS GOING OR OBSERVE THE SECTOR BEFORE GOING ON DUTY FOR THAT SECTOR.