It's a homemade smoke
Built with elements aeronautical, copy of fuel tanks, AN fittings, aluminum tubes, flop tube from Van's...
The tank did fiberglass of 9 gallons with a breakwater and valve (as the tank)
The liquid is mineral oil.
The pump is a Holley competition fuel pump.
The smoke you see between the two exhaust pipes is generated in that area (turbulence) again get oil smoke. It also does something weird with the oil vent oil system for inverted flight
The picture was taken on Sunday at the airshow of 25 de Mayo, Buenos Aires, Argentina, by Gabriel Luque expert photographer, I encourage you to view your photos on page http://www.airliners.net/