Heidfeld's 'engine situation'
Nick Heidfeld has claimed he is losing ground on the straights compared with his team mate Kamui Kobayashi.
They drive identical Sauber cars, but the speed traps usually show Japanese Kobayashi with better speed in a straight line.
Heidfeld, 33, joined the Swiss team after serving test-driving roles with Mercedes and Pirelli earlier in 2010 and is looking for a full-time job for 2011.
So far in his three races alongside rookie Kobayashi the German has been out-qualified twice and has yet to finish a race ahead of the Japanese.
Heidfeld said on his website nickheidfeld.com that his speed deficit compared with Kobayashi was "due to his engine situation".
He took over ousted predecessor Pedro de la Rosa's allocation of eight engines for 2010 after the Spaniard had several problems with his Ferrari units.
"The remaining engines have to cover a lot of extra miles," Heidfeld said. "This unfortunately leads to an engine power loss due to having 'older' engines, which is the reason for losing out on acceleration and top speed"