Di Grassi (left) and Senna impressed Honda boss Brawn
Honda will take their time before deciding whether one of Bruno Senna or Lucas Di Grassi will drive for them in Formula One next season.
At the end of three days of winter testing in Barcelona, Honda boss Ross Brawn said: "We will take some time to carefully consider our findings."
Senna completed 107 laps on Wednesday and was faster than Di Grassi, who did 110 laps of the circuit on Tuesday.
"Whether what I did is good enough is for the team to decide," said Senna.
Senna had his first full day in a Formula One car and the nephew of F1 great Ayrton added: "It has been a really good day and I'm very pleased.
"But for me personally, for my first time in a Formula One car, I have to be happy with what I achieved today.
"The Honda team are very professional and I am proud to have spent the time with them during this very special week for me."
Germany's Sebastian Vettel was fastest in Barcelona for the second successive day for Red Bull Racing, the team he has joined from stablemate Toro Rosso, with a best of 1:19.295.
Senna's quickest lap was one minute, 21.676 seconds, while Honda lead driver Jenson Button was fifth fastest of the 12 on the circuit on Wednesday with a best of 1:21.387. Di Grassi's fastest lap on Tuesday was 1:22.283.
Button's contract with Honda expires at the end of the year, though he looks likely to remain, but Senna and Di Grassi are vying for the spot occupied by Rubens Barrichello, who also hopes to stay.
Brawn added that both Senna and fellow Brazilian Di Grassi had been "a pleasure to work with".
"Both drivers spent one and a half days in our car which has enabled the team to assess their performance and level of technical skill.
"Lucas and Bruno have both performed admirably over the course of the week."
Di Grassi took part in the testing for Honda after being overlooked by Renault, who have stuck with drivers Fernando Alonso and Nelson Piquet Jnr for 2009.
The 24-year-old has raced in GP2, which has provided several drivers for F1 since its incarnation in 2005, for the last three seasons, finishing second in 2007 and third this year.
Senna finished runner-up to Italian Giorgio Pantano in the GP2 feeder series.
Honda had a dismal 2008 season, with Button picking up just three points from 18 races.
The testing is to help develop the 2009 car and Button worked through a series of aerodynamic and suspension evaluations.
"It's nice to be back in a car that I enjoy driving," said Button.
"Taking a lot of the downforce off and running on slick tyres suits my driving style a lot more than grooved tyres.
"I've had a fun couple of days and it's been very useful as we have tested many things which should help us with the new car.
"It's been a positive start to 2009 already and I'm very pleased."
F1's rules are changing for the 2009 season, with the sport reverting to slick tyres and adopting heavily revised aerodynamics to try and create more overtaking.
Brawn added that Honda had been running two modified RA108 chassis during the testing and had conducted an intensive programme with the Bridgestone Potenza slick tyres.