The Formula 3 European champion remained with Strakka Racing for day two in Spain, and again topped the times in both the morning and afternoon sessions.
The Italian's best lap on new tyres in the final hour was the fastest time set in a FR3.5 car at the Spanish track, and it put him four tenths of a second clear of Carlos Sainz Jr's best lap for DAMS.
"These two days with Strakka Racing have gone really well," said Marciello, who will switch to Arden Caterham for the third and final day of the test.
"The car was good, easy to drive, we didn't have any problems so it was quite easy to push to the limit and that's what we did with the lap record."
Sainz enjoyed a brief spell on top before Marciello improved for the final time and was a comfortable second by the end of the day, while Formula Renault Eurocup runner-up Oliver Rowland was a frontrunner for the second day running as he took third for Fortec.
2013 FR3.5 racers Jazeman Jaafar and Nikolay Martsenko completed the top five.
Rowland's FR2.0 rival Pierre Gasly was sixth for Arden Caterham having set the pace early on in the afternoon session.
Combined Thursday times: Pos Driver Team Time Gap 1. Raffaele Marciello Strakka 1m38.976s 2. Carlos Sainz Jr DAMS 1m39.428s +0.452s 3. Oliver Rowland Fortec 1m39.719s +0.743s 4. Jazeman Jaafar ISR 1m39.782s +0.806s 5. Nikolay Martsenko Zeta 1m39.794s +0.818s 6. Pierre Gasly Arden Caterham 1m39.888s +0.912s 7. Luca Ghiotto Draco 1m39.938s +0.962s 8. Sergey Sirotkin Fortec 1m39.987s +1.011s 9. Zoel Amberg Arden Caterham 1m40.077s +1.101s 10. Pietro Fantin Draco 1m40.086s +1.110s 11. Will Buller AV 1m40.157s +1.181s 12. Nico Muller SMP/Comtec 1m40.228s +1.252s 13. Matias Laine Strakka 1m40.371s +1.395s 14. Nick Yelloly Carlin 1m40.565s +1.589s 15. Mathieu Vaxiviere Pons 1m40.633s +1.657s 16. Marlon Stockinger Lotus 1m40.711s +1.735s 17. Kimiya Sato Lotus 1m40.741s +1.765s 18. Roman Mavlanov Zeta 1m40.850s +1.874s 19. Alex Lynn DAMS 1m40.859s +1.883s 20. Marco Sorensen Tech 1 1m40.891s +1.915s 21. Dean Stoneman Carlin 1m40.981s +2.005s 22. Andrea Pizzitola AV 1m41.126s +2.150s 23. Riccardo Agostini Pons 1m41.447s +2.471s 24. Jordan Oon Tech 1 1m43.812s +4.836s 25. Liam Venter SMP/Comtec 1m44.495s +5.519s
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