Both McLaren drivers will run upgraded Honda engines this weekend in Belgium.
In a bold move, the Japanese manufacturer has used seven of its remaining tokens in an effort to further close the gap to the main midfield runners.
Both Fernando Alonso and Jenson Button will run all-new units this weekend featuring the upgrades to the combustion chamber, turbocharger and compressor. It is also understood ExxonMobil has brought a new fuel to Spa compliment the upgrade.
The upgrade follows the previous update at Silverstone, and is once again aimed at improving the efficiency of the engine as opposed to increasing out-and-out grunt.
Neither driver will incur a penalty this weekend as a change of unit is within their allowed allocation, however the move sees the Spaniard reach his limit on all six components while his teammate also reaches his limit on all but the Energy Store and Control Electronics.
While the new units will be run on Friday, the team has yet to decide whether they will be retained for the remainder of the weekend or saved for Monza.
The Woking team is currently three points behind sixth-placed Toro Rosso.
Check out our Thursday gallery from Spa, here.