If you go to any F1 news website you'll see a story about the engine homologation rules and how the teams that have a currently homologated engine will be able to now develop during 2015 rather than freeze their engine spec before the season starts. However there seems to be a few conflicting reports of how much of a big thing this really is, so I just wanted to take a moment to look at this sensibly.
Firstly it's important to understand that the new complex power units that arrived in 2014 had to be homologated (read frozen) for the whole of the season to prevent costly engine development spending. The manufacturers would then be allowed to update their engines during the off-season. However to keep a lid on costs the manufacturers could only make so many updates, and each year this amount of updates will decrease.
The entire power unit design was split into 66 'tokens', representing parts and allocated according to their influence on performance. Manufacturers could change a maximum of 32 tokens for 2015, 26 for 2016 and so on, on a sliding scale to almost nothing in 2019 and 2020.
In 2014 as the manufacturers all have brand new engines, it was important that date was set in the regulations by which all had to present and freeze their engine specification. This then is fair for all. Sadly the FIA forgot to add a date in the regulations for the homologation of the 2015 power units which has now meant that the FIA has had to concede and allow the engine manufacturers as long as they like to set their engine specifications for the season. Whilst those who struggled in 2014 will be happy that this buys them more time to get the upgrades right it does mean that if they don't wish to homologate their new power unit they will have to start with a 2014 unit and then switch once homologation to the new unit has been made. As all teams must race with homologated engines.
So potentially those that don't homologate their 2015 engines pre-season will be hampering their teams with the same engine they had the previous year whilst others run away with upgraded ones. Stories about teams being able to apply upgrades throughout the season really are just rubbish, that is not how this will have to work otherwise teams could face protests and disqualification if they are running a non-homologated power unit.
Honda of course will have to homologate their power unit pre-season as they don't have a 2014 homologated unit to fall back on, so if they want to race at all....
So where does this leave F1 in 2015? What if Renault (for example) decides that they don't wish to homologate their power unit until the Spanish GP, They then have to make their teams run with a 2014 unit that point, in a car that has probably been built around the new power unit, thereby losing ground in the first four grand prix to everyone with an optimised 2015 package. So what then if in the first four GP's you need to take a replacement power unit due to a fault / failure / accident? That will still come out of your allocation of four units for 2015. So if Renault then homologate a new power unit, you'll be forced into another change and be on your third power unit in the fifth grand prix! That's not a great situation to be in is it?
Having longer to homologate your power unit doesn't feel like such a blessing after all...