Instead of wasting that production, you choose one of these instead: money, babies, approval, or war. Wiser folks here can tell you what the conversion cost is, I do not know that.
From the PlanetaryProjectDefs.xml file the relevant values:
<InternalName>ProjectEconomicStimulus</InternalName>
<ManufacturingPerBonus>4</ManufacturingPerBonus>
<EffectType>ColonyGrossIncome</EffectType>
<BonusType>Flat</BonusType>
<Value>1</Value>
<InternalName>ProjectResearchProject</InternalName>
<ManufacturingPerBonus>4</ManufacturingPerBonus>
<EffectType>Research</EffectType>
<BonusType>Flat</BonusType>
<Value>1</Value>
<InternalName>ProjectCulturalFestival</InternalName>
<ManufacturingPerBonus>10</ManufacturingPerBonus>
<EffectType>Approval</EffectType>
<BonusType>Multiplier</BonusType>
<Value>0.10</Value>
<InternalName>ProjectBirthingSubsidies</InternalName>
<ManufacturingPerBonus>10</ManufacturingPerBonus>
<EffectType>Growth</EffectType>
<BonusType>Multiplier</BonusType>
<Value>0.25</Value>
This means:
Economics: Social Manufacturing Points are divided by 4 and then are should be converted 1:1 to raw gold, but i see a different ratio in the game.
Research: Social Manufacturing Points are divided by 4 and then are should be converted 1:1 to raw research, but i see only about 1:4 in the game.
Cultural: If Social Manufacturing Points are divided by 10 and then > 0 then your cultural point generation is increased by that times 10%.
Birthing: If Social Manufacturing Points are divided by 10 and then > 0 then your growth rate is increased by that times 25%.
I think they nerfed Cultural and Birthing to limit a number of strategies which used these to great effect. I myself have shown both the effective use of both in various threads, among others: Game allows forced overpopulation, [Functional request] Proportional population growth instead of constant growth, [Bug?][.41] Never-ending Birthing Subsidies
