OK. You WERE talking about something I knew nothing about. And once again, the information available on it is very cryptic bordering on non-existent.
So I gather that you're supposed to use just gathered materials to get a guardian modification put on the FSD itself, not the booster. The question then becomes: do you put that modification on an already fully engineered grade 5 FSD, or do you get a stock, unmodified FSD and then put the guardian modification on it?
There are YouTube videos that go into this if you have a search, although quality varies and many presenters rush things and assume prior knowledge newer players may not have.
To be clearer than I/we have been so far, the
Engineered FSD V1 is not any kind of booster or Guardian technology, it is a 5A Frameshift Drive that already has grade 5 increased range and grade 5 increased boot speed at the same time engineered into it. This is why it is sometimes referred to as "Double Engineered". It's also referred to as "pre-engineered" even inside the game. You purchase it using the following materials, not credits:
18 Datamined Wake Exceptions
26 Tellurium
26 Electrochemical Arrays
28 Chemical Processors
If you use Inara to keep track of "blueprints" you want to engineer, there is a Tech Broker section that lets you add this Engineered FSD V1 "Tech Broker Unlock" so that you can see what materials you are missing:
So I would need 24 more electrochemical arrays, 10 chemical processors and 6 Datamined Wake Exceptions to unlock another one. I unlocked my 6th one of these earlier in the week.
The Human Technology Broker is one of the Contacts in a station that has one. As always, Inara can help you find the nearest by searching for Station Services - Technology broker.
https://inara.cz/elite/nearest/
This will list all technology brokers near you, including Guardian Technology Brokers. Look for "Human Technology Broker" and fly to that station. Once docked, go into Contacts, select the Human Technology Broker and you will see a list of items they can "sell" you for materials. If an item is shown in red, it means you don't have the materials required to purchase it. You should see Engineered FSD V1 listed and be able to choose it if you have the materials. Once you have done that you will find it in Stored Modules in this station. You replace your current FSD with this new "Pre-Engineered" 5A FSD. This is only useful for ships that use a size 5 FSD - DBX, Asp X, Phantom, Krait, Python, Orca etc.
You can then fly to Felicity Farseer, go into engineering workshop, click on FSD drive, on the left side of the engineering screen click on one of the rows of ticked icons under Increased Range, the experimental effects button will enable, you can click on it and purchase Mass Manager (so long as you have the materials). It would be easier if I could share a screen shot here, but I'm 1100ly away from Felicity right now.
Note that you are prevented from making any engineering modifications to this "Pre-Engineered" FSD other than adding or changing the experimental effect.
None of this is connected with Guardian FSD boosters. You can add one Guardian FSD Booster to your ship in an internal slot just as before.
I use the following when I want to find materials for ship engineering:
Source: https://youtu.be/iHl-SsKQfe4
If you decide to make the trek out to HIP 36601 and Outotz LS-K D8-3 to collect raw materials, I recommend doing it in Horizons so that you can find the crystal shards "Biological Signals" more easily. Finding these sites is harder in Odyssey, but there are lat long coordinates somewhere for good locations to go to.
As you know by now, Elite Dangerous is complex, and so is trying to explain parts of it. Most people will keep posts relatively short and rely on people searching for more detailed information themselves based on terms like Engineered FSD V1.
The following video is in Horizons and done by one of the better YouTubers. It might help you visualise where you need to go (skip the first 40 seconds of promotional material).
Source: https://youtu.be/FTTrGLElIYY?t=41