This scenario isn't really how you worded your first question, hence the "garage" solutions.
For what you want, you'll need to install a system that constantly circulates the air over a period of hours, filtering the air for dust, pollen, etc. and possibly charcoal to remove odors. Heating, cooling, and dehumidifying it to what ever you want. Basically a commercial air exchanger. If the space you are referring to is small enough you could, possibly, get by with a high output capacity furnace A/C with added filters and leave the fan on constantly.

my wife loves the smell of racing gas exhaust. :) No reason to get rid of it

I didn't read this whole thread. My house is less than 10 years old and we moved in 5 years ago. It has a double car garage which does not have an entrance to the house from the garage. 2 walls and the ceiling are part of the house. I don't normally let my cars idle in the garage for more than a minute. I don't leave any liquid containers open for very long. My house never smells of gas or exhaust fumes. What does smell is my clothes when I am working on a car. If I don't put on fresh pants and a shirt within say 3 days my bedroom will smell like a shop. I usually put a fresh shirt on each day but sometimes I will wear the same pants for a week. I do put clean clothes on later in the day when I have finished working in the garage.

The strongest smells I find are cleaning solvents and spray paint. Lacquer thinner, grease & wax remover, used oil and spray primer are the worst. Rags that have any of those liquids on them are stored in a sealed plastic bag and then thrown out. I don't normally spill anything on myself. It seems that these smells just get into the air and then into my clothes. They are more noticeable in the winter when the large door is closed compared to the summer when the door is open and I have 2 large fans blowing from the back towards the front. It may also help if you rig up some kind of sensor to turn those fans on for say 2 minutes when you enter and leave with a car.

Crushed rose petals soaked in lavender poured down the carb will sweeten the exhaust fumes. ;) Don't tell my wife that I buy roses for the car and not her. lol.

If I were you, I would drain all the fuel tanks and add CamII 120 Octane to all the cars. Start them for 5 minutes and shut them off. Let that magnificent scent linger for days. I even ran it in my riding lawnmower and weedwacker.

I don't know if all racing fuels have an odor. I ran C16 in all my turbo cars and it has no odor.
I also ran unleaded race fuel on the street. It smells like weed killer. DO NOT SNORT THIS STUFF.

Race fuel smells great to me. That’s not the smell I’m encountering. I wish I could pinpoint it, but it’s more like old exhaust fumes and old stale gas, which doesn’t make sense to linger so long. I just hoped some of the hardcore collectors could chime in and tell me what kind of filtration systems they were using because my mini split isn’t bringing in fresh air and I’m going to eventually look to build a nice garage to fully enjoy my collection.

That Smell 🤧
 

Here’s what I did and it works perfectly ….. for me.

When I had my small back yard garage built for my two Survivor GTO’s, I designed the back wall to have 4 exhaust fans installed.

Since I back my cars in I purposely located the 2 pair of fans directly in line with the 2 cars tailpipes.
These fans are quiet, powerful and efficiently pull the air from the pipes and entire garage with the front garage door open.
The fans have automatic shutters to keep the critters out, plus I installed the galvanized hoods on the outside to protect from the rain.

Open the front garage door.
Flip the single wall switch for all 4 fans.
Start the cars, let them run and you won’t smell like a 60’s muscle car exhaust when you go into the house later.

Thank you. Very good idea! I don't think I can incorporate that into my garage based on how its set up, but I like the idea. My garage shares common walls with the house on the garage back wall and 1 side. Also have a second story bedroom above the garage. So that only leaves one side wall to add ventilation. Ventilation or air circulation appears to be the answer thou so I'm going to look into my options. Or maybe just live with it until I can find a permanant solution for storing the cars as again its already packed full and its more of a storage locker at this point then somewhere I can enjoy the cars. This hobby has been something I wanted to do for years so when I finally got into it its become an obsession and I ran out of room fast. Thanks for potential solutions so far guys, keep them coming.

..move. :)