Q: what engines are compatible with a 86 firebird trans am

You are constrained by what the original engine was because the original engine is matched to your vehicle’s onboard OBD-I computer and vehicle wiring harness. Also, the present suspension in the vehicle (if it is all original) was matched to the original engine/transmission weight. Basically, if you look at the eighth digit of your vehicle’s VIN number if that digit is "2" you should install the 2.5L engine; if the eighth digit is "S", you should install the 2.8L engine; if it is "H" OR "G" you should install the 5.0: carbureted engine but you will have to determine the VIN of the donor car to see if the donor engine was an "H" or "G") and; finally, if your VIN is "F", you should install the fuel injected 5.0L engine.

If you are looking for an engine (and transmission as well) for your 1986 Firebird, simply go to Car-Part.com and you will find an exact match for your car (there are many listed and lots of buying options). If you are interested in an engine replacement (OEM to OEM), YourMechanic professionals in certain locales can assist with that. Please simply inquire based on your locale. If you have further questions or concerns, do not hesitate to re-contact YourMechanic.