Help, I have a 85 iroc with the 305 and its tired and i was thinking of swaping out the 305 for an lt1 for the extra hp but i have no idea what the difference is between the two other then the displacement? and what would it take to go with the six speed?

 

Either the PCM and wire harness must be changed to the LT1 parts, or the LT1 intake must be modified to accept a distributor. Since you would presumably be using the LT1 block, the cooling system would be less of a hassle than the typical modification of LT1 intakes for older engines/vehicles. You would only need to provide an expansion tank and the necessary hose connections from the engine.

The LT1 will likely also have an engine oil cooler which must be either adandoned or plumbed.

Frankly, since the 1985 ECM is so slow and limited compared to even later TPI versions, I'd tend to opt for retrofitting the car with the LT1 PCM and wire harness, then reflash the PCM for whatever changes and transmission you have installed.

All the mechanical parts will bolt up to your ezxisting engine mounts and transmission, provided the flywheel is designed for use with the LT1.