I am considering making the change. Can I make the change without burning a new chip? Would I have to get a 165 ECM that came out of a 305? If it came out of a 350 would kind of problems would I have? I know the injector size is different. What else?

 

at a bare minimum you have to match the injectors to the calibration. even then id make sure to get a 305 memcal

 

I have been considering changing to 22# injectors so that wouldn't be a problem. I think 22# is what is on the 350 for 86-89. correct? Where would I get the memcal for an 85 305? The 870 doesn't have a memcal I don't believe.

 

The injectors would still be a problem, but not a big one.

The memcal they are talking about is also called the Calpack, it contains the memcal (calibration for your vehicle) and the Prom chip all on one unit that plugs into the ECM.
Check the classifides on this site for anyone selling a 165 ECM with calpack, Check E bay too. If you are going to be keeping the 305 set up for a while then get one for a 305, pre 1989 so you don't have to deal with VATS.

I just did this swap a year ago, so if you have any ?? feel free to ask away.

 

Why?

 

The chips are entirely different from the 6870 to 165. Your 6870 uses a 2732, and the 165s use a 27128.

Your chip fits in a Nugget Robinson type holder and the 165 uses a memcal which is completely different.

A 1227165 is a 1227165, the prom data in the PROM part of the memcal defines the application.

If you get a 165 from a 350 then just reburning the prom with the appropriate 305 entries gets you going.

 

Because even though you put 22/lb injectors in your car and are running a 350 prom, the prom code is for a larger displacement engine.