I'm planning on doing an Ls1 and t56 Swap on my 87 GTA. Will I need to swap the Ls1 Radiator and all the cooling system form the Ls1 as well? What do i need to do regarding the Cooling system???

Not needed no. The stock 3rd gen rad is actually bigger than the LS1 rad I believe. Dual electric fans are recommended though.

There isnt anything else that you have a choice on...... The radiator is the only "off engine" part to the cooling system.

You can use an LS1 radiator.
Pros: Hose inlet/outlet positioning works with stock 4th gen hoses...some use a different lower hose. You have a fitting for the steam line so thats a no brainer. You can then use the 4th gen dual electric fans because they'll mount right onto the radiator. You KNOW its adequate for the LS1.

Cons: You'll have to do a little fiddling to make it fit. Not a big deal though. It is a TAD thinner than the 3rd gen. But making a piece to take up the gap isnt difficult. If you dont have one from a donor car, you'll need to purchase one.

Or you can use the 3rd gen rad.
Pros: Fits 100%. You already have one. If you are retaining A/C, your condenser is fine where it is.

Cons: Might have to look into what hoses will work. Have to decide on which method to connect the steam line. Might need to figure out a fan upgrade if you dont have dual fans already.

Cant go wrong either way really. I went with the 4th gen unit due to ease of hook up and because I could mount the 4th gen fans as well as the 4th gen a/c condensor right to it...making those installs easier. Also I had one sitting right there from my donor car.

J.

I went with the complete ls1 setup in my car, rad, fans, and condensor. fits pretty nice, not much to making it fit.

I'll send you a pm with some more info.

Stock third gen rad here and stock third gen single fan. Never rises above thermostat temps this thing runs coooooooool so no worries regarding the dual fan IMO its nice but not nec

I ran the LT1 radiator/fan setup with the a/c condensor with my LT1 swap. Fans plugged right into the stock LT1 location and the PCM controls them just like it as in a 4th gen, no problems at all. Matter of fact, I have never had the second fan ever kick in on the LT1.

I went with a 3rd gen one.

The LS1 radiator is a tad less wide that the stock 3rd gen rad. it leaves a gap of abt 1/2 inch on either side. That concerned me because air has a place to flow around the radiator.

(I still have to figure out how to run the steam pipe and attach the LS1 fan setup)

the 2nd fan in a dual fan setup i think is for the ac system. it only kicks on when the ac comprossor clutch is running (in stock application). so if u dont have ac it wont work.

I am keeping the LS1 ac so , it will run when I turn the ac on.

If I was not going to put ac , I would run a 2nd temp sensor somwhere with higher temp (say ON-240/OFF-200 )and so the 2nd fan will turn on if u ever hit that temp for some reason. (drag racing at 3 in the afternoon at 105 deg track temo )