Okay, I just got an 84 trans am and am planning on swapping the LG4 for a 350. It is a 1971 350/300 horse with 10:1 compression and is 4 bolt main with a torquer cam. My question is what to do about the computer controlled carb. Can I just bolt it up like it is and expect decent performance? Do I need a new computer chip, or even a new computer? It seems to me a computer intended to run a 150 horse 305 wouldnt run a 270 horse 350 very well. I cant afford a new carb, and would really like to just bolt it up. What do I need to do to get the 350 to run to potential or for that matter to run at all with the ccc?

 

Try tracing all the wiring in your engine compartment eg:starter,dist.,alternator, oil-temp. sensors should all be coming out of the drivers side and the other wiring: a/c computer stuff
comes out of the passenger side.
Try detaching all the wiring on the pass. side then see what happens.
I've got an 87 Firebird with the lg4 305 and I don't have any problems. Before you do anything get a GM service manual it will help you greatly.

 

Take care as you will soon discover that the oil dip stick is now on the drivers side. You will need to modify your exhaust manifold. I put on headers and a Y pipe from Hedmen. This made the installation much easier and it was a good excuse to get headers.

 

Im finishing up a 2.8 V6 to LG4 swap, and was wondering about the wiring too. Ive got the complete harness and computer for the LG4 but was wondering if I can run the car without the computer. What wires do I need to keep, and what can I get rid of?

 

The computer isn't that smart. It has a default fuel and spark curve for open loop operation when cold, looks for the proper fuel mixture via the O2 sensor when warm, controls the spark advance based on engine speed and load, and controls the EGR and TCC lockup, but that's about it.

The CC carb is an excellent choice for a 350. You didn't say what year your LG4 is, but if '85-later it will also have a knock sensor, nice when you're running that much compression on the street. 150 vs 270 hp is inmaterial to the carb. Adjusting the idle speed and choke, and tuning the secondaries is about all you'll have to do to it.

A different chip will give you a more aggressive spark advance curve, but that's about it. If you don't have a knock sensor, then you might not want that.

A CC carb must have the computer as well as the CC distributor and all of the sensors to work properly. Without, it will be in the full enrichment mode all the time - not a good situation.

 

Ive got the V8 harness in the car right now. I ran it through the fender and have the ECM plugged into it. Under the hood I have it plugged into the relays and whatever else I could mathc the darn plugs too! The engine is going in on Saturday, and I will then plug up the harness to the carb and distributor. Im not gonna use the stock air cleaner with stove pipe and intake hose, Im gonna use the K&N filter and lid. Is the carb and distributor the only things that I need to plug the ECM up to other than the coolant temp plug by the thermostat? What about the oil pressure plug? Where exactally is it? I have no emissions equipment whatsoever, do I have to use an O2 sensor? Will the car run fine without it? Its got Heddman shorty's and I bought the O2 reducers in case I need to use the O2. The seperate harness thats plugged up to my lights and fan acts on its own, seperate from the ECM, is this correct? I left the V6 portion of that harness installed for lights and fan rather than use the V8 one. Let me know!!!

 

The ECM needs the info from the carb & distributor, as well as the manifold absolute pressure sensor, barometric pressure sensor, O2 sensor, coolant temperature sensor (on the thermostat housing) and vehicle speed sensor (on the back of the speedometer). It also expects the solenoid for the EGR to be there, and has connections to the A.I.R. control valve and torque converter clutch.

The electric coolant fan operates independent of the ECM, using a switch in the passenger side head. I used the light harness from the V6, but the fan harness & relay from the V8 (the V6 had a belt-driven fan).