Chevrolet Repair: engine swap, o2 sensors, coolant temp

Question
I have an '84 K20 3/4 ton 4 speed with a carburated 350. I would like to get the power and milage EFI can afford me and I'm thinking that a newer 350 would help do the trick. An aftermarket EFI seems far too expensive with all those later model 350's just lieing around. Are there any gotcha's I need to worry about?

Answer
Hi Earl,

1984 was the era of very little computer control.  Mainly looking at Manifold Vacuum and coolant temp.  

In the later years, these motors went from basic and fairly easy to computers that control based on speed, temperature of environment, to pressure in gas tank, to distributorless ign, to crank and cam sensors that must agree, to if the a/c is on or off, and more.  Very complex.  All of these variables control fuel delivery.  Dodge Ram of now with Hemi actually turns off 4 cylinders while on the highway.  This makes it a '4 banger' at crusing speed.  That doesn't save much on gas.  

I have heard of a good brand carburator that is not a monster, tuned in correctly on an older motor that gets equivilent mileage as fuel injection.  

O2 sensors regulate the fuel on today's motors and they gunk up and give false readings.  You won't notice this quick, since it takes time to happen.  CAT is required on post 1996 and a O2 before and after the CAT must agree.  

Installing the motor is going to fit, but the wiring, computers (more than one), transmission may need to match.  Computer may not be set for your truck with your trans, rear axle and 4 speed.  May not run right.  These projects usually turn into Frankensteins.  

It is a lot of work and the likelihood for success is at best 50%.  I would just buy a newer truck, or stay with the old one and get a great tune up and carburator.  

I have a 1994 Yukon with 5.7L automatic 4x4.  I get about 12 mpg on a good day.  When I pull trailers, it is no better than 8mpg.  I see new Ford's claiming 14City and 17 HWY.  

You could try smaller tires, keep the air full in them.  Try a better breather (K&M maybe).  Get a good Holly carb.  Make sure timing is right.  Make sure the brakes are not dragging.  Make sure the exhaust is breathing,  maybe get some headers.  Use dual exhaust.  Make sure cooling fan is not dragging.  Take off unnecessary pulleys (air pump, etc.).  Loose the CAT.  These things may help some.

C J S