Convert carbed motor to TBI?

[fatbob]

Well the 350TBI motor in my '88 crewcab blew chunks so I'm checking out replacement options. Since the old motor is toast I'll have to spring for a core charge on either a rebuild or a crate motor, which brings the price up to $1300 or $2000. So I'm eyeballing a used carb motor [from a 79 dually] I can get for much cheaper, for the time being. I plan on swapping all the tbi & smog stuff on to this motor.
So my main question for now is;
1.will it run alright with the carbed cam, or will I need to swap in a tbi cam
2 other than the 2 piece flexplate and the fuel pump block off plate, are there any other differences I should be aware of?


P.S. The carbed motor has a manuel on back and my truck has an auto.
Thanks

 

[Thunder]

you can do it two ways:
Bolt the TBI heads and intake to the old block. That way you wont have to do any adapting to get the linkage and TV cable set right. and you will have all the hook ups for vaccum and sensors.

Or you can get an adapter plate for the carb intake manifold. So you can bolt the throttle body to it. You will prolly have to do a little adapting to get the TV cable right and a little plumbing to get the vaccume lines and EGR working right.

Just to be safe I would install a computer frendly cam in the motor.

 

[pauly383]

Bob , I have a flexplate for you for the swap .

 

[JEBSR]

You could also have the center bolt holes of the intake drilled to fit the old style heads.

 

[kgblazerfive]

Or just drill the heads, thats what i did and it works

 

[Russell]

I just did this with my 89 half ton. It blew it's 305 up, and I swapped a 350 from a 73 Nova in to replace it.

I got myself a set of 350 TBI heads, then bolted the TBI intake to it. For the fuel pump, I just pulled the push rod out, so it just acts as a fancy looking delete plate.

You'll also need to replace the oil pressure sensor, and oil pressure switch. I used a set from a 81+ truck, it had a neat little oil pressure T, with the sensor, and switch bolted to it. I found that the older sensor works perfectly with the 89's gauge. Both will need to have their connectors cut off and replaced with the older style oil pressure switch etc.

Another thing you'll need to do, if you use the factory non-efi cam like I did, is replace the ring gear on the bottom of the distributer from one from a big cap HEI. The newer gear will not mesh correctly with the old cam, and will chew the cam up. However, It'd be very easy to swap the old cam from your TBI 350 in, assuming it is in good shape yet, and would also save you any EFI issues you may have due to the non-efi lobe seperation. I have not had any major problems with my non-efi cam, but at the same time, I still have not quite worked out all the bugs from the 305 -> 350 swap as far as electronics go, and an issue may still show up yet.

Other than that, it was just a matter of bolting the serpentine setup on, and plugging in all the sensors.

When you install the engine, don't make the same mistake as me, and ignore a minor exhaust leak on the driver's side manifold, lol -- The 02 sensor is directly below the manifold, and an exhaust leak has a nasty little tendancy to tell the computer that you are running excessively lean, causing the ECM to run nearly full enrichment, causing a lot of fuel blowby into your crankcase, which eats away at old cork gaskets, causing a massive oil leak that'll cause your engine to start knocking, and possibly eat the bearings!

Trust me, I learned that one by experience! I gotta go get some plastigauge tommorow to check on the bearings

 

[dyeager535]

You'll also need to replace the oil pressure sensor, and oil pressure switch. I used a set from a 81+ truck, it had a neat little oil pressure T, with the sensor, and switch bolted to it. I found that the older sensor works perfectly with the 89's gauge. Both will need to have their connectors cut off and replaced with the older style oil pressure switch etc.

If you have to go through this much work, ditch the separate sender/switch and get a combo one. Makes wiring and plumbing that much easier. FYI

 

[Russell]

Didn't know that such a thing existed till now. Only took about 10 minutes to pull at the wrecking yard, and 10 minutes to install and wire up, lol

But yeah, a combo setup would make it far easier!

 

[fatbob]

Thanks for the info guys I was worried about the cam working with the computer, and did not think about it meshing with the dist. Good catch. I'll check out the engine tomorrow and see if it's wore out, or good enough to do all this work to.
And thanks Paul, I might give you a call tomorrow.

 

[TrcksR4ME]

Another thing you'll need to do, if you use the factory non-efi cam like I did, is replace the ring gear on the bottom of the distributer from one from a big cap HEI. The newer gear will not mesh correctly with the old cam, and will chew the cam up.

I am in the process of doing this swap with a BB, this is the first time I heard of this particular issue The efi distributor is already in, and I seem to recall it was a little troublesome to get all the way seated, maybe thats why?

 

[Russell]

Before you start it up, make sure you pull it out and change that!

You can do a lot of damage to your cam with that newer gear in there!

Big cap EFI HEIs are just fine, but the small cap HEI need to be changed out!

Basic rule of thumb, for both small block and big block -- If it had points, or big cap HEI, you are fine with points or big cap HEI, if it had small cap, then you need to use a small cap, or switch over to the older ring gear. Its a very simple process, just stick your dizzy in the vice, take a punch and very carefully tap the roll pin out, then put the new gear over, and tap the roll in back in.