Engine swap questions

Hey guys, I tried to post this a few days ago but it did something crazy, so here it goes again.

We, me and my Stepdad, are building an engine for his 1992 C1500 W/T that has 510,000 miles on the body and transmission (5spd). It was originally a V-6 powered truck but it has a 5.7 in it now. The first V-6 was replaced by V-6 #2 at about 225,000 (give or take a few thousand). Then V-6 #2 was replaced with a "pig in the poke" 350 at about 460,000. The 350 used more oil than gasoline on the trips between Alabama and Texas. So we pulled it out and did a very quick refresh job on an older model 350 we had in the shop. You know what I mean, slap some bearing and rings in it and go. That motor has about 50,000 miles on it now.

The reason we are pulling the current 350 is because the block busted at the out side starter bolt. The new motor was supposed to be a slow build but we have had to step up the pace. My question is this; Will a 350 run with the 4.3L computer??? Because this truck will and does it pretty good. Also he can't remember whether or not he change the throttle body when he put the first 350 in. The first 350 "pig in a poke" was transplanted by him and a friend in Texas, I was not involved. Any way I think it runs because it is a pretty low tech system recieving basic info from the few sensors it has and comparing that to the data with the set parameters.

Any way back to the build. We have a the "pig in a poke" a 92 model 350 2 bolt main block at the machine shop getting worked over. The machinist said it will clean up at .040". The crank was in good shape with the mains polishing to .001" and the rod staying standard. We are using a set of GM powdered metal rods out of a Vortec that was run under water, popped the heads. We are using a set of 191 heads off an '87 350 I got from a local repair shop owner for $100. The heads were on top of a good 4 bolt main block but the crank and rods were trash. The heads are athe machine shop now and if they are not cracked they will be getting a bath and a new valve job.

Every thing will be stock except for a few beefed up items and a set of Flat-top hyperutectic coated pistons. we upgrades to a double roller timing set and moly coated rings. Also, we are using ARP bolts in the bottom end and new GM bolts for the heads. The cam is OEM style stick, if you call that a cam!

My main concern is the computer and TBI giving us trouble so any help there would be great. Also will the boost in compression be a problem? I think the head are swirl ports with 65.3cc chambers at least that is what GM says on their replcement engines for this truck. He will not racing or any thing but may pull a loaded trailer on occassion. I just want some feed back and suggestions.
thanks alot

Well I'm not sure but I think you answered your own question. If you have a 350 in it now then logically it will run with the new 350 right. Most of the time you need to change the ecm out of another rig on these swaps and they will work.

Well I'm not sure but I think you answered your own question. If you have a 350 in it now then logically it will run with the new 350 right. Most of the time you need to change the ecm out of another rig on these swaps and they will work.


I know it works , but the underlying question is this.... is it working correctly or is it just getting by?
Also how do you tell the differnce between a 4.3L TB and a 5.7L TB??

also got the engine and heads back from the machine shop friday. $570.00!!! But he did a good job. The 191 heads are heavy duty with hardened valve seat inserts and sodium filled exhaust valves with the large valve stem. Also he said they were around 67cc chambers. He had to resize a few rods and I failed to take my ARP rod bolts with the rest of the parts so now I cant use the bolts. Other than that I am satisfied.

I hope to have it in a running by saturday. Maybe I can post a picture of it later. Thanks

Guys this engine swap is getting kind of aggrevating. By the time I get through with this engine, the engine in my 1998 GMC Jimmy (224,000 miles) will need rebuilding from all the trips into town for those "unexpected items".

Tuesday it was bolts, yesterday it was pulleys and a seal for the tranny, today I have got to pick up the new knock sensor, a throttle body gasket ( kit does not come with one ), and some fan bolts.

I wish some one would publish a list of every part you need to rebuild these things but then the list would be as heavy as the engine.

Good news is we think we can have it in and running by this afternoon, hopefully.

Does anyone know if the radiator out of a 89-95 c/k with the 454 will work with a 350 shroud? Reason I asked is we are going to replace the radiator and shroud and are looking at options. I figured the 454 radiator would have to cool a 350 pretty good. If it will not work we can just get a stock radiator.

Well we started it up yesterday and my heart fell to the floor. It ran like a piece of Sh*t. I checked the timing, the plug wires and tightened the TB again. I mean this thing would not even idle. The engine would rev good but when it was idling you could litterally see the fuel spraying... no, pouring out of the injectors. I came in and started searching the forums, and they were a big help. Many of them said check the ECT sensor, but this motor has a new one so I kept looking for possible problems. I finally called another set of eyes to come look at it. Turn out to be the MAP sensor vacum line. I thought it was plugged into the map sensor but it was wedged between the port and mounting bracket. We connected the vacum line started the motor up and BAM! runs like a brand new motor.

We set the timing with the ECU advance disconnected and locked down the distributor. It still has a little bump-bump when it idles and smells a little rich. I think it is because it does not have a CAT and it has the wrong ECU and TB. I have not got to drive it yet because during our install the clutch slave cylinder and the fork did not get lined up properly. So we have to take the slave cylinder back out and line it up. Also the radiator now has a crack around the water neck. But it revs good untill about 4000-4500 rpm wich is about the limit on the stock heads and cam. it holds 50+ psi oil pressure idling with a stock pump, and runs about 170-180 degrees with a 180 degreee themostat and a Flexalite fan.

I would still like some info on the ECU and throttle bodies and what really needs to be changed when you swap to a v-8 from a v-6.

I would like to thank all the other people whose posts I searched for information. This is a great forum.:smokin:

You will definitely need a different shroud to install the BB rad in any sb or v6 truck. However, there is a four core rad available for the small blocks, and that shouldn't have any problem cooling the engine. I'm using a three core in my non-AC 92 K2500 and the temp gauge doesn't move in the summer when hauling a loaded car trailer. But the only other options my truck has is engine oil cooler, external tranny cooler, and power steering cooler.