Replacing 4.3 L with 350

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Bill Johnson - 26 Nov 2004 06:42 GMT

I have an 1988 GMC 1\2 ton with a lunched out 4.3L v6 and will be
replacing it with a 350 from an 1989 Suburban which I purchased as a
complete running vehicle. Both are 700r4 autos as well as TBI.

What parts will not fit the 1\2 ton from the Burb and what will I need
to swap for sure like exhaust manifolds, Rad etc.

I will be rebuilding the 350 and installing flat top pistons as well as
a Crane Truck Power Cam which is compatible with the the stock computer.

Will I use the computer from the Burb or swap the prom chip to the 1/2
ton computer??

Will I have to relocate the frame mounts or are the positions the same
as far as the engine mounts??

Anything else to look out for???

Thanks

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Whitelightning - 26 Nov 2004 21:20 GMT

> I have an 1988 GMC 1\2 ton with a lunched out 4.3L v6 and will be
> replacing it with a 350 from an 1989 Suburban which I purchased as a
> complete running vehicle. Both are 700r4 autos as well as TBI.

All 700R4's are not created equal so there is one part to use from the
"burb".

> What parts will not fit the 1\2 ton from the Burb and what will I need
> to swap for sure like exhaust manifolds, Rad etc.

Obviously six cylinder manafolds are not going to fit an eight cylinder
engine, nor are the exhaust pipes going to line up. So scarf the front pipe.
Cats are the same so the easy way to change is pull front pipe and cat. as
assembly, and with a little luck the pipes from the pick up will line up
perfect and bolt together.
5.7 ltr generates more heat so the rad and fan shroud will be needed from
the burb. but given the money you are going to put in the engine, go to NAPA
and get a new Modine heavy duty rad for it, and new hoses, and dont for get
a heavy duty thermo fan clutch. Fan clutchs loose about 100 rpm per 10,000
miles.

> I will be rebuilding the 350 and installing flat top pistons as well as
> a Crane Truck Power Cam which is compatible with the the stock computer.
>
> Will I use the computer from the Burb or swap the prom chip to the 1/2
> ton computer??

If the computers have the same OEM part number, 1227747, you dont have to do
a thing, but if the burb has OEM 1228747 then you need the burbs comp.

> Will I have to relocate the frame mounts or are the positions the same
> as far as the engine mounts??

frame mounts will have to be moved foreward.

> Anything else to look out for???

Engine bay wiring harness is going to be a problem. The engine is going to
be longer, so the wiring going to things like the alternator and ac
compressor are going to be a tad short. The throttle body will sit further
foreward as well as the temp sensor.
Throttle cable may be too short on the p/u. Use the speedo adapter from the
tranny in the p/u. do both trannys have the same tail shaft length? Are
the front yokes the same(meaning same spline on slip joint and same
diameter)?
Both trucks use the same fuel pump, but probably should replace with new ac
delco unit and new sock
Front spring rates are different, so you need the springs out of the burb
assuming both 1500's.

And I am sure others will add to the list. Sure was easier before fuel
injection.
Whitelightning

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