Engine/Transmission Options 86 C20 engine swap?

[Mstreman]

Newbie to the forum: I am contemplating a 350 motor swap given that "Old Blue"-- blew a head gasket leaving NJ 2 weeks ago. All things considered, rather than replacing the head gasket / possible warped heads etc, an engine swap seems simpler/quicker.  I have found another 350 motor mated to a THM350 which came out of an 86 C20. I am awaiting confirmation on whether I have a THM350 or 400 Tranny.  I have gotten different answers so what was the Original Equipment for an 86 C20 2wd with a 350ci Chev?

I have an apparent donor sedan engine already changed out by a former owner owing to some clamped off emission lines around the manifold. Not having the truck here in Tennessee, It is a guess as to what is in it now. Do I have any issues if I mix or match the THM 350 vs the 400?  I believe I have a 2 piece drive shaft.

 That said--As long as I am pulling the engine, I thought I might look upgrade the 3 speed for a 4 speed.
 I pull the occasional heavy trailer but would like better gas mileage. What are my options?  4-speed Turbo Hydra-Matic 700R4 or ?  What 4 speed could I be looking for and will I also need a different driveshaft?

Any advice on what to look out for is welcomed.

[zieg85]

I can tell you a 350 engine was available in a C20

[Kren420]

I can tell you my '86 C10 came with a 350 with a TH400.  I also know this was not the norm

[zieg85]

I can tell you my '86 C10 came with a 350 with a TH400.  I also know this was not the norm

Not calling you out on this unless it is a very late 1986 what is your 8th digit (letter) of your VIN?  Just real interested is all.  Never heard of any 350's making it into 1/2 tons unless it was a rare very early TBI model in late 86

[Mstreman]

During today's further reading I see that the 4 speed is not a good choice for a PU.  Whichever I use of the 3 speeds, the THM350 or 400, either one will bolt up as most of the differences are internal.   Anyone know off hand if there is a torque converter difference I should be aware of?

[Kren420]

I can tell you my '86 C10 came with a 350 with a TH400.  I also know this was not the norm

Not calling you out on this unless it is a very late 1986 what is your 8th digit (letter) of your VIN?  Just real interested is all.  Never heard of any 350's making it into 1/2 tons unless it was a rare very early TBI model in late 86

The eight digit in my VIN is a M.  I'm also in Canada don't know if that made a difference
*EDIT*  first 8 digits are 2GCEC14M

[zieg85]

M is a 350, Them Canadians ya know...  I learned something, thanks

[Kren420]

No problem, glad I could help increase your knowledge.   

[Kren420]

During today's further reading I see that the 4 speed is not a good choice for a PU.  Whichever I use of the 3 speeds, the THM350 or 400, either one will bolt up as most of the differences are internal.   Anyone know off hand if there is a torque converter difference I should be aware of?

I'm pretty sure the TH400 converter is like an 1" in diameter bigger.  Not sure if interchangeable, and I could be wrong about that as well.  I also apologize for slightly hi-jacking your post lol.

[zieg85]

The TH350 and TH400 use different torque converters.