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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: heavychevy91 on January 31, 2010, 07:46:32 pm

Title: 4.3 to 5.7 swap
Post by: heavychevy91 on January 31, 2010, 07:46:32 pm

I have a '86 C10 with a carbureted 4.3 in it, and th350 trans. I am planning to swap out the 4.3 for a 355 I am building and was curious as to what exactly would be necessary for this swap. I know the 4.3 is basically a 350 with the front 2 cylinders chopped off and that my trans and motor mounts and front acc. should hopefully bolt up. Do I have a computer-controlled carb in my truck? I plan on staying with a carburetor just for simplicity. Also what other little problems might I run into?

Thanks for the help in advance

Title: Re: 4.3 to 5.7 swap
Post by: frito-bandito on January 31, 2010, 10:27:55 pm

Are you sure its carburated? If your positive that its carburated, the only wires going to the carb should be your electric choke. If this is the case, the swap will bolt right in. The only thing you'll have to change is the fan shroud and possibly the radiator. Chevy didn't put throttle bodys (computers) in trucks until 1987. Hope this helps you out, good luck keep us updated!

Title: Re: 4.3 to 5.7 swap
Post by: 4x4HighSierra on January 31, 2010, 11:21:47 pm

i did a 4.3 to 5.7 tpi swap in my 85 lowrider and the only thing i had to do was go to the junk yard and get 350 motor mount brackets thats bolt to the front crossmember.  When i bolted them in and set the motor in i found it set to close to the fire wall. So i had to drill new holes in the crossmember to get the spacing right. 

Title: Re: 4.3 to 5.7 swap
Post by: Irish_Alley on February 01, 2010, 03:57:35 am

what years are the motors?

Title: Re: 4.3 to 5.7 swap
Post by: heavychevy91 on February 01, 2010, 08:33:54 am

Okay yeah i was pretty sure i didnt have a computer but i heard rumors i had a "computer controled carb" and i had no idea what the heck that was haha, but the truck is a 1986 with the stock motor and im building a V8 for it the block is out of a early 90's chevy work truck, but i plan on carbureting it. Also should i upgrade the stock fuel pump or do you think it will be sufficient?

Title: Re: 4.3 to 5.7 swap
Post by: three8six on February 01, 2010, 09:38:40 am

THey are probably referring to TBI. If you do this swap you will have to get a new fan shroud(a dime a dozen in the junkyards here). The 4.3 v6 shroud is alot bigger than the v8. Also v8 mounts out of a similar truck.

Title: Re: 4.3 to 5.7 swap
Post by: eventhorizon66 on February 01, 2010, 11:24:48 am

Electronic Q-jet (notice the three pin connector to the right)
(http://www.hotrodders.com/gallery/data/500/Q_Jet.jpg)

Title: Re: 4.3 to 5.7 swap
Post by: frito-bandito on February 01, 2010, 11:43:19 am

 ??? Wow?!

Title: Re: 4.3 to 5.7 swap
Post by: Stewart G Griffin on February 01, 2010, 12:19:17 pm

What kind of mpg are you getting?

Title: Re: 4.3 to 5.7 swap
Post by: three8six on February 01, 2010, 01:34:12 pm

wow........I bet that could get to be a mess....

Title: Re: 4.3 to 5.7 swap
Post by: frito-bandito on February 01, 2010, 01:47:59 pm

Quote from: three8six on February 01, 2010, 01:34:12 pm

wow........I bet that could get to be a mess....

Agreed!!

Title: Re: 4.3 to 5.7 swap
Post by: heavychevy91 on February 01, 2010, 01:49:39 pm

oh yeah my carb dosent have that connector, haha good. and right now im at about 14 mpg