86 k5 305/350 engine swap question

[Justin Fleming]

Hello

My 86 k5 blazer has a 305 q-jet motor and I am swaping in a 350 q-jet motor. The question that I have is my 305 fuel pump has two barb fittings and one pipe thread fitting. I assume 1 is pickup, 1 is return, and the pipe is the pressure line. The 350 motor has 1 barb and 1 pipe thread. The 350 has a brand new pump on it and I want to know what the additional line is on the 305 motor? Do I need it?

The other question I have is the 350 motor has what my dad referrs to ram horn manifolds vs. the 305 has stanard manifolds. Are the ram horns worth it or not? Cause I would have to rework the exhaust.


thanks

 

[scrappyk5]

the 305 pump has three lines. the pipe fitting to the carb. large barb should be the supply line. the small barb would be the return. when you install the 350, put the 305 pump on the 350, so you can keep all the lines the same. The ramshead manifolds are betta flowing than the 305 manifolds. I would keep the ramshead on there if you can afford to change the exhaust.

 

[76zimmer]

I think the 3rd line is a vent to the tank, or maybe the carbon filter canister by the drivers radiator support.

I did that swap and used the 305 fuel pump and never had an issue. I also used the 305 carb with no mods. When I put headers on it, and a Performer intake, I had to open up the jetting a little.

The rams horns are the best flowing iron exhaust. What year block do you have?

 

[Justin Fleming]

The block is a 75 4 bolt

 

['86erfixer]

I swapped out my 305 for a new crate 350 in my 86 Blazer. I needed a new flexplate (shouldn't be a problem for your '75 350) and had to slightly mod power steering brackets. The old 305 used the driver's side exhaust manifold stud for the bracket. I put headers on, so needed to alter the bracket some. Other than that, it's a pretty simple take out, put in process.

 

[76zimmer]

I couldn't use the drivers' side manifold because of oil dipstick location being on the other side of the block on pre-80 blocks. 80+ blocks pass side, pre-80 pass side.
I had to get a junkyard manifold.

 

[Justin Fleming]

Looks like the 305 exhaust manifolds will not work as the bolt pattern seems to be different on the 305 head. It apears that there is an extra ear on the head for the manifold bolt to bolt up and the 350 heads are not that way.

Anyone have a line on the best fitting headers for the 86 k5 blazer?

or should I be able to find a junk yard manifold where the 86 blazer was a 350? What the dump spot be the same as my 305 manifold or would I still have to rework the main exhaust system?

thanks

 

[76zimmer]

I think you'd have to find a HD K20/K30 to get a 350 engine in the mid 80's.