Hello guys, i have a 1985 firebird with a bad 2.8L with the mpfi , and i will be installing a gm zz4 350/350hp that has a bowtie intake, and a holly single feed carb currently installed. The motor is in a friends truck that has been sitting for 4 years. I dont know if the holly is the cause, but the spark plugs were so fouled with carbon, that a few would not come out until soaked in WD-40. I think the carb will need a rebuild / so i am considering installing a new carb. What carb would be best ? Also what mods have to be done to the fuel tank because of the fuel injection? Is there any type of vapor return to worry about? I will be running a mecanical fuel pump from the block. THANKS

 

Welcome aboard thirdgen.org.

Fuel - You can run the in-tank electric pump if you use a return-style regulator like a Mallory 4309 (all 3rd gen f-bodies have a return line). However, the V6 pump, if factory or an OEM-type replacement, will not properly feed a ZZ4. A TPI pump, or aftermarket upgrade like a Walbro 255, will supply all the fuel it can use. If you do use a mechanical pump on the engine, you either need to keep the in-tank electric pump operating (with the return-style reg in the line between the mechanical and the carb), or completely remove the in-tank pump (see the sticky in the top section of this forum about converting an EFI tank pick-up to mechanical style). In theory, you could use a return-style mechanical pump like all 3rd gen carb V8 cars came with, with the in-tank pump and without a regulator, but I haven't heard of anyone who has tried that.

Carb - Everybody has their favorites. What transmission are you going to run? How will you be using the car (street-only, track-only, mostly street some track, etc.)? A dual feed Holley 650 double pumper would fit most duties.

Vapor - No "vapor return", but there is a vapor line from the tank to the canister in the engine compartment. The charcoal canister provides the venting for the fuel tank, so you need to consider which of options that are available you want to go with.

For the basics on the V6 to V8 swap itself, read the sticky in the top section of the "Engine Swap" forum.

 

There was another guy who did a similar swap, 2.8 to something larger and he had fuel delivery issues. Make sure the fuel line diameter is large enough to feed that motor or else you will run it for a bit, or at WOT for a while and it will die from the lack of volume of fuel.