I have an 87 Z28 that had a 4 barrel 305/5-speed in it when I bought it (stock, the last year). I have since then put in a 350 with a Holley 4-barrel 700cfm double-pumper carb. when I did that I realized I had an electric fuel pump in the tank and a mecahical fuel pump on the block. Because of the electric fuel pump, the mechanical pump has an extra outlet on it, which I assume to be a "release or excess fuel" outlet. But now I want to upgrade to a high volume mechanical pump. how do I get around the electric pump? do I install a regulator with a "release" outlet in it? And will the electric pump even flow enough to keep up with a high-volume fuel pump?

Thanks everybody

 

Welcome aboard.

That third line is a return line, which sends excess fuel back to the tank when pressure at the carb is high enough. My '86 has it, even though it does not have the electric pump in the tank.

Why do you want to "upgrade" the mechanical pump? My stock replacement is doing fine, even with my mods. The electric with mechanical is the ideal situation - it will keep up. It's there to provide volume to the mechanical pump (so the mechanical pump doesn't have to "suck"), and the mechanical provides the pressure and regulation to the carb.

Unless you've got a really wicked, high power, high rev'n 350 in there, a stock AC replacement will feed the engine just fine. You might consider a light-weight pushrod, though.

 

If you aren't having a fuel starvation problem, stick with the stock pump. It will support plenty of power.

 

I'll just assume you have a good need to upgrade, as they already covered that

You can probably get away with not doing anything to the intank pump. If the new pump doesn't have a provision for a return line, just block or cap it off and call it good. If the intank pump is dead and clogging things up, then you'll have to drop the tank and repace it with a pickup or piece of hose.

 

Thanks for the input guys. I wasnt sure if the stock replacement, a Parts Master pump, could keep up with my engine once I put the new heads on. I'll be running the same carb as before, the 700cfm holley, with a comp cams extreme energy cam XE268, with some aluminum Trick Flow 23 degree heads, at about 10:1 compression.
I'm glad to have finally signed up!

 

With that combination it should keep up without a problem

 

FWIW, the GM HO 350 Conversion kit includes an in-tank electric pump and 3-port regulator. There is no mention of a mechanical pump in the parts list, and I haven't seen the kit installation instructions to know if it tells you to reuse your mechanical pump or not.

 

I'll have to check that out