im switching from a 2.8 multi port to a 5.7 carbed. i have a mechanical fuel pump for it alreayd but my question is do i HAVE to take out the electrical one out of the gas tank? or can i run both?

 

The 2.8 mfi fuel pump will have way to much pressure.
if it is hooked up. and two much resistance if it isn't.
But you can probally get a sending unit for a carb car and
just use the mechanical pump

 

The mechanical pump will not pull through the intank pump. Your best bet is to drop the tank and pull off the pump and replace it with rubber line. Or, you could use the intank pump and bring the pressure down to carb-happy PSI with a regulator but I'm not too sure how powerful V6 pumps are... it might not be able to supply enough fuel.

 

88 how do you know a mechanical pump won't pull through the intake pump? not knowing any better i've put mechanical pumps and carbs on 2 former tbi cars and left the pump in the tank.

 

My 84 Z(w/carb) came from the factory with a mech. and electric fuel pump in the tank.

 

The operating pressure for 2.8 mfi is about 35psi.
A tbi fuel pump run 9 - 12 psi.
and a carb runs 3-7 psi depends on carb?
A regulator might work with a Tbi fuel pump but not a MFI fuel pump.
Unless you can find one of the discontinued vacuum controlled ones
They worked real good adjustable with return more fuel on the load.

Just a thought

 

so wut would u guys recommend. the regulater? or removing the electric pump? or just leaving it the way it is?

if i go with the regulater where do i mount that ?

 

Some people say they've done it but when I hooked my Holley Blue up all it did was make a lot of noise and dribble fuel out ...it was really struggling with the intank pump still hooked up.

I don't think running a regulator using the stock pump is a good idea. Yes it will work and I did it for years but if you plan on building a healthy motor or modifying it for more power that hi-pressure / low-volume intank pump is going to become a restriction. Might as well get rid of it now. If you are deadset of using it buy a Mallory 4-port return style regulater (PN 4309? or something like that I think) or anything similar ...You need a return line or else your intank pump will burn up.

 

i just posted that same question about fuel pumps with no response. just found out for myself. my car has been going for a week now using a mechanical fuel pump on the block and an electric pump in the tank. the electric pump is disconnected. the mechanical pump pulls fuel through it with no problem. im not using some flashy trick pump either. its oem specs for a 73 vette. and its feeding a demon 750 dp with no problems.

 

how did u disconnect it?

 

trial and error really. used a volt meter and a jumper wire to the battery. touched wires to the battery until i heard the fuel pump kick on. then i taped its wire up. the wire on my car is light brown with a white tracer.

 

ooo so then it doesnt kick in because theres no power. i get it. how did u run ur fuel lines thoguh? just curious

 

i ran 3/8 rubber gas line from the fuel lines beside the steering column, under the core support, and up to the fuel pump. you need a 3/8 reverse flare fitting to go into the stock fuel lines, then use 3/8 barb fittings to connect the lines. (brass fittings) it took me about 30 minutes to do this.

 

barb fittings? wut r those? also where can i get them and how much if u no

 

barb fittings are brass fittings that connect rubber or poly lines together. they have ridges on them so the line wont come off. you can get them at your local hardware store. they are fairly cheap. you must use hose clamps on barb fittings.

 

You DO NOT have to remove the stock electric fuel pump from the gas tank. Don't do it, you'll be WASTING you're time. It's so unnecessary to do that, especially considering the psi factor.

Just get yourself an adjustable regulator. Mallory came out with a new one for this very application (replaces the #4309), and the quality of this piece is excellent. The regulator comes equipped with the 'return' line you'll need.... and with the psi that you're stock pump is pushing, there is NO WAY that it will burn up (this regulator was DESIGNED for this very reason).

Get one, their only about $80.00. After you install it, set you're fuel pressure at 6psi, and you'll be set.

 

I ran the mallory reg/TPI pump on my carbed car for over 2 years, but my pump finally died just a week or so ago (car has over 160k miles on that pump, and it ran for over 2 years like this so I doubt the regulator setup or anything caused it to die...). I'm converting over to mechanical fuel pump, so I'll have a used Mallory regulator to sell very shortly if you're going to be running this setup and want it... This worked fine to power my 350, but I had the stock V8 TPI pump, I don't know if that's different from the v6 in-tank pump (pressure will be about the same, but does the v6 pump flow enough to feed a healthy V8??)...

I asked in another thread, but I'll ask again here, is there any reason why I can't run a section of rubber hose as the pickup in place in the in-tank TPI pump? I have some "multi-fuel compatible" 3/8 inch hose that fits up on the remaining section of tube after you remove the pump, but I'm just a little leary of rubber submerged in gas for all eternity, it won't break down after a short period will it?? I would assume not since it's supposedly for fuel line but I'm just looking for reassurance I guess... I just got the tank/pump out today (pain in the *** that's for sure), I was hoping there would be a easy way to use metal tubing as the pickup but it doesn't look like it. The rubber hose will be real easy to attach if I can just be sure that won't end up screwing me later...