Dave C. '97 Z28

Hi all...
I wanted to get some opinions about running a Walbro or equivalent pump outside the tank (like where you put a booster pump for a SC or NO2 setup, but WITHOUT using the intank pump?

Basically having the Walbro external suck gas through the regular fuel line, except that instead of a fuel pump inside the tank there is a hose replacing it, going down to the bottom of the bucket.

I can't think of any reason why it wouldn't work since the pump is below the gas tank, but can anyone else think of a reason? Has anyone does this successfully (or not)?

Thanks
-Dave C. '97 Z28

LPEdave

I haven't actually done that, but most aftermarket pumps are made to push, not to suck. So it's probably not enough that the pump is physically lower than the tank (you'd be counting on some sort of syphon effect), you need the lines to come out the bottom of the tank. At least that's the way I did it, and was recommended to me at the time.

I have some pics in the fuel section of my web site, if you're interested...

Dave

Dave C. '97 Z28

I understand that, but the pump has to "suck" (that sounds too funny) to get fuel into it in the first place. So whether it's a 1/4" or 3 feet, I wonder if there is a difference?

I was thinking of running some lines from below. I was just wanting to use the "bucket" in there to help with sloshing. (setting up for road course, not drags).

-Dave C. '97 Z28

PS: I see on your website that you punched through the baffle. Pretty cool! Maybe I'll try doing something like that instead.

Red96Lt1

He's right. Most pumps are designed to push instead of pull. Just the same way that some pumps are designed to pump liquids instead of gas. This is why if you run out of gas, it causes premature wear on your fuel pump, because it is pumping air instead of liquid, and thus is over working.

Dave C. '97 Z28

Actually you wear your pump out because it overheats since it uses the fuel to cool it. (while it's pumping it through)

Red96Lt1

I think it's more of a combination of the two, but do you get the point?

LPEdave

I can tell you that on the road course, I could get down to about 1/3 tank before I started to suck air on turns. Not great, though I suppose my trick with the bucket helped a little.

Depending on how serious you are going to be on the track, you might want to do it right the first time, with a smaller sump tank that gets fed from the main tank, and a secondary pump in that small tank. That's a pretty good answer to the problem, or possibly foam in the tank could be used for a lower end solution.

Dave

Dave C. '97 Z28

Yea, good idea. I am not 'real' serious yet, but the car is set up for that and I want to start getting more involved with it. I just took out the 454 and I am putting the LT-1 back in, so alot of stuff was changed around. When I was running the big block, since it used a carbuerator I used a Holley Red pump the fuel system was configured like I was mentioning, but the pump only produced 7psi for the carb. Also, since the bowls held fuel it was harder to notice if it was getting air pockets in the line.

I'm just trying to get the car on the road for now. If I have problems I'll go back and change the config, but for now I think I might just try the config I was talking about.

On your setup, how did you run the return line? Did it go back in the bottom, or did you run it to the top? I would think you'd want to run it to the top.

-Dave C. '97 Z28

LPEdave

Once you've done one fuel setup and got rid of all the stock stuff with goofy fittings, it's much easier to do a second one actually

I ran the return back in the bottom, for what it's worth. I guess I kind of figured it was under pretty high pressure, so why not. And it meant I could disconnect everything from the bottom of the tank and not have to remove it again. But I see your point, in the top somehow feels more correct...

Dave

Dave C. '97 Z28

That brings up an interesting thought...
If the fuel pressure is setup as a differential across the spring in the regulator, I wonder if you have higher fuel pressure with a full tank of gas than with a almost empty tank, since the weight of the gas in the tank is pushing on the fuel coming down the return. The weight is probably insignificant compared to the pressure, but it could be a couple psi when full... That's way off topic, though...