I am doing a motor swap in a 68 chevelle, and plan on running my Holley Commander 950 FI system I recently purchased. I have heard so many opinions on what to do about the fuel tank and sending system. Can anyone tell me if they have used a tank off of a GrandNational or Caprice to solve the sump problem? Or do I just have to bit the bullet and go through ROck Valley.

I dunno about the Caprice/GN options...

But Rock Valley is just too darn much $$$ as far as I am concerned.

I have been looking at this for a '68 El Camino and see a couple of ways to go. One, and the way I am leaning these days, is to open up a tank and build in a trap door sump with baffles. The other, and how I was planning on doing it, is to setup an external sump/surge tank. I have all the hardware to do this including the two electric fuel pumps and a water filter housing for the tank. The reason I am rethinking is the redundancy of having two fuel pumps and the added headache of mounting the stuff.

Sounds like good info. I hope to hear from someone who has this kind of setup and it did not cost them $1000.00. I just cannot afford that, but I am afraid that is what I am going to have to do.

I thought about diffrent ways too. But when you start adding your time and what it's going to look like under the car not to mention were to put a surge tank were it's not in the way. It's best to bite the built and go with an after market tank. I went with Rock Valley and have been disapointed.Every time I have a full tank and hit the brakes gas comes out of the vents.Like there's no baffels.They said they woul look at it if I send them the tank. That means car down for 4 to 6 weeks Don't think so. I just ran the vent up through the trunk and back down.But when I bought mine they were the only ones now there are others. Just my 2 cents worth.
Jugg

Every time I have a full tank and hit the brakes gas comes out of the vents.

My RV tank does this too... but no worse than my stock tank. My stock tank would GUSH fuel out when full especially on warm days. The RV tank is just a light trickle.

However, I've added a large fuel filter oriented vertically in the vent line to serve as an accumulator; the vent has to fill the fuel filter up completely with fuel before it can go out the top and onto the ground. This helped a LOT. I also extended the vent to dump back by the license plate. I'm going to make the accumulator tank larger at some point to caputure more vented fuel. As long as the fuel tank vent feeds the bottom of the tank and your vent to atmosphere is on the top that's really all that matters. The tank will puke out the vent and fill the accumulator, which will capture as much fuel as it can. When the pressure on the tank relieves the fuel in the accumulator tank will drain back down into the main fuel tank. The trick is to make that accumulator big enough to capture all the fuel puked out of the main tank so the extra fuel never makes it all the way out the vent line and onto the ground. That being said, my 2" x 4" canister fuel filter isn't big enough. It captures most of the fuel that comes out the vent but not all.

You have the right idea running the vent line high up into the trunk; you're using gravity to your advantage to return the fuel expelled out the vent back into the main tank. If you an accumulator of some sort (piece of pipe with fittings on each end, large canister fuel filter, etc) and that will greatly help the problem. You need a little "surge" tank on the overflow to capture what fuel comes up.

There's really no getting around these fuel tanks puking unless you retrofit an EEC system with a canister to give the fuel somewhere to go, especially with our cars wide and relatively shallow tanks. The shallow tank means it's really easy to have fuel slosh into the internal vent. If the tank were a lot taller it would be much less likely to have these problems.

As far as the Caprice tank, I believe it's about 1/2" too wide to fit between our frame rails. However, an 80's A-body EFI tank should fit with no issue, as the tanks on those cars were somewhat narrow because of the spare tire well extending down on the passenger side. I don't know if the length would clear though. That would certainly be the most economical route to pursue. Hit up a junkyard and take some measurements...

Troy

I have read of someone installing a Caprice tank in their 2nd gen Camaro. It fit rather well, though they had to heat the (plastic) tank to "mold" it to clear the rear end.
HTH

You know, if I spent close to $1000 on a new fuel tank it had better not spit fuel. Ever. We have the technology to fix this problem and for that kinda change I would expect it to be incorporated.

One of the things it takes is more than one vent in the tank so that there is a vent that is not submerged. Combine that with an external elevated chamber to combine the vent lines into and you should get virtually no spilling. Pretty much like what you see on later A-body cars, especially 71 and later with the EEC system. I final piece of the puzzle is a filler neck designed to extend just far enough into the tank to maintain a bit of air space at the top and you should be good to go.

The fuel cell folks at Fuel Safe make some very interesting in-tank sump products. Small 6x6x4 boxes with trap doors or check ball valves. Some with baffle wings. Looks like a very effective EFI baffling/sump solution. The hard part is getting one into the tank, well not really because the hard part is getting the tank sealed back up after cutting a 6x6 hole in it :)