Lift pumps and EFI surge tanks

[CDMBill]

At the risk go being repetitive I'm looking for the collective BS wisdom on surge tank lift pumps. I'm fabricating a tank within a stock tank setup, see my project cars thread under GIRTST, and I've ordered a Carter OEM'S replacement pump to pull gas from the main tank into the Aeromotive sump/surge tank which will feed the A1000.

Is there a better alternative? I'm not running a true fuel cell due to cost, nor a true surge tank as prefer to keep the fuel tanks isolated from the cabin as this is in a convertible and I have a sold steel trunk floor which the fuel tank rides under unlike earlier Mustangs.

[hauen]

I think with a minimum of baffling you could just run an inline pump, that sump seems plenty deep. At the risk of sounding like a total 'tard I think you could make a louvered lid/cap/baffle with the louver openings facing forward that just sits over the top of the sump so fuel flows down and in so when you pick the front end up the fuel has to really work to climb out. With the troubles I've been having lately, I'm probably the last guy who should be giving fuel system advice though.

[OldMachinist]

I just did this and the instructions say drill a 3/8 hole on each side of the sump at the bottom of the stock tank. I actually drilled 2 holes on each side about 1 1/2 " from the ends. Don't you think this will supply the sump adequately? Or am I not understanding something here?

[TheSilverBuick]

Am I reading this right, you are setting a pump up to pull from the main tank and pumping into the sump area in the main tank? Sounds overly complicated and an extra strain on your charging system to me. Baffle and those one way flaps I would think would be adequate with enough fuel in the tank. Do you plan on being less than a 1/4 tank at WOT? I know it's extra weight, but I'd figure at at around 1/2 tank with a sump like the one I've seen in your pictures that uncovering the pickup point would be near impossible when accelerating forward. Like hausen though, I may not be the best source of fueling advice

[CDMBill]

So Randall you are right in that I'm trying to run with the least amount of fuel on board as possible. With holes drilled more or less as Oldmachinist describes, which reflect the standard recomendation from Aeromotive I'd still have to have 1/4 to 1/3 of the tank full at least to avoid starving the pump inlet on acceleration. It's deceleration that is trickier with low fuel levels even with the deeper, much bigger sump than I have now. Deccel at the drags happens to a minor degree at the end of a burnout and to a very major degree at the end of a run and the turn out. I experience this now at any level below about 2/3's of a tank so I have been running it full (20 gal.)

The other issue is for auto-x and road course which was why they recomended the one way valves on the front and sides, and which has led me to the lift pump idea so I can have the sump be quite full even with the main tank almost empty. In addition to the one way valves they suggested adding baffles which would divide the tank into thirds with a tapered baffle extending from each of the corners of the sump out towards the front corners of the tank. Part of the issue there is that the side walls of the sump lean in so the one way valves would be slightly open under nuetral conditions and I would end up with identical fuel levels in and out of the tank unless I reconfigure the sides of the baffles. The front side is angled out and presentes no issue other than deciding on the height of the location

I was planning to add top baffles to the sump to better contain slosh, but still allow the fuel to be added through the orginal filler neck and to spill over filling the rest of tank when its time to hit the road. I haven't started cutting yet so all options are open.

The power required by the little lift pump is tiny compared to what the main pump draws and that is dwarfed by the electric fan. All of which is fed by a 200 amp alternator, so I am good on power.

Lastly, I want to be able to mix 100 octane unleaded into a small amount of the pump premium in the event we start getting E10 or worse 'summer' blends at some of the gas stations as I am at the edge of the pump gas window with 11.86:1 compression. So far so good with Cali Chevron 91, but on the road you never know what you may get. So using the sump as a kind of surge tank for a particluar run makes that easier.

This is how I think myself in circles.

[TheSilverBuick]

IMO, if you are going to a surge tank set up, then go all out on a surge tank set up. Box in the whole sump area except a small hole on the very top that might be 1.5-2.0" in diameter for filling up at the gas station. No side or top baffling or flaps, just adds complication and ways for things to go wrong. Let the Carter pump (it's an intank pump right?) pump into it full time and an A1000 it from there. The Carter pump doesn't have to keep up with the A1000 on volume either, just has to be close enough to your expected fuel consumption rate while auto-crossing. Works best if your EFI return line goes into your surge tank as well.

Mine is a little under 1 quart in volume I figure, and the mechanical pump rate feeding it is a bit less than the electric pump feeding the injectors. By my math it would take nearly 12 minutes of WOT at maximum electric pump capacity for my surge tank to run dry with the mechanical pump pumping into it at it's peak rate. Now based on my actual fuel consumption (injector flow rates and duty cycle) the mechanical pump just barely lags and may go forever without starving or like an hour, but in either case, not even a Bonneville 10 mile course run would run the <1qt surge tank dry. If your's is a few gallons you'd be in great shape I'm sure.

[CDMBill]

Randall, that's the conclusion I'd reached as well, but I wanted to bounce it off the folks here to see what I was missing. The lift pump adds another point of failure which is whay I was equivocating on the baffles and one way valves which are pretty simple. I have a spare A-1000 that is for the N20 setup I'm not running at Drag Week and the little semi-generic Carters (yes its an in tank unit) are available everywhere. The EFI return is to the sump/surge tank so that is covered.

[TheSilverBuick]

I had repeated failures of cheapy universal electric pumps(12psi TBI versions), so went to a mechanical fuel lift pump. Might of been my installation (not convinced of it, but could be) or from using bottom shelf parts, I don't know, but about once a year I was getting stranded because it would quit pumping, and popping a new one on there would work every time.

You run a fuel pressure gauge so should be able to tell pretty easily when there is a hiccup, plus you could put a couple gallons in the fill spout (if it goes right into the surge part) to go several miles on the surge tank if the lift pump fails. I'm contemplating installing one that feeds into the MSIII.

**Maybe a small ball style check valve at the bottom of the surge tank that allows tank fuel into the sump when the fuel level goes lower than the tank level for driving purposes and if the carter pump fails. But my K.I.S.S. feelings is not to use flaps and such that would be more prone to seeping/leaking back into the main tank when parked and pumps off. Keep the surge tank always topped off.

I've ran my car down to within a gallon of the specified capacity of the tank (and where I have ran out years ago) with no hiccups or mis-firing of the engine.

[Matt Cramer]

I don't like the idea of using an OEM Carter fuel pump to feed an Aeromotive A1000 unless you're using three or four of the Carters - it seems to me like the Carter pump is going to be a restriction instead of helping. And if you're using multiple Carters, you can just skip the A1000. Or depending on your horsepower level, you may be able to use a single in-tank Walbro.

[TheSilverBuick]

I don't like the idea of using an OEM Carter fuel pump to feed an Aeromotive A1000 unless you're using three or four of the Carters - it seems to me like the Carter pump is going to be a restriction instead of helping. And if you're using multiple Carters, you can just skip the A1000. Or depending on your horsepower level, you may be able to use a single in-tank Walbro.

Have you seen the size of surge tank he is running? The dang thing looks like a 5-gallon gas can! Well maybe 2 gallons anyways. The Carter just has to keep up at normal cruising since the A1000 EFI return line goes back into the surge portion. At WOT and the Carter could be completely turned off and Bill will have what appears to be a couple gallons of fuel for the A1000 to pull from before there is trouble. I know he isn't at WOT very long on the Autocrossing courses, not with 1,000 ponies on tap. Some simple flow rate math would be able to tell for certain though.