T&T Racing

For my 944, I am installing a fuel cell below the trunk floor. The original factory installation has the fuel pump mounted so the fuel tank floods the pump inlet. I was planning to use the existing fuel pump but mount it at the same elevation as the trunk floor. Thus, the fuel pump inlet is above the fuel cell and the pump needs to have sufficient suction to lift the fuel into the pump inlet. Are there any issues with this arrangement or what needs to be done to correct this issues? Who has done this before?

michaelmount123

Fuel pumps are designed to push, and not pull. Therefore, it's important to get the pump as low as possible relative to the fuel level, ideally on the level of the bottom of the cell. Admittedly, this is not always possible, but you can certainly get it lower than the pump floor if it's mounted along the frame rail under the floor.

At least you're putting all that fuel weight low where it should be. I've seen way too many 944's with a cell mounted on the rear floor!

michaelmount123

Here we go again, Robstah.... The OP asked for advice. Do you have any? What is your point in the statement above?

If you have anything to add, please re-read the original post and offer something useful/intelligent. Your MO is to google the subject and paraphrase comments you find on the web. That's poor form. Do you have any real world experience?

If anyone thinks I'm being a bit harsh, please look over Robstah's posts and the responses he's received and I think you'll quickly understand.

s14kev

I agree. I thought it was fairly common knowledge that roller cell type fuel pumps (which account for the majority of EFI pumps) work by compression of fuel and in principle don't "suck" fuel well from the supply. Almost all roller cell pumps are either mounted immersed in tank or at the tank outlet down low. It's not to say you can't top mount them but most that are, are fed from a swirlpot (which is usually fed by a low pressure pump). If robstah is just used to seeing pretty pictures of fuel pumps mounted in the trunk while surfing the internet, this may be why he has made the opinion that tons are mounted up high. What he may have missed is the swirlpot sitting next to most of these.

Turbine style fuel pumps which are much less common tolerate mounting position better since they do "suck" at the inlet.

I think a blanket statement like "There are tons of top mounted fuel pumps, so I don't understand where you are getting this from." is somewhat ignorant of how fuel pumps work.

T&T Racing

s14kev, I appreciate your input. I would agree that a roll cell type pump needs a flooded suction while a turbine style pump can create sufficient vacuum to lift the fuel from the fuel cell. The fuel cell manufacture prefers to have the fuel pump mounted slightly higher than the top of the fuel cell. I will need to determine if my fuel pump is roller or turbine.

I am doing a trick setup of the fuel cell. I will post photos when I get finished with phase I. The initial mockup engineering will take a few days of fab time, but everyone who wants to convert a 944 to a fuel cell will save muchoo hours of fab installation time. The fuel cell can be installed with minimum invasive surgery of the trunk. More on this later. Just enough for now to keep you intrigued.

s14kev

The stock Bosch pump is a roller cell style pump. You may be best off using a cheaper low pressure pump to feed a swirlpot reservoir mounted above the fuel cell and have the swirlpot feed the stock porsche pump.

Will definitely be interesting in seeing pictures of your setup. I'm not sure how you can get a single fuel cell mounted with its COG as low as the stock setup with the transaxle in the way.

s14kev

To help correct some simple inaccuracies

No. Most in tank pumps are located down low. They are mounted in tank for a number of reasons. One is that they are designed to be mostly submerged to help with cooling. Another is electric pumps are noisy. Submerging a pump affords some degree of noise dampening. Having the pump mounted inside the tank at the top is not common.

Having a fuel pump located external to the tank is no less safe than an intank set up. If a common in tank setup were to have any fuel lines "ripped/pulled" out in a collision you can guarantee that fuel will be pumping all over the place since the pump is located in tank and the outlet will always be pressurized. Of course we must acknowledge that most manufacturers have installed inertia switches anyway as a safety measure. Quite possibly, if a 944 had things "ripped" away from the tank in a collision, the pump itself may very well be ripped away which could mean that fuel leaks out only by gravity through the outlet rather than being pumped out by a still working pump.

There is a simple reason. The reason why is because fuel cells are a safety feature. The rubber bladder and foam filled structure reduces the risk of a major flood of fuel coming from the fuel cell in the event that it is breached. Tear a standard fuel tank open and fuel will be flooding all over the road.

Roller cell pumps work on positive displacement of a fluid column. They really don't suck at all well and will also vaporize fuel somewhat if made to do so leading to tiny vapor bubbles in the fuel outlet. As an example try taking an unprimed (ie air filled, brand new) roller cell fuel pump and connect the inlet to an empty (ie. air filled) hose. Hold the pump 6 feet off the ground and with the other end of the hose in a container of fuel before you turn it on. It will have quite a difficult time sucking that air through the line. If you mount a roller cell up high, when a vehicle is turned off, fuel is apt to drain out of lines and leave the pump somewhat empty leading to a no start condition if the pump is unable to pull air to prime itself, or a long crank time before starting as the roller cell pump struggles to move the air to prime itself. Of course check valves are routinely installed in most fuel systems but they can't always be guaranteed to work.

Hopefully this clears up some misconceptions. Anyone feel free to chime in if I am incorrect with anything. I am not a professional mechanic. We are all here to learn.

T&T Racing

I investigated the Bosch replacement fuel pump for the 944. The Bosch is a turbine fuel pump. When I remove the existing fuel pmp, I can verify if it is a turbine style pump, but the shape and canister color are the same as the Bosch replacement pump. It has a non-return valve included so when the pump is off the non-return valve will hold the suction fluid in place.

T&T Racing

Update: I completed 50% of the "bread board" mockup for the fuel cell. My plan is to complete the mockup on 4/5, let it cure, and then prep it for the next step. My fabricator contact for manufacturing the fuel cell is out of town until mid week of 4/8. Once we discuss a pathforward, I will post photos of the mockup prior to making productions drawings for fabrication. I apologize for not being able to share the progress but I need to negotiate an agreement to benefit me and the fabricator ( a win-win situation for all)

T&T Racing

Finished the "bread board" mock up for the fuel cell bladder. Letting in cure and then will pop the mold.

T&T Racing

I finalized the design with ATL Fuel Safe. The fuel cell is mounted in the 944 spare tire well and fuel cell top is flush with the trunk floor. The fill plate has an adjustable 2 1/2" fill connection that can be plumbed to the existing fuel fill connection. A fuel level sensor is installed. The net fuel volume is 10 gallons.
My contact at ATL was Drew.

Main advantages are: no removal of existing fuel tank until the tranmission needs to be removed; no cutting of the trunk floor; no fabrication and welding required to reinforce and stiffen the trunk area; to fabrication and welding required to mount the standard fuel cell container. A conservative estimate to cut, fabricate, reinforce, and weld for a standard fuel cell is 10 - 12 hours. Plumbing is extra. Covers to isolate the fuel cell, fuel pump, and fuel filter need to be fabricated by a sheet metal technician.

My system is for a DIY: I will start plumbing for the fuel cell in early June. The fuel cell ship date is June 10. I plan to run SVRA at Mid Ohio June 26-30.

I will update the progress with posts and photos.

T&T Racing

Fuel Safe will be shipping the fuel cell the June 17th via 2-day air. I purchased the aluminum to make the cover over the fuel cell, fuel pump, and filter to isolate the fuel spillage from the cockpit. The fabrication will be done by June 10th. Purchasing the AN fittings and hose to re-plumb the fuel pump and fuel filter to the trunk area (driver's side). The fuel cell should have a net capacity of 10 gallons.

Photo's and detail description to follow once the fuel cell arrives. No welding required to install fuel cell and components into the race car. The fabrication of the cover will require welding by the fabricator remote from the race car. More details to follow.

T&T Racing

The fuel cell shaped was designed by T&T Racing and fabricated by ATL Fuel Safe. The fuel cell fits in the spare tire well. I did not need to remove the original fuel tank. This fuel cell is a nominal 10 gal. I will be calibrating the fuel cell level sensor by June 23, 2012. My contact at ATL Fuel Safe was Drew Barney. These photos are the fuel cell, the spare tire well, and the fuel cell in the spare tire well. I plan to include fabrication details and list of materials on my website porsche944garage.com (not up and running but purchase the domain site.

T&T Racing

UPDATE:
More photo's of the installation to follow in about a week.

I ran the 944 with the fuel cell at SVRA Mid Ohio Mechanic Bank event, Juen 27-30. The fuel system performed flawlessly. The fuel cell capacity is about 11 1/2 gals. I ran the fuel down in the cell to 5 gals and no pick up problems. The fuel pressure was steady. Used the existing Bosch fuel pump mounted in the trunk area along with the fuel filter.

The engine performance was not compromised.

It is a great DIY way to add a fuel cell. I would offer modifications to my original design of the "dog" house. The "dog" house provides the bulkhead isolation between the fuel cell mounted in the spare tire well and the drive cockpit area.

PM for details

Van

Looks pretty clever. However, I'd have a few concerns... well, two, really. 1) in rear impacts, I've seen that spare tire well crumple a bit - but usually the trunk floor forward of the transmission cross brace doesn't have much deformation, so I'd think you want the fuel cell to be as far forward to give it more "cushion" from impacts.

2) Fuel weight is such a changing variable, I'd want the fuel cell mounted as close to the center of gravity as possible.

But kudos for thinking outside the box, as it were.