Adding an elec. fuelpump to an Impco vaporizer+425 setup

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BigBlockMopar
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Adding an elec. fuelpump to an Impco vaporizer+425 setup

Post by BigBlockMopar » Mon Dec 31, 2018 3:06 pm

I'm thinking of adding a (low pressure) electric fuelpump near the propane tanks in my '73 Dart.

Why:
Mainly to keep the flow/pressure going 'forward' in the main line to the vaporizer in the car.

Whenever the fuel tanks in my car are getting down to around half full or less, I notice an obvious loss in power during firm accelerations.
Even so when coming out of a corner and try to firmly accelerate.
This gets even worse when the tanks are getting to 1/4 full.

I'm fairly certain this behaviour comes from the fact that the liquid fuel is being sloshed away from the tanks pickup tubes and don't replenish the mainline quick enough with liquid fuel.

There are 2 fuel tanks in the car, connected together with a twin check-valved T-connector, so the liquid propane can only go forward and not flow back into the tank, or transfer to the other tank.

So, I'm thinking with the help of an elec.fuelpump just after the T-connector, this will maintain pressure on the liquid propane in the mainline and won't starve the vaporizer from fuelflow.

Ofcourse I will power the fuelpump with the same power that the lockoffs are powered with so there's no chance the pump will remain running when the rest of the system is powered down.

What would anyone's opinion be with the 'additional' 6-7psi of pressure in the system?
And would there be any other issues I might be overlooking?
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'73 Dodge Dart - 360ci - 11.3:1cr
MegaSquirt + HEI 7-pin timing control - Edelbrock AirGap - Cold Air Intake
IMPCO E / 425 mixer - A518 OD-trans - 3.55 gears - 225/50/17" tires.

storm
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Re: Adding an elec. fuelpump to an Impco vaporizer+425 setup

Post by storm » Mon Dec 31, 2018 9:50 pm

The 1st thing that comes to my mind is will an off the shelf low pressure electric fuel pump be able to hold the pressure of liquid LPG?
What type of pump are you thinking of? Something like this? if yes then I doubt it will hold the pressure.
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Re: Adding an elec. fuelpump to an Impco vaporizer+425 setup

Post by BigBlockMopar » Tue Jan 01, 2019 6:51 am

I thought too lightly about it and agree the already existing pressure in the system would demand different specs to a pump.
An in-tank pump would have it 'easier' because of the relative pressure it will operate in (and that it's already designed to deliver a high pressure), but I doubt there are retrofit electric fuelpumps available for the 'vapour' tanks.
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'73 Dodge Dart - 360ci - 11.3:1cr
MegaSquirt + HEI 7-pin timing control - Edelbrock AirGap - Cold Air Intake
IMPCO E / 425 mixer - A518 OD-trans - 3.55 gears - 225/50/17" tires.

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Re: Adding an elec. fuelpump to an Impco vaporizer+425 setup

Post by Frank » Tue Jan 01, 2019 11:04 am

If what you suspect is true about fuel slosh, an external electric pump might have a problem running dry during acceleration because it would still be supplied with vapor instead of liquid.

What is the size of the liquid line from the tanks to the converter?
Are the tanks oriented perpendicular or parallel to the axle?
Do you experience this problem year-round or mainly in the winter?

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Re: Adding an elec. fuelpump to an Impco vaporizer+425 setup

Post by BigBlockMopar » Tue Jan 01, 2019 3:21 pm

I would *think* even with vapour being pumped, the remaining liquid in the line would still be pushed forward by this and solve the issue.

The mainline is 6mm.
Tanks are positioned having 1 cylindrical tank under the package tray, and the other, a donut-shaped tank, laying flat in the spare-tire wheel well.
I do know the donut-tank has its pickup-tube located to the front of the car. This of course is 'bad' when accelerating.
The issue happens year-round, but is more pronounced when the package tray-tank empties itself first because of warmer cabin temps and the donut-tank is being used while driving.

Besides the annoyance at times, it can sometimes cause some confusion and dangerous situations on the road when the car suddenly stops accelerating after driving away from a stop. Only after a second or two, the power comes back and slower acceleration is possible again.

The lean-out condition is also confirmed by the car's AFR-gauge which leans out when the issue happens.
https://www.bigblockmopar.com
'73 Dodge Dart - 360ci - 11.3:1cr
MegaSquirt + HEI 7-pin timing control - Edelbrock AirGap - Cold Air Intake
IMPCO E / 425 mixer - A518 OD-trans - 3.55 gears - 225/50/17" tires.

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Re: Adding an elec. fuelpump to an Impco vaporizer+425 setup

Post by storm » Tue Jan 01, 2019 7:55 pm

BigBlockMopar wrote:
Tue Jan 01, 2019 3:21 pm
The lean-out condition is also confirmed by the car's AFR-gauge which leans out when the issue happens.
I'm not saying that this isn't the case here but an engine can actually be extremely rich and show lean on an O2 gauge under certain conditions (e.g. ignition misfire).
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Re: Adding an elec. fuelpump to an Impco vaporizer+425 setup

Post by C3H8 » Wed Jan 02, 2019 12:58 am

I find this interesting as I can't see a pump fixing your pressure issue if vapour is getting in the line. As Frank stated a pump will not pump vapour. The sympton you are describing would indicate a loss of liquid to the vapourizer. This can happen a couple of ways. Fuel slosh or a faulty excess flow valve. In Holland I believe you use a propane/butane mix that changes with the seasons. Correct me if I'm wrong on that. It used to be true a few decades ago. Back to the pump. Two issues, one is vapour in the system. The second was stated by a guy named Bennet that made on of the first liquid injection systems. He believed an inline pump would have cavitation issues. He was the first to approach Sleegers on manufacturing a tank with a built in pump. There was a Canadian company also was involved in liquid injection that did use an inline pump. I can't recall the name at present. In their case they used a regular gasoline pump and encased it in a horizontal canister so the pump was surrounded by liquid the same as it would be in the tank. As far as I know it worked fine, however they knew it would be compromised and lose pressure if it got vapour. Since it was a return system to the tank they also stuck with a gasoline start. In addition, as far as I know, they submitted their design to the local government for approval along with engineering specs.

As for pressure, an IMPCO system will work very well down to even a few PSI with HD5 (90%) propane. I have driven my old company trucks in temperatures down to -40 :mrgreen: without any issues. In theory that's 0 PSI, however in Canada 80% of our LPG comes from NG. The residual NG seems to maintain a little pressure even at those temperatures allowing the fuel to get to the vapourizer. At those temps though it is important to give the engine some extra warm up time before putting any load on it. If you do have a butane mix there it can affect tank pressures. What about rotating your tank? Will that change the orientation of the pick up?

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Re: Adding an elec. fuelpump to an Impco vaporizer+425 setup

Post by BigBlockMopar » Wed Jan 02, 2019 3:14 pm

We indeed have a mix here of Propane and Butane.
I don't know if or when a change is made between winter/summer blends. I've never seen it posted and will probably need to dig a bit for that kind of information.

Rotating the tank 180° will position the pickup to the rear of the car.
This will most likely fix the issue "if" the upper tank is emptied first. A new, longer piece of line will need to be fabbed.

I have some modifications in store for the car, which 'could' possibly help the solving the issue;
One is to install a separate Impco F-830 filter upfront in the car just before the lockoff valve. This will put an additional amount of liquid propane near the vaporizer, hopefully helping matters.
I also would like to combine both 6mm lines from the tanks into a new 8mm line going forward.
https://www.bigblockmopar.com
'73 Dodge Dart - 360ci - 11.3:1cr
MegaSquirt + HEI 7-pin timing control - Edelbrock AirGap - Cold Air Intake
IMPCO E / 425 mixer - A518 OD-trans - 3.55 gears - 225/50/17" tires.

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Re: Adding an elec. fuelpump to an Impco vaporizer+425 setup

Post by Frank » Wed Jan 02, 2019 3:42 pm

I think rotating the torroidal tank so that the pickup is at the rear of your Dart will fix your fuel starvation problem and will be far simpler solution than adding a fuel pump.

Upgrading your line size to 8mm will also help. First, because it will reduce the pressure loss and second because it will increase the liquid volume in transmission by 78%.

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Re: Adding an elec. fuelpump to an Impco vaporizer+425 setup

Post by BigBlockMopar » Wed Jan 02, 2019 3:55 pm

I will mostly likely turn the tank around.
As for the larger diameter fuelline, there will also be more liquid (weight) in position that could be affected by acceleration, which could be pushed back a bit again against the rear check valves in the T-connector. But the additional 'storage' inside the Impco filter will probably cover that up if it were to be an issue.
https://www.bigblockmopar.com
'73 Dodge Dart - 360ci - 11.3:1cr
MegaSquirt + HEI 7-pin timing control - Edelbrock AirGap - Cold Air Intake
IMPCO E / 425 mixer - A518 OD-trans - 3.55 gears - 225/50/17" tires.

storm
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Re: Adding an elec. fuelpump to an Impco vaporizer+425 setup

Post by storm » Wed Jan 02, 2019 9:26 pm

Why do people use such small fuel lines? 6 mm = (approx) 1/4", 8 mm = (approx) 5/16 /", 10 mm =(approx) 3/8".

In Australia, and I am assuming NZ as well considering both nations use the same standards, 8mm is used as standard and most people opt for 10mm this leaves the lockoffs as the restriction.

There was a guy in Australia, I think it may be the Bennett C3H8 mentioned, who was an early pioneer of Liquid Phase Injection. He added an intank fuel pump and it was a return system. He come across a problem with pressure build up in the tank because of the increase in temp as the fuel was circulated around the system. Last I heard he stopped developing his system and his website is gone as well. He used OEM petrol injectors so the vehicle could remain duel fuel and cut a slot into the injector near the base for the Liquid LPG to be fed through. After it had gone past all the injectors (at the top of the engine where heat rises to) it was then returned to the LPG tank where due to the increase in temp the pressure inside the tank rose.
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Re: Adding an elec. fuelpump to an Impco vaporizer+425 setup

Post by BigBlockMopar » Thu Jan 03, 2019 4:36 pm

6mm is the "default" diameter used here for years in the Netherlands on older car propane-installations.
'Performance' engine usually get an upgrade to 8mm but I haven't heard or seen any 10mm installations (which would be kind of overkill imo as you can imagine how much liquid compressed propane can flow through one).
What's more 'worrying' is I know the common lockoff valves in use here have an even smaller diameter hole inside. I think to recall is was something in the range of Ø 3mm.

I noticed on the dyno fairly recently my propane-system starts to become a bottle-neck at around 4500rpm during a full throttle run.
https://www.bigblockmopar.com
'73 Dodge Dart - 360ci - 11.3:1cr
MegaSquirt + HEI 7-pin timing control - Edelbrock AirGap - Cold Air Intake
IMPCO E / 425 mixer - A518 OD-trans - 3.55 gears - 225/50/17" tires.

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Re: Adding an elec. fuelpump to an Impco vaporizer+425 setup

Post by storm » Thu Jan 03, 2019 8:01 pm

BigBlockMopar wrote:
Thu Jan 03, 2019 4:36 pm
I noticed on the dyno fairly recently my propane-system starts to become a bottle-neck at around 4500rpm during a full throttle run.
An Impco 425 is approximately 450 CFM. At 100% VE (which is race engine territory) a 365 (360 +.030") will run out of puff at 4250 RPM. At 85% VE you are looking at 5000 RPM. Any restriction in airflow at all (e.g. air filter) could be a problem for your engine.
Every job is a self-portrait of the person who did it. Autograph your work with excellence.

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Re: Adding an elec. fuelpump to an Impco vaporizer+425 setup

Post by BigBlockMopar » Fri Jan 04, 2019 3:20 pm

I agree with that.
I did however notice the mixture getting leaner above 4200 on the dyno, which basicly says the propane starts to drop back while the airflow is still available.
If the 425 was already the bottleneck, power in general would just drop off instead of a change in mixture.
https://www.bigblockmopar.com
'73 Dodge Dart - 360ci - 11.3:1cr
MegaSquirt + HEI 7-pin timing control - Edelbrock AirGap - Cold Air Intake
IMPCO E / 425 mixer - A518 OD-trans - 3.55 gears - 225/50/17" tires.

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Re: Adding an elec. fuelpump to an Impco vaporizer+425 setup

Post by C3H8 » Fri Jan 04, 2019 5:51 pm

For the lean mixtures, have you removed the fuel restriction plate in the 425. If you look in the vapour inlet of the mixer you will see a brass coloured plate with about a 3/4" hole. The plate can be removed just by hooking it and yanking it out. This will enlarge the vapour opening to about 1.125 inches. After that the only restriction will be the power valve. The mixer was originally designed for NG and the plate compensates for the BTU difference in the fuels, however that is based on just regular OEM engines designed 40 years ago. Removing the plate should get you more fuel at higher RPM's.

Bennet's LPEFI system was sold to Schwan's Food Delivery company which operates thousands of trucks.. They continued to develop it based on the 454 engines in GM Topkick Trucks. When they decided to go public with it they wanted distributors to pay them 8 tp 9K US or about 12K Canadian. We really didn't see any way to sell a $14K to 16K kit to our customers. I don't know if they are still making the system for their own use. The system worked well. I drove some of the originals in about 2002 in a Ford E350 with a 6.8L V10.

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