LPG system type?

[Felix]

Hi guys, while I sorta know how my LPG system works, I would like to know what type of system it is as I want to change my carb and I will need a new mixer to suit.

My gas system has a converter which takes vacuum from the air box, and one gas line out to the 'power valve' which splits into two lines which go to the mixer. The mixer just looks like two flat tubes which stick out into the air stream on top of the carb- not like a venturi mixer. I have tried googling all sorts of terms but can't figure out what type of system this is, and where to get a new mixer to suit.

I have a prime button if that makes any difference...And the only word on the converter i can see is reggio emilia?

Thanks!

[slug_burner]

have a look for it here (http://www.emmegas.net/index.php)

This (http://www.alibaba.com/member/it100625981.html) is where I got a first hit

[bee utey]

Hi guys, while I sorta know how my LPG system works, I would like to know what type of system it is as I want to change my carb and I will need a new mixer to suit.

My gas system has a converter which takes vacuum from the air box, and one gas line out to the 'power valve' which splits into two lines which go to the mixer. The mixer just looks like two flat tubes which stick out into the air stream on top of the carb- not like a venturi mixer. I have tried googling all sorts of terms but can't figure out what type of system this is, and where to get a new mixer to suit.

I have a prime button if that makes any difference...And the only word on the converter i can see is reggio emilia?

Thanks!
You are running a complex converter and AMOS brand simple mixers. These mixers are effectively a venturi mixer, just look a bit different. The diagnostic is where the idle mixture control is. It will be on the converter. If you said what carby you are planning on (probably Holley?) I could advise a mixer suitable. If it is a Holley, a New Gen style mixer is most appropriate. They pop up on ebay regularly under a number of aliases (e.g. "gas hat") depending on the seller's ignorance.:D

[Felix]

Thanks guys! Yep I'm planning on running a holley 350- I was looking at those new gen (by sprintgas??) mixers when they pop up on ebay but wasn't sure if they were suitable. Can they be fitted into an enclosed filter housing? Just so I can run a snorkle....

Thanks!

[bee utey]

Thanks guys! Yep I'm planning on running a holley 350- I was looking at those new gen (by sprintgas??) mixers when they pop up on ebay but wasn't sure if they were suitable. Can they be fitted into an enclosed filter housing? Just so I can run a snorkle....

Thanks!
New Gen mixers were made by at least 3 different companies. Cutting up a steel carby style air cleaner and fitting it over the new gen is a fairly simple job, but you may be struggling for height unless you have a body lift. An old Holden V8 air cleaner may be most suited but they are getting hard to find these days.

Personally I don't like the new gen unless used with a large open chrome air cleaner. There are other ways, such as the adaption I made for a 2 door 3.5 last year:

http://www.aulro.com/afvb/attachment.php?attachmentid=34734&stc=1&d=1301784392

The RRC air cleaner is easier to service and keep dust-leak free.

[Felix]

Ok, so I could use a normal venturi style mixer also? I already have an old holden style air cleaner on the top of mine at the moment, with the aforementioned AMOS mixer glued into it.

I was thinking of running either a RRC airbox like the one in the picture or a K&N cone type thing (which is very similar) and just a venturi ring but wasn't sure if it would work?

FYI I have a 2" body lift so I don't think clearance is a problem here. Also I'm not scared of chopping my bonnet up if I need extra height (I need extra ventilation anyway).

Why would you not use the new gen with an enclosed filter? Are they not efficient when enclosed?

[bee utey]

Ok, so I could use a normal venturi style mixer also? I already have an old holden style air cleaner on the top of mine at the moment, with the aforementioned AMOS mixer glued into it.

I was thinking of running either a RRC airbox like the one in the picture or a K&N cone type thing (which is very similar) and just a venturi ring but wasn't sure if it would work?

FYI I have a 2" body lift so I don't think clearance is a problem here. Also I'm not scared of chopping my bonnet up if I need extra height (I need extra ventilation anyway).

Why would you not use the new gen with an enclosed filter? Are they not efficient when enclosed?

The function of any simple mixer is to create a vacuum in the gas hose proportional to the air flowing through it. It's shape is unimportant, but the size/effect is. You can fit the amos or a venturi shaped mixer to a custom holley top adaptor.

Mentioning K&N in LR circles won't win you many friends. They aren't fabled for their dust prevention, especially when over loaded or dried out.

The new gen desgn is not very efficient, period. I modify it for somewhat better results. Their main claim to fame is their ability to lift up the inefficient mixer plate with a vacuum lift for petrol. This is needed on Holleys as they hate restriction from the air intake. As far as the big chrome air filter is concerned, that is what little boys demand so they get it. Then they can have petrol performance unchanged for the days at the drag races (or traffic lights). I won't fit a new gen to a straight gas setup, there is always something more efficient.

[Felix]

Oh ok, yeah the only reason why i mentioned the k&n was the fact that they do sell an air filter enclosure like the landy one.. but I agree on the filtration properties!

In your opinion, what would be the best option for me? Its a 4.4 p76 engine with a 350 holley and a snorkle. I'm not looking for huge horsepower, I just need a replacement for my current setup!

You've been really helpful!

[bee utey]

Oh ok, yeah the only reason why i mentioned the k&n was the fact that they do sell an air filter enclosure like the landy one.. but I agree on the filtration properties!

In your opinion, what would be the best option for me? Its a 4.4 p76 engine with a 350 holley and a snorkle. I'm not looking for huge horsepower, I just need a replacement for my current setup!

You've been really helpful!

I suggest you fab up or find an adaptor that gives you a 76mm (3 inch) steel inlet pipe, fit up a venturi mixer of 40 to 43mm bore size, add an early RRC 3.5EFI air cleaner and adapt the snorkel up to it.

Look on ebay for a while, your 6 cylinder holden/ford efi mixers are quite common and would do nicely.

By the way you need a balance hose from the air cleaner inlet to the converter. It means the breeze across your snorkel head won't cause mixture variations. You may already have one, you metioned something about a hose and "vacuum" which would likely be it. My picture below shows one from the inlet side of the air cleaner.

[Felix]

Ah yes, balance hose thats what it would be! I was wondering what that hose did.

Ok, that sounds like a plan then. Thank you for your help, I'm a 4th year apprentice and do you think I can find someone to teach me info on LPG? Sucks!

Cheers!

[bee utey]

Notes on mixer design: a gas mixer is supposed to cause a vacuum in the lpg supply hose proportional to the air flow through it. Air flow over a hole perpendicular to the flow will create a vacuum (Bernoulli's principle I believe) Now an efficient mixer will create a vacuum signal for the lowest pressure drop across the mixer. To do that the air flow at the gas outlet must be faster than the average air speed through the mixer. A traditional venturi shape mixer is good at that, providing the gas outlet is a continuous slot right around the mixer, at the point of minimum diameter. Many venturi mixers feed gas through a series of holes and are not as efficient as the air flow across bare metal provides no vacuum.

The AMOS mixer is not bad as the nozzle jutting out into the air stream creates a local zone of higher air speed. But they are a bit asymmetric and can cause mixture imbalance when too close to the cylinders, ie not enough flow length to properly mix the gas/air. Some EFI engines are not suitable for them. They work best through carbies which help mixing.

The new gen mixer has a series of holes spaced apart so that only 1/3rd of the air flow produces a vacuum. Poor design. To fix this issue I get a thin steel ring cut out and fasten it over the ring of holes. This joins all the holes together and faces the gas outlet towards the engine. I can then raise the air plate 1-2mm and get better performance right across the range.

Now another thing about mixers. The gas flow is about 1/15th of the air flow, so there must be an immediate increase in diameter of the venturi downstream of the gas inlet. Otherwise the gas entering the air flow caused a pressure wave that effectively reduces the venturi diameter. Sometimes I can modify a poor design mixer in the lathe to improve it by creating a step at the gas outlet, usually 1 to 2mm deep.

I actually designed and patented a new type of efficient mixer years ago, but nowadays gas injection is where the action is so it doesn't matter anymore.