Hi all.

I've just had the joy of pulling off my intake piping on my gas converted EF II and found an ugly mixer in there with a huge restriction. So, I spent 5 mins thinking about it and I'm going to TRY an intake piping design that I've got in my head.

Basically, it will have two passages the air can take to the engine controlled by flaps actuated by small stepper motors. This will allow me to run the gas mixer in one passage and divert all air through there when I run on gas, but leave the intake unrestricted when on petrol.

Comments? Suggestions?

like this? (impco)

Sounds good, not entirely a new idea. The LPG system I had on a V8 XC 18 years ago had a cable operated flap that you opened to run on petrol. Your dual passage system seems to be a modern improvement to an old idea.

Nah, I don't think he means like yours fuzion, yours still has to run through the mixer when on petrol.
Yeah it's a good idea. But only if you actually use petrol. To me petrols an emergency fuel now. Especially with the high prices. So the extra weight and cost of a dual intake system would just be a pain in the a** to me. But for someone who reguarly runs both fuels it's a top idea.

tw, im straight gas

str8 lpg 4 me too...i dont even have my fuel pump hooked up...

Yeah I knew that. But in this case he's looking at seperate piping for each of the fuels and a switch to change over which piping it uses when he changes fuel. So I was just saying that say yours was duel fuel, as you asked "like this?".
Anyways, it's a good idea, but I don't see why people use two fuels, I mean LPG's so much cheaper. And if you ever go back to running on petrol just get the injectors cleaned.

yes but to get the injectors cleaned cost $$
might as well run petrol through em
and saves alot of hassles!

good idea! man do it!

This ise my reason for wanting to make up this intake.

The car is dual fuel. While no-one puts LPG on a car to increase power, I see no reason why you should sacrifice petrol power in favour of LPG economy. I want the best of both worlds! Even the Tickford setup reduced petrol power output by 7kW @ the fly compared to a petrol only engine. The ELKO gas on my car seems to reduce petrol power my a lot more that 7kW.

I measured up the gas mixer, and the area of the throttle body is about 3 times larger that the area the air has to pass through with the mixer in place. Area of air passage in mixer - approx 5000mm2. Area of throttle - approx 14,000mm2. That is one mighty huge restriction if you ask me. No air cleaner/snorkle setup in the world can compensate for that restriction.

The only thing that might stop it from working if that the mixer would be a fair distance from the throttle body. I'm hoping that won't worry is as it relys on the pressure difference bewteen each side, and the pressure difference would stay relatively the same with an increased distance from the throttle.

If you want to have a little fun and build a better lpg system, why not spend the effort on building a liquid injection system.

At the least you will get similar power to petrol, at best more power than petrol. In either case you will get great cold start, low consumption, more torque, no risk of ignition within intake plumbing, yada yada yada. Once your satisfied with power, you can also toss the petrol tank and other unessesary bits which would result is a few less kilo's to drag around.

lpg liquid injection theory is simple - lpg tank with internal fuel pump and piping runing to an injector rail and back to lpg tank (possibly via a cooler), a phenolic spacer to thermally isolate the intake from the hot head, maybe ceramic coated exhaust to keep heat inside teh exhaust, a modified engine map (or piggy back comp which modifies injector pulse width) and side or bottom fed injectors should seal the deal.

In any case lpg liquid injection seems more interesting than stuffing around with the poor cousing of a carburettor

Oh, and if it's too much to develope, i am told a comercial lpg liquid injection systems will be on the market in hopefully 6 months at $2500 installed

Cheers, Itchione

Holden are offering duel fuel Commodores from next month featuring sesquential injection LPG.

You just missed the whole point of my thread. Congratulations!

I'm talking about a low cost modification to RETAIN the power of petrol in a DUAL FUEL vehicle and not the the intake restriction of LPG hinder the petrol system.

The power loss associated with LPG use is hardly due to any restriction caused by
a mixer in your intake system and i very much doubt that the mixer is loosing
you any appreciable petrol power output either.

If you believe that you do loose petrol power due to the lpg mixer, why not apply
an engineering approach to the problem and test this on a dyno with and without
the lpg mixer ? You will quickly learn what the differance is and have some real
info to plan further work on - a base line if you will. Such info would be worthwhile
and give you an idea of what you could gain with dual intake assuming no
futher restriction was caused by the new plumbing. Done on a 'dyno day', it should
be a cheap investment on getting this data yourself. Without such baseline testing
how would you know if the mods you propose would give you any benifit at all ? As i
suspect there may be next to no noticable gains to be had !

As for setting up a dual intake system and not creating other restriction problems,
this is not a trivial task - if it was simple and resulted in any sort of gain, it
would have been done already. I would expect you could have a petrol side intake
with similar restriction to standard petrol only system but the lpg side would be
horendously restricted as space for the plumbing would be limited. Even more
compromises than a standard dual fuel system would have to be made.

The reality is that most dual fuel system are a real compromise especially when running
on lpg. The fact that (tick)ford run a dual ignition map to advance the timing when
running on lpg and only loose some hardly noticable 7 kw says much for the good design
of their system. You could learn lots from it.

Just consider how much power you would loose on a modern I6 running on petrol if you
removed the injection system and installed a carburettor (and had to meet pollution
requirements). Conceptually this is what (tick)ford have had to do with the lpg setup
so you should appreciate their current lpg system even more so.

Your suggested solution for a lack of power on lpg is to spend effort improving petrol
power in a compromised dual fuel system seems backwards to me, especially when you want
an lpg system to save the folding stuff when refuelling.

I was mearly stating that another, and in my view more appropriate solution to your
problem is to optimise one fuel and that a liquid injected lpg system would give you
more power than a petrol only system and be much more interesting an engineering problem
than intake plumbing.

You wanted comments and suggestions so i gave them but now you say for the first time
that your looking for a low cost solution and congratulate me on missing the whole
point of your thread.

Maybe my mistake was to make a very big assumption that your car was well tuned and
maintained and thus running optimally, within the current limitations of your
system, on both lpg and petrol.

Maybe i should have answered you with a range of service and maintanace advice to solve
your low lpg power problems, or maybe i should have just answered 'wow that cool can't
wait to see that' as i suspect you would have been happier with such an answer.

Do what you will but whatever you do, nothing is free as it will cost you in either time
or money but i just hope you take a bit more of an engineering approach and spend a bit
more than 5 minutes assessing what you real problem is before jumping
at a solution.


Cheers, Itchione

You're still missing the point itchieone.

I didn't convert my car to gas. It was bought with dual fuel. It doesn't have tickford gas on it. Please read my posts.

The economy of LPG is a bonus, but you can not seriously say that reducing the throttle area by 64% isn't going to cause any power loss. It is well known, tested and proven that a good snorkle/air filter setup will give you more power.

The extra restriction that a standard snorkel/air filter setup gives you over a good setup is no where near 64%, yet it's been proven that a standard setup will decrease power. You say it won't. Could you please start a new post informing everone not to waste their money on K&N air filters and XR8 snorkels?

If I had any desire to run one fuel, it would still be petrol.

Now, thankyou for giving me your view on teh dual intake idea. I did not ask for your opinion on a gas only setup, nor did I ask for you speculation on whether or not I maintain my car that I have only had for 5 days.

There's a member who tested that theory, dynoed his car before, then put the mixer on the lathe and removed some of the inside to increase the hole that the air travels through, then dynoed the vehicle for an 8kw increase.