CNG Air Blockage

[oyomantis]

Hi all,

Just wanted to ask

1. If blocking the air passage necessary for CNG?
2. Also when converting back to petrol, what negative impact this blockage can have?
3. I have Tomassato Lovato 4 CIP Advancer/Emulater, it means that i dont need to manually rotate the distributor, right?

Thanks all.

[Xulfiqar]

if your venturi is not correctly sized you may need to block the air inlet for gas suction purposes.

Ive done a CNG conversion on a freinds Accord and my moms carby Accord too with the regular Landirenzo unit, no air inlet blocking etc, and it works perfectly at 35 degrees base advance - that setup is so good that the rpms rise as fast as petrol and if I go full throttle - and the secondary throttle opens up - the CNG regulator diaphragm maxes out (cannot supply enough gas to the engine).

I have replaced the regulator with a larger engine one, it uses vacuum signal lines to move the diaphragm quickly

[luckybilal]

Gurus here at PW don't recommend air intake block. But most illiterate mechanics do this. I have experience of driving my mehran with both block and unblock settings. But unblock is so smooth and top speed is also great.

[cracked]

i dont knw much about cars frankly but air block is plain stupid..there is a screw on cng kit to adjust air-fuel mixture...

[ahmadbila]

my city idsi's intake is blocked 60%. i once took it off, didnt feel any considerable difference on petrol but the engine wud stall on cng instantly.is there any way to keep it alive on cng widout the blockage?

[Getafix]

^^
If you take it off then you just need to adjust the knob again as mentioned by cracked.

[zealous]

my city idsi's intake is blocked 60%. i once took it off, didnt feel any considerable difference on petrol but the engine wud stall on cng instantly.is there any way to keep it alive on cng widout the blockage?

same problem here. but is this knob available in all kits?

[oyomantis]

If i remove the air passage...wont it mean i have to "richen" the gas mixture and lose some economy?

Also because of the advancer, i need not adjust the distro by rotation, right?

Thanks for all the replies.

[Xulfiqar]

my city idsi's intake is blocked 60%. i once took it off, didnt feel any considerable difference on petrol but the engine wud stall on cng instantly.is there any way to keep it alive on cng widout the blockage?

You need an genuine LandiRenzo venturi - the ones our pakistani CNG shops install are stupid - die cast and have an injection pipe sticking in it.

The original venturis are fed gas from its outer edges through tiny slots all around the venturi - the throat of the venturi is crafted like a wing and tapers downward into the throttle bore. As the engine is accelerated and negative pressure pulls gas through the slots - the air volume is trying to multiply due to the wing effect and flowing gas on the venturi surface but cannot because of the throttle plate, this effect pulls out more gas from the regulator.

get the idea. thats how my experience got me to a point that the regulator was maxing out before wide open throttle - (CNG mechanics and sellers looked at me and my car in disbelief) - Engine mein itna suction kaise hai woh bhi itni puraani car mein - and yes even if I open the air cleaner top - my engine will not stall - it may reduce revs by a 100 but not stall or misfire. All because I used the original precision cut venturi (they cost about Rs 8500/) for a small car

Ive also converted a couple of Mercedes Benz 230E (K Jetronic) to CNG with original precision machined LandiRenzo Venturi (they cost about 220 Euros) and one is running LPG - the LPG one is very very nice n smooth with nearly 90% similar power as petrol

now if your venturi is stupid and ugly and was made with no precision - your engine will not suck gas properly and then you need to block air for the negative pressure (vacuum) to suck gas into the engine. Cheap as$ way to send a customer back home who only cares of sitting in the driving seat

[smijaz]

^^
Nicely elaborated, thanks for the input

[dr3vil]

i tunned CNG yesterday and mechanic was blocking my mehran's intake as i have plans for sports intake in the car in near future i told him to adjust rather then block but still car is knocking it needs complete remap of tapets
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[shoodi]

FLOP IDEA ..
It will Ruind ur engine
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[shoodi]

Ist Tuned ur Car in Petrol ..
Then try the best CNG SETTINGS AND IDLE .. RPM
dont block the pipe ..

[Navigator]

@Xulfiqar, thanks mate, u cleared one misconception I had about the Venturi. Two questions though.
1. Where to find the originals ( especially Lahore )?
2. Which type of venturi would fit best in Civic, 7th gen?
Appreciate ur help in that regard.

[Temojin]

@Xulfiqar

You have provided us with a complete solution yet for people like me who can't afford such a utility at the moment would go with blocking the air intake Is there any way around as there are for sure which includes having the same kind of venturi by some local or cheaper manufacturer which would last a bit lesser yet good enough to provide the necessary operations for a year or so. And yes I too want to ask the venturi type for 6th gen civic. I have noticed that carby engines don't need any blockage at all but local venturi/s do the job. They also don't need advancers and don't knock on gasoline whenever driven on it. I too have an issue with the advancer and need to change it as I manually need to advance or retard timing (I have no. 12 wrench for it) but it is annoying almost all the times so would you suggest any advancer which can eliminate this issue as there are many yet I need to know the one which would really work even at higher speeds while providing good economy as I am getting now a days.

Cheers n thanks for the information that has already been provided.

[Xulfiqar]

any proper advancer should work, some intercept the crank sensor pulses to provide their own (some intercept map/maf signals) some are used to intercept the ignition feedback signal on toyotas

for a proper venturi - theres no subtitute - you may get nearly good performance with a burner (hole aperture) venturi - but those are hard to come by too. Other than that I can recommend that the feed pipe be placed on the throttle in such a manner that as soon as the throttle is opened gas is sucked in - its ideal to have it facing the side of the throttle blade that is out - it will get maximum vacuum signal that way

[themaster]

@ Xulfiqar, can you please post the picture of original landi ranzo venturi? i never seen the type of venturi you stated. and what is the price of that venturi?

thx in advance

[Vaqas1]

In Carb cars they drill a hole in the carb and install that injector thing now with that you dun need any air blockage and your car willl even run without any air filter box. Though most people dont like this system but i found it to be very reliable one i mean its been 1 year i never ever faced any cng problems.

[asad1]

Zulfikar can u show the pic of venturi ?
wats the difference ??
does local venturi leak gas or vacuum?

[Xulfiqar]

These pieces are precision machined - not your local piece of junk that you get. Let me find a Honda Accord Carby one - its got two feed pipes