4000cc, 6 cyl, CNG/ Petrol Issue. Some imp questions

[noman8ff]

Dear colleagues, before directly going on to the topic, let me first define my vehicle.

I have an 89 model land cruiser with original 3F 6 cylinder carburetted engine 4000cc. The engine has never been opened before and the current mileage is 3,43,000 KM's. The vehicle was in use of ISI and is in mint condition.

It was giving me an average of 6KM's in a ltr (roughly 12 Rs a KM) so decided to convert it and therefore installed a landi renzo cng kit with 2 X cylinders some 6 months back and now the average has come to almost half, like 5.5 to 6rs a KM.

It would touch 165KM on motorways on petrol and goes till 130 to 140 on CNG now. No venturi and no injector.

The air intake is blocked 60%. Last week i got some impression from a different thread that blocking air is bad for the vehicle.

Last week i had a plan to modify it in a way that i should have a manual cable inside the dash board like that of a ckoke, which if released, will block the air intake to 60% and if pulled, will keep the air flow 100%. The vehicle already has an advancer which on pertol keeps the timing on 10 and on CNG it takes the timing to 20 or 22. So by this modification i will get best performance on both fuels. Remember, its a single butterfly carburetter.

Now have said all this i have few questions.

1. Is air blocking bad for the vehicle on petrol only or it has some bad effect on CNG as well?

2. If i install a venturi in it, would it not effect the performance on petrol?

3. Should i go for the manual air blocking modification or should i go for the venturi? My mechanic said that if i want to have the venturi system we can fix a 6 cylinder chevrolet venturi in it.

Your valuable comments will be highly appreciated.

Noman Hadi

[iLLDuDe786]

Unblocking it will give you issues on idle, unless you tune your car correctly on petrol.

[memad]

Masha Allah, cleanliness is impressive. This army really took good care of this beauty.

I have seen that bigger engines do not need air blockage. If no venturi then how gas is injected in the carb?

[hash4u]

6 rupees a km in army and isi jeeps, this is where all our tax money goes into

anyways

air blockage has no harm on cng . its all done to have a perfect combo of air/cng and to make the car iddle smooth
however on petrol, engine has to put more stress for air suction, economy and performance drops from the blockage

venturi also restricts air to some extent but if right now ur air intake is blocked 60 percent, even after venturi, still u would need to block the intake

i think the manual choke idea isnt bad if u frequent run the car on petrol. most cng users run car 99 perc on cng. so even if its 80 percent blocked, people dont care

[Drift_Boy]

Good' Old carby simple engines no electronic crap

[alee1]

Is air blocking bad for the vehicle on petrol only or it has some bad effect on CNG as well?
air blocking is bad for petrol,cuz it has higher clorafic value,hence needs more air to burn if u give it less ur landcruiser engine will tow ur ride like mehrans engine is towing it.(at times ull feel k gari ka dam ghut gaya hai).
2. If i install a venturi in it, would it not effect the performance on petrol?
i will discuss this with my dad as he is asleep now.will comment on this later

1. Should i go for the manual air blocking modification or should i go for the venturi? My mechanic said that if i want to have the venturi system we can fix a 6 cylinder chevrolet venturi in it.
   manual is superb idea as u can still adjust it.(in my mind is something like knob or air throw in car.u turn it more u get more air,u restrict it u get less air.to be specific it will help u alot as u can tune your car while actually running it.which is obviously better cuz even the computerised tuning is done when cars at rest and engine running without loads.when ur car would be set on load.obviously u will get max power n max efficency.which also says ull get max economy

[alee1]

venturi helps alot in proper mixing of gas.do get it installed.if u want me to explain the phenomenon of how venturi works.just letme know n i will do it for u.
regards

[noman8ff]

@ hash4u, thanks for the advise brother.

@ alee1, thanks for the detailed answer. But you are approving both manual setting or the venturi system so i am confused. Please suggest only one out of these two. Also did you discuss the venturi matter with your dad?

@ all, i am still waiting to hear more output on this.

Regards
Noman

[ahmadbila]

many many experts have written in different threads that air blocking isnt gud for the engine on cng and petrol, both.they also wrote that a well trained mechanic CAN make a car idle smoothly on cng withOUT the blockage, although, when asked as to HOW to tune the car that was (after removing the blockage) no one answered my query other then saying that a "well trained mechanic" can do it... now, my mechanic is really really well trained, worked under a proper automobile engineer for years but still hes unable to do this job... i wonder just how much WELL TRAINED mechanic is needed for this job

[xenerking]

@ hash4u, thanks for the advise brother.

@ alee1, thanks for the detailed answer. But you are approving both manual setting or the venturi system so i am confused. Please suggest only one out of these two. Also did you discuss the venturi matter with your dad?

@ all, i am still waiting to hear more output on this.

Regards
Noman

it depends upon the cng kit u r using...as per landi renzo official....common kits are using negative pressure created by corburator thats why to achieve maximum efficiency air has to be blocked....

otherwise u need to intall an inteligent omega kit which uses variable gas flow automaticaly being adjusted by microchip to achieve effeciency but thats v expensive...

this information was givem by mr Murtaza Ali deputy manager technical landi renzo pakistan

[noman8ff]

@ ahmadbila, janab aap nay meray dil ki baat keh di. My mechanic is also very sound and deals with all new and old technology vehicles. But he tells the same story what you say.

@ xenerking, thanks, will discuss this option as well.

[Proverbial_Slang]

many many experts have written in different threads that air blocking isnt gud for the engine on cng and petrol, both.they also wrote that a well trained mechanic CAN make a car idle smoothly on cng withOUT the blockage, although, when asked as to HOW to tune the car that was (after removing the blockage) no one answered my query other then saying that a "well trained mechanic" can do it... now, my mechanic is really really well trained, worked under a proper automobile engineer for years but still hes unable to do this job... i wonder just how much WELL TRAINED mechanic is needed for this job

Bro it is not possible to explain how to tune an engine on CNG. The process requires multiple adjustments and fine tuning after after removing the blockage. It also requires several test runs to check the adjustment. If you want, I can do it for you but I really won't be able to explain it here.

As far as the blockage is concerned, I never recommend blockage and have successfully tuned a few engine on CNG after removal of intake blocakge. The performance gain is marvelous.

[noman8ff]

@ Proverbial_Slang, brother thanks for the reply. I would again ask the same question.

Would the blocking air is only bad for petrol or it harms the working on CNG as well. If it is only bad for petrol, than i'll think something different for blocking and freeing the air flow manually (from inside the vehicle) for both the fuels. And believe me, i have good ideas for that modification. But let me first get everyone's opinion.

[accord7362]

Pakwheels is such a great place @Noman
@illdude,@provilbile_slang,@xenerking,@ahmad,@ali,@hash,@memad they are all great people to chat & gain knowledge, they all are rite and you are also rite & this physical method which you are using is very good and I'm getting impression that mentally you are satisfied with it so go ahead, mental stratification is the main thing and you know your car the best.

according to my personal experience I used to tune my 83accord myself without blocking air & I will copy @provibile_slang that there is no written method to achieve that setting its just a hit and trial method.

& blocking air intake will not harmful on CNG but yes on petrol your engine need to struggle for sucking air its same if you block one of your nostril.

[devilzz1]

intake.jpg (0 Bytes)

I've got an intake (which means more than normal air) installed in my car (Khyber carby) which is running on CNG / Petrol, the car performes exceptionally well on both kind of fuels. Air intake is installed on a ventury.There is no issue when the car is idle either on CNG or on Petrol. The only care i have to take is to keep the air filter clean i.e. have it aired every now and then.

[alee1]

@noman8ff
i have explained method of tuning in another thread by gulsher,title how to do cng tuning,i dont know the name exactly.but it means same as i stated.
air blockage is necessary as petrol is long continues long chained hydrocarbon-let it be and leave it for time being.while cng,i.e methane is hydrocarbon posessing short structure ch4.during combustion this matters alot.petrol has a very high calorific value.and long chained hydrocarbons need more air to form carbon dioxide from hydrocarbon and water vapors.while in gas it has low calorific value.since petrol has high number of hydrocarbon it needs more air and gas having less hydrocarbons needs lesser air as compared to petrol.that is why air blockage is needed.
i hope u got what i said.
now without blocking.
IMO without blockage when u give more air intake-u obviously need more gas to run reaction (combustion) in forward direction.more gas means less milage.
so far i havent done this experiment in my car.my car is 95 margalla.i tune it myself,do tappits myself.and it gives me 160 in city w/o ac.on longer runs it easily fetches 200+ kms in single 55kg cylinder.max limit is 207kms.
i will practically try to do tuning without air blockage and tell u ppl results asap.
now i will answer your questi0n which you asked.
sir venturi is something else and manual air setting is something else.i will try to tell u what these things are actually according to my limited knowledge.
venturi is a pipe.it has a little hole in it.when air is passed through this pipe takes air from that hole and vaccum is created.here another pipe is connected to the hole which is of gas.so according to flow of air the gas is taken accordingly and the mixture is just a perfect receipe.yummy.ur car`s performance would be superb.excellent economy.alla pick etc etc...
respected sir air blockage would still be needed even if u install venturi.the reason being is k u have cng kit which has pressure regulator in it which controls the amount of gas intake as per your throttle responce.but u dont have anything to control the amount of air intake.or do you?
the air intake has its size and keeps constant.it dosent decreases neither increases.only the amount of air passing through can vary-when high revs are attained,higher amount of air is su*ked and vice versa.but that air intake is designed for petrol.and petrol needs more air then gas as i explained earlier.so this air blockage has to be there in every case.
what i extracted from your words that u wanted to install manual air blocking system.i was very excited to see as i interpreted as "you wanted to install some mechanism by which you can restrict the blockage of air intake by having some choke sorta mod.what i planned for you was something like air throw adjuster like rheostat.like fan regulator.u can maximise air flow and you can fully block it.it was go0d in sence k we dont have hard and fast rule for air blocking,and by hit and trial method and by running your car and then setting air intake would seriously help with very go0d results.in that case u can set air flow for optimum performance on gas.open it completely when you are driving on petrol and it may act as CHOOR switch when u block the air intake and in that case your ride wount start even it is nuclear powered (kidding)
i hope this article helps in answering your most of queries and clearing your misconceptions regarding CNG.still if i missed something you can ask me.or if i m wrong at any place you can guide me.thanks
regards

[noman8ff]

@ alee1, brother thanks for the detailed reply. I understood the matter completely.
I think i shall go for the manual modification. And for your interest, i have planned three different types of mods. Will reconsider their practicability in detail and choose one. Defenately, will give pics when start doing it.

[xenerking]

@noman8ff
i have explained method of tuning in another thread by gulsher,title how to do cng tuning,i dont know the name exactly.but it means same as i stated.
air blockage is necessary as petrol is long continues long chained hydrocarbon-let it be and leave it for time being.while cng,i.e methane is hydrocarbon posessing short structure ch4.during combustion this matters alot.petrol has a very high calorific value.and long chained hydrocarbons need more air to form carbon dioxide from hydrocarbon and water vapors.while in gas it has low calorific value.since petrol has high number of hydrocarbon it needs more air and gas having less hydrocarbons needs lesser air as compared to petrol.that is why air blockage is needed.
i hope u got what i said.
now without blocking.
IMO without blockage when u give more air intake-u obviously need more gas to run reaction (combustion) in forward direction.more gas means less milage.
so far i havent done this experiment in my car.my car is 95 margalla.i tune it myself,do tappits myself.and it gives me 160 in city w/o ac.on longer runs it easily fetches 200+ kms in single 55kg cylinder.max limit is 207kms.
i will practically try to do tuning without air blockage and tell u ppl results asap.
now i will answer your questi0n which you asked.
sir venturi is something else and manual air setting is something else.i will try to tell u what these things are actually according to my limited knowledge.
venturi is a pipe.it has a little hole in it.when air is passed through this pipe takes air from that hole and vaccum is created.here another pipe is connected to the hole which is of gas.so according to flow of air the gas is taken accordingly and the mixture is just a perfect receipe.yummy.ur car`s performance would be superb.excellent economy.alla pick etc etc...
respected sir air blockage would still be needed even if u install venturi.the reason being is k u have cng kit which has pressure regulator in it which controls the amount of gas intake as per your throttle responce.but u dont have anything to control the amount of air intake.or do you?
the air intake has its size and keeps constant.it dosent decreases neither increases.only the amount of air passing through can vary-when high revs are attained,higher amount of air is su*ked and vice versa.but that air intake is designed for petrol.and petrol needs more air then gas as i explained earlier.so this air blockage has to be there in every case.
what i extracted from your words that u wanted to install manual air blocking system.i was very excited to see as i interpreted as "you wanted to install some mechanism by which you can restrict the blockage of air intake by having some choke sorta mod.what i planned for you was something like air throw adjuster like rheostat.like fan regulator.u can maximise air flow and you can fully block it.it was go0d in sence k we dont have hard and fast rule for air blocking,and by hit and trial method and by running your car and then setting air intake would seriously help with very go0d results.in that case u can set air flow for optimum performance on gas.open it completely when you are driving on petrol and it may act as CHOOR switch when u block the air intake and in that case your ride wount start even it is nuclear powered (kidding)
i hope this article helps in answering your most of queries and clearing your misconceptions regarding CNG.still if i missed something you can ask me.or if i m wrong at any place you can guide me.thanks
regards

+1

[xenerking]

Bro it is not possible to explain how to tune an engine on CNG. The process requires multiple adjustments and fine tuning after after removing the blockage. It also requires several test runs to check the adjustment. If you want, I can do it for you but I really won't be able to explain it here.

As far as the blockage is concerned, I never recommend blockage and have successfully tuned a few engine on CNG after removal of intake blocakge. The performance gain is marvelous.

it really pains me whenever i c air intake of my car blocked, and i believe that its injustice with the engine and engineering being put into it...

so after couple of trouble free cng running months...one day i decide to remove the air blockage...so first i get the plugs sorted out...airfilter removed and TB cleaned with different sprays...and them i remove the bloakcge with big hopes....and start try to tune it ... to my surprise i have to open up the gas from gas flow controller and somehow i succeed in getting it idle smoothly....but i never stays like that....it stall on turning on the air conditioning....but performs really well...

so after enjoying lot of torque and lots of stalls and start ups....i go back to same air blocking technique....

BTW....i can tune carburator engine perfectly with out air bloackge...but had little succes on efi...

i would really appreciate if u cud help me in this regard...plz contact me and we can fix some time for this DIY...thanks in advance!!!

[alee1]

@noman8ff
most wellcome sir.the pleasure was all mine