Adverse effect of cyclone air filter on engine

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Originally Posted by PhilipA

Just remember that the maximum airflow requirement of a petrol engine is only at maximum torque or horsepower .

At all other times the airflow requirement is governed by how open the throttle blade is and at usual operating the airflow is a fraction of the maximum requirement.

Having said that, when I used Unifilter socks in my RRC 3.9 snorkel, I could tell when the socks were starting to impede airflow as the engine felt constrained after about 3 days use.

The only real way to ascertain impedance to airflow is to place a Magnahelic pressure gauge in this case on the outside near the cenrifugal filter and the other sensor in the snorkel. This will give the pressure drop in inches of water . Under 10 is good over say 30 is bad.
Your filter body probably will give more impedance than the snorkel.
My wife doesn't like the one when I place it on my D2 TD5 because of the noise it makes.

Regards PhilipA
PS , IMHO it is only desirable and necessary to fit if you are on long stretches of dirt.

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As an experiment, I made a guard out of a carved up 2 litre soft drink bottle to explore the possibility of restricting the induction noise from mine. The very thin plastic made huge difference to the noise entering the cab through thee open window. When I get some spare time I'll make up something more permanent........probably after I'm dead[biggrin]
Don.

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Originally Posted by PhilipA

Hmm Lebanon is mostly mountains with a coastal strip.

I dont think there are large stretches of dirt except in the mountains and certainly not many/any bulldust stretches or long tracks like the GRR as in Australia.

I chickened out on going to Lebanon from Syria as many expats were being carjacked in the Bekaa valley when I was there in the 80s. I accidentally got onto the Beirut highway in Damascus but turned around as soon as I could even though I had an invitation from our Beirut based Locally Engaged Staff. Have looked over Lebanon from Crack de Chevalier.

One of our friends in DFAT was held as a hostage in a cave in the Bekaa Valley for AFAIR 8 weeks but luckily lived to tell the tale.

Regards PhilipA

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That was more than thirty years ago, Lebanon was the center of all possible and imaginable conflicts on earth.

Things have changed a lot yet I can't say it is over yet. Nevertheless a large part of the country is safe and secure. Last Spring I received a friend from the U.K. who is a prominent LR journalist, we had a two days trip to the highest peak in the middle east while visiting local wineries and gin distilleries .

You are absolutely right when you say that most of Lebanon is mountains, yet above 1800 meter the green lush vegetation disappears leaving the space for shrubs and small vegetation that can survive both the arid climate in summer and the snowy month of winter.
This area is very dusty and was the cause for installing the cyclone filter, yet at these altitudes as air get thinner, more air is needed for a proper combustion (naturally aspirated engines like the Rover V8 show a drop in performance.

As many have suggested I am going to replace the cyclone filter with a traditional ARB snorkel top to check the difference.

Cheers

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Originally Posted by Tins

I was tipping he might venture a little further...

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indeed, before the war in Syria I have visited Jordan many times, Syria, Turkey and Greece. When driving in a Land Rover the call for driving off-road tracks is permanent. [biggrin]

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Originally Posted by AK83

This could be due to so many factors, not just air intake(restriction).

Worn lifters, cam, or rocker shaft(assuming this 4.2 is a RV8) .. or carb tune, fuel pump .. etc.

Simple diagnosis is to remove the pre filter and see if you gain any lost power back on a run over a given road.

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The engine has been totally overhauled, with most parts replaced (Rocker shaft, lifters, cams, piston rings, crank shaft shell bearings,.....)

The only possible source is the carb tune.
I have the knowledge and the appropriate tools to successfully tune SU carbs.

The issue with the carbs on this engine is that when tuned to run properly according to the emission level at idle speed, it fails to reach its max power on acceleration, while if tuned rich it gives the power at high rpms while it is rich on idle speed.

I have had mixed opinions on the cause of this problem, for some the needles in the carbs are not the appropriate one to feed a 4,2 since they were fitted on a 3.5, for others the difference in the engine's volume doesn't require a change in needles and those already fitted could properly serve the engine.

I thinking that if the carbs are tuned properly at idle speed, could the cyclone filter and the raised air intake tube diameter restricting the amount of air needed by the engine to use the amount of fuel delivered by the carbs?

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Originally Posted by lebanon

The engine has been totally overhauled, with most parts replaced (Rocker shaft, lifters, cams, piston rings, crank shaft shell bearings,.....)

The only possible source is the carb tune.
I have the knowledge and the appropriate tools to successfully tune SU carbs.

The issue with the carbs on this engine is that when tuned to run properly according to the emission level at idle speed, it fails to reach its max power on acceleration, while if tuned rich it gives the power at high rpms while it is rich on idle speed.

I have had mixed opinions on the cause of this problem, for some the needles in the carbs are not the appropriate one to feed a 4,2 since they were fitted on a 3.5, for others the difference in the engine's volume doesn't require a change in needles and those already fitted could properly serve the engine.

I thinking that if the carbs are tuned properly at idle speed, could the cyclone filter and the raised air intake tube diameter restricting the amount of air needed by the engine to use the amount of fuel delivered by the carbs?

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Good to know .... that you know! [thumbsupbig]

I would try the test simply without the cyclone filter on. You don't necessarily need the snorkel top on it.
I've run my D1 TDi with and without it(just to see how it is affected) ... and noticed zero difference in the way it runs, which includes fuel economy. The only slight change was a slight drummy noise at a certain speed, which I assume is the flute effect as the top of the snorkel now would have air passed over it like a flute(maybe) ... not sure.
Obviously you don't want to run it like that all the time, and have debris and water fill the snorkel .. but all I suggest it to remove it and run it like this for a run or two and see if there is any more power without it on.

ps. I've also run the tip facing both backwards and forwards and at least on the low breathing tdi .. again zero difference in the way it runs, both performance and noise. Only slight difference in having it face backwards is a few less bugs get scooped into it.
If I were to waste my time and change it again from forward facing to rear facing, it would be only for the rare situation where you may drive through a swarm of insects and they get scooped into it.
But strangely even tho I had it facing backwards for a few weeks, it still got bugs inside it(at the bottom of the filter box) .. so my thinking here is that most of the bugs don't get scooped into it, they more likely see it as a nice secluded nesting place while car is at rest(maybe).

I'd also suggest that another test you could try is to disconnect the snorkel altogether, at the air filter inlet .. that is to save the hassle of removing it, all you want it the shorter path of air to the airbox.. not via the snorkel tubing. See if this helps with your power issue.
And to be sure, I'm suggesting to try these as single drive tests, not long term so it's not going to kill your engine in any way .. even if you run it without air filter for a quick trip.

Is it using an electric fuel pump?

A turbo will counteract restrictions in the intake whereas a NA engine will suffer from intake restrictions.

As for SU needles, just because the mixture is OK at idle doesn't mean anything for the mixture at higher airflows. I've reduced needle thickness, achieved by spinning the needle in a drill in emery cloth.

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Originally Posted by Graeme

As for SU needles, just because the mixture is OK at idle doesn't mean anything for the mixture at higher airflows. I've reduced needle thickness, achieved by spinning the needle in a drill in emery cloth.

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That's very interesting, by how much did you reduce the thickness of the middle and tip of the needle?

Cheers

I don't recall the reduction (it was more than 50 years ago) but I used a micrometer to check the progress and to make the 2nd one match. Only the middle section was reduced as the mixture was only too lean around mid throttle / mid power.

Remember that in naturally aspirated the higher you go the richer the mixture as the air mass is lower.
Regards PhilipA