Air Intake

Hello,

Just a bit of scientific philosophy for you to mull over regarding my new air intake / exhaust system. I had been running my 2.5 N/A with a K&N like filter bolted immediately onto the intake manifold, meaning that the maximum length of pipe the engine had to draw the air along was less than 30CM. The exhaust ran to the complete rear of my 90 with both a central and a rear silencer. Now my engine has the original air intake system fitted, with a re-enforced intake pipe of about 50CM in length running to the air filter box, and then the cone shaped intake arm sticking off that for about another 35cm drawing cool air into the air box from under my passenger side wing. My exhaust system is now a straight through pipe which exits at the side of my vehicle, just after the passenger side door.

Here's my line of thinking:

Think of the whole stove and flu system. In order to start a fire effectively, you would open the flu completely but restrict the amount of air that the fire can draw in, which with science applied, creates a strong vacuum as the fire draws in oxygen and the flames are very ferocious. If however, you restrict the amount of air flow through the flu, and have the front of the stove open, the fire will struggle to start, regardless of the fact that the fire is exposed to all the air that it needs.

Can I apply this theory to my engine? Now that the intake has been restricted to some extent, it will work harder to draw the air in, and now that the exhaust is less restricted, the general air flow through the system should be much improved. I know that there are technical differences here, such as the fact that the combustion is only apparent when there is compression in the cylinder - at which point the exhaust valve is closed, and therefore there is no continuous flow of air through the system. I am also aware that there is no continuously burning fuel at any given time requiring air in order to burn, which makes me think that the more air the engine can intake on the intake stroke will provide a much cleaner and more effective burn of the fuel, which I would, or should not be able to achieve with my current (original) intake system.

So what is truly the most efficient intake / exhaust system that you can fit to optimise engine performance? I'm a bit cafuffled! Any thoughts / opinions / theories?

-Pos

i rekon ya jus need as much air as yu can get and as cold as possible.

pos said:

Think of the whole stove and flu system. In order to start a fire effectively, you would open the flu completely but restrict the amount of air that the fire can draw in, which with science applied, creates a strong vacuum as the fire draws in oxygen and the flames are very ferocious. If however, you restrict the amount of air flow through the flu, and have the front of the stove open, the fire will struggle to start, regardless of the fact that the fire is exposed to all the air that it needs.

Can I apply this theory to my engine? Now that the intake has been restricted to some extent, it will work harder to draw the air in, and now that the exhaust is less restricted, the general air flow through the system should be much improved. I know that there are technical differences here, such as the fact that the combustion is only apparent when there is compression in the cylinder - at which point the exhaust valve is closed, and therefore there is no continuous flow of air through the system. I am also aware that there is no continuously burning fuel at any given time requiring air in order to burn, which makes me think that the more air the engine can intake on the intake stroke will provide a much cleaner and more effective burn of the fuel, which I would, or should not be able to achieve with my current (original) intake system.

So what is truly the most efficient intake / exhaust system that you can fit to optimise engine performance? I'm a bit cafuffled! Any thoughts / opinions / theories?

-Pos

Click to expand...

To start a fire, you want the opposite of what you said, lots of air, you want to open the bottom of the stove, or open the ash pan door for an open fire to get as much air as possible flowing up from under the fuel. In the case of a stove you do not want to let much air bypass the stove and go up the flu so close the bypass (unless it’s very windy and it starts to suck your kindling away).

Once a naturally aspirated engine starts running it creates a sort of siphon effect, where air will start rushing through the intake system rather than actually being sucked in as and when it needs it, and with the speed at which things are happening it can always go somewhere so it just keeps going. Your science doesn’t quite make sense here. An engine is not a stove; it just wants LOADS of air, as much air as possible, so each cylinder can get as much in as possible so that it can try and combust ALL the diesel.

So in answer to your question, the best setup is a turbo – simply adding a turbo without the injection pump boost compensator would be the best intake setup for a naturally aspirated engine, with regards to exhaust, it just wants rid of it. 6inch drain pipe for all it cares.

cold air is good as its more dence , but restricting the air flow to produce more of a vacume will only lead to less air going into the cylinders ( turbos do this for you by cramming air inro the system , but more fuel is needed to account for the extra air ) .

throw your flue idear out the window as id doesnt work that way for internal combustion engines , basically you need to get rid of the exhaust gasses as quickly as possible to allow the next induction stroke to be a free of spent gasses ( you will never get this 100% due to valve overlap ) .

run your motor with no centre section to reduce back pressure , that will help a bit , but dont reduce your intake pipe size as you will be starving the engine of air .

As cold as possible yes and as much air as possible yes, but this is the thing. If there is just one great big hole drawing in air, as opposed to a smaller and lengthier system, it's not really going to draw in as much as it can is it because there's a much larger surrounding volume of air which isn't really drawn in. It's hard to explain!

Ahh right. Why did land rover not just put a big fat air intake box on there in the first place then? Is the conical extension of the air box just to reduce noise some how?

discomania said:

To start a fire, you want the opposite of what you said, lots of air, you want to open the bottom of the stove, or open the ash pan door for an open fire to get as much air as possible flowing up from under the fuel. In the case of a stove you do not want to let much air bypass the stove and go up the flu so close the bypass (unless it’s very windy and it starts to suck your kindling away).

Once a naturally aspirated engine starts running it creates a sort of siphon effect, where air will start rushing through the intake system rather than actually being sucked in as and when it needs it, and with the speed at which things are happening it can always go somewhere so it just keeps going. Your science doesn’t quite make sense here. An engine is not a stove; it just wants LOADS of air, as much air as possible, so each cylinder can get as much in as possible so that it can try and combust ALL the diesel.

So in answer to your question, the best setup is a turbo – simply adding a turbo without the injection pump boost compensator would be the best intake setup for a naturally aspirated engine, with regards to exhaust, it just wants rid of it. 6inch drain pipe for all it cares.

Click to expand...

With regards to starting a fire in a stove, we've got a wood burner in the garden, and it would seem that the best way to get the fire picking up is to open up the vent at the bottom (below the grill)and then hold a sheet of news paper accross the grill at the front so that the burning paper / twigs draws more air though and gets going. Then when you can hear it roaring, you'd remove the sheet of paper and the fire would settle down and burn nicely.

discomania said:

simply adding a turbo without the injection pump boost compensator would be the best intake setup for a naturally aspirated engine.

Click to expand...

You wont see much in the way of power increase as doing it this way as diesels draw the same amount of air each stroke whether its at idle or flat out , the only thing that changes is the amount of fuel injected . Turbos in relation rams the air into the cylinders but without the extra fuel to make use of this extra air its waisted yeah you get a cleaner burn as there is more air , but no real increase in power due to lack of extra fuel .

so you'll be fitting a Morso under yer bonnet next Pos ?

I doubt it!

pos said:

With regards to starting a fire in a stove, we've got a wood burner in the garden, and it would seem that the best way to get the fire picking up is to open up the vent at the bottom (below the grill)and then hold a sheet of news paper accross the grill at the front so that the burning paper / twigs draws more air though and gets going. Then when you can hear it roaring, you'd remove the sheet of paper and the fire would settle down and burn nicely.

Click to expand...

ya rate bout ya stove,the paper ova the front meks the air draw under and thru the fire,mekin it pickup n burn hotter.

pos said:

With regards to starting a fire in a stove, we've got a wood burner in the garden, and it would seem that the best way to get the fire picking up is to open up the vent at the bottom (below the grill)and then hold a sheet of news paper accross the grill at the front so that the burning paper / twigs draws more air though and gets going. Then when you can hear it roaring, you'd remove the sheet of paper and the fire would settle down and burn nicely.

Click to expand...

You said you would open the flu completely but you were talking about a garden stove so you just mean, all air out the top (what the hell does it heat?).

In a normal house stove if you open the flu - the bypass - all the air goes in above the fire and there is heehaw sucked though the fuel. Down low is an ash pan and the air inlet control which may be thermostatically controlled or just a little sliding/turning door, opening the ash pan door will let in HUGE amounts of air, up through the fuel (stove door closed) out into the flu (flu bypass closed so all air MUST come from the stove).

'ere pos, i see what youre trying to say, but...
your flu relies on the heat of the fire to pull the air in.

the engine relies on the vacuum created by the piston moving down.

So, you want as little resistance as possible - why else go to the trouble of polishing the ports of an engine?

As for the question of why LR don't fit K&N's from the factory

do you think you K&N will cope as well with hundreds of miles across deserts, with dust, sand, as well as muddy areas, snow, etc, as the clever cyclone filter system on the LR?

Also, i bet your K&N is louder than the stock filter.

In fact i know it is, cos i have one too.