Please explain how the intake and exhaust manifold works

Ive always wondered how the intake and exhaust manifold works on the older tractors.
For example you pop the hood of a truck the carb is sitting on the intake which is on the top of the motor each cylinder has a port that goes from the intake to the heads.then your exhaust comes out of the side each cylinder has and exhaust port.



You look at a tractor the carb is hanging from the intake and the fuel mixture goes up the tube then into the motor.

For example my 8n ford has a 4 cylinder engine in it i currently have the manifold off its got a total of 6 ports so how does it work with out each cylinder having a intake and exhaust port. The intake and exhaust manifold are one piece.


Ive owned and worked on a bunch of antique tractors but never really understood how that setup would work.


Does anyone have any pictures or a simple way to explain it

Thanks

The older cars shared an intake manifold so the exhaust would warm the intake mixture and help it vaporize.

No need on fuel injected cars, that is why newer ones have manifolds on opposite sides.

Air fuel mixture is drawn in the engine head thru single port but Ys off to adjacent cylinders in the head, via porting inside the head.----------------------Loren

The older engines that share intake runners are called siamese intakes.

These are next to impossible for port fuel injection, thus it is an obsolete design.

Your Ford has EI IE EI IE.
As has been explained , the intake feeds 2 cylinders south of the Carb and 2 cyl north of Carb.

It was never a very good system, but worked. too much mixture differences between cylinders.

My way of saying it is that the intake manifold facilitates the
volume of air required when the piston moves down on the
Intake stroke with the intake valve open.
Likewise the exhaust manifold facilitates the removal of the
spent air fuel after combustion with the exhaust valve open.
All possible because atmospheric pressure is about 14.7 psi,
and the engine is an air pump.
Air is displaced by the movement of the pistons and positive
atmospheric pressure rushes to fill the void.

The older engines, could be in a tractor, or car, truck, boat, just about anything, used an "updraft carburetor". The main reason was to keep the carb low, so no need of a fuel pump.

The manufactures wanted to keep everything as simple as possible. They actually wanted their product to last and be trouble free, and be field serviceable. Hard to imagine that concept today!

As for how the intake works, if you'll trace the flow, you'll see why there is only 6 ports instead of 8.

Before we start, keep something in mind. The moving gasses, whether they be fresh air with suspended gasoline vapor going in under a partial vacuum, or flaming hot, still burning exhaust gasses coming out under extreme pressure, they both have velocity. They follow the law that "an object in motion tends to stay in motion, an object at rest tends to stay at rest". The design of a good manifold will take that law and use it to the best advantage to make the engine as efficient as possible.

Starting with the exhaust, each port coming from the engine dumps into a common collector, or the body of the manifold. The collector is constantly pulsing with start-stop bursts of hot, still expanding gasses. The object is to use these pulses of energy to create a draft effect that actually creates a vacuum on the adjoining ports, helping to draw out as much of the trailing end of the exhaust stroke as possible. Exhaust manifolds are somewhat effective at this, but the effect favors some cylinders over others. That is the reason behind performance engines using "headers". Real headers are constructed of equal length tubes, converging into a common collector. That way each tube draws close to the same vacuum at the end of each exhaust cycle, making for a more equal distribution of charge in each cylinder.

Perfectly clear, right? It gets better!

The intake. Looking at the intake, notice there are only 2 ports, which means 2 cylinders have to share each port. Doesn't sound very efficient does it? Well, look at it this way, only one intake valve is open at a time, so in reality the common port only has to supply one cylinder at a time, so no need for a separate port for each cylinder. But... Think about the exhaust and the "scavenging" effect, this is just the opposite, the "ram" effect of the moving air/fuel mix. It's actually better to keep the flow moving in a steady stream instead of stopping it every time the valve closes. This way, when one valve closes, the one next to it opens, ready to receive the already moving flow instead of having to start the flow every time the valve opens. That also helps smooth out the flow through the carburetor. carbs like smooth, steady flow, not choppy start-stop flows.

Even V design engines use this effect. Most down draft intakes have paired runners that divide the flow into the most efficient, smoothest directions.

Of course there are many different designs. Not all manifolds use paired runners, some are straight in, a runner for each cylinder. That still gives a ram effect, but a choppy flow. Some carbs can handle it, fuel injection likes it.

Way more than I can explain here or even imagine that I understand. All kinds of theories, but the dyno tells the final result, that and the emissions test...

It gets very complicated!

and on a lot of intakes the longest or furthest away from the carb usually will result in the valves being burnt first, due to leaner mixture.

I will add some to Steve and Rustred good descriptions.

The pulse of fuel has intertia, so it will continue to flow. The valves on the adjoining cylinders open in a bang bang then wait sequence. This timing causes the second valve opening to get extra fuel that was still planning to go to the first valve, thus the adjoining cylinders will not have equal air to fuel ratio. The runners must always be kept warm, or the fuel that was vaporized in the carburetor will rain out in the passages and not make it to the cylinders. The longer distance running leaner is also worst when accelerating, due to the delay in getting the needed richer mixture to the cylinders.

Fuel injection at the intake valve gets rid of all these issues.

If I remember right many of the older straight 6 engine used in car and truck had the intake and exhaust manifold one above the other. Intake on top and exhaust on bottom like on the Chevy 250

The intake manifold is just a hollow chamber that holds a cloud of gas and air. The pistons then draw the gas fumes into the cylinder as they go down and closes the intake valve. Then the piston comes back up where the gas fumes are compressed and the spark plug fires driving the piston down. Then on the next stroke the piston comes up where the exhaust valve opens and the burnt gas is let out through the exhaust manifold and then through the exhaust pipe. Because of the heat they couldn't just hook the exhaust pipes to the engine. The cast iron exhaust manifold dissipates enough of the heat the exhaust pipe can handle it.

Oh, there is way more science than that.

My way of saying it is that the intake manifold facilitates the
volume of air required when the piston moves down on the
Intake stroke with the intake valve open.
Likewise the exhaust manifold facilitates the removal of the
spent air fuel after combustion with the exhaust valve open.
All possible because atmospheric pressure is about 14.7 psi,
and the engine is an air pump.
Air is displaced by the movement of the pistons and positive
atmospheric pressure rushes to fill the void.

I was wondering when someone would get to that. Stan

Atmospheric pressure. Void a space and air rushes in to fill it on the intake side. On exhaust the piston pushes the spent fuel and air out . Valves are timed to permit this to happen.

Should I post this, ya, why not.

And then there is the centrifugal separation of fuel from the air when going around curves.

Lean mixture on the inside of the turn, drippy wet wall on the other...

seeds in
corn out
make straight lines of it
start early work late
get done before winter

I'm still stuck on "pink anti freeze" I thought that was the stuff for the RV plumbing


intake = suck
exhaust = blow
intake compression power exhaust
negative pressures it sucks
positive pressures it blows
cold going in hot coming out
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A similar question: If the muffler was left off of a tractor during a rainstorm, where would the water end up?

Agreed but was trying to keep it basic.

(quoted from post at 11:26:31 10/22/19) Agreed but was trying to keep it basic.

Click to expand...

ell, 'basic' is like your throat for intake and the opposite end for exhaust!