Uitlaat

 

De uitlaat had nog een tikkie groter kunnen zijn.

Bij het zien van boven afgebeelde foto zou Herr Maurice een hartaanval krijgen.

Dit is dan ook geen 720 cc motor, zoals Addax, maar de standaard 602 cc motor.

Bij Addax had ik een speciale uitlaat, luchtfilter en sproeiers aangeschaft.

Op de rollerbank is een en ander afgesteld.

Bij Trapper is op de uitlaat na nog alles origineel.

 

De 2/1 uitlaat kwam bij ons onder het chassis te liggen.

Het nadeel van de 2/1 uitlaat vonden wij toch de herrie.

De boven afgebeelde uitlaat stelt ons in staat om het chassis te voorzien van een vlakke carter beschermingsplaat.

Deze  "halve" uitlaat komt uit de 2CV Cross wereld.

Kennelijk is het daar een beproefd concept, dus wie ben ik.

De praktijk zal het gaan uitwijzen.

Voor de liefhebber het volgende: "Stof tot nadenken.".

Dit heb ik even van de site van Herr Maurice gejat. Herr Maurice een beetje kennende heeft hij hier geen bezwaar tegen.

Destroying a myth.

Some say that “an engine needs backpressure to work correctly.” Is this

true?

No.

It would be more correct to say, “a perfectly stock engine that cannot

adjust its fuel delivery needs backpressure to work correctly.” This idea is a

myth. As with all myths, however, there is a hint of fact with this one. Particularly,

some people equate backpressure with torque, and others fear that too little

backpressure will lead to valve burning.

The first reason why people say “backpressure is good” is because they believe

that increased backpressure by itself will increase torque, particularly with a stock

exhaust manifold. Granted, some stock manifolds act somewhat like performance

headers at low RPM, but these manifolds will exhibit poor performance at higher

RPM. This, however does not automatically lead to the conclusion that

backpressure produces more torque. The increase in torque is not due to

backpressure, but to the effects of changes in fuel/air mixture, which will be

described in more detail below.

The other reason why people say “backpressure is good” is because they hear

that cars (or motorcycles) that have had performance exhaust work done to them

would then go on to burn exhaust valves. Now, it is true that such valve burning

has occurred as a result of the exhaust mods, but it isn’t due merely to a lack of

backpressure.

The internal combustion engine is a complex, dynamic collection of different

systems working together to convert the stored power in gasoline into mechanical

energy to push a car down the road. Anytime one of these systems are modified,

that mod will also indirectly affect the other systems, as well.

Now, valve burning occurs as a result of a very lean-burning engine. In order to

achieve a theoretical optimal combustion, an engine needs 14.7 parts of oxygen

by mass to 1 part of gasoline (again, by mass). This is referred to as a

stochiometric (chemically correct) mixture, and is commonly referred to as a

14.7:1 mix. If an engine burns with less oxygen present (13:1, 12:1, etc...), it is

said to run rich. Conversely, if the engine runs with more oxygen present (16:1,

17:1, etc...), it is said to run lean. Today’s engines are designed to run at 14.7:1

for normally cruising, with rich mixtures on acceleration or warm-up, and lean

mixtures while decelerating.

Getting back to the discussion, the reason that exhaust valves burn is because

the engine is burning lean. Normal engines will tolerate lean burning for a little bit,

but not for sustained periods of time. The reason why the engine is burning lean to

begin with is that the reduction in backpressure is causing more air to be drawn

into the combustion chamber than before. Earlier cars (and motorcycles) with

carburetion often could not adjust because of the way that backpressure caused

air to flow backwards through the carburetor after the air already got loaded down

with fuel, and caused the air to receive a second load of fuel. While a bad design,

it was nonetheless used in a lot of vehicles. Once these vehicles received

performance mods that reduced backpressure, they no longer had that doubleloading

effect, and then tended to burn valves because of the resulting over-lean

condition. This, incidentally, also provides a basis for the “torque increase” seen if

backpressure is maintained. As the fuel/air mixture becomes leaner, the resultant

combustion will produce progressively less and less of the force needed to

produce torque.

Adapted from Thomas V.

What other wannabee mechanics say:

„What about exhaust systems? Well, my favorite quote is, "That system

doesn't provide enough back pressure for good low end power. You need

back pressure for good low end and mid range on the street.“

Simply put the above is bullshit and reveals more about the speaker's lack of

knowledge in exhaust tuning than anything else. He probably gives out lots of

advice like this because he likes the sound of his voice or loves to see his name in

print on forum boards. Back pressure (I assume our friend means

restriction/resistance to flow) does not "help" mid range power.

 

De discussie gaat nog even door. Een en ander wordt met grafieken "bewezen".

Herr Maurice zet je wel aan het denken.!

Enne, Addax verkeert met z'n trip in Marokko en China nog steeds in een goede "gezondheid".

Voor mij nu zaak om de kleur van de bougies goed in de gaten te houden.