Intake restriction question
 

Hi,

I have a little Mitsubishi 'i' car with a 660cc turbocharged engine. I discovered the intake piping has, at its lowest point, an opening with a rubber flap that opens outwards and would act to let water out, if any got in. Otherwise it's shut.
I removed the flap and put some speaker cloth over the opening to stop dirt ingress. Now the engine can breath in through that opening. I wondered if I'd notice any effect, as the opening is only 2cm or so wide, and I do see that on the overrun, the engine is pulling a slightly higher vacuum.

EDIT:
A couple of days later I noticed that the vacuum on overrun was the same as before this 'mod'. So I think it was an unrelated effect of the weather or something.

during overrun, engine airflow is already at its lowest. gains in vacuum are not going to be from increases in flow capability. you would need to decrease flow to increase vacuum.

Picture? I come from a more performance seeking point of view...

Although aftermarket intakes are everywhere they are fairly universally recognised as producing no power increase except in rare occasions where the stock intake is really bad. The main effect is usually more noise.

The aim of your pipe is most likley to take unheated air to the engine (cold=more dense=more oxygen for a given volume so more fuel can be burnt =more power).

It may or may not make a difference but you could replace the pipe with a larger diameter one. Hardware stores have lots of flexible pipes that would do the job.

Looking at your question again, Robert is right and you need to look at the whole intake path to answer the question properly, what sort of air cleaner do you have? fuel injected? Does it have a warm air intake for warm up...

Often just cleaning the throttle body makes a positive difference in the intake tract. Oil from pcv collects in there, soot can build up from egr... look on a forum related to your model or something similar and its likley that you will find a discission of these issues.

piping
 

Mitsubishi builds aircraft and submarines 'n other stuff including automobiles.
They're no newcomer to fluid mechanics.
I suspect that the OEM manifold has already been flow tested and optimized as it is,and that under 99% of operation it will perform to best performance.
Allowing air to enter an 'exit' may compromise the tuning of the pathway(like reverse-direction pumping sewage uphill and through a toilet).And since you're making no change to the exhaust system,may be un-balancing the intake.
Intake/Exhaust is just like algebra: whatever you do to one side of the equal sign,you must do the to other.

Engineer's don't always get it right or have other constraints to deal with:

AutoSpeed - Powering-Up the 1.9 litre TDI, Part 2

A case of the factory intake being deliberately restricted to match the exhaust!

right
 

So the modified intake reduced engine performance.

He got more lower end and top end, who cares about the middle?

Now if he had used a kn filter......:eek:

Others on here have tested restriction plates in the air intake and seen increases in mileage.
opening up a drain to allow air to enter seems like a bad idea, you are going to mess with the fluid dynamics of the air intake as well as bypassing the air filter.
for the air intake you want to maintain momentum of the air, opening up a drain like you did is going to dampen that momentum.

True, engine designers have too much constraints. Its trying to get more power out of a light engine while at the same time cope with the aerodynamics of a pedestrian safe car (yeah go figure) at the same time making money for the company.

In the Autospeed test car, they had to reflash the ECU. Because anything moved to market in the 21st century would need to have the ECU control every single aspect of the combustion. Especially turboed engines. The irony is that you have this as part of the engine design doctrine but the marketing people wants the interior and suspension to be soft and plushy while at the same time able to connect to the Net or your phone or both; so people would want to buy it. Call it the 'Experience'. People want the 'Experience' of driving a car.