Intake Query

[HtwCHACtkh]

Hey,

A this could be a pretty stupid intake question. I'm thinking of a CAI to replace the stock snorkel and then I got thinking, now I am in two minds when it comes to the diametre. I am not an engineer or auto mechanic but have a general understanding of fluid mechanics.

Bernoulli's theorem tells me that a smaller intake would mean the air would come through at a higher velocity maintain the required CFM wouldn't this in turn make the turbo spool quicker and improve response?

I understand if you have it dramatically smaller than that your IC piping you're increasing the risk of compressor surge (where the pressure in the IC hosing is higher than that before the turbo in the intake and the air attempts to go back out the intake).

But what is the advantage/reason of having an intake larger than that of your IC piping wouldn't it be better to have it just slightly smaller?

[WYTSKY]

to be honest, with my cai and heatsheild, bigger the better for intake.

I see the point you make, but it was my understanding that your not trying to make it blast air into the turbo, which to be honest I can't see being much up until atleast 100kms/h at which point you legally cannot go much faster on our roads, as the turbo definitely has enough suction/boost to do that on its own. you are simply allowing the turbo to not suck in hot air from the engine bay, which can cause quite a large drop of response/power and instead have some nice <45degree air from outside, inwhich case, the more the merrier.

[HtwCHACtkh]

  WYTSKY said:

to be honest, with my cai and heatsheild, bigger the better for intake.

I see the point you make, but it was my understanding that your not trying to make it blast air into the turbo, which to be honest I can't see being much up until atleast 100kms/h at which point you legally cannot go much faster on our roads, as the turbo definitely has enough suction/boost to do that on its own. you are simply allowing the turbo to not suck in hot air from the engine bay, which can cause quite a large drop of response/power and instead have some nice <45degree air from outside, inwhich case, the more the merrier.

lol it was actually your write up that really got me thinking! "Why would I really need to cut that hole bigger?"

I understand a CAI essential goal is to get cold air into the intake (duh ) but I'm thinking about intakes in general though as I want to rework the stock airbox snorkel as it won't fit with my custom IC piping anyway.

  Quote

but it was my understanding that your not trying to make it blast air into the turbo, which to be honest I can't see being much up until atleast 100kms/h at which point you legally cannot go much faster on our roads

Without spewing out too much maths, with a smaller intake the air travelling through the intake will be moving at a higher velocity no matter what speed the car is going at.

It's the conservation of mass/energy, hypothetically and ideally (which means ignoring compression/other forces, so this may sound weird) say the engine is breathing at at a rate of 10 oxygen molecules per second - if you have an intake that can only fit 1 oxygen of molecule at a time that is 1 metre long, each molecule has to move at 10m/s as the engine demands 10.

If you have an intake that can fit 2 molecules the oxygen has to move at 5m/s.

Thinking a little bit further, the turbo would have to do more work to convert the kinetic energy into density though.

Past the basics, my knowledge on how an engine works is very limited so I'm really uncertain, and at most curious if it would effect the responsiveness or not; forgetting about ph4t boost *gasp* for a second.

[TiTAN]

The smaller the pipe the more energy the compressor wastes to draw the air in past the restriction. What you want is a nice pipe with minimal restriction to it (reasonable size with a good filter).

[tridentt150v]

Nice idea, but you are assuming that the turbo comp wheel is just sitting there waiting, however it is a slave to the turbine wheel. So unless your air was highly compressed to start with [ie compressor surge is an example of bad effects] then I cannot see it being of any benefit. As Titan said, less restriction is the best solution.

Your idea would work much better on an NA motor. I seem to remember a couple of drag bikes that had their cylinder head in reverse. This way the faster they went, the more forced induction they achieved. This was a common thing on older parallel twins in the '60's and '70's. Triumph Bonnevilles and Norton Commando's spring to mind.

[Adriano]

Agreed, you are assuming the air has +ve pressure before the comporessor wheel being forced in by the movement of the car. The opposite is true, as the comp wheel is sucking the air

[HtwCHACtkh]

Ahh touche, so no benefit.

Back the drawing board. I think I've got a new idea on what to do.

Thanks all.