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post #1 of (permalink) Old 9th July 2008 Thread Starter
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The difference between sucking & blowing!

I was getting embroiled in a bit of a difference of opinion regarding the principles behind turbocharging, so rather than hijack someone else's thread, I'll explain what I mean in greater detail.

I believe that since the exhaust part of the turbo is spun by high pressure gases escaping (i.e. blowing), the induction part whereby fresh air is introduced to the engine is driven by low pressure (i.e. sucking).

One equalises the other, and the balance of nature is restored.

Now the thread I was originally adding to, related to how a high-flow air filter can assist with a turbocharger's efficiency - well, if you've ever driven a car with a dirty air filter - you will appreciate the relationship between airflow & power/economy (i.e. more of one = more of the other). This is because the spinning action of the induction side draws more air by creating a low pressure point, which nature is driven to minimise.

Granted, once the air has passed the filter and has entered the turbo , it will then start to be compressed, but just in the same way as per an normally aspirated engine. (i.e. part of the otto cycle - suck (there's that word again ), squeeze (this is where the pressure begins to increase), bang (pressure), blow (release of pressure).

As you can see, it is only the compression stage onwards where the air is under positive pressure.

If air wasn't drawn into the induction (induce means to lead/draw - not push), then all cars would need a supply of compressed air for combustion - there would be no driving force for the air to enter the filter.

Again, if proof were needed - check out the inlet manifold on your car, and compare it with the exhaust - the inlet one runs quite cool (strange, if it were pressurising air, it should be hot), whereas the exhaust manifold is where the heat is at (admittedly partially because of the spent hot gases being carried, but also because they are under pressure), which is why free-flowing exhaust systems can also improve engine efficiency.

Hope that helps to set my stall out.

No doubt some will differ with my postulations - but this is the place to do so.


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