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In your opinion/experience does air filter choice affect the turbo's lifespan?

The difference between sucking & blowing!

16K views 69 replies 17 participants last post by  hondo 
#1 ·
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 :rolleyes: ), 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.

Paul:)
 
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#3 · (Edited)
Hey Paul, how's it going mate?

I posted on the thread you mentioned about the principals of turbo charging. All I can offer is my undestanding of the way it works. I by no means mean to say you're wrong or belittle you in any way. You've helped me in the past and I am greatful. Just here to offer my opinion

Here goes. :d

A turbo is split into two halves, A compresser and a turbine.

You are right in what you say, high pressure exhaust gas does spin the turbo, it does it by passing through the turbine, in a very similar way to how steam is used to spin a turbine in a power plant to create electricity. That is the only job the exhaust gas does, spin the turbine.
The turbine is linked to the compressor side via a shaft, the compressor does 2 jobs,sucks air in and compresses it. It is then forced it into the engine at a mucher higher positive pressure than a N/A engine.
I think normal pressure without modding is around 7 - 8 psi (is on an RS turbo anyway) with the option of going up to about 14psi or 1 bar without the need for a bigger turbo, a bigger turbo means a bigger compsessor. This means the air is already compressed and is under positve pressure before it reaches the cylinder where it is then compressed futher by the piston. The reason a turbo car uses lower compression pistons is because if you use standard compression pistons the air will heat up too much (as a result of being compressed) and will ignite the fuel (like a diesel) before the spark plugs gets a chance, resulting in pre-ingnition.

The way a N/A engine sucks air in is by the piston moving down on the induction stroke. It sucks in ambiant air from the atmosphere (0 psi if you will, I know it's not that but lets just keep it simple) and is only then compressed on the compression stroke by the piston itself. Just to clarify, the air passing through the inlet manifold is at ambiant, 0 psi, pressure until it enters the cylinder where it is compressed. In a tubro engine, compressed air passes through the inlet manifold at around 8 psi or more where it enters the cylinder and is compressed further.

You are right, the inlet manifold is cool compared to the exhaust, in an N/A car anyway.
This is because ambiant air is passing through it, the only reason the air is passing thorugh it is because of the suction action created by the piston as it's moving down on it's cycle.
In a turbo car, without the use of an intercooler the inlet manifold would get hot. Granted, not all turbo cars have intercoolers, but as a result they can't compress the air too much or it will get too hot, resulting in pre-ignition, but in theory if you removed the intercooler from a turbo car that is meant to have one fitted, it would get hot, very hot indeed. This is because when you compress air you generate heat. Basic rule as to why a diesel runs without spark plugs.
The intercooler is meant to cool the air, nothing to do with colder air contains more oxygen ( the colder more ogygenated air needs to be intorduced before it's compressed, hence the reason for a decent induction system made up of a Cone filter, I don't rate pannels as they are prone to heat soak), but to enable the turbo to run at higer psi and compress more air. More air compressed means more air forced into the engine resulting in more fuel being added meaning the faster you go. :d

Top thread by the way, always nice to have a good discussion like this.
 
G
#14 ·
In a turbo car, without the use of an intercooler the inlet manifold would get hot. Granted, not all turbo cars have intercoolers, but as a result they can't compress the air too much or it will get too hot, resulting in pre-ignition, but in theory if you removed the intercooler from a turbo car that is meant to have one fitted, it would get hot, very hot indeed. This is because when you compress air you generate heat. Basic rule as to why a diesel runs without spark plugs.
The intercooler is meant to cool the air, nothing to do with colder air contains more oxygen ( the colder more ogygenated air needs to be intorduced before it's compressed, hence the reason for a decent induction system

I've just read this bit again Mikey, the last bit is a little flawed.

There is not enough compression in a turbo to generate heat. The heat comes from the turbo having hot exhaust gasses passing through it. The intercooler is indeed to cool the air, but because cold air is more dense so you can get more of it into a set volume, especially if it's pressurised.
 
#5 ·
Thought I was Pat :d

K, if atmospheric pressure is 1 bar/ 14.5 psi, a turbo can produce pressures of between 7 and 29 psi (approx half - 2 bar) above this. Sorry to confuse.

Knew I should've gone to college to study engineering, not poxy carpentry as this is where my passion lies! I'm pretty much self taught :d :rofl:
 
#6 ·
Would I be correct in presuming that we are pretty much in agreement that a less-restrictive air filter would help a turbo?

Regardless of where the pressure is created?

This was the crux of the other thread before it kinda went south in direction:crazy: .

Good natured debate is always welcome. Thanks for joining in:) .

Paul:)
 
#8 · (Edited)
Hi Paul, my take on the induction kit thing is inluded on page 3 or 4 or 5 (can't quite remember now lol) I think on that Clio K&N thread. Got one on my Lag II, just a breif post on how I did it and how I would do it on other cars.

IMO I'd stay away from pannel filters, they don't do much except offer the abilty to be cleaned. Cone filters fitted corectly are the way forward! :d And they offer more surface area too, less chokage!! But yea we're in agreement!
 
G
#11 ·
Hi Paul, my take on the induction kit thing is inluded on page 3 or 4 or 5 (can't quite remember now lol) I think on that Clio K&N thread. Got one on my Lag II, just a breif post on how I did it and how I would do it on other cars.

IMO I'd stay away from pannel filters, they don't do much except offer the abilty to be cleaned. Cone filters fitted corectly are the way forward! :d

That really depends on how you get the air to the filter.

F1 cars use panel filters
 
#18 ·
I think that this is a great discussion.
To through something else in. When measuring the power output of a turbo engine it is always given as an estimate as the actual power is effected by several things including the current air temp, humidity and hight above sea level.
These facters also effect a N/A engine but much less
so. To have the most power from a turbo engine you want a nice cold humid day at sea level as this will give the maxium amount of oxygen in the air.
For a good example of this is the argentina rally which is run high up in the mountains and the WRC cars are well down on power to the point where the drivers complian.
The intercooler is ment to drop the temp of the air which does relase more O2 which (to my limited understanding) has combined with other elements at the high temps as well as reducing its volume.
Back to the original point and anything that causes the air to slow down (even on a N/A engine) is bad which is why you want any tubing/ducting to be as straight as possible and if you do need to bend it then nice flowing curves are best as once the air is draw in to the induction system it behaves like afluid and harp courners cause eddies and back flows which is why cone filters normaly give betterresults than pannel filters which don't always give the best air flow as they have to fit them in to the engine bay.
 
#19 ·
Its gratifying to see that I'm not the only one who thinks along similar lines:) .

From the other thread, I was getting the impression that what was being put forward was that the air was being pressurised before it passed through the turbo (which I couldn't follow).

I view it this way; I'm sitting with my favourite (but all too rare drink - a McDonalds Strawberry milkshake), I need to get the substance from the cup along the straw into my mouth - I don't pressurise the contents of the cup to push the milkshake along the straw, I create a lower-pressure area (almost vacuum if the milkshake is thick enough) in my mouth, than what the milkshake is subject to in the cup, and there then exists a driving force for the milkshake to defy gravity.

That is how I see the inlet aspect of the turbo working - it pulls more air in as more exhaust gases leave - its not instantaneous (that's why turbo lag exists), but its pretty much correlated once in motion.

I do accept there is then positive pressure on the gas once it passes the turbo, but unless the inlet has a direct feed and the vehicle is already in motion, it will only be the negative pressure which pulls the air into the inlet.

Thanks for the input, its always good to air our views.

Paul:)
 
#20 ·
A turbo is just an vane type air compressor.
This is powered by the exhaust gases which are expanding and hence drive the turbine blades which are conected directly to the compessor vanes forcing more air in.
This is exactly the same way that a gas turbine works except that the engine is replaced by a combustion chamber. This type of engine is far more efficent than an internal one but they don't do low revs very well and there may be a bit of noise.
A jet engine Also works in a simular way but with this engine you are after the exhuast gases as these push the plane along this works on Newtons third law of motion.
A jet ski use this as well.

I feel that i may have rambled a bit in this.
 
#22 ·
"A turbocharger is an exhaust gas-driven turbine that compresses the intake air"

But only once the intake air has passed the vanes of the turbo - surely?:confused:

Good link though.

Paul:)
 
#25 · (Edited)
But only once the intake air has passed the vanes of the turbo - surely?:confused:
True. On the inlet side of the compressor it's sooking - just as the piston does on a N/A engine in the cylinder on it's induction stroke, but on the discharge side the air is compressed.
As explained in the link, the only sections of the inlet system that are under positive pressure are after the turbo ....... pipework to the intercooler, intercooler, pipework to the inlet mainfold. So, when the inlet valve opens, there is positive pressure in the manifold waiting to rush into the cylinder. The piston does no real work in drawing in the charge of air.

A wee bit more bumph HERE courtesy of Wikipedia.

On a wee side note Paul, I always thought of the Otto cycle as being like a good night out with the girlfriend - suck, squeeze, bang , bl .......
 
#27 ·
Gonescenile;379537 On a wee side note Paul said:
Ha-ha!:rofl: I note you said 'girlfriend' not 'wife'!:d

Nice one - I was going to mention that one myself, but thought if I combined that with the thread title - it'd be a bridge too far!

Paul:)
 
#28 ·
It may help if to realise there is no such thing as suction in the world of physics. Whether its in a jet engine, turbo or vacuum cleaner there are only areas where there is a pressure difference and a gas will always flow from a high pressure area to an area of lower pressure. All engines are under air pressure (unless you are in space) and that is whatever the ambient air pressure happens to be at the time. This can vary depending on altitude and weather. Engines always run best on clean dry air as any moisture contained in it will mean less oxygen content.
Diesel engines can't pre-ignite as petrol engines can simply because there is no fuel present until the injector introduces the fuel just before maximum compression in the cylinder when the tempertures are raging hot enough to ignite the fuel/air mix.
 
G
#34 ·
Then that wouldn't be injection - would it :confused:

It might be into the intercooler, not sure to be honest.

Adding water into the fuel air mix is certainly a performance boost. It increases the compression ratio, and improves the burn rate.
 
#33 ·
Water injection in some cases increases the density (has a similar effect of increasing the ambient air pressure) of the inlet air and lowers it temperature thus preventing pre-ignition. This only works when the gases going into the engine are an air/gas mix. Whilst it may reduce the risk of pre-ignition and the resulting power loss it will not assist the fuel/air mix to burn more efficiently. On high performance engines this is a bit of a trade-off especially when using high octane fuels which have lower ignition temperature - hence more likely to cause pre-ignition and serious engine damage like a smashed crankcase with a con-rod poking its leg out (in our part of the world this is referred to as calving).:rofl:

Additionally the metals in the engine will suffer spalling which will seriously shorten engine life but when racing, etc generally that is not a problem as many engine are designed only to last one racing session anyway.:)
 
#35 · (Edited)
There are systems that spray water on to the fins of the intercooler to cool it,and also water injection systems that spray water into the inlet manifold or anywhere into the turbo pipes after an intercooler.

The water injection systems use high pressure to create more of a mist rather than just squirting water into the system.:)
 
#40 ·
Had to vote yes........not that I know enough about turbos and the principles that they work under. Reading the above hasn't helped either.......wooooosh :rofl:

I can't see, however, that manufacturers of after market air filters would produce below standard products that could be damaging to the engine/turbo. Surely vast amounts of money would have been spent in the design of such products....I'm talking branded products here!

Anyhow, if it invalidates your warranty....remove it and replace with original prior to taking it to the garage/dealer :rolleyes: :rofl:
 
#43 ·
It all depends on what engine the 5bhp was gained on.If it was a 140bhp engine,then thats a reasonable gain for not a great deal of work.:)

Water injection is used in a lot of high boost engines as it prolongs engine life,I know Subaru at least use it in their WRC cars.
 
#46 ·
I can understand why most people think that more oxygen is the deal solution for running a petrol engine. The fact is that there is a trade off between too much and too little air.
Petrol concentrations below 1.4%, in air the mixture is too lean to ignite, and for those above 7.6% too rich; at all concentrations between these two limits, a mixture of petrol vapour and air will ignite.
But with more air (think oxygen) the combustion is likely to be complete with some oxygen not being used - this is the most efficient i.e. better economy. On the other hand reducing the air allows more power per stroke to be developed. So in reality allowing more air into the engine may reduce its power output but improve its economy. You just can't have the benefit of both although lean-burn engines such as the IDE and Gdi have attempted to address this problem but as we all know it hasn't been without its difficulties. No doubt engine designers for the public motor market have to strive to get the balance between the two - so it is actual possible that by allowing more oxygen into the fuel mix power output may be reduced. It all about getting the mixture correct for whatever you want an engine to do at a particular time throughout its power range. From my experience I have found petrol engines perform that wee bit better when the fuel mix is slightly rich but tend to be that bit thirstier and I have yet to see a high performance engine easy on fuel.


Hve a look through the attached link

http://books.google.co.uk/books?id=...&hl=en&sa=X&oi=book_result&resnum=3&ct=result
 
G
#49 ·
Perhaps this thread is getting a little off track again :rolleyes:

I may be wrong (it happens more regularly than I would like :eek:) but I don't think the question was what is the perfect mixture, more is a free flowing airflow preferential on a turbo engine and how would that effect the performance of the turbo.

The way I understand a turbo is that the exhaust fumes are the main drive, but it's actually a balance of pressures/flows that allow it to spool up rather than a volume of exhaust gas alone. So, if the air in the intake remains static but more exhaust gas is being pushed through, the turbo's rpm increase will be restricted. I’m positive that it won’t matter which end the restriction is, if the air in the intake is allowed to flow as freely as possible there must be less restriction on the compressor making it easier for the exhaust gasses to spool up the turbo.

I would assume that any restriction as mentioned above could add a load to the bearings that the turbo shaft runs on and that this load would not be ideal. As to this decreasing the life of the turbo, I have no idea, but surly it can’t help.
 
#50 ·
My understanding of compressers is that if you restrict the air flow (ie put your hand over the intake) then it will still spin but just not compress. A turbo will be he same so in terms of a turbo doing its job the more free flowing the air intake the better the turbo will perform though i don't think thatit would make any ifference to the life of the turbo there are far to many things that effect its life for the filter type to make much of a difference.
 
#53 ·
It's no coincidence that in F1 terms,engines had a minimal air filter and a minimal exhaust system.

If the exhaust gases can escape with less restriction,then the more capable they are of spinning the turbo.

If the air it displaces is free flowing,then the easier the turbo can spin.

I don't think the type of air filter used is the most important factor in turbo life,but it can't hurt having a free flowing air supply to it.:)
 
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