[Klepper1]

I have a question about intakes and drop in filters on turbo charged cars:

I understand on a normally aspirated engine how taking out restrictions gets you more power - less restrictions lets more air into the engine, more air means you can burn more gas, more gas gives you more power!

I don't understand how it works on a turbo charged engine. Isn't the amount of air getting into the engine "fixed" by the boost pressure. If the max pressure the turbo puts out is say 10 psi, how does removing restrictions on the 'suction' side of the turbo help get more air into the engine?

Or am I thinking about it all wrong?

[jcarlucci1]

More air that comes through intake means higher efficiency for the turbos..a turbo can always be set at 10 psi but its cfm (cubic feet per minute) can change. For instance, a larger turbo set at 10 psi will flow MUCH more air than small turbos on the 335

[Klepper1]

But isn't the 10 psi the manifold pressure? So if the manifold (fixed volume) is maxed at 10 psi, the cubic feet of air in it is fixed (regardless of the size of the turbo)

[Klepper1]

Any other thoughts?

[lawdude]

Originally Posted by Klepper1

Any other thoughts?

Shiv said the right air filter can increase hp on a turbocharged car. Terry thinks so too since he sells his own air filter.

The only other thought I have is that the correct terminology is naturally aspirated.

[Klepper1]

Originally Posted by lawdude

Shiv said the right air filter can increase hp on a turbocharged car. Terry thinks so too since he sells his own air filter.

The only other thought I have is that the correct terminology is naturally aspirated.

I know a lot of people say it does, but the physics behind it escape me, Does not seem to make sense.

Also, from wikipedia: "A naturally-aspirated engine or normally-aspirated engine (or "N/A" - aspiration meaning breathing) refers to an internal combustion engine (normally petrol or diesel powered) that is neither turbocharged nor supercharged" -

[stillclaimndp]

Originally Posted by Klepper1

I have a question about intakes and drop in filters on turbo charged cars:

I understand on a normally aspirated engine how taking out restrictions gets you more power - less restrictions lets more air into the engine, more air means you can burn more gas, more gas gives you more power!

I don't understand how it works on a turbo charged engine. Isn't the amount of air getting into the engine "fixed" by the boost pressure. If the max pressure the turbo puts out is say 10 psi, how does removing restrictions on the 'suction' side of the turbo help get more air into the engine?

Or am I thinking about it all wrong?

Shiv, historically with Evo's and Subaru's, has been very anti-intake as the stock intake boxes allowed for ample air flow even with high boost. The 335i, however, is restricted from taking in (intake!) a sufficient volume of air through the stock box when running 14+psi with a good tune. Same idea as trying to breath in very fast through a (or blow out of in this case as you are compressing air) straw. Terry has seen gains of 15hp at the wheels and on a full on race gas tune Vishnu saw a 30whp gain with a dual cone intake vs. the stock airbox (still running stock downpipes in this particular test and on race gas).

DP

[Klepper1]

Originally Posted by stillclaimndp

The 335i, however, is restricted from taking in (intake!) a sufficient volume of air through the stock box when running 14+psi with a good tune...
DP

This is the confusing part. Once you hit a 'max' pressure (say 14psi), the constraint on getting air into the engine is no longer on the suction side of the turbo (the intake and filter), but it's on the discharge side of the turbo (the max pressure being hit in the manifold). No matter how much I free up the air getting into the turbo, the amount of air on the discharge side is maxed at the 14psi x the manifold volume (at constand temperature).

What am I missing?

[stillclaimndp]

Originally Posted by Klepper1

This is the confusing part. Once you hit a 'max' pressure (say 14psi), the constraint on getting air into the engine is no longer on the suction side of the turbo (the intake and filter), but it's on the discharge side of the turbo (the max pressure being hit in the manifold). No matter how much I free up the air getting into the turbo, the amount of air on the discharge side is maxed at the 14psi x the manifold volume (at constand temperature).

What am I missing?

Have you ever read how a bigger turbo at the same psi, say 14psi, flows a higher volume or CFM than a smaller turbo at the same psi? I think that sort of relates to the idea... The intake doesn't allow the sytem to receive as high of a volume of air to match with fuel...?

[jcarlucci1]

Originally Posted by Klepper1

This is the confusing part. Once you hit a 'max' pressure (say 14psi), the constraint on getting air into the engine is no longer on the suction side of the turbo (the intake and filter), but it's on the discharge side of the turbo (the max pressure being hit in the manifold). No matter how much I free up the air getting into the turbo, the amount of air on the discharge side is maxed at the 14psi x the manifold volume (at constand temperature).

What am I missing?

The amount of air flowing can change, even at the same psi..its that simple

[lawdude]

Originally Posted by Klepper1

Also, from wikipedia: "A naturally-aspirated engine or normally-aspirated engine (or "N/A" - aspiration meaning breathing) refers to an internal combustion engine (normally petrol or diesel powered) that is neither turbocharged nor supercharged" -

Since you put so much stock in wikipedia, check out THIS cache of the same page.

A naturally-aspirated engine or (often incorrectly referred to as) normally-aspirated engine

Which wiki is correct?

[scalbert]

To generate X amount of boost may require Y RPM in the turbo. This is based on the ability to pull air in. Lessen the resistance to pull air in, the turbo can now spin at a lower RPM to generate the same X boost. Spinning at the lower speed allows it to be more efficient. This does two things, the wastegates will open sooner lessening the backpressure in the exhaust ports which increases HP. It will also induces less heat into the charge air which further helps HP.

[Klepper1]

Originally Posted by jcarlucci1

The amount of air flowing can change, even at the same psi..its that simple

It really isn't that simple. The mass of air in a fixed volume (manifold) at a fixed pressure, with temperature constant, is the same. Bigger turbos can flow more air, but it must have somewhere to go. If the space and pressure are fixed, it has nowhere to go

Originally Posted by scalbert

To generate X amount of boost may require Y RPM in the turbo. This is based on the ability to pull air in. Lessen the resistance to pull air in, the turbo can now spin at a lower RPM to generate the same X boost. Spinning at the lower speed allows it to be more efficient. This does two things, the wastegates will open sooner lessening the backpressure in the exhaust ports which increases HP. It will also induces less heat into the charge air which further helps HP.

Now this makes perfect sense! Thank you!! I knew I was missing something.

[bdkevoIX]

Intake manifold pressure just tells you how much pressure air is exerting onto the manifold at a given time. What it doesn't tell you is how much air is in there.

Pressure and volume are two different things.

Let's say we have an engine operating at 5000rpm with stock twins at 10psi.
And we have an identical engine operating at 5000rpm with a GT35r at 10psi.

The stock twins are able to move enough air to pressure the manifold so that each square inch feels 10 pounds of pressure. But the surface area of the compressor is much smaller so the amount of air moved is smaller than GT35r at the same boost pressure and also at slower velocity.

The air coming from stock twins creeps into the cylinder at a slower velocity than the air that came from GT35r. Also, more efficient compressor on the 35r packs more air making it more dense. Therefore, at the start of the combustion cycle, you have more oxygen molecules to burn in air from 35r than stock twins.

Removing restriction from cold side will allow compressors to move the air more efficiently, therefore more power.

http://www.rx7club.com/showthread.php?t=645551

Check the link, it should help you out alot.

[raceyBMW]

Assuming temperature is constant, and for a fixed volume like the intake manifold, 10psi is going to be the same amount of air, regardless of how much volume is flowing to the manifold.

And the air coming from the stock twins is only going to the manifold slower than a larger turbo if the RPMs are fixed. The smaller stock turbos could still be moving the same volume (CFM) of air as the larger turbos, but they will have to work a lot harder to do so. This will decrease the efficiency of the turbos since they have to work at such a high RPM, which means that the air will be heated more.

The larger turbos have to do less work than the smaller turbos to pressurize the intake manifold since they can move a greater volume of air with greater efficiency and at less RPMs than the smaller turbos can.

[bdkevoIX]

Originally Posted by raceyBMW

Assuming temperature is constant, and for a fixed volume like the intake manifold, 10psi is going to be the same amount of air, regardless of how much volume is flowing to the manifold.

And the air coming from the stock twins is only going to the manifold slower than a larger turbo if the RPMs are fixed. The smaller stock turbos could still be moving the same volume (CFM) of air as the larger turbos, but they will have to work a lot harder to do so. This will decrease the efficiency of the turbos since they have to work at such a high RPM, which means that the air will be heated more.

The larger turbos have to do less work than the smaller turbos to pressurize the intake manifold since they can move a greater volume of air with greater efficiency and at less RPMs than the smaller turbos can.

Everything above is true but the first.

Even though the volume of the air is limited to the volume of the intake manifold, 10psi from small turbo and large turbo will not have same amount of air.
You just said that smaller turbo can move same volume as large turbo but have to work harder which will heat up the air.
Pressure only tells you how much force is being exerted onto the manifold surface. It doesn't tell you how much oxygen molecules are present that could be used in combustion. The air coming from larger and more efficient compressor is denser thus have more oxygen molecules in them.

Also, reduced backpressure from having bigger turbine also attributes alot to efficiency.

[droptop335]

Okay, this might be a simplistic question, but it seems to me that the stock airbox and associated plumbing absorbs all of its heat from the engine bay, then transfers that heat to the incoming charge air. If this is true, has anybody attempted to insulate the airbox and plumbing, perhaps by wrapping it in some thin insulating material? Wouldn't this prevent the engine bay air from heating the airbox, reducing the air temps inside the intake route?

[raceyBMW]

Originally Posted by bdkevoIX

Everything above is true but the first.

Even though the volume of the air is limited to the volume of the intake manifold, 10psi from small turbo and large turbo will not have same amount of air.
You just said that smaller turbo can move same volume as large turbo but have to work harder which will heat up the air.
Pressure only tells you how much force is being exerted onto the manifold surface. It doesn't tell you how much oxygen molecules are present that could be used in combustion. The air coming from larger and more efficient compressor is denser thus have more oxygen molecules in them.

Also, reduced backpressure from having bigger turbine also attributes alot to efficiency.

PV=nRT. Pressure tells you everything if you know what the volume and temperature are of where that pressure is measured. What you are saying is correct only because in reality, the smaller turbo will heat up the air under compression more than the larger turbo, thus the air is being denser. But if we were to assume the temperature was the same in the intake manifold, then whether the air got there by either a small or large turbo, for a set PSI, there is ALWAYS going to be the same amount of air (which is the nR part in the ideal gas law eq. above). Obviously though if the air were cooler with the larger turbo than with the smaller one, then the air would be denser and would make more power.

Agreed on the back-pressure issue significantly increasing the efficiency of the larger turbos.

[O-cha]

Originally Posted by stillclaimndp

Have you ever read how a bigger turbo at the same psi, say 14psi, flows a higher volume or CFM than a smaller turbo at the same psi? I think that sort of relates to the idea... The intake doesn't allow the sytem to receive as high of a volume of air to match with fuel...?

Originally Posted by jcarlucci1

More air that comes through intake means higher efficiency for the turbos..a turbo can always be set at 10 psi but its cfm (cubic feet per minute) can change. For instance, a larger turbo set at 10 psi will flow MUCH more air than small turbos on the 335

Holy crap where are you guys getting this. Let's all put freight turbos on the car.

A bigger turbo can flow more CFM, but it doesn't at the same pressure. The only reason it might is because the smaller was being run way out of efficiency but that has nothing to do with this. The amount of airflow is determined by the VE pressure and RPMs all other things equal.

[O-cha]

Originally Posted by raceyBMW

PV=nRT. Pressure tells you everything if you know what the volume and temperature are of where that pressure is measured. What you are saying is correct only because in reality, the smaller turbo will heat up the air under compression more than the larger turbo, thus the air is being denser. But if we were to assume the temperature was the same in the intake manifold, then whether the air got there by either a small or large turbo, for a set PSI, there is ALWAYS going to be the same amount of air (which is the nR part in the ideal gas law eq. above). Obviously though if the air were cooler with the larger turbo than with the smaller one, then the air would be denser and would make more power.

Agreed on the back-pressure issue significantly increasing the efficiency of the larger turbos.

Not really, the temperature difference will not be significant unless the small turbo was way out of its efficiency. Similar with the backpressure as long as the smaller turbo is not way out of efficiency once it's spooled the wastegates will open to a point where as the large turbo will have to keep them closed longer to spool as well as more to keep the greater mass of the larger compressor/turbine spinning.

It's a matter of the turbo being the proper size for the application you can't just say it's always like that.

[bdkevoIX]

Originally Posted by raceyBMW

PV=nRT. Pressure tells you everything if you know what the volume and temperature are of where that pressure is measured. What you are saying is correct only because in reality, the smaller turbo will heat up the air under compression more than the larger turbo, thus the air is being denser. But if we were to assume the temperature was the same in the intake manifold, then whether the air got there by either a small or large turbo, for a set PSI, there is ALWAYS going to be the same amount of air (which is the nR part in the ideal gas law eq. above). Obviously though if the air were cooler with the larger turbo than with the smaller one, then the air would be denser and would make more power.

Agreed on the back-pressure issue significantly increasing the efficiency of the larger turbos.

If everything worked as ideal gas law right? Too bad in reality, we are not making as much power as we're supposed to..

[bdkevoIX]

Originally Posted by O-cha

Holy crap where are you guys getting this. Let's all put freight turbos on the car.

A bigger turbo can flow more CFM, but it doesn't at the same pressure. The only reason it might is because the smaller was being run way out of efficiency but that has nothing to do with this. The amount of airflow is determined by the VE pressure and RPMs all other things equal.

um....no....

Then tell me why my stock turbo at 24psi made 350whp, and my pt61 made 470+whp at 24psi when nothing but the turbo was changed.

The amount of air flow is actually determined by the compressor itself. Not by its volumetric efficiency.