exhaust theory

[JAP63]

Today someone told me they fitted a 3 inch exhaust to their rex and the boost went down..thats right,the boost pressure decreased after the fitment of the exhaust.......could reduced backpressure do this?

Example..
If you had a stock vr4 and it was on say 10 pound...you fit a full Hi-flowing 3 inch exhaust..would you expect the boost pressure to drop..or go up?

I know flow goes up and backpressure goes down....
But I though the boost always went up a couple of pound

 

[JAP63]

Today someone told me they fitted a 3 inch exhaust to their rex and the boost went down..thats right,the boost pressure decreased after the fitment of the exhaust.......could reduced backpressure do this?

Example..
If you had a stock vr4 and it was on say 10 pound...you fit a full Hi-flowing 3 inch exhaust..would you expect the boost pressure to drop..or go up?

I know flow goes up and backpressure goes down....
But I though the boost always went up a couple of pound

 

[JAP63]

Today someone told me they fitted a 3 inch exhaust to their rex and the boost went down..thats right,the boost pressure decreased after the fitment of the exhaust.......could reduced backpressure do this?

Example..
If you had a stock vr4 and it was on say 10 pound...you fit a full Hi-flowing 3 inch exhaust..would you expect the boost pressure to drop..or go up?

I know flow goes up and backpressure goes down....
But I though the boost always went up a couple of pound

 

[bazeng]

it would generally go up, it would also increase the chance of boost spike / creep...

back pressure would increase the torque down low, but would reduce the power up high...

i dont see why boost would decrease.....

 

[bazeng]

it would generally go up, it would also increase the chance of boost spike / creep...

back pressure would increase the torque down low, but would reduce the power up high...

i dont see why boost would decrease.....

 

[bazeng]

it would generally go up, it would also increase the chance of boost spike / creep...

back pressure would increase the torque down low, but would reduce the power up high...

i dont see why boost would decrease.....

 

[GVR40]

boost would decrease because its a poobaru

 

[GVR40]

boost would decrease because its a poobaru

 

[GVR40]

boost would decrease because its a poobaru

 

[rob323]

I have my own thoughts on this, let the dribble begin:

In theory, if the amount of "air flow" (ie. volume of air) remained the same and the restriction (ie back pressure) was reduced, then the pressure in the system will also drop so, in theory, yes, your boost pressure should drop. BUT.....

Throw into the equation, a car, a turbo, cams, valves and an exhaust system and all that all goes out the window because if there is less back pressure, the exhaust gasses will be flowing faster which in turn will make the the turbo spin faster and make it pump more air, the more it pumps into the engine, the more comes out the exhaust manifold to spin the turbo up more and so on and so forth bla bla bla...so even if boost pressure remained the same, the amount of air flowing through the motor is increased (hence the increase in power obtained from a free flowing exhaust system).

I think the usual increase in boost pressure that comes with a free flowing exhaust is something to do with increased speed of the exhaust gases which spin the turbo faster and the wastegate only being able to "relieve" the exhaust wheel of a certain amount of airflow (ie boost creep).

Apart from all the above, add some big words like "volumetric efficiency" and it all gets too confusing.

You put an exhaust on, your boost will increase, enjoy it . If it decreases, I would suspect that there was something not right elsewhere in the system like the blow off valve not being able to hold the extra airflow and relieving the pressure.

I need to go lie down now, my head hurts.

 

[rob323]

I have my own thoughts on this, let the dribble begin:

In theory, if the amount of "air flow" (ie. volume of air) remained the same and the restriction (ie back pressure) was reduced, then the pressure in the system will also drop so, in theory, yes, your boost pressure should drop. BUT.....

Throw into the equation, a car, a turbo, cams, valves and an exhaust system and all that all goes out the window because if there is less back pressure, the exhaust gasses will be flowing faster which in turn will make the the turbo spin faster and make it pump more air, the more it pumps into the engine, the more comes out the exhaust manifold to spin the turbo up more and so on and so forth bla bla bla...so even if boost pressure remained the same, the amount of air flowing through the motor is increased (hence the increase in power obtained from a free flowing exhaust system).

I think the usual increase in boost pressure that comes with a free flowing exhaust is something to do with increased speed of the exhaust gases which spin the turbo faster and the wastegate only being able to "relieve" the exhaust wheel of a certain amount of airflow (ie boost creep).

Apart from all the above, add some big words like "volumetric efficiency" and it all gets too confusing.

You put an exhaust on, your boost will increase, enjoy it . If it decreases, I would suspect that there was something not right elsewhere in the system like the blow off valve not being able to hold the extra airflow and relieving the pressure.

I need to go lie down now, my head hurts.

 

[rob323]

I have my own thoughts on this, let the dribble begin:

In theory, if the amount of "air flow" (ie. volume of air) remained the same and the restriction (ie back pressure) was reduced, then the pressure in the system will also drop so, in theory, yes, your boost pressure should drop. BUT.....

Throw into the equation, a car, a turbo, cams, valves and an exhaust system and all that all goes out the window because if there is less back pressure, the exhaust gasses will be flowing faster which in turn will make the the turbo spin faster and make it pump more air, the more it pumps into the engine, the more comes out the exhaust manifold to spin the turbo up more and so on and so forth bla bla bla...so even if boost pressure remained the same, the amount of air flowing through the motor is increased (hence the increase in power obtained from a free flowing exhaust system).

I think the usual increase in boost pressure that comes with a free flowing exhaust is something to do with increased speed of the exhaust gases which spin the turbo faster and the wastegate only being able to "relieve" the exhaust wheel of a certain amount of airflow (ie boost creep).

Apart from all the above, add some big words like "volumetric efficiency" and it all gets too confusing.

You put an exhaust on, your boost will increase, enjoy it . If it decreases, I would suspect that there was something not right elsewhere in the system like the blow off valve not being able to hold the extra airflow and relieving the pressure.

I need to go lie down now, my head hurts.

 

[JayRome]

damn rob323... after reading that now i need to lie down! although i agree ......

 

[JayRome]

damn rob323... after reading that now i need to lie down! although i agree ......

 

[JayRome]

damn rob323... after reading that now i need to lie down! although i agree ......