Boost vs. restriction and efficiency?

[0-60n4]

I know you guys can answer this one pretty quickly and I think I know but want confirmation:

With manual boost control, if you go with a more efficient and less restrictive intercooler, will you see lower indicated boost pressure if you don't change the boost settings?

 

[Mr.Spool]

boost is a measure of what doesn't get into the motor.

 

[Dusty Bradford]

With less restriction between the turbo and engine, you will see higher boost in the intake.


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[bison]

Less restriction before or after the turbo including after the exhaust outlet will reduce drive pressure requirements to generate the same mass flow at a given pressure. Usually manifold pressure is the reference point but a lot more could be looked at to determine the turbos workload and a lot can be predicted. Basically the turbo is allowed to work as it should if restrictions are removed. Every compressor and turbine has an operating range where it's very efficient and does the most efficient work. This doesn't mean the most work. Had a car last week that was trapping 132-133mph with 27-28psi as read on a gauge. Put an xfi on and removed the MAF restriction and boost control became a problem. The owner went back to a weak spring actuator. I wouldn't be one bit surprised if the car picked up 7-8mph in the quarter at 3psi less boost. It's still a stock location Intercooler and I'm sure that the Intercooler is choking off power on the combo. Unfortunately we don't have the exhaust pressure data but you can be sure that it has dropped a bunch yet the compressor is able to do more work. More work with less energy required means you're about to kick ass. Dropping drive pressure also helps empty the cylinder on the exhaust stroke because the lowest pressure you will have at tdc on the ex stroke is the higher of either the exhaust or manifold pressure. It probably won't be manifold pressure in most fast spooling non nitrous street applications. So you are left with exhaust pressure. Dropping that pressure 10psi will do a lot for cylinder fill at all positive boost operating speeds and especially at higher speeds. The lower the pressure at tdc the faster (less crank degrees) the cylinder can begin to fill.


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[fastblackracing]

I know you guys can answer this one pretty quickly and I think I know but want confirmation:

With manual boost control, if you go with a more efficient and less restrictive intercooler, will you see lower indicated boost pressure if you don't change the boost settings?

boost is a measure of what doesn't get into the motor.

• As dusty stated less cooler restriction = more air to fill the Engine, if you lessen the pressure drop you will see a slight manifold pressure increase and also the turbine pressure would drop an even smaller amount due to the load on compressor wheel being reduced...... A good cooler will have less than 2 pounds of pressure drop...... and using the same cooler on 2 engines, one making 300 HP and the other Making 600 HP will have a much greater pressure drop on the 6oo HP due to the greater amount of passing through the cooler.
• I do not agree that "boost is what doesn't get in the motor", that is somewhat confusing ....... Think of boost as a measure of the density of the air that is in the intake system waiting to get into the Engines cylinders..........more boost equals a denser or heavier more tightly packed given volume of air, the "boosted air" does get into the engine only now there is more of it......picture a round ball 1" in diameter, the first ball is hollow, the second ball is made of wood, and the third ball is made of steel...........they all have the same volume but there density changes drastically.........Air has weight and that is why compressor wheels are rated for there ability to move xxx pounds of air per minute @ xx pressure ratio.

 

[Mr.Spool]

I do not agree that "boost is what doesn't get in the motor", that is somewhat confusing ....... Think of boost as a measure of the density of the air that is in the intake system waiting to get into the Engines cylinders..........

actually I thought it was very straitforward and it is the air that's is not getting in or waiting to get it,density is the content of the air.

 

[Mr.Spool]

Had a car last week that was trapping 132-133mph with 27-28psi as read on a gauge. Put an xfi on and removed the MAF restriction and boost control became a problem. The owner went back to a weak spring actuator. I wouldn't be one bit surprised if the car picked up 7-8mph in the quarter at 3psi less boost.

did the car use more fuel?

 

[0-60n4]

Maybe it's not as simple as I thought.
I have manual boost control. I was running 17 psi boost. I replaced the original factory IC with an RJC front mount. I know it has less pressure drop and much better cooling. I only got to drive the car for a few minutes the other night but a couple WOT runs was showing 15 psi boost. My thoughts were, (assuming I have all my hose connections good and tight) the boost gauge is reading pressure at the manifold. The lower pressure drop across the new IC should increase boost pressure at the gauge. But the cooler and denser air might result in lower boost pressure at the gauge.

Does my 2 psi lower boost pressure sound normal? My next step is to start raising pressure.

 

[Mr.Spool]

But the cooler and denser air might result in lower boost pressure at the gauge.

usually the colder air will show more boost on the gauge.boost is just a number,did your car use more or less fuel at 15psi on the new intercooler vs 17 on the stocker?

 

[GN87Mike]

Where are you measuring boost.....the turbo or the intake?

 

[0-60n4]

usually the colder air will show more boost on the gauge.boost is just a number,did your car use more or less fuel at 15psi on the new intercooler vs 17 on the stocker?

I only tested if a few minutes and parked it.

 

[bison]

did the car use more fuel?

I don't know what the pulse width was when it was a chip. So I can't say how much more it used.


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[V6sleeper]

Without getting too far off topic, at what point does the Plenum play a roll in the efficiency at higher boost levels? as far as stock vs after market vs ported and a 1" spacer in building a higher volume of air going into the motor?

 

[Ttype6]

• I do not agree that "boost is what doesn't get in the motor"

If your map sensor receives its signal from the intake plenum,it's reading the pressure inside the intake manifold. The reason there is pressure is because there is more air entering the intake than the engine is consuming.

If we reduce restrictions with larger valves,larger ports,bigger cam,higher revs and force the same amount of air into the engine,the pressure inside the intake will fall. Why? Because more air is entering the engine. Now we are making more power with less pressure in the intake. If boost pressure was a measure of how much air was entering the engine,the pressure would have gone up in this scenario. The reason it didn't go up is because we are measuring the air that can't get in.

The other thing we can do is run the same pressure in the intake as we did before the modifications. In this scenario the engine makes more power than it did before the mods and it does it with the same amount of pressure inside the intake manifold. Again,we are making more power but the pressure in the intake stayed the same. It didn't rise. Why not? because we are measuring the air that can't get in the motor.

If we were measuring cylinder pressure,we would note a rise with both of these scenarios.

 

[bison]

If your map sensor receives its signal from the intake plenum,it's reading the pressure inside the intake manifold. The reason there is pressure is because there is more air entering the intake than the engine is consuming.

If we reduce restrictions with larger valves,larger ports,bigger cam,higher revs and force the same amount of air into the engine,the pressure inside the intake will fall. Why? Because more air is entering the engine. Now we are making more power with less pressure in the intake. If boost pressure was a measure of how much air was entering the engine,the pressure would have gone up in this scenario. The reason it didn't go up is because we are measuring the air that can't get in.

The other thing we can do is run the same pressure in the intake as we did before the modifications. In this scenario the engine makes more power than it did before the mods and it does it with the same amount of pressure inside the intake manifold. Again,we are making more power but the pressure in the intake stayed the same. It didn't rise. Why not? because we are measuring the air that can't get in the motor.

If we were measuring cylinder pressure,we would note a rise with both of these scenarios.

There's a lot more to it than this. Cams with too much overlap can actually hurt cylinder fill on these engines especially the way most run them. The compressor/turbine is designed to do work with exhaust energy. The result of the work is increased mass flow. Whether it be from boost or increased mass efficiency for other reasons more mass flow equals more power. Saying it's the air that doesn't get in the engine isn't the correct way to identify a turbocharged engines operation especially with no reference to the exhaust stroke and the exhaust pressure that's generated on a turbo engine. The compressor and turbine are designed to work at a certain pressure ratio and mass flow. You could actually be running in surge or way out of breath even if intake to exhaust pressure ratios are ok (wrong turbo). Also the cylinder pressure isn't totally dependent on mass flow and cylinder pressure isn't what dictates power otherwise the engines with the highest cylinder pressure would make the most power. The racers that are really flying are keeping cylinder pressure in check over a wider and higher operating range and are also minimizing inert gas in the cylinder at the end of the exhaust stroke so that the cylinder fill will begin asap on when the intake valve opens. It's easy to get cylinder pressure. It's not as easy to get mass flow through the engine otherwise everyone would be flying.


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[Mr.Spool]

getting the air in and out is what makes the power.having a better motor significantly helps the in and out but in reality the air is being forced into the engine.a combo making 24psi and going 10.0s and another combo going 10.0s at 30psi given the same weight,tells me a lot about both combos.the lower boost combo had a more efficient motor/not better as both are going 10.0.the motors ability will effect the turbos ability to make boost which is air that's not at that time getting into the motor.

 

[fastblackracing]

getting the air in and out is what makes the power.having a better motor significantly helps the in and out but in reality the air is being forced into the engine.a combo making 24psi and going 10.0s and another combo going 10.0s at 30psi given the same weight,tells me a lot about both combos.the lower boost combo had a more efficient motor/not better as both are going 10.0.the motors ability will effect the turbos ability to make......[boost which is air that's not at that time getting into the motor.].......

Ok lets think about it like this.......on a given engine ....."since boost is air that is not at that time getting in the motor"........turn the boost down 10 pounds on that same given engine and tell me what is going to happen?.....we both know that engine will now make less power since their is less air getting in the engine due to 10 pounds less boost .....boost is really just a unit of measurement we use that tells us how densely we are packing the cfm's that are going into the said engine.........another confusing term I see used a lot is " motor"...... motors are electrical devices.....engines are what we have in our turbo regals to throw boost and cubic dollars at......

 

[Ttype6]

Saying it's the air that doesn't get in the engine isn't the correct way to identify a turbocharged engines operation


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I'm not trying to explain all the intricate operations of the force fed internal combustion engine.
Just speaking in the simplest terms. If we force the same amount of air into a small engine and a much larger and higher revving and therefore less restrictive engine,the pressure in the intake manifold of the larger,higher revving,higher powered engine will be lower. Why ? Because there is less air stacked up that can't enter the engine. After all,if we measure the air pressure inside the intake plenum,we're measuring the air that hasn't entered the engine. We can be sure of this because of where we are measuring the air.

A measurement of the air pressure inside the intake manifold plenum of a boosted engine is a measurement of the air that can't get in.
The MAF measures the air that can get in.

Would you agree that when I measure the pressure inside my tires with a tire gauge,I'm measuring the air that can't get out?

 

[Mr.Spool]

boost refers to the amount by which intake manifold pressure exceeds atmospheric pressure.this is a representative of the Extra Air pressure that is achieved over what would be achieved without forced induction.thats Wikipedia.an engine or motor is a machine designed to convert one form of energy into mechanical energy Wikipedia.