Volumetric Efficiency.

[oab_au]

Not wanting to keep any body from there work. I thought we could discuss the affects of forced induction, on the Volumetric Efficiency of the engine here.

On another thread, the VE is quoted as 95% and used as the basis for predicted output. It probable is 95% at some rpm, but it is not a constant figure. The VE is the % of air that the engines cylinder can capture, with the swept vol given as 100%.

This figure is controlled by the mechanics of the engine, the inlet and exhaust tracts, and the cams profile. These components are chosen to suit a particular rpm. So it is at this engine speed that the maximum VE, thus torque is produced. The VE figure for the EG33 reaches 105% at 4000 rpm, 110.8 at 5000 rpm. This is achieved, due to the effect, that resonate action in the inlet and exhaust tracts, and the cam profile, has on cylinder filling.

If a positive displacement pump is fitted to increase the air pressure in the inlet, the VE will increase in proportion to the increase in applied pressure, but the rate of change of the VE will still be dependent on the mechanical components that the engine is fitted with.

The extra pressure will not cause the resonate frequency to occur at a higher rpm, so the VE curve, hence the torque, will still drop off at the same rpm as the original engine.

Harvey.

[GreenMarine]

I love reading your posts Harvey... They actually make me think and use the knowelage that I am gaining in school

Do you use AOL Instant Messenger?? If so, you should drop me a line sometime... I'd love to crunch numbers with ya on the mechanical workings of diffrent components in the car

[Phast SVX]

Originally Posted by oab_au

Not wanting to keep any body from there work. I thought we could discuss the affects of forced induction, on the Volumetric Efficiency of the engine here.

On another thread, the VE is quoted as 95% and used as the basis for predicted output. It probable is 95% at some rpm, but it is not a constant figure. The VE is the % of air that the engines cylinder can capture, with the swept vol given as 100%.

This figure is controlled by the mechanics of the engine, the inlet and exhaust tracts, and the cams profile. These components are chosen to suit a particular rpm. So it is at this engine speed that the maximum VE, thus torque is produced. The VE figure for the EG33 reaches 105% at 4000 rpm, 110.8 at 5000 rpm. This is achieved, due to the effect, that resonate action in the inlet and exhaust tracts, and the cam profile, has on cylinder filling.

If a positive displacement pump is fitted to increase the air pressure in the inlet, the VE will increase in proportion to the increase in applied pressure, but the rate of change of the VE will still be dependent on the mechanical components that the engine is fitted with.

The extra pressure will not cause the resonate frequency to occur at a higher rpm, so the VE curve, hence the torque, will still drop off at the same rpm as the original engine.

Harvey.

I was under the influence that HP will continue to increase in a positive displacement blower. I dont think tq was really ever the issue.

[oab_au]

Originally Posted by Phast SVX

I was under the influence that HP will continue to increase in a positive displacement blower. I dont think tq was really ever the issue.

Your bin spending too much time with Rob.

HP can't keep increasing, if the torque is dropping off. Over the same rpm range, the torque has to increase, for the HP to increase. HP is just an effect of torque over time. Anything you do to the engine to increase power, has to increase the torque, or there will be no HP difference.

Harvey.

[Phast SVX]

then how do you explain this
http://www.whipplesuperchargers.com/...obra_graph.gif
http://www.whipplesuperchargers.com/...gers_Graph.gif

[Trevor]

[QUOTE=oab

The extra pressure will not cause the resonate frequency to occur at a higher rpm, so the VE curve, hence the torque, will still drop off at the same rpm as the original engine.


Surely the design criteria ot the original induction system will be completely upset if forced induction is introduced and therfore the original effects will not occur. A supercharger will normally provide poitive pressure in line with engine RPM and this over riding factor will negate the original concept in respect of a specifically designed inlet tract. A completely different curve must apply.

[Phast SVX]

[QUOTE=Trevor][QUOTE=oab

The extra pressure will not cause the resonate frequency to occur at a higher rpm, so the VE curve, hence the torque, will still drop off at the same rpm as the original engine.


Surely the design criteria ot the original induction system will be completely upset if forced induction is introduced and therfore the original effects will not occur. A supercharger will normally provide poitive pressure in line with engine RPM and this over riding factor will negate the original concept in respect of a specifically designed inlet tract. A completely different curve must apply.[/QUOTE]

Trevor! how ive missed you! (and how far ive come with my car since we last talked )
phil

[oab_au]

Originally Posted by Phast SVX

then how do you explain this
http://www.whipplesuperchargers.com/...obra_graph.gif
http://www.whipplesuperchargers.com/...gers_Graph.gif

Whats to explain Phil? The first is a comparison of an Eaton V a Whipple.
The second shows an increase in torque, with a corresponding increase in HP.

Is that what you see?

Harvey.

[oab_au]

[QUOTE=Trevor][QUOTE=oab

The extra pressure will not cause the resonate frequency to occur at a higher rpm, so the VE curve, hence the torque, will still drop off at the same rpm as the original engine.


Surely the design criteria ot the original induction system will be completely upset if forced induction is introduced and therfore the original effects will not occur. A supercharger will normally provide poitive pressure in line with engine RPM and this over riding factor will negate the original concept in respect of a specifically designed inlet tract. A completely different curve must apply.[/QUOTE]

Gid'ay Mate, I knew you were still around.
Atmospheric pressure does have an effect on the resonate frequency. To the effect of changing the speed of the sonic wave. But it still increases the VE when it resonates, and the VE will still drop off when the resonate peak is pasted. The increase in boost pressure will still increase VE over the standard engine, but it will still reduce as the resonate effect reduces.

Harvey.
P.s. Happy Birthday, you still got 10 years on me.

[Trevor]

Originally Posted by oab_au

Your bin spending too much time with Rob.

HP can't keep increasing, if the torque is dropping off. Over the same rpm range, the torque has to increase, for the HP to increase. HP is just an effect of torque over time. Anything you do to the engine to increase power, has to increase the torque, or there will be no HP difference.

Harvey.

NO not so, but yes you correctly said, "torque over time". More correctly "torque within a period of time".

Put simply one could say, shortening the time by increasing RPM provides more periods of applied torque within a given length of time and therefore an increase in resultant power.

In order to increase power output the torque does not have to increase and in fact can fall off if offset by increased "effort/energy". This is indicated exactly by riding a bicycle in a lower gear. Less applied torque, but increased RPM can result in an increase in speed from the generation of more power. Not rocket science. (In this instance the gear ratio makes this possible but has nothing to do with "Torque/RPM/Power" as a factor.)

[Trevor]

[QUOTE=oab_au]

Originally Posted by Trevor

Gid'ay Mate, I knew you were still around.
Atmospheric pressure does have an effect on the resonate frequency. To the effect of changing the speed of the sonic wave. But it still increases the VE when it resonates, and the VE will still drop off when the resonate peak is pasted. The increase in boost pressure will still increase VE over the standard engine, but it will still reduce as the resonate effect reduces.

Harvey.
P.s. Happy Birthday, you still got 10 years on me.

Thanks Harvey, it was yesterday.

The specific point I made was that a different curve will apply.

[Phast SVX]

thank you, that was the only point i was attempting to make

phil

[oab_au]

Originally Posted by Trevor

NO not so, but yes I guess this means, you agree with me? you correctly said, "torque over time". More correctly "torque within a period of time".

Put simply one could say, shortening the time by increasing RPM provides more periods of applied torque within a given length of time and therefore an increase in resultant power. Yes thats the way it normalys goes

In order to increase power output the torque does not have to increase and in fact can fall off if offset by increased "effort/energy"another name for torque?.

This is indicated exactly by riding a bicycle in a lower gear. Less applied torque, but increased RPM can result in an increase in speed from the generation of more power. Not rocket science. (In this instance the gear ratio makes this possible but has nothing to do with "Torque/RPM/Power" as a factor.)

Yes it has nothing to do with increasing HP without increasing RPM. "Lowering the gearing. Less applied torque, but increased RPM" will not increase the speed or generate more power. Just allows you to remain at the same speed, with reduced torque.

Harvey.

[shotgunslade]

There is a significant different between the behaviour of positive displacement compressors like the Whipple and the centrifugal compressors typically seen with turbochargers. A positive displacement device delivers a fixed volume of gas depending upon its speed of rotation. The actual mass flow will be dependent upon that volumetric flow and the pressure drop on the inlet side of the compressor. Pressure drop on the inlet side will reduce the density of the incoming charge and thus reduce the delivered mass flow. The mass flow is not significantly affected by the pressure drop on the discharge side. The main effect of restriction on the discharge side is to increase the power required to rotate the compressor. This increase in parasitic power is small compared with the increased power generated by the increased mass flow. So, the power increase of a positive displacement device is not very sensitive to pressure drop between the compressor and the engine, and dynamic tuning of that conduit has little effect. Mass flow through a centrifugal compressor on the other hand is dependent upon pressure drop on both sides of the compressor as the compressor generates a pressure differential without creating a fixed volumetric flow. Thus tuning and resonant design of the conduit between the centrifugal compressor and the engine can generate increased mass flow of air into the engine, by reducing the pressure against which the compressor is working. A centrifugal compressor can be deadheaded without destroying anything, because it cannot generate flow at a given speed of rotation against backpressure above a certain level,. A positive displacement compressor, if deadheaded, will either explode something on the discharge side, or will break the compressor drive.

[Trevor]

Originally Posted by oab_au

Yes it has nothing to do with increasing HP without increasing RPM. "Lowering the gearing. Less applied torque, but increased RPM" will not increase the speed or generate more power. Just allows you to remain at the same speed, with reduced torque.

Harvey.

Harvey you are creating a smoke screen by twisting your words during a debate and one which you initiated. You have previously stated here, quote - "anything you do to the engine to increase power, HAS to increase the torque." This statement is incorrect.

Alterations such that effective RPM are increased CAN and often do, increase power, even at the expense of torque; i.e. even if less torque is available there can be more power as a result of alterations.

Regards, Trevor.