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My mistake, previous post edited.. IVC at 50deg BBDC would just result in no cylinder filling and amazingly high dynamic compression. You would greatly compromise power and efficiency for no reason.

As for an example, just look at how much power is gained on a turbo car with even a mild cam swap and you'll realize that going in the opposite direction would not be helpful.

Mr. Sir

Doward... I know.

I'm just trying to prove horsepower exists, and that it's directly related to how much air moves through and engine in a given period of time. I know turbos increase VE, which increases torque. I'm trying to prove that a unit of work (hp) exists, and it's related to grams/minute of air flowed through an engine.

Wouldn't the dynamic compression be amazingly low? The point of reducing NA efficiency is to get the 6.2 to emulate 4.8 liters of displacement, so that in FI form you can get the same power from the 6.2 as the 4.8. I already know there's very few practical applications for a cam that would hurt low/midrange, when a new turbo/normal cam would be a more beneficial route to go. As for the cams specs... not sure how much they would reduce apparent displacement, I was just throwing them out there for comparison. maybe 5 degrees BBDC would get the 6.2 to act like a 4.8?

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Yet again you are describing an impossible scenario. Taking a 6.2 and destroying it's efficiency is not going to make it have the power curve of a properly set up 4.8.

Maybe DCR would be low because of no cylinder fill but the compression cycle would now be starting at BDC. Research cam specs used in the 1800's before they considered something called inertia.

Put it this way, if you take a stock 6.2 and turbocharge it efficiently to say, 600hp then install a cam with an IVC at 5 deg BBDC you would probably lose at least 200hp, probably more.

BTW, like a Moth to a high wattage lightbulb I'm finally burnt out.

I'm really starting to think you are just intentionally posting up the most ridiculous scenarios you can think of.

Next I'm going to have to explain why an engine can't make more horsepower running on lemonade or how much efficiency will be gained if you chainsaw a bank of the engine off during a dyno run.

Mr. Sir

But if you took a 6.2 and a turbo designed for a 4.8 and got the 6.2 to only accept the same mass of air as the 4.8, wouldn't it effectively function as a 4.8?

Doward

You can not state that "a turbo increases VE"

Put a T3-50 trim on a 454 and tell me it increases VE.

An engine consists of a system - analzying individual parts neglects that fact.

"Horsepower" does not exist, it is an abstraction describing how much force is available in a unit of time. It is not a force. It is a unit of measurement, specifically of work.

Does a 'pound' exist? No. You can have a 'pound of X' but never just a 'pound' of nothing.

427

iTrader: (3)

Doward meet Mr Sir, Mr Sir meet Doward.

Problem solved Jim, don't eat the light bulbs.

Kurt

Mr. Sir

Considering torque is directly related to VE, I guess that "you cannot state that a turbo increases torque. Put a T3-50 trim on a 454 and tell me it increases torque".

This is what I've been trying to prove. Also, it just so happens that this "unit of work" is directly related to airflow, which I've also been trying to prove. I know hp isn't the same as torque (in terms of measurability), since hp can't exist without torque and rpm. However, it's still a valid property to consider when creating an engine. It's exactly what you called it; a unit of measurement, specifically of work.

slow67

iTrader: (2)

Wow you have a little ways to go.....Centrifugal Compressors are not mass flow devices, they are volumetric flow devices. Turbines are mass flow devices.

Doward

Somebody pass the light bulbs....

You're confusing so many terms I honestly think you're simply trolling at this point.

How is torque 'directly related' to VE? You can't even begin to claim that!

Compare two engines, both 100% VE, one with a 2" stroke, 4" bore; the other with a 4" stroke, 2" bore

Both spinning 4000 rpm, same airflow through the system.

According to your claims, since the mass airflow is the same through both of these systems, they will produce the same power.

The 2nd engine will have significantly increased torque compared to the first one, due to a higher mechanical advantage working on the crankshaft.

Mr. Sir

I don't think there'd be as much of a difference as you think. Can't prove it, but given each engine is seeing X power applied to each cylinder, I doubt there'd be any difference, unless you opened the exhaust valve early on the oversquare engine. The overstroked engine will retain piston velocity better after pressure is bled off.

as for torque being directly related to VE: VE goes up, torque goes up. simple. (I know 120% VE for one engine is only 40% for another. I was more or less referring to the turbos; They increase VE, which increases torque. It also increases grams/second of air, which is why hp is increased. Since I know you'll argue with that simplified statement: at 6000 rpm, the engine is ingesting 30% more air. This means
a) 30% greater VE
b) 30% greater torque (directly related to VE)
c) 30% greater horsepower (directly related to torque)

So now do you see what I'm trying to prove (that an increase in airflow will increase hp, as well as torque so long as the engine is operating at a constant rpm)?

NemeSS

iTrader: (127)

All i know is that a turbo is like posi-track. How does it work?
It just does!

Orr89rocz

iTrader: (13)

LOL x2. Thats all you need to worry about

Zombie

iTrader: (2)

They are mass flow but you can derive a volumetric flow from mass flow since 1lb/min of air = 14.472 cfm. Don't let manufacturers choice of specs confuse reality.

If they were a simply a volumetric flow device then you would not be able to compound compress because the larger turbos greatly outflows the smaller turbo (based on simple volumetric flow CFM). If they only operated in the volumetric plane then the smaller compressor would not be able to increase the pressure ratio of the already compressed air it's being fed because the larger turbo has already exceed it's flow capability and it would therefore do nothing but act as a restriction to flow.

Hypothetical over simplified example based on made up compressors operating as a volumetric flow device only.

Small turbo can flow 600 CFM, big turbo can flow 1800 CFM. We compound them. Big turbo is flowing 1800 CFM into the small turbo's inlet, what is the output? It would have to be 600 CFM since the small turbo is only capable of flowing 600 CFM. But we should all know that this is not what happens because compound turbo charging works.

Hypothetical over simplified example based on made up compressors operating as mass flow devices at normal atmospheric pressure of 14.7 PSI, I'm ignoring rpm, engine size and compressor efficiency for simplicity.

Small turbo can flow 60lbs/min at a pressure ratio of 2:1 (14.7 psi boost) when run at normal atmospheric pressure (14.7psi or 0psi boost, normal air we breath), big turbo can flow 120lbs/min at a pressure ratio of 2.5:1 (22 psi boost). Big turbo outputs 120lbs/min at 2.5:1 (22psi) into the inlet of the small turbo which then compresses that 120lbs/min by 2:1 (22psi * 2) to get 44psi. Mass flow coming from the output of the small turbo is now 240lbs/min @ 44psi boost or a pressure ratio of 4:1 or you could say the air is now 4 times denser than normal.

1lb/min = 14.472 cfm

Through the beauty of compression in the time span of one minute you have now managed to stuff 3743 cubic feet of air into that engine or to abbreviate 3743 CFM.

So centrifugal compressors are mass flow devices.

** just a note, compressing a gas like air does not increase it's mass since it still has the same number of atoms, we are only increasing the mass flow rate through compression by cramming more of those atoms into a smaller space over a given time period which increases the pressure. In a static system like a scuba tank you can store many cubic feet of air in a tiny space by compressing it and storing it at high pressure.

In turbocharging a internal combustion engine we are doing the same thing but our storage medium is dynamic but the principal is the same. More air molecules = ability to add more fuel = ability to get more bang in a given volume (your engine size).

98Z28CobraKiller

iTrader: (17)

Correction. Properly stalled autos only have 1000 rpm shift extension.

As for this thread,

I call it mental masturbation.

slow67

iTrader: (2)

You have it backwards. If it was mass flow, a small turbo compressor could NEVER flow as much as it could. That's why when figuring math for compound setups, you can't use the standard compressor map listed in lb/min, you need cfm. The small turbo flows the same cfm as it did without a bigger turbo in front of it, but the air weighs more than it did before (more lb/min than the map indicates).

Also, 1lb/min of air does not always equal 14.472 cfm, it depends on the temp/ambient pressure. At a certain shaft speed and Pressure ratio, the compressor always moves the same cfm, just the density of the air changes with pressure and temp.

Zombie

iTrader: (2)

And you just described why turbos are actually mass air flow devices not volumetric flow devices.

CFM = volumetric flow
Lbs/min = mass flow

If you have one cubic foot of air that's compressed to two times it's normal pressure, you just flowed twice the mass of air in that same cubic foot of air you moved, hence mass flow.

As for 1lb/min of air does not always equal 14.472 cfm comment, of course it depends on conditions but I was simplifying.

slow67

iTrader: (2)

If they were mass flow devices how can a tiny turbo move way more than what its "rated" for on its compressor map? It doesn't care what the air ways. It takes X amount of CFM of a gas, and compresses it down into Y cfm after the turbo. Yes, it multiplies its density. It doesn't care if its moving 100 lb/min or 200 lb/min, its taking X cfm, and its being slowed to Y cfm after.

tomz28

iTrader: (20)

Someone kill this thread it is spreading like A STD.

Zombie

iTrader: (2)

Straight from Borg Warner http://www.3k-warner.de/products/tur...ompressor.aspx

As you said, flow comes into play, but with a compressor you are increasing the pressure (putting more stuff in the same space) and therefore flowing more total mass per unit. That makes a centrifugal compressor a mass flow device. Unless of course you don't plan to use it as a compressor, then it can be considered a flow device because it's not changing the mass flow of the air going through it, just the flow.

Hope that makes more sense for you.

Orr89rocz

iTrader: (13)

x2

They dont move more air than they are "rated" for. The rating is the rating and thats it. The wheel flow capability is defined by impeller design and spin speeds, meaning it can only turn so much rpm before mechanical stress limits are imposed, and it can only pass a certain amount of flow in those speed ranges. This is how the "map" is created.

If you took X cfm and compressed it to Y cfm, Y would be less than X and the car would basically make less power. Higher density takes up less volume. This is gas specific volume, just the inverse of density.

The formula for CFM is CFM= mass flow * specific volume. Specific volume is calculated from a given mass mixture by its pressure and temperature using various gas properties for the constituents in the mixture.

So logically, as specific volume goes down due to higher and higher pressures, the only way to match the same CFM is to increase Mass Flow.


As long as you know the gas properties you can use Volume flow or mass flow, as each can be calculated from the other. But 500 cfm is not 500 cfm on different engines at different pressures/temps. They can have different mass flows.