I can, the temperature. That can specifically cause a bottom end to fail. Do I win a drawing?????

 

I cover Temp several times in the past. We all know it exists. There is some delta T, some change in T of the air, that occurs from the filter to the head, on every engine. We all know temp generally rises as it moves from filter to head, but it can be forced to go down as well. A very high temp can kill an engine as easily as a very low temp. There is some optimal range for all individuals. If you are not controlling temperature in any application you have bigger issues than performance related ones, it need not be mentioned (because we are all aware of it) that you had better be on the ball when it comes to delta T of air temp, in any application, boost or not.

 

If you made a classical physics equation that related fuel consumption to weight moved (horsepower), you could create a single coefficient that represents the parasitic loss of the rotating parts. Actually finding it would require some testing, since there are a range of conditions (temps, densities and expansion rates of materials) but you could certainly use a "dummy" value that fit a wide range of autos. The coefficient would be quite small, next to the weight of the vehicle, i.e. there is a much larger consumption of fuel moving from 1000lbs to 3000lbs than there is moving from 2L to 6L of displacement in traditional, modern engines. And sometimes the coefficient gets "lost" (negligible) in heavy vehicles, due to the overpowering effect mass has on such an equation. Again, the equation for horsepower relates the weight to the distance moves per time, nothing to do with the horse itself, even though the horse needs to eat, we just assume it is what it is, part of the cost of breathing.

You bring up an interesting point about Temp again. I'll take a step back and re-analyze the temp issue. We want air as hot as possible in the largest mass possible for maximum power(hotter air contains more energy, however little), except that this is not good against fuel quality and creates problems (explosions). There is a trade off at play here. For an economy vehicle, the exhaust should be allowed to get as hot as it can (without hurting parts) since the dynamic (cruise) compression should be low (no fuel quality issue) we can allow the EGT and other temps to rise for better engine efficiency. The more Temp rise we can trap in the exhaust system and engine, the better our economy should become (until fuel Q issue crops up and pressure begins to spike). We also want to minimize EGT coming out of the valve, to get the most of our fuel. Ideal EGT would be less than IAT, to prove we extracted more energy from the fuel. Performance is similar except that now fuel quality is a bigger issue. We want to dump the temp rise when it gets above a certain point to protect the engine (against fuel quality issue) just like when cruising, however, we also want the mass increasing effect of a low intake temp which does not matter during a highway cruise (no need to max VE and air mass together while cruising). We run the IAT down as low as you can go, and again allow the EGT to get as high as it wants until a set point, at which you take measures to control it. The main difference is that when extracting maximum performance, you remove extra temperature for safety, thus the idea behind 160*F thermostats and water injection and intercooling and all similar ideas. This is safety against the fuel quality, an important correlation to keep intact, since as colder air becomes more dense, there are more air molecules, the engine makes more power, and what is it that kills stock piston LT1 engines? Apparently, it is making too much power (regardless of temp they fail around 400-450hp right?). So there is some low temperature which will provide enough air molecules to kill an LT1 piston, around the same number of air molecules that would kill it in a boosted application I would have to guess. Temperature is just another way to adjust molecules/area the way boost pressure does, it can be used in a similar way. This is why I am emphasizing control of temperature and pressure in the engine. Heat shields, blankets, wraps, coatings, meth/water, intercooler, create duct, extra large fans, aux cooling, they all have places in performance application for control.


My argument against low coolant temps is only on engines which have trouble getting the oil temperature up in a daily driver application. Sometimes you put a 160*F thermostat and now the oil takes twice as long to hit 200*F if you are just driving the car around town and idling. A properly tuned configuration (more than just the computer's tune, the way the engine is dressed and blanketed is part of the "tune") will not throw alot of temp rise into the coolant (we want to minimize energy lost to the coolant and use as much of the fuel as possible to drive the piston) and together low oil temps and daily drivers is a bad combination for the engine, as it has been shown to increase engine wear and tear. There have been plenty of studies of low fluid temps creating longevity issues that I do not feel the need to elaborate.

 

If a turbocharger is sized appropriately, the path of least resistance is both the (disconnected) turbine and the open wastegate. In other words, sure some exhaust will flow through the wastegate, at first quite a bit of it. But as you pointed out, at some point the engine will want more room to breath, at which point EGP will begin to climb and it will seek the path of least resistance- the turbine. Yes the turbine still flows exhaust gas even when the wastegate is wide open, and it does present a low resistance path for exhaust to take. If the application is big power with small displacement, the turbine will barely spin as it easily provides a low resistance path for the tiny engine. If the application is tiny turbo with large displacement, you might actually get some "over boosting" (more than 1~psi on the gauge) due to the increasing EGP. So it depends on the combo (turbo/engine) how well an un-clamped turbine will flow.

 

Outside of the "ram air" effect, NA engines are pulling in air, boost is "cramming" it in.

 

Pics?

No way, bro. SLP says differrn't!

 

From a classical physics approach, we are looking at the same exact thing. You are just trained to see it as "sucking" instead of "blowing". Let me fix that. The atmosphere provides the weight of air. When an engine "sucks" it is actually being "supercharged" by the weight of the air molecules extending miles up into our atmosphere. Without so many air molecules stacked up for miles, we couldn't breath either, as it is this weight that forces air molecules into our lungs when we inhale. Speaking of which, when you inhale, you are doing the same thing as a piston descending, creating a low pressure area for the weight of the column of air molecules extending miles above you to seek entry. Boost is simply extra weight, extra pressure from even more air molecules, put a mask on your face with 1psi of air pressure and watch how much easier it is to draw breath. A head/cam is a pre-existing condition, just like having lungs and a mouth. Alternating head/cams (or mouths and lungs) changes the way the engine breaths, but it is still at the whim of the miles of air molecules extending above you. That is where I emphasize control with a dial, if you are experienced and qualified, you can determine where to set that dial for each condition, yes. THEN you can go back to the engine, and install the head/cam for the powerband you desire. I am not against head/cam modifications, they are absolutely necessary for attaining a proper well matched combo per given operating ranges (for engines without variable camshaft control and so forth).

 

How does a motor who gains power by VE changes equate to the same motor minus the VE changes but now with more air density?

 

pictorals?

 

Many, if not all modern engines, naturally aspirate engines, utilize a "ram air" effect to some extent. This is why you see varying runner lengths on manifolds. The engineers have determined from a model what the most common operating ranges are, and have provided runner lengths/designs which emphasize those ranges through acoustic tuning. This effect is demonstrated in the exhaust system as well. Anytime air molecules move from point A to point B it was because of a pressure differential, a change in pressure from one point to the next. Doesn't matter if the engine is N/A or boosted, the same rules apply i.e. the acoustic tuning of intake manifold runner lengths applies equally to boosted engines and N/A engines, since from the engines point of view the only thing changing is the weight of the column of air molecules extending miles into the atmosphere.

 

Scavenging. The word you are looking for is scavenging. NA engines use scavenging to increase VE (even over 100%).



You can BYPASS the turbine. You cannot disable it. There's an important distinction in the difference. In either case, you still have the restriction of exhaust flow through the wastegate and around the Turbo. Plus you still have the weight of the Turbo. And you still have the additional restriction on the intake side to, even if you did bypass the compressor...... No mater what, that turbine will be spinning (from the work of the engine) and so will the compressor. And you'll still have the additional mass of the turbo and all it's plumbing to deal with. ALL leading to reduced fuel economy.




What magical universe do you live on? Let's blame the fuel! Why don't you just run top fuel? Wait, they don't use Turbos....... But 22:1 plus 2.5 bar yo! Or let's be realistic and go with what 99% of every single person driving today is going to use; gasoline.... from the pump..... at the gas station..... down the road..... for $1.87/gal........

Oh wait I get it. What you're saying is, that if I built a high compression turbo motor using a stock LT1 all would be fine if I run Meth injection for $27.96/gal, 110 Octane (bad for power BTW) for $11.93/gal, and have a top notch intercooler. AND if I install a turbine "disable" future (like a clutch right?), I'll GAIN FE? Yup, makes sense now that you put it that way......



Peak BSFC is actually not tied to peak torque or horsepower. A little research would tell you that. Peak VE is tied to peak Torque however, also directly tied to BMEP.

Brake Mean Effective Pressure, is just that; how much mean effective pressure would it take within that engine to produce the output it does. Mean Effective Pressure= pressure in excess, averaged through out all cycles of an internal combustion engine, to produce usable power to perform other tasks.



So much wrong here. Reducing vacuum will increase FE, so long as the additional power is not more than needed. An engine at WOT is more efficient than one with a closed throttle body, the power output difference is telling in that manner. Why do you think OEM's are trying to DELETE the throttle body????

Cruise has little to do with actual speed and more to do with maintaining a speed. You'll use less fuel per mile maintaining 120mph than you would doing 2mph then stopping, 10mph, stopping, 8 mph, stopping, 45mph, stopping, 25 mph, stopping....... I think you get the point. Well I hope you do cause I'm not going to keep typing all that stop and go traffic none sense and how it results in accelerating, decelerating, accelerating, etc, etc.

What speed the vehicle is most efficient at while cruising is irrelevant.


Cadillac Escalade 2WD vs AWD. You obviously have zero experience with anything that transfers power to move a lot of mass huh? There's a lot NOT installed at ALL on a 2wd truck vs 4WD or AWD when it comes to drive line. This argument is invalid, all it shows is your ignorance.



Sparingly and light are two different things. Boeing uses mass on their airplanes sparingly, they are still incredibly heavy. LOL at Subaru's design being stronger. Seriously? You can't be serious? You mean to tell me that the Subaru has at least an 8 inch ring and pinion? Oh wait it doesn't. You're looking at an R180 (or similar). That would be 180mm, or 7.08". That's smaller than the stock weak *** **** our LT1 F-bodies came with. The Corvette's are stronger still.



Lower RPM does not always give better cruise economy. If that were the case 4 bangers would cruise at a lower RPM than they do. There's a reason they don't. That reason was explained in my last post, the one you quoted, and responded to with incorrect information, like this comment......

Why don't you run higher compression ratio on the Turbo?..... Is it because there's a Turbo? And you can't run high compression ratio's (read: high expansion ratios, read: higher efficiency????) unless you run fuel that costs 10x as much as the **** at the pump?

You can't guarantee anything. Name one production car that added a Turbo WITHOUT making the engine smaller that GAINED MPG. It's never happened. Think, listen to what is being told to you, think some more, you may realize why.......

This is all you needed to say, but noooooo.......

It IS the Turbo. Without the Turbo, I can run higher SCR (static compression ratio) which gives me higher ER (expansion ratio), which improves fuel efficiency all on it's own. The cooler air (from not being compressed by a turbo) is less likely to detonate and requires only the fuel you intend to burn to do mechanical work, not additional fuel to cool the engine down too.
In other words the limitations of the fuel being used is exceed BECAUSE of the Turbo. You can't magically blame it on the ACTUAL material being used to do the work! The FUEL IS what moves the car, the FUEL is what does ALL of it. Not the Turbo, the fuel. The fuel is more important than the turbo.



This isn't pretend land. I'm not playing in pretend land.

Basically this is what you said " if we ignore reality and physics and only apply what I think will happen, what do you think will happen?"




No, it's like I'm making "a list of facts".....

Gibberish, that's all I got out of this paragraph. Gibberish.

Here's a better comparison. Cadillac Escalade 2WD vs. AWD., 1 MPG difference highway.



Changing Air density is increasing Mass. VE tables are done in percentage, but they are used to calculate MASS of airflow. So if you crammed 2 bar of air at any RPM VE would be 200% (theoretical), but it's actual volume is not 200%, it's still at 100% (or less), it's MASS is at 200%. But, it's MASS that is needed because that is what the fuel is calculated at and from, mass. Mass doesn't change, it's always constant. Volume and density may change, but mass is constant.

To be more clear here. 14.7:1 is 14.7:1 regardless of air density, temp, or whatever else because 14.7:1 is by weight (mass).

 

This intake air temp issue.... Um, why don't NA cars have this issue???

 

Not VE tables, actual volumetric efficiency. You can change stock VE with heads/cam, but a stock motor VE won't change with a turbo.

 

Yes and no. In it's natural state air is pushed into the engine as the piston creates a low pressure travelling down the bore. But, we are also dealing with fluid dynamics. Fluid in motion. Scavenging creates a sucking effect too, effectively ram charging the incoming air into the cylinder via suction. So an NA engine actually does both.

 

Tracking. So how do you account for the fueling change?

 

VE is constant, a turbo just changes density. A motor can ingest what it can ingest hence the constant VE aspect to a air pump.

 

Right, but if you're increasing density, you're going to need to add fuel.................


No wait, I'm confused. Are you saying the VE tables do or don't change?

 

a pic of sick combo would be alsome right about now...

 

I am saying if a motor/pump is 80% volumetrically efficient from wear/tear whatever, you can change that with better flowing heads/intake/cam. But if you do not change that, the turbo will not change how efficient the motor is. It can only only the density of air going into the motor.

Semi logical?

 

Yes. I agree. But that doesn't translate into the VE tables correct? The VE tables show more VE even though the engine it's self isn't more efficient volumetrically. The VE tables are used to account for the added air mass, even though it's not actually adding volume. Is that what you're saying? Or does the VE table below 1 bar still show the same and over 1 bar shows the added VE?

I'm trying to picture a 2bar VE table with VE under 100% for the second bar (although that would make sense). I'll have to look at the tables to see this I guess. Maybe KingTal0n can't post up one of his hundreds of tunes showing this......