Different theory on turbo cams

[mutant]

Ted, are you saying that there's no such thing as forced induction?

[Ted B]

The term "forced induction" is a misnomer in this context for the reasons I stated previously.

[mutant]

So what is the correct term? 'Enhanced density induction' ?

[Ted B]

LOL

Yes, that would certainly be a more accurate expression. The engine isn't seeing an increased volume of air, just increased density. Increased density means more oxygen molecules per unit of volume.

For the equation:

PV = nRT

The turbo or SC is increasing the air density (P) while the engine displacement (V) remains constant. The other factor is temperature (T), which is what intercoolers do (cooler air temp yields increased density).

The only two places in the system where the volume is increased are at the inlet and exit, where the pressure is ambient (or close to it). This is from the air filter to the turbo inlet, and somewhere past the exhaust downpipe.

[mutant]

Yes, but an increased volume of air is going thru my air filter, and a corresponding increased volume of exhaust comes out the tailpipes. So how can an increased volume of air not be going thru the engine?
And what about van der Waals equation of state?

[Ted B]

Yes, but an increased volume of air is going thru my air filter, and a corresponding increased volume of exhaust comes out the tailpipes. So how can an increased volume of air not be going thru the engine?

The volume of flow is increased ONLY where the pressure is ambient. Taking a large volume and compressing it into a small area makes the volume smaller, but it raises the density (which raises the pressure). The volume of air flow is larger at the air filter and exhaust tip than at the throttle body, but the air MASS is the same.

The turbo or SC is essentially an air compressor. It compresses a LARGE volume of air into a smaller volume (the engine). In order to do this, the pressure of the incoming air must be increased, which increases the density. The increased density iincreases the cylinder pressure, which we all know is what determines hp.

Those greater densities in the cylinder mean that the hot exhaust gases will ALSO create greater pressure when they expand and depressurize as they exit the cylinder. This pressure of these hot gases is GREATER than the pressure of the intake air. This is what is referred to as the Pressure Ratio (PR). Most decent street turbo apps will run a PR of 2:1, which means the exhaust gas pressure peaks around 2X the intake presure. All-out race cars will run close to 1:1. The PR of a stock SVO becomes unfavorable quickly as the boost is turned up.

When the PR becomes excessive, turning the boost higher makes no difference in power. It's like hitting a brick wall. The high pressure in the exhaust is just too great to allow more intake air in. To alleviate this, we can go to a larger turbo hotside, and in the SVO's case, a better exhaust manifold and downpipe. The larger hotside slows exhaust gas velocity at slow speeds (more lag), but will flow more exhaust gas at high hp, which allows us to use more boost effectively.

[Ted B]

And what about van der Waals equation of state?

I doubt the pressure of the systems in question are sufficient to cause them to deviate far from ideal gas law, but if you want to fiddle with it, be my guest. It doesn't change anything I've stated here.

[mutant]

I understand completely. ( I have from the beginning.)

[Ted B]

If both intake and exhaust are pressurized proportionally - where's the need to change cam timing?

To get back to the original question (re: cam timing), for the EVO (obviously a 4-valve setup), a fair amount of overlap that is dialed in intentionally creates stronger midrange cylinder pressure, which spools the turbo quicker and generates a tremendous amount of torque.

From this statistical trend, it becomes apparent that depending upon turbo size, exhaust configuration, etc., a fair amount of overlap is beneficial until a point whereby the PR overcomes the benefit. With smaller to moderately sized turbos, with decently sized hotsides but run out of compressor around 6000-6500rpm, this seems to be of the greatest benefit.

The attached graph shows several dyno runs, all done back-to-back. The only change was cam timing. Compare the following:

Run #2 - 118LC Int / 112LC Exh / 115 LSA - 412whp / 420 ft lbs

Run #5 - 106LC Int / 108LC Exh / 107 LSA - 410whp / 462 ft lbs

This case is statistically consistent with what we observe, in that when used carefully, overlap courtesy of a tight LSA can be a good thing. In this case, an additional 42 ft lbs and 400rpm quicker spool, with better average hp AND tq throughout the powerband.

Other engines, properly configured, tend to respond similarly.

[85ttops]

So what is the correct term? 'Enhanced density induction' ?

turbo = altitude compensator

[SVOBart]

turbo = altitude compensator

Funny you mention that, because in small aircraft engines they're often referred to as "turbo-compensators" and are used primarily to allow aircraft to have similar performance at high altitudes as they would at or near sea level.

[85ttops]

I Have Some Input On This Condenced Air Is Not More Volume Thing

When You Condence Something It Is Making It Smaller Hence The Word Condence , So If Your Condencing Air In Essence Your Taking A Large Amount Of Air And Making It Smaller Witch Would Allow You To Add More To The Condenced Area , So If You Add More Condenced Air Into The Same Area Wouldnt That Be More Volume Of Condenced Air In The Same Area That Wouldnt Normally Support That Amount Of Air

Kinda Confusing After You Read It But Read It A Couple And You Might Understand What Im Tring To Say

Some Times It Sounds Real Good In My Head But When Its Time To Put It Down In Writing It Doesnt Come Out Right

[Ted B]

So If You Add More Condenced Air Into The Same Area Wouldnt That Be More Volume Of Condenced Air In The Same Area That Wouldnt Normally Support That Amount Of Air

When you take an empty air cylinder and put 2500psi of compressed air into it, does the volume of the cylinder change? No.

Does the density of the air inside it change? Yes.

Does the amount of oxygen per cubic inch of air inside of it change? Yes.


Does that help?

[under pressure]

Turbocharging increases the VE (volumetric efficiency) in the engine. Valve overlap has the main benefit of scavaging the combustion chamber in a normally aspirated engine. The air temp. & the intercooler have a greater effect on air density than valve overlap. There are alot of Theories in the World. When they are proven then they become a Law, such as Ohm's Law. Rick

[Ted B]

Turbocharging increases the VE (volumetric efficiency) in the engine.

No it does not.

Valve overlap has the main benefit of scavaging the combustion chamber in a normally aspirated engine.

Valve overlap is a benefit to those who know how, when and to what degree to use it, and remains a mystery to others.

There are alot of Theories in the World. When they are proven then they become a Law, such as Ohm's Law. Rick

Apparently you missed the dyno chart and data I posted previously.