[killerbee]

Guess I just don't see what you do.

From what I know, most turbine work performed is a result of leftover adiabatic (or near so) expansion of combustion gases, energy that would be wasted if the turbo were not there. Cogeneration, more or less.

The turbos ability to spin with little parasitic loss (producing more than it consumes, via use of a waste product) has always been its main selling point, albeit with a backpressure tradeoff. To suggest there may be a significant gain opportunity, you must be suggesting that is not the case with this VVT.:shrug:

The belt driven supercharger, by contrast, is 100% parasitic, if it is being fully funded by the power stroke, with no backpressure consequence.

Not criticizing, I see what you are after. Hope you have good results.

Perhaps you can post some of those drive P charts from PUSU here, that might be good for discussion.

 

[stevebos]

Disclaimer: This discussion is far beyond my understanding; I shall not be responsible for my stupidity! ointlaugh

Are a jet engine and hydro-electric generator both considered turbines? If so, is there more than one manner of force applied to drive them (ie: expansion of gases in the jet engine, flow of water in the hydro-electric generator)?

 

[killerbee]

That is right up Jon's alley. He works with steam turbines in his profession I believe.

 

[fingers]

We have two seperate topics here.

One is the cost, in HP, of the restriction caused by the turbo. The other is the how a turbo gets power out of the exhaust stream and why it is such a good thing on an engine.

First one first. Regardless of wether there is a turbo on the exhaust pipe or just a restrictive muffler, the backpressure takes real horsepower to overcome. In purely mechanical terms, this is the force over time needed to push the exhaust out of the chamber. I think everyone can see that. Reducing the backpressure allows the power to go to turning the driveshaft instead of to push the piston up against the backpressure. On the Dmax, this turns out to be 1.4xx HP per PSI of backpressure. In relation to the turbo, the less backpressure the better if only for the power it frees up in the motor.

All turbines get there power by changing the speed and/or direction of the fluid/gas they work with. In doing so, you end up with a Differential Pressure (DP) across the turbine. The greater the velocity of the fluid/gas, the greater the power imparted to the turbine when it changes the direction. Part of the efficiency of the turbine is characterized by the ratio of DP to the work being done. In the turbo charger case, how much boost you make compared to the drive pressure.

One of the things that can make TurboCharging so attractive is the "still expanding" gas affect. I think we have all seen the flames coming out of the pipes on drag cars. Yep, still expanding. Nearly all engines do a similar thing at full load. Maybe not so spectacular, but similar. Not enough to be useful in the engine chamber though. The flame is accelerating the gas even faster than it left the chamber. Since our turbo's power is directly related to the velocity of the gas it seems like a free lunch.

But the engine itself is what has to push against the "still expanding" gas to get exhaust into the pipe. The turbo is on the other end pushing toward the moter with its DP. IF you add them up, you find the power to run the turbo (turbo output plus drag, friction....) is exactly the same as the power the engine uses to overcome backpressure. No free lunch.

 

[Turbotug]

Not free, but definitely from the value menu!

 

[idahofox]

Does any one have a Cam ° map for the DMax ?

 

[TheBac]

Do you mean lift/duration specs, Idaho? If so, Eric has them. I think DieselTech does, as he's had cams ground. Trippen might, too.

 

[idahofox]

The Power venue of any turbine is " Heat ".

Heat, is the Power Source, for Creating Boost ( do work ).

Any modification to Heat movement, Back Pressure ( intentionally or incidental ), modifies the power Available to do work ( create boost ) in the device ( turbo ).

The Heat ( BTU’s ), not used for Work, must then be exhausted from the system, where; one of the coolants.

The VVT ( any VVT ) is/are, levels above non VVT’s from an efficiency view. None VVT’s are " Fixed Vane ", " Fixed Performance ".

IMO, the VVT, 4.5 to what ever, is by design, EPA driven ( scavenging ? ); to achieve specific levels of dilution of " Combustion Charge ".

Go Fingers !

 

[idahofox]

Do you mean lift/duration specs, Idaho? If so, Eric has them. I think DieselTech does, as he's had cams ground. Trippen might, too.

Would any one Post them ?

I have an interest in stock overlap, intake/exhaust. Dilution of intake gasses.

Using My oxygen before I have a chance.

 

[TheBac]

They aren't state secrets, so I don't see why not. I'll try giving Eric a call, see if he can look them up.

 

[Diesel Tech]

Here is a plot of a camshaft that I worked on with Comp Cams on to replace a stock camshaft. This should give you what your looking for, as valve overlap is something we work hard with.

 

[idahofox]

Here is a plot of a camshaft that I worked on with Comp Cams on to replace a stock camshaft. This should give you what your looking for, as valve overlap is something we work hard with.

Diesel Tech,

Thank you for the graph.

See if I read it right.

Stock cam Ramps are Very slow.
Stock cam has cross flow for more than 45 crank °.
Stock cam cross over is BTDC, ( high pressure/heat exhaust ).

COMP cam reduces cross flow by more than 7 crank °.
COMP cam moves cross over to TDC.
COMP cam, intake, ramps much quicker.

Were the changes noticeable in performance ?

Thanks again.

 

[Diesel Tech]

You need to go back and look closer as the numbers, you are off. The truth is that you need to forget about anything below the Hot Lash line as that is not valve movement but lifter movement. What does matter is the total area under the curve in both cases they are very close to the same with slightly different peaks.

 

[stevebos]

Just checking to see if I understand correctly. I should've paid more attention in auto shop class! :damnit

We're looking at the area under the overlap curve; the area above the effective hot lash line, beneath the intake curve on the left and the exhaust curve on the right.

It appears total overlap areas for the OEM and Comp Cam profiles are similar. The Comp Cam profile:

1. intake opens later.

2. exhaust closes the same time.

3. lift at point where intake and exhaust lift is the same is greater.

It appears in the Comp Cam profile both valves are open at greater lift, but less time.

What benefit(s) does this provide?

 

[fingers]

The comp cam is much more agressive. Look how quickly it is opening/closing the valves compared to OEM. The area under the curves is roughly proportional to the window where gases can cross over. This graph is of the Exhaust-Intake transition near TDC, so the relative pressures are almost exactly backpressure Vs Boost.

 

[D Lafleur]

The comp cam is much more agressive. Look how quickly it is opening/closing the valves compared to OEM. The area under the curves is roughly proportional to the window where gases can cross over. This graph is of the Exhaust-Intake transition near TDC, so the relative pressures are almost exactly backpressure Vs Boost.

I assume with the level of tech in these engines we have roller lifters? That improved crossover looks great, do we need the extra lift? Any opinions on detriment vs. benefit? Will the rockers handle this well? One of my previous engines was limited to .500 lift, there was some perf. beyond that, however the valve train components didnt handle it well.

 

[Diesel Tech]

The comp cam is much more agressive. Look how quickly it is opening/closing the valves compared to OEM. The area under the curves is roughly proportional to the window where gases can cross over. This graph is of the Exhaust-Intake transition near TDC, so the relative pressures are almost exactly backpressure Vs Boost.

Now Jon don't be giving away all the trade secrets. This camshaft design has close to the same total lift as a stock camshaft and it is the smallest of the cams we designed with Comp Cams for the Duramax. We do not offer this cam in our camshaft line as it's basically a stock replacement part with just a little more punch. The camshafts we do offer are more for the guy who want's to hotrod and they are exclusive to TTS and come with our EDM Keyway drive which is another feature not offered by Comp Cams. How the air starts to move once the valve opens and what it does during crossover play a big roll into emissions tuning.

I only posted this to give you guys and idea of the level of detail needs to try and figure out everything that's going on and how one influences the other. So you can see how the BP that is created by the turbo effects cylinder filling during crossover. Do not forget that any exhaust forced up into the intake during crossover also gets drawen back down into the cylinder so you losse twice as much................ once when pushing the exhaust into the intake and once again when you pull it back into the cylinder for the next powerstroke. So reducing the BP has a huge affect on the overall engine, not just for power alone.

 

[D Lafleur]

Now Jon don't be giving away all the trade secrets. This camshaft design has close to the same total lift as a stock camshaft and it is the smallest of the cams we designed with Comp Cams for the Duramax. We do not offer this cam in our camshaft line as it's basically a stock replacement part with just a little more punch. The camshafts we do offer are more for the guy who want's to hotrod and they are exclusive to TTS and come with our EDM Keyway drive which is another feature not offered by Comp Cams. How the air starts to move once the valve opens and what it does during crossover play a big roll into emissions tuning.

Do you suppose the typical dealer shop would recognize the differance of this "replacement" cam? If it isnt available in your catalog how would someone get this cam? The exhaust lift appears to be a little different from stock.

 

[fingers]

We are a bit off topic here, but the problem with the agressive opening/closing rate isn't the OEM roller lifters. Moderately high reving engines will start to have problems with the pistons chasing the valves though. The upper valve train isn't stout enough, IMO, to control valve float over about 3500 RPM with the stock cam. Let alone a more agressive one.

 

[Diesel Tech]

The stock cam is very slow by most of todays standards in camshaft design. The Comp Cam is not event considered fast open either. This camshaft will work fine with the stock valvetrain up to 4000 RPM. If you want to run high RPM we do have a new setup for springs and retainers that will allow 5500 RPM with this camshaft. If you were to want one of these camshafts we would special order it as it's not one we have in our line as we figure most would not want/need something that small. Special orders would take about 2 weeks from order date. I doubt the dealer would ever figure out this camshaft is in the motor unless they were told.