CAT IVA (Intake Valve Actuator) Defined...Kind of

mrtheavyhaul · Feb 9, 2014

Scrapper said: ↑

I posted this on a thread I probably shouldn't have. I've been messing with them and others have to. I have heard of mpg gains and better running but if the proper function of them is true. We should see gains when they are properly set and working correctly. Just trying to figure out wether to acuate or not to acuate. lol.

Here is what I found...first is the def of the Miller Cycle...this has been around a long time and used in many import cars. The second is what I found from CAT about the function of them.

So what I'm trying to decide...is it for emissions...or increased efficiency or maybe both. They can be a headache when the malfunction...they do put added pressure on the rockers from what I have read. Why if the miller cycle adds efficiency do we seem to see gains in mpg from backing them off?

Here is the def.

A traditional Otto cycle engine uses four "strokes", of which two can be considered "high power" the compression stroke (high power consumption) and power stroke (high power production). Much of the internal power loss of an engine is due to the energy needed to compress the charge during the compression stroke, so systems that reduce this power consumption can lead to greater efficiency.
In the Miller cycle, the intake valve is left open longer than it would be in an Otto cycle engine. In effect, the compression stroke is two discrete cycles: the initial portion when the intake valve is open and final portion when the intake valve is closed. This two-stage intake stroke creates the so called "fifth" stroke that the Miller cycle introduces. As the piston initially moves upwards in what is traditionally the compression stroke, the charge is partially expelled back out the still-open intake valve. Typically this loss of charge air would result in a loss of power. However, in the Miller cycle, this is compensated for by the use of a supercharger. The supercharger typically will need to be of the positive displacement (Roots or Screw) type due to its ability to produce boost at relatively low engine speeds. Otherwise, low-rpm torque will suffer.
A key aspect of the Miller cycle is that the compression stroke actually starts only after the piston has pushed out this "extra" charge and the intake valve closes. This happens at around 20% to 30% into the compression stroke. In other words, the actual compression occurs in the latter 70% to 80% of the compression stroke.
In a typical spark ignition engine, the Miller cycle yields an additional benefit. The intake air is first compressed by the supercharger and then cooled by an intercooler. This lower intake charge temperature, combined with the lower compression of the intake stroke, yields a lower final charge temperature than would be obtained by simply increasing the compression of the piston. This allows ignition timing to be advanced beyond what is normally allowed before the onset of detonation, thus increasing the overall efficiency still further.
An additional advantage of the lower final charge temperature is that the emission of NOx in diesel engines is decreased, which is an important design parameter in large diesel engines on board ships and power plants.
Efficiency is increased by raising the compression ratio. In a typical gasoline engine, the compression ratio is limited due to self-ignition (detonation) of the compressed, and therefore hot, air/fuel mixture. Due to the reduced compression stroke of a Miller cycle engine, a higher overall cylinder pressure (supercharger pressure plus mechanical compression) is possible, and therefore a Miller cycle engine has better efficiency.
The benefits of utilizing positive displacement superchargers come with a cost. 15% to 20% of the power generated by a supercharged engine is usually required to do the work of driving the supercharger, which compresses the intake charge (also known as boost).

I also found this from CAT

An Intake Valve Actuator or IVA (also known as a Varible Valve Actuator or VVA) is a device that contacts the intake rocker arm and holds the intake valve of an ACERT Cat engine open in an effort to lower the cylinder temperatures of the engine. This is done to help lower NOX emissions.

The Actuator is electronically controlled and hydraulically activated very similar to a Jake Brake. Your engine has 6 of them. One for each cylinder.

The variable valve actuators are used in order to control the closing of the inlet valves. The variable valve actuators do not operate until the engine oil has reached a desired temperature. The oil for the variable valve actuator flows from the oil filter base to an oil rail that is outside of the head. If the oil temperature is below the desired temperature, the diverter valve in the oil rail is open. The open diverter valve allows the oil to drain back into the head. When the oil temperature is increased, the diverter valve is closed. This closing pressurizes the oil rail and the housings for the variable valve actuators. The pressure in the oil rail will be 250 ± 50 kPa (36 ± 7 psi) higher than the rest of the lubrication system. Bleed holes are located in the housing in order to exhaust the pressurized oil.
The variable valve actuators hold the inlet valves open. The valves would normally close with the profile of the camshaft lobe. The solenoid is energized while the inlet valves are open. The solenoid allows pressurized oil to fill the cylinder. The pressurized oil pushes down the piston. As the inlet valve starts to close, the valve rocker arm for the inlet valve contacts the piston. The piston holds the inlet valves open.
In order to close the inlet valve, the solenoid is de-energized and the oil is allowed to leave the cylinder. The valve spring force pushes up on the rocker arm. The rocker arm pushes the piston back into the normal position of the piston. The inlet valves are then closed.

Apparantly what I was told about them being open and letting exhaust back into the intake to be reburnt was wrong. But seems like if you are lowering combustion chamber temps this is good. Your turbo is giving you compression as is the cylinder. From what I read the actuator works only during the first 15% of the compression stroke...Accorrding to Miller Compression actually doesn't happen except during the last 70-80% of the compression stroke. So in theory you should not be loosing any compression from the IVA's....you should not be loosing any power from the IVA's...you should gain effieciency. You are not pushing out any burnt gasses into the intake...it is clean air that was just sucked in by the engine. So I do not see how it would cause the soot in your intake?

I backed off a set on an 05 T600 with an accert when I did the overhead. Doing this as an experiment. I think I'll let the truck run as it is for now...and just see if we have any changes. But it looks as though we should be gaining from the system.
Click to expand...

This backs up my theory about why the engine brake on my SDP sucks. Especially once the motor is at operating temp.

motovader · Apr 4, 2025

Can any of you that were making changes to your C13 Acerts here please tell me how your particular changes ended up affecting your engines, if at all? I just have a 2009 Schlumberger spec'd Peterbuilt 365 with a C13 Acert LEE deleted or possibly partially deleted since the CGI appears to not have been blocked off at the motor and it still has an egr cooler on it that apparently wasn't blocked off either. I am trying to decide what to do with the iva/vva's. It is down right now with a burnt number 6 injector with a broken spring that was letting diesel into the coolant reservoir, as well as 2 other broken injector springs that hadn't yet bounced around enough to do what 6 did. Refitting them with remanned injectors and don't know if I should make sure the iva/vva's backed off all the way, if I should set them to .040, or if I should set them normally. The truck seems to run too cold, especially if I am running the A/C on a warm but not hot enough day it will run cold like 100 degrees or maybe not even that. Do I need to change the thermostats or make changes to the ecm programming. It will rarely run at 200 degrees of water or oil temp unless it is a hot day or I am pulling loaded, normally grossing 50 tons, sometimes 60 tons, with 4.11 gearing and a 9LL transmission. Also the CGI pipe and system was not blocked off, allowing sooty exhaust to get sucked in, I guess, since the dpf was removed from it's housing but the housing itself was left on the truck. I just took it off and ran a straight pipe and plugged the CGI pipe, but still want to remove the EGR of CGI cooler or whatever it is and block off the holes before that fills up with soot like my ISX did after another incomplete delete done before I bought it. Oh, I forgot to mention that I think Schlumberger had it set up with a pump on the PTO to pump mud all day, so the truck only has just over 200k miles, yet the motor probably has about 500k miles or more equivalent in hours, I don't know as the hours were obviously messed with in the ECM, but it is obvious the chassis has low mileage. Also, 3 of the 4 injectors whose springs broke were remanned injectors, with one other remaned injector that isn't broken and 2 of the original CAT injectors that are still also okay.

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