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

**Frenzy** · 02.22.2012

Originally Posted by HISPEED428

Now I'm really curious as to where the soot in the intake side of the head could be comin' from...

There is some exhaust gas left in the cylinder when the exhaust valve closes. The incoming air mixes with the left over exhaust gases. In the Miller cycle the intake valve is left open slightly during the compression cycle so that a portion of the mixed intake air and left over exhaust gas is forced back into the intake manifold. That is where your soot is coming from.

**Scrapper** · 02.22.2012

Okay, all this being said.

Which will be better for longevity of the engine? If I loose a few hp by backing the actuators back to where they work...but do not contact the rockers...that would beneficial because I will have fewer "moving parts" that can leave you derated miles from home and with a repair bill. Also taking pressure off of the rocker arms I see as a benefit. If we are not getting the "real" benefit of the Miller Cycle...and it was put on for emissions and not effciency I'm thinking without problems I'll leave them backed off.

Now will this cause excess pressure in the cylinder that wasn't designed in...and more heat during the combustion cycle...in stock form I would think it would be fine...now when you start dealing with tunes and higher boost pressures...I think i would leave them working...or at least let your programmer know you backed them off.

Kind of where I stand right now.

**GP1500SC** · 02.23.2012

I think I am getting it through my thick head, Cat don't use internal egr the soot that get back into the intake to be reburned is valve loop, or millers cycle
It also clears up why it takes 15.2 liters @ 50-60 pounds boost to make 550 hp vs the 14.7 liter @ 28-30 pounds boost 6nz

Now on a more serious note did Cat up the compression to pass the emissions and improve the throttle responds then after it's warmed up and under a load activate the vva's to lower the compression?
just guessing

**HISPEED428** · 02.23.2012

Originally Posted by Mr. Haney

The Acert is a derivative af the Miller Cycle, but I don't think it is a true Miller Cycle engine in the way you're researching it. When it first came out it was explained to me that it used the Miller Cycle Theory strictly to lower NOX emissions without introducing exhaust gases into the engine to lower the combustion temperatures. I don't think the intake and exhaust valve timing was optimized as a Miller Cycle for efficiency and Hp gains.

The Acert does run a high compression piston. You are also dealing with much higher boost pressures.

One of the things that may also cause the accumulation of what looks like soot in the intake manifold is valve overlap. Every engine has a certain amount of this. The reason is during the exhaust stroke the exhaust valve is open, but at soon as the piston reaches the top of the bore and before it can go down on the intake stroke, the intake valve can start to open. It's not uncommon for engines to have both valves open at the same time depending on how the camshaft is ground and its duration. With the high boost pressure of the twins, it also generates high exhaust gas back pressure in the exhaust manifold. It is very possible with the valve overlap of the intake and exhaust valves, that as soon as the intake valve starts to open that you get exhaust gases going past the intake valve and into the intake manifold. Unfortunately everytime I've heard of anybody doing a Exhaust Gas Back Pressure test on an Acert, the pressure in the exhaust manifold is higher than the intake. So if there is a substantial amount of valve overlap in the camshaft, then you can very well be pushing exhaust gases into the intake. You can't control the valves with high ramp rate speeds to eliminate valve overlap easily. If you would try this then you'd have to increase valve seat pressures to keep the cam followers on the lobes of the cam. Once you increase valve seat pressures than you have to combat the extra heat the spring will generate, the heat will cause springs to break eventually. Its a complex puzzle, change one thing and it effects another.

That's pretty much the same conclusion I came to.

Originally Posted by GP1500SC

I think I am getting it through my thick head, Cat don't use internal egr the soot that get back into the intake to be reburned is valve loop, or millers cycle
It also clears up why it takes 15.2 liters @ 50-60 pounds boost to make 550 hp vs the 14.7 liter @ 28-30 pounds boost 6nz

Now on a more serious note did Cat up the compression to pass the emissions and improve the throttle responds then after it's warmed up and under a load activate the vva's to lower the compression?
just guessing

The static compression of the Acert is higher but the dynamic compression ratio might not be any higher than a 6NZ. Just a guess at that.

**C16KIWI** · 02.23.2012

Originally Posted by Mr. Haney

The Acert is a derivative af the Miller Cycle, but I don't think it is a true Miller Cycle engine in the way you're researching it. When it first came out it was explained to me that it used the Miller Cycle Theory strictly to lower NOX emissions without introducing exhaust gases into the engine to lower the combustion temperatures. I don't think the intake and exhaust valve timing was optimized as a Miller Cycle for efficiency and Hp gains.

The Acert does run a high compression piston. You are also dealing with much higher boost pressures.

One of the things that may also cause the accumulation of what looks like soot in the intake manifold is valve overlap. Every engine has a certain amount of this. The reason is during the exhaust stroke the exhaust valve is open, but at soon as the piston reaches the top of the bore and before it can go down on the intake stroke, the intake valve can start to open. It's not uncommon for engines to have both valves open at the same time depending on how the camshaft is ground and its duration. With the high boost pressure of the twins, it also generates high exhaust gas back pressure in the exhaust manifold. It is very possible with the valve overlap of the intake and exhaust valves, that as soon as the intake valve starts to open that you get exhaust gases going past the intake valve and into the intake manifold. Unfortunately everytime I've heard of anybody doing a Exhaust Gas Back Pressure test on an Acert, the pressure in the exhaust manifold is higher than the intake. So if there is a substantial amount of valve overlap in the camshaft, then you can very well be pushing exhaust gases into the intake. You can't control the valves with high ramp rate speeds to eliminate valve overlap easily. If you would try this then you'd have to increase valve seat pressures to keep the cam followers on the lobes of the cam. Once you increase valve seat pressures than you have to combat the extra heat the spring will generate, the heat will cause springs to break eventually. Its a complex puzzle, change one thing and it effects another.

WOW. . . . you have a gift, to be able to explain this a way I can digest.
Thanks.

**Mr. Haney** · 02.24.2012

Originally Posted by C16KIWI

WOW. . . . you have a gift, to be able to explain this a way I can digest.
Thanks.

Thank you, I just visualize how it can happen in my mind, then try to explain it

**Mr. Haney** · 02.25.2012

Originally Posted by Scrapper

Okay, all this being said.

Which will be better for longevity of the engine? If I loose a few hp by backing the actuators back to where they work...but do not contact the rockers...that would beneficial because I will have fewer "moving parts" that can leave you derated miles from home and with a repair bill. Also taking pressure off of the rocker arms I see as a benefit. If we are not getting the "real" benefit of the Miller Cycle...and it was put on for emissions and not effciency I'm thinking without problems I'll leave them backed off.

Now will this cause excess pressure in the cylinder that wasn't designed in...and more heat during the combustion cycle...in stock form I would think it would be fine...now when you start dealing with tunes and higher boost pressures...I think i would leave them working...or at least let your programmer know you backed them off.

Kind of where I stand right now.

The VVA system is still trying to function. If the ECM sees a actuator that it feels isn't responding, it will still derate the engine regardless of how they're set.

As far as removing pressure from the rocker arm to increase its overall life, I don't see this as a problem whether the VVA is working or not. The actuators are the component that fails and puts the ECM into a derate mode this can happen whether you've got them adjusted properly or backed off.

The cylinder pressures will increase with the VVA disabled. I tell all my customers to keep the VVA system running as it was intended too whether the ECM is stock or tuned.

**fastfitz70** · 03.07.2012

Great thread thanks been looking for a lot of this info. a piston moves slow at the top and bottom because the crank moves in a circle. it stops a 0 and 180 degrees and reaches top speed at 90 degrees so keeping the intake open to 30 deg past BDC should be overcome by 50lbs of boost. The problem is in the chart Hispeed provided it looks like the VVA's hold it open to around 100 deg, way past miller cycle parameters. By the way I believe the reason nobody uses Miller cycle is the 15% increase in efficiency doesn't equal the 20% need to run the blower.
In a Diesel it doesn't matter how much air you put in the cylinder as long as you don't get it too hot pumping it in there, the fuel will burn what it needs and the rest goes out the exhaust. And since emissions are measured in parts per million the more air you have the lower the PPM (the EPA hasn't outlawed air yet, have they?)
The trouble with creating more boost than needed is it increases exhaust back pressure. As a race engine builder that worked with 3 NHRA champ Mike Saye, I can tell you all engines have EGR but the fastest one's get the most exhaust out and the most mixture in. If the pressure in the exhaust is higher than in the intake when both valves are open (valve overlap) you know which way the wind is blowin! Then you hold the intake open, bring the piston up to mix it up good, shut the intake, compression, fuel and a nice cool burn. Cool=low emissions. HEAT MAKES POWER!!! anything you do to reduce heat kills power period. However heat also melts thing like pistons so there are limits. Exhaust gas doesn't burn (it already did) so it reduces heat which is why reducing VVA shouldn't Increase cylinder pressures much and may also reduce boost (thus exhaust back pressure) cause the turbo won't have the push back from the piston.
As some one who has seen a dumpster load of broken valve train in my life I can tell you it is rarely pressure that breaks rockers but the follower missing the acceleration or deceleration ramp on the cam and slamming into the flank. In high speed engines it is caused by valve float but a VVA hanging up would have the same affect.
No diesel expert here but but pretty good on gas and both are 4 cycle (suck, squeeze,bang, and blow) and 07 acert looks like the latest engine available without the electronically controlled,satellite monitored chrome muffler bearing so I'd like to get it figured out. thanks

**fastfitz70** · 03.07.2012

Originally Posted by underpsi

I'm having a hard time seeing a benefit to having the intake valve left open for the first 15% of the compression stroke after the intake stroke is complete.

If intake stroke is complete the piston is then coming back up and beginning to build pressure in the cylinder for compression stroke. Why you you want that intake valve left open and relieve some pressure that was in that cylinder?

Lets say it was a good running Acert so it runs around 50psi of boost under heavy load, so you have 50psi of boost in your intake and your having a cylinder beginning to produce pressure upwards of over 500psi. What good is that 50psi gonna do against the 500psi on the other side of the valve. Your gonna be releasing some of that cylinder pressure into the intake and therefore losing efficiency by not having as high of compression in the cylinder before the fuel is injected.

UNLESS that first 15% of the compression cycle the pressure is below the boost pressure at which it would allow more air in through the intake before the piston creates more pressure then whats in the intake. Now that would make sense. Is it what happens? I have no idea but It has to be one or the other either its relieving pressure or its letting a little extra in.

If it is letting a little bit of boost in through the intake at the beginning of the compression cycle then it should increase efficiency by allowing more air in. In which, why would anyone wanna mess with their IVA's when they should be making the engine run better.

also a 16 liter engine with the piston 25% of the way up is now a 12 liter engine, not counting boost. a 350 chevy on a spintron (electric motor) produces 175 psi, a 6nz would be higher

**Jfaulk99** · 03.07.2012

Originally Posted by Mr. Haney

The cylinder pressures will increase with the VVA disabled. I tell all my customers to keep the VVA system running as it was intended too whether the ECM is stock or tuned.

I was wondering since the cyl aren't actually seeing the 50-60pai of boost because of the VVA's on a normal ACERT if disabling them would be a head gasket killer. ARP needs to makes some studs!