[Silver Surfer]

Looks like the OTR's miss the mark on this detail...

"Ensure the MAF Sensor is mounted in the middle of a minimum 6 inch length of 4 inch diameter tube, and is a minimum of 10 inches from the throttle body."

https://www.chevrolet.com/content/d...d/02_pdfs/ls3-and-lc9-e-rod-crate-engine-control-system-40tooth-and-17tooth.pdf

 

[pir4te01]

Yes, this appears to address it. It was quite frustrating trying to convince them they had an issue for nearly 5 years though.

Yes, this is the same exact problem, it will allow unmetered air into the engine, causing it to run leaner than it should at idle, and part throttle, but richer than it should at WOT because it will carry over the learned fueling. So, not only can it develop a vacuum leak, but it actually can cause a drop in power, which is the exact opposite that you should want with performance mods :wink

Perhaps you are mistaken either about which pipe it is and / or where it connects on the intake. It is definitely not the same problem, PCV breather pipe vents before the MAF tube / throttle body, attached to the airbox plenum after the filter.

Looks like the OTR's miss the mark on this detail...



"Ensure the MAF Sensor is mounted in the middle of a minimum 6 inch length of 4 inch diameter tube, and is a minimum of 10 inches from the throttle body."



https://www.chevrolet.com/content/d...d/02_pdfs/ls3-and-lc9-e-rod-crate-engine-control-system-40tooth-and-17tooth.pdf

I think the issue is the possibility of incorrect MAF reading due to turbulence (simply put).
With 3" either side of the MAF card there is laminar flow, no problem, which it states.

However I found it is not an absolute requirement to locate MAF centrepoint 10" away from the throttle body. That would preclude all OTRs on our car, as you say.
Both Rick Crawford and Pat G and all tune shops I've visited here in Australia recommend fitting the MAF at the obvious location with an OTR:

Although it is possible to have different types of interference corrupting the reported frequencies, I have 4" dia X 6" long tube (as below) and logged the MAF in high resolution over five years tuning with this particular intake, and pod style elbows and that has never been an issue.

 

[andy@livernois]

Perhaps you are mistaken either about which pipe it is and / or where it connects on the intake. It is definitely not the same problem, PCV breather pipe vents before the MAF tube / throttle body, attached to the airbox plenum after the filter.

Nope, not mistaken.

The factory tube is on the silencer box, which is post MAF, and pre Throttle body. This is because the PCV system eventually allows air into the intake manifold, and this air needs to be metered as it's actually using that air for some of it's intake source. By putting that piece in front of the maf, you allow air to enter into the pcv system, and then it enters the intake manifold, causing the car to run lean.

Please, don't make the same mistake VCM did and fight us on this. It doesn't reflect well when a company doesn't understand how the intake system works, yet they manufacture one.

 

[jeffnrockwall]

Good looking OTR intake but i agree probably safer bet with a Rotofab, as you stated no gains were found when testing either unit. Both preformed admirably well.

 

[pir4te01]

Nope, not mistaken.

The factory tube is on the silencer box, which is post MAF, and pre Throttle body. This is because the PCV system eventually allows air into the intake manifold, and this air needs to be metered as it's actually using that air for some of it's intake source. By putting that piece in front of the maf, you allow air to enter into the pcv system, and then it enters the intake manifold, causing the car to run lean.

Please, don't make the same mistake VCM did and fight us on this. It doesn't reflect well when a company doesn't understand how the intake system works, yet they manufacture one.

Ok I just want to clarify what you mean, not argue. There is some confusion here about PCV vacuum line, which on my car - L77 - looks like this:

PCV System.
Hose A-B
Fresh Air Supply Line.
From Air Intake Pipe to Front Right Valve Cover.
(Supplies fresh filtered air to the PCV system)

Hose C-D
Foul Air Line.
From Rear Left Valve Cover to Front Right Intake Manifold.
(Supplies foul oily air from the PCV orifice in the valve cover to the intake manifold for consumption by the engine)

If I understand your point correctly, the location of A is critical. Please illustrate or point to some research that explains why the air at A should be metered by the MAF?

Because the fresh filtered air at A has a critical effect on foul oily air entering the intake manifold at D?

I have no issue as mine is a full custom tune that compensates for such. I see that stock tune with unmetered air is an issue, yes.
However a MAFless OTR like the one above fitted with a MAF is not junk, fitted to the fastest Zetas in fact, just full custom tune (recommended) or fit the "A" coupler using a 90° nipple somewhere near post MAF / pre-throttle in the intake tube.

 

[small batch]

Ok I just want to clarify what you mean, not argue. There is some confusion here about PCV vacuum line, which on my car - L77 - looks like this:

PCV System.
Hose A-B
Fresh Air Supply Line.
From Air Intake Pipe to Front Right Valve Cover.
(Supplies fresh filtered air to the PCV system)

Hose C-D
Foul Air Line.
From Rear Left Valve Cover to Front Right Intake Manifold.
(Supplies foul oily air from the PCV orifice in the valve cover to the intake manifold for consumption by the engine)

If I understand your point correctly, the location of A is critical. Please illustrate or point to some research that explains why the air at A should be metered by the MAF?

Because the fresh filtered air at A has a critical effect on foul oily air entering the intake manifold at D?

I have no issue as mine is a full custom tune that compensates for such. I see that stock tune with unmetered air is an issue, yes.
However a MAFless OTR like the one above fitted with a MAF is not junk, fitted to the fastest Zetas in fact, just full custom tune (recommended) or fit the "A" coupler using a 90° nipple somewhere near post MAF / pre-throttle in the intake tube.

I chatted with Mace Engineering Group about buying this intake for mine. They did tell me that this intake would require a tune, and said I should look at buying the VCM if I didn't want to tune my SS.

 

[pir4te01]

I chatted with Mace Engineering Group about buying this intake for mine. They did tell me that this intake would require a tune, and said I should look at buying the VCM if I didn't want to tune my SS.

Yeah that makes sense, the Orssom is awesome with a tune.

 

[andy@livernois]

OK, so let's trace this as simply as possible. I well reference your pictures.

D. that is the port on the intake manifold. This is where the PCV system get's it's vacuum source. The intake draws in air from the crankcase as it connects to C on your pictures, which is the left side valve cover, or on an LS3, it connects to the valley plate and figure C is capped off. Now, where does figure C, or the valley cover get air from to allow the intake manifold to draw air? The short answer is from the crankcase, however, GM doesn't want much vacuum in there, so they have the "fresh air hose", figure A, run to the silencer portion of the air inlet, from figure B, the right side valve cover.

Now, think about the flow. Since it's all connected, you are ultimately bring in air from the air intake into the crankcase, and eventually into the intake manifold. Here's the problem with that, since it's fully metered from the factory, there is no amount of unmetered air entering the engine from any source. Because of this, once you put that hose to atmosphere, or in-front of the MAF, you now have unmetered air entering the engine. The issue is this amount of unmetered air changes every single day, Barometric values, humidity, altitude, temp, etc. all impact this. This is often why we see tuned with these OTR setups have the lean codes disabled (super wrong way), or have their fuel trim limits set below the fault threshold (slightly less wrong way). So jsut because it's tuned, and doesn't set a light, doesn't mean it's right. Truthfully, there isn't a way to calibrate it correctly since it's a mechanical variable.

All of this from companies not understanding how the PCV system functions.

 

[pir4te01]

OK got what you are saying, thanks.

Truthfully, there isn't a way to calibrate it correctly since it's a mechanical variable.

So recalibrating the MAF and commanding more fuel would not possibly overcome the lean issue?

 

[andy@livernois]

OK got what you are saying, thanks.




So recalibrating the MAF and commanding more fuel would not possibly overcome the lean issue?

in a big hammer approach, yes. However, since you are telling the maf that there is a hard amount of error, when it changes, the MAF never knows this, so let's say you back in 3%, but it's a cold, dense, high baro day and it's actually allowing in 7% more air, now it's only 4% off, but it's still off because of an issue.

 

[pir4te01]

in a big hammer approach, yes. However, since you are telling the maf that there is a hard amount of error, when it changes, the MAF never knows this, so let's say you back in 3%, but it's a cold, dense, high baro day and it's actually allowing in 7% more air, now it's only 4% off, but it's still off because of an issue.

I appreciate you taking the time to explain. Yes Aussies generally dig a big hammer fix - mine: MAF frequency conversion, decreased stoich 0.5% which is fine on e85 during PE and LTFT can handle trims around 8%. No spikes across a range of operating conditions, confident that particular OTR is good with a (workaround) tune.
I agree though, simpler and more effective overall to plumb in "A" post MAF, and I intend to do that, thanks again.

 

[Blushirt35]

Installed 3 days ago, had Vararam before that

 

[Jess G]

Thanks everyone for all the great info. Really helps in deciding if to get a new OTR CAI or a cone style CAI.

 

[JJay03]

I know that VCM has finally fixed the vac issue and I do like the look of the VCM the best but I am still undecided. The down side possibly I heard of the VCM is that the filter gets dirty fast and it may be more of a pain to get the filter out? Would be nice to see one in person.

 

[pir4te01]

FWIW I did rejig per @andy@livernois advice and that really helped like idle 550 rpm with mid 20's cam and stabilised open loop tuning.
Recently wore out the OTR panel filter and bought a complete VCM OTR for a few bucks more. Very happy, great sound.