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Filter Minders for Dummies - davidbrady - 03-20-2013 11:29
Folks, a friend asked me about the Filter Minder and it's suitability as an intake plenum diagnostic tool. One such use would be in determining whether the LXi's DD Series-60 has an overly restrictive fresh air intake system.
The Filter Minder (FM) is a device that measures intake restriction and potentially indicates the need for air filter replacement.
The FM has 5 predetermined click off points. The FM is graduated on the side of it's clear plexiglass chamber with 5 hash marks. The hash marks are available in a variety of calibrations to suit many applications. A quick google led me to these common calibrations:
All values in inches of water vacuum pressure:
a) 4, 8, 12, 16, 20
b) 7, 10, 15, 20, 25
c) 8, 11, 15, 22, 25
d) 14, 16, 18, 22, 25
e) 15, 18, 22, 27, 30
As the FM detects vacuum a yellow cylinder advances in the plexiglass chamber. If the vacuum exceeds one of the five click off points then the cylinder is latched at that point. In effect the FM locks a peak vacuum reading value, and one of five values can be locked with the last value considered the "red zone" where air filter replacement is suggested.
There are some issues with using the FM outside of it's intended design use as a filter replacement indicator.
1) The resolution of the FM is the distance between the hash marks. Choosing (a) above, for example, if the intake plenum has an actual vacuum of 18 inches of H2O, then the filter minder will log it as 16 inches of H2O. Here the resolution is 4 since any value between 16 and 20 will be logged as a 16.
2) The accuracy of the FM is +- 10%. Again, choosing (a) above, if the "true value" of vacuum in the plenum is 20 inches of H2O, then the FM can read this anywhere between 18 and 22 inches of H2O and because of it's resolution some FM's may lock the reading as 16 while others lock it as 20 inches of H2O.
3) The FM, as installed in our LXi's, is a fast response sensor. This is true because BB installed the device directly into a 1/8" NPT bung tapped into the 7" intake plenum. As a fast response sensor, the FM is susceptible to measuring transient conditions. The Detroit Diesel Series-60 Installation Manual specs the following intake restriction tolerances:
All tests should be performed with the engine operating at maximum rated speed and wide open throttle (full fuel):
The maximum permitted inlet restriction for a system with a clean air cleaner is 12 in. H2O (3 kPa).
The maximum permitted inlet restriction for a system with a dirty air cleaner is 20 in. H2O (5 kPa).
What DD is measuring here is steady state intake restriction, not transients. The steady state condition specified is continuous operation at maximum rated engine speed and continuous full fuel. What it's not measuring is transients such as downshifts, on the fuel off the fuel, cruise mode immediately followed by full throttle full load. The FM can't distinguish between transient and steady state so is apt to report vacuum conditions created by a turbo boost surge or by slow or stuck wastegates. To make an accurate determination of intake plenum restriction we want readings at steady state max rpm, max fuel, max load conditions as specified by Detroit Diesel.
4) The FM is susceptible to it's mounting location. Detroit Diesel is very clear in where a vacuum probe should be tapped into the intake plenum. DD specifies 5 inches before the turbo and after the last bend. Installing an FM at an elbow, whether at the inside radius or outside radius, can distort the readings. Installing the FM at tapered reduction or expansion diffuser can distort the readings. The FM is also susceptible to dirt and grime. Any clogging of the port or of the FM can distort the readings.
Before I'd recommend cutting metal, we need a precise continuous real-time vacuum measuring probe. We need an analog sensor that has high accuracy, low resolution, high repeatability, and low response time, with the ability to measure and log steady state vacuum conditions. We also need a continuous real-time dash mounted display. We also need to tap the vacuum probe into the intake plenum according to the manufacturer's (Detroit Diesel) specifications. The Filter Minder doesn't meet these needs.
Only when these requirements are met can we be sure that the data we're collecting is meaningful enough to allow us to make thoughtful modifications to our intake systems. Until we measure with high quality measuring devices and collect accurate and precise data, we can't say that we know anything about the system. Anything less is hacking, not engineering.
Here's a link to pdf's of a high quality analog vacuum sensor and a display offered by Engineered Products Co that suits our needs:
http://wanderlodgegurus.com/Thread-Intake-Plenum-Vacuum-Measurement-Probe?pid=1061#pid1061
Here's a pic of your typical Filter Minder:
RE: Filter Minders for Dummies - davidbrady - 03-20-2013 18:47
Here's an idea. Don't 1/8" NPT tap mount the Filter Minder directly into the 7" diameter intake plenum. Instead take a length of 1/4" diameter hose, maybe 10 feet long, you can coil it up, and mount the Filter Minder to this and connect the other end to the intake plenum 1/8" NPT bung. This way you'll filter out transients and be left with steady state readings. You may need to experiment with the length of tubing required. Then go for a full throttle drive, at high rpm, at full load, up a nice long grade. (Folks, save your money).
RE: Filter Minders for Dummies - davidbrady - 03-23-2013 14:53
Pressure differences between the throat of the intake opening and the intake tube within 5" of the turbo is what we want to measure. The FM can't do this - another reason not to base design decisions on it.
The FM is a tire pressure gauge. It measures vacuum relative to its ambient pressure which is the pressure of the engine compartment. How much positive pressure do you think the fan at full tilt creates. As ambient pressure increases so does the FM's perceived intake tube pressure drop.
Folks, DD specs a clean air filter system at 12" of H2O and a dirty one at 20. That 8" difference is 0.30 psi or about the pressure developed when you blow out your birthday candles. Another perspective: take an LXi with slide open, now close the slide, the room pressure increased by one psi.
Don't rely on the filter minder to guide you in cutting metal. More precise investigation is needed.
RE: Filter Minders for Dummies - al perna - 03-24-2013 08:53
David . lets ask this question , with our engines, will a more direct air flow serve a positive result ?
does a turbo work harder if the air is forced to make multiple turns prior to being compresed ?
Now remember , KISS keep it Simple Stupid ha ha ha . tell me what you think ?
RE: Filter Minders for Dummies - davidbrady - 03-24-2013 19:31
Hi Al,
Thanks for asking. Yes, with a reduction in intake restriction, fuel economy and throttle response should improve do to a lessening of pumping losses. I don't think power will improve unless the fuel map is changed, turned up.
My intuition is that we haven't identified the root cause of our yellow and red zoning Filter Minders, and blindly throwing air flow improvements at it may mask the root cause and result in unnecessary intake modifications.
I believe this for a number of circumstantial reasons:
A) my bus runs too good for there to be an out of spec induction system, I have low turbo lag, power and fuel economy are exceptional, and it never smokes. It just doesn't behave like a bus that's choked,
B) a visual inspection reveals an intake system that should conform to spec: starting at the turbo, there's a 6" ID 90* elbow, into a 6" ID x 48" tube with one 90* elbow, into a 7" ID 18" air filter, then out the top of the air filter into a bell topped 7" ID x 18" tube which pulls air out of a large still box. I count three 90 deg bends. The restriction imposed by the paper air filter should be negligible compared to the restriction of the system overall.
C) What we have in our LXi's is almost identical to what Prevost uses except they have an additional 90* elbow and their 6" tube is 5.5" ID. They also have a 20" of H20 Filter Minder installed.
D) The zoned-out FMs occur on WB's (8V and S60) and LXi's (S60), and maybe other wanderlodges that we haven't identified yet. The fact that it seems to hit all the 500hp buses leads me to think that there's something else going on, and that could be where the FM is mounted, conditions within the engine compartment, tolerances, resolution, and calibration of the FM's themselves. I'd be surprised if BB undersized the induction systems on all these buses for almost a 15 year period.
E) I spoke with the folks at Filter Minder and they confirm that they've seen problems with zoned-out FM's in bus applications. Could be the vast intake plumbing to and from the Charge Air Cooler, could be the size of the Charge Air Cooler, could be the high power cooling fan blowing air into the engine compartment and over the FM, could be the nature of a high power diesel pusher.
This topic has captured my interest so I will eventually
instrument my intake to get some hard data. We need a differential pressure gauge set up to measure the vacuum drop properly to see if the intake is out of spec. I think it merits more investigation.
RE: Filter Minders for Dummies - al perna - 03-25-2013 17:53
hello David , now i did ask you to keep it simple LOl .
I believe that it is not a problem if the fillter minder stays in the yellow , it is if it increases over time to the red ,that creates the need to change the filter . would you agree ? lets say we replace the filter , would the filter minder go directly to the yellow ? if so is this not the base of our reference ? from this point we monitor the minder , if it does not move we are not in need of replacement . I know if I clear the filter by pushing the button , it will return to the same reading prior to clearing it .
like your bus , our coach seems to be running well . 7.65 mpg overall on 5 trips up the east coast , towing a car .
are we saying that a more direct air flow will increase our mpg or , will it save us money on turbo repairs down the line ?
hope you can understand my question here .
AL
RE: Filter Minders for Dummies - DOSZORROS - 03-25-2013 21:29
I think the proper way to determine whether or not you have a restriction is to put a differential pressure port and monitor gauge just upstream of your turbo inlet. This will tell you how much restriction you have in the total intake system to the turbo.
I have a 500 hp series 60 and I can get about 26 lbs. boost at standard conditions. That is assuming the boost gauge is reasonably accurate (I have not calibrated it). This leads me to believe that I do not have much restriction in the inlet system.
Where I would like to see more restriction is betweem the fuel fill hose and my bank account.
RE: Filter Minders for Dummies - timetravelers - 03-25-2013 23:00
X2 George, of course there's also a direct link between all the excess stuff we haul and that bank connection.
I have to confess if I think the air filter is still OK, I just reset the FM back to green.
RE: Filter Minders for Dummies - davidbrady - 03-26-2013 01:53
Hi Al,
My favorite DD Series-60 tech, Gonefishen over on the dieselenginetrader site, has long recommended changing air filters annually, which is what I do. I don't think we understand yet what the Filter Minder is telling us so I'd simply ignore it, pending more investigation.
Diesel engines are air rich. At cruise just enough fuel is injected to keep things going with air fuel ratios (AFR) going as high as 40:1. The S60 doesn't run a lambda (O2) sensor. It injects fuel based on the throttle position sensor and the boost sensor. For a given load the ECM wants to see a specific boost pressure. Because a diesel can run with a wide range of AFRs, to make power it needs to either inject more fuel or cram in more air. Less restriction means more air, and for the same power or same boost it means less fuel. This means less exhaust heat, less exhaust back pressure, less turbo work, and higher engine efficiency, which translates to better fuel economy.
RE: Filter Minders for Dummies - al perna - 03-26-2013 09:34
Thanks David , sounds like a mod on the air intake makes good sense .
at a recent rally David , Randy over on the WOG forum noticed Blue Bird made changes to the air intake stack over the years. on my 2000 it is higher and cut on a 90 degree angle . On the 2001, BB reduced its height and put a cap on it raised around a inch or so . I have not figured out how to take pics, and post them so maybe you could take one of your LXI and other S60 owners could do the same . It would be nice to compare the changes BB made along the way .
Thank you for your clear explanation above and look forward to this upgrade .