About the backwards facing snorkel conundrum

After many unsuccessful attempts to google a definitive answer to this issue, we decided to conduct our own test to try to determine what happens when you turn your snorkel's intake backwards.

I'm happy to say that we believe that we were able to quantify the difference in intake restriction between a forward and a backward facing snorkel on a Land Cruiser UZJ200 test vehicle.

You can see our test and its results here. Don't worry if you don't know Spanish. Just scroll down until you find the same entry in English.




Please note that because I live in a tropical country, I have absolutely no experience using a snorkel equipped vehicle on snow.

Good work......

NOW, what I would like to see, is actual CFM making it to the air box... and pressure difference i the air box.

I like what you did though, good numbers, repeated.....

Chase

I turn my snorkel backwards during the winter months to keep snow, during travel, but more importantly road salt from getting sucked in. The salt issue is not about the motor inhaling salt, but clogging the filter up, especially on dry days when cars kick up salt dust.
Salt collects in the snorkel tube, which will be a PITA to clean out. We have a LOT of salt put on our roads, enough to turn the outer snorkel tube white.
I can imagine the inner tube if I didn't turn the snorkel head around... :Wow1:

Very nice job and some solid data. I also like the barometer you made. Simple solution to a measurement problem.

cheers

Fun project, thanks for sharing the results.

Unfortunately, my Mantec snorkel only allows the head to face rearward

Very cool project, thanks for sharing

Another triumph for science! Thanks for answering this question definitively -- I've often wondered the impact. I'll keep looking forward...

Actually, what was built is a manometer not a barometer. A barometer is used to measure atmospheric pressure while a manometer is used to measure small pressures usually below atmospheric. A barometer is also a closed system where a manometer, like this one, is an open system. 1 standard atmosphere is 14.7psi or 760mm of mercury.

Not that this all matters, but as long as it was a training session, I thot I would add the correction to the terms (not trying to be an azz, just adding to the learning).

Anyway, that said, this test is cool but I agree with what was said by Chase, a CFM difference would be interesting to see. The pressure drop shows that the speed of the air getting to the air box is reduced, but it does not show what the consumption of air by the engine is in each situation. What I mean is, is the engine really starving, or is there more air than is needed with the snorkel forward. The engine is not concerened as much with air pressure as it is with air volume. If the engine needs to consume 2CFM at a set speed and a set condition, getting the air to the engine faster makes no difference but if the air gets there to slow to meet the 2CFM, then you have a problem.

Please do not misunderstand, I applaud the use of science and the technique used in this experiment, the results are very interesting. But I don't feel it is still the complete story, or, the definitive answer, to the question, more that it is more clues toward the results.


Also MAJOR kudos to you guys for building a homemade manometer, that was really cool

to achieve any true "Ram Air" effect, the intake point has to be well above the aero profile of the vehicle. unless you mount the snorkel head 2ft above the roofline, you are not going to net any usable results. the rear-facing snorkel head will naturally create a low pressure zone in the dead spot immediately in "front" of the snorkel head. obviously, air will then diffuse from a high pressure to a low pressure zone. this effect is only realized at high speed.

you can look at Pro Stock drag cars (hood scoops) and NASCAR Cup cars (cowl induction) to see how air induction is supposed to work.

i applaud the scientific attempt at settling this debacle once and for all, but the data is misrepresented. the low pressure zone created by the backwards-facing snorkel will not adversely affect high-rpm engine performance. a pressure drop of 1.8cm Hg is negligible, especially compared to the vacuum created by an engine under load.

moreover, the negative pressure zone (relative to the air bypassing the snorkel) will only encourage more airflow into the snorkel.

if i had a snorkel, and i was really bored, i would hook up my scanner and drive around town with the snorkel facing forward, rearward, and sideways for the hell of it. i could then monitor real-time engine parameters and interpret engine efficiency, in terms of MAF+TPS, O2S pre- and post-cat and timing retard readings.

regardless, the "performance" effect will be negligible, and far outweighed by the security gained by turning it backwards - no debris sucked into the airbox, and less chance of getting snagged.

i've yet to hear of anybody experiencing an engine failure - let alone a rich misfire - from turning the snorkel head backwards. just sayin...

Thanks for the science Tucan! I recall posting a year or so ago about this, and receiving a bunch of pictures of race trucks with snorkels backwards as proof of my error... Now your experiment shows there might be more to it. :sombrero:

Thanks to all of you for your kind comments. We really had a lot of fun doing this.

Azlugz said:

Actually, what was built is a manometer not a barometer. A barometer is used to measure atmospheric pressure while a manometer is used to measure small pressures usually below atmospheric. A barometer is also a closed system where a manometer, like this one, is an open system. 1 standard atmosphere is 14.7psi or 760mm of mercury.

Not that this all matters, but as long as it was a training session, I thot I would add the correction to the terms (not trying to be an azz, just adding to the learning).

Anyway, that said, this test is cool but I agree with what was said by Chase, a CFM difference would be interesting to see. The pressure drop shows that the speed of the air getting to the air box is reduced, but it does not show what the consumption of air by the engine is in each situation. What I mean is, is the engine really starving, or is there more air than is needed with the snorkel forward. The engine is not concerened as much with air pressure as it is with air volume. If the engine needs to consume 2CFM at a set speed and a set condition, getting the air to the engine faster makes no difference but if the air gets there to slow to meet the 2CFM, then you have a problem.

Please do not misunderstand, I applaud the use of science and the technique used in this experiment, the results are very interesting. But I don't feel it is still the complete story, or, the definitive answer, to the question, more that it is more clues toward the results.


Also MAJOR kudos to you guys for building a homemade manometer, that was really cool

Click to expand...

Yes, you are absolutely right about our device being a manometer, but I have also used the reference to a barometer when explaining what we were trying to do to others. Also, I have to say that for building it, I got the idea from some Australian magazine I saw maybe ten years ago. I just don't remember which.

In relation to the test itself, please consider the dirty air filter warning lamp sensor you can find in 80 series Land Cruisers. In this case, the pressure drop resulting from the airf low restriction caused by a dirty air filter is used to light the lamp. This might be a very easy to understand example to show that pressure drops are directly related to restrictions in air flow. And, just as in the case of a dirty air filter, the restriction in airflow that we can see as a pressure drop when we turn around our snorkels, can result in power loss and increased fuel consumption.

Based on this, we could say that if we have determined that installing the snorkel intake backwards can negative affect engine performance if you are driving at very high speed.

I can agree that determining CFM difference should be a more direct way to asses this situation. But I have to say that right now, I can't think of an easy, reliable and inexpensive way to do it. Maybe if we could fool around with air flow meter readings. Considering that my Land Cruiser uses a hot wire sensor, which measures intake air mass directly, which means we can relate sensor output voltage to air grams/sec. I can certainly try.

Thank you very much for your comments, you got me thinking.

alexrex20 said:

if i had a snorkel, and i was really bored, i would hook up my scanner and drive around town with the snorkel facing forward, rearward, and sideways for the hell of it. i could then monitor real-time engine parameters and interpret engine efficiency, in terms of MAF+TPS, O2S pre- and post-cat and timing retard readings.

regardless, the "performance" effect will be negligible, and far outweighed by the security gained by turning it backwards - no debris sucked into the airbox, and less chance of getting snagged.

i've yet to hear of anybody experiencing an engine failure - let alone a rich misfire - from turning the snorkel head backwards. just sayin...

Click to expand...

Yes. Fooling around with the air flow meter output is what I'm thinking now. I completely agree that the actual differences are very small. So small that we had to build our manometer in order to measure them. So small that driving at 90 mph and 5,500 rpm there is only a 0.25 psi difference in the pressure drop when you turn the snorkel intake backward.

But small as it may be, the point is that we believe we could tell for sure that there is indeed a negative effect to turning the snorkel intake backwards. And I totally agree in that we will never see anyone facing engine problems just from turning the snorkel around.

Tucan, in reference to your sig... You have EXCELLENT English. Indeed, it is exponentially better than many whose first language is English!

Azlugz said:

The engine is not concerened as much with air pressure as it is with air volume. If the engine needs to consume 2CFM at a set speed and a set condition, getting the air to the engine faster makes no difference but if the air gets there to slow to meet the 2CFM, then you have a problem.

Click to expand...

A quick correction.
The engine doesn't care much about pressure or volume, what it needs is mass. To produce a given amount of power, the engine will have to burn X grams of fuel. In order to burn that fuel, you will need about 14.7xX grams of air (for stoichometric combustion anyway). So that can be accomplished by either low pressure high volume; or high pressure low volume.

Of course all three are related (mass, pressure, volume); but in this scenario volume is actually the dependent variable and is a function of the other two.

my $0.02.

alexrex20 said:

Tucan, in reference to your sig... You have EXCELLENT English. Indeed, it is exponentially better than many whose first language is English!

Click to expand...

Thank you. But it is really difficult for me as I have many doubts in relation to what is or isn't correct.

For instance, please take a look at this thread's subject. Is backwards correct? Or should I have written backward? Every time I have used the word backward or backwards here I have hesitated, not knowing if I was using it correctly. I don't know how many times I have had to think twice before deciding to use the word in or the word on in a sentence.

There are many other cases in which I'm not certain if I'm using the right words or not, or if I'm constructing certain phrases correctly.

That is why I really appreciate when anyone takes a few moments to correct any of the errors I'm afraid to be making all the time.

I'll take this opportunity to thank once again those of you who have taken the time to PM me with comments and/or corrections since I adopted this signature.