About the backwards facing snorkel conundrum

[Paladin]

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.

Exactly right.

There's talk in this thread about the CFM being reduced with the head backwards. This is not really relevant.

The engine requires a fixed mass of air to produce a fixed amount of power to drive at a given speed (in this case, 90mph).

When the snorkel head is facing backards, the pressure in the snorkel tube is reduced. Therefore, the density is decreased. Yet, the engine needs the same mass of air. Therefore, the only way to achieve that mass is to increase the VOLUME of air. It follows that the simply measured CFM of air will actually INCREASE. This is counterintuitive to many in the engine-tuning community, but this is in fact how it works. This increase in volume is achieved by opening the throttle wider. If you could measure the throttle angle, you would see this is true. You have to step on the throttle more when you have the snorkel backwards.

Normally this will have no effect on engine efficiency. A fuel injected engine always maintains 14.7:1 Air/Fuel Ratio. The only exception to this is when it goes into open-loop mode. This usually happens sometime after half-throttle. There will be a measured change in the fuel efficiency of the engine because since you have to open the throttle a little more to generate the same power, you will cross the open-loop threshold more often on a given drive.

The only time the backwards snorkel will actually affect the engine power, is when comparing scenarios when the throttle cannot be opened anymore. ie: full throttle. In this case, the backward's facing throttle will achieve a maximum horsepower which is reduced by a similar amount to that of the air pressure. In the case of 90mph, the air pressure drop is 1.7% of atmospheric, and I would expect the horsepower drop to be similar.

Thank you Tucan for doing the experiment and getting the data. Did you have the sampling tube connected before or after the filter?

 

[jbaggy]

Very cool, thanks for the information.

While watching Dakar, I noticed a lot of the vehicles had positioned their snorkels backwards....I knew they must have known something that I didnt. Thanks for posting it up. :smiley_drive:

 

[Tucan viajero]

There will be a measured change in the fuel efficiency of the engine because since you have to open the throttle a little more to generate the same power, you will cross the open-loop threshold more often on a given drive.

The only time the backwards snorkel will actually affect the engine power, is when comparing scenarios when the throttle cannot be opened anymore. ie: full throttle.

Thanks for the comments.

All our readings were taken at full throttle, that is what I meant by "full load" when I posted: "our test Land Cruiser was driven at 90 miles per hour and 5,500 rpm under full load". Sorry for the misunderstanding if that is not the right way to express it.

 

[redthies]

And my wife thinks I am a nerd!:elkgrin: I still think they "look" wrong when facing backwards. Although I have turned mine around a few times in super heavy rain or snow...

 

[cruiseroutfit]

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

The the exact same can be said for not turning it backwards. In the millions of miles driven by my customers and myself, I've not every had an issue with a forward facing snorkel.

Obviously the jury is still out, while I can't cite a person having air supply issues with a backward facing snorkel, I can point out those that have supply issue with a standard forward facing inlet, not a function of the snorkel head but the snorkel body cross section and head loss. I'd venture to say that in 'most' cases it won't matter which way the head points but in a select few it might and even in those cases it might not make enough difference to notice.

I too would love to see more testing done on the subject but kudos to you for your work thus far. Regarding measuring CFM, manifold pressure, intake temp, etc... I wish I was still in college, we had a 4.3l GM motor on a stand in the thermodynamics lab that had all of these functions and with a giant fluids with wind tunnel on campus too it would have made a ripe experiment. Sadly I was too busy building a Mini-Baja car with the schools money

 

[chasespeed]

Really, I dont think it'd make a lick of difference either way.....

Most with a snorkel, arent as concerned with topend performance as some others...

I need a lot more airflow than most, and consequently a standard size snorkel wont do the trick.....

SO.......:victory:

Chase

 

[Paladin]

Obviously the jury is still out, while I can't cite a person having air supply issues with a backward facing snorkel,

I have had snow stick to the back of the snorkel throat and block it about half way before I remembered to turn it around. It is a serious issue with snow. IMO, sand doesn't stick the same way, but will eventually clog the filter.

 

[cruiseroutfit]

I have had snow stick to the back of the snorkel throat and block it about half way before I remembered to turn it around. It is a serious issue with snow. IMO, sand doesn't stick the same way, but will eventually clog the filter.

? And see I've driven in the snow for 10 years and never worried about turning mine around, never an issue. Could be that famous Utah powder versus the soggy snow in the east

 

[alexrex20]

a little moisture through the intake isn't a bad thing anyway. it helps clear out the carbon deposits in the combustion chamber.

 

[Azlugz]

Just gives you a custom water injection system!!

 

[762X39]

Some people run a "snorkle" with a pre-filter so there is no "backwards" position and some manufacturerers build the snorkle facing back as stock.I think the testing was very interesting but it may not matter (maybe that was the point).

 

[Paladin]

? And see I've driven in the snow for 10 years and never worried about turning mine around, never an issue. Could be that famous Utah powder versus the soggy snow in the east

Yes, that must be the case, because this did happen.

(maybe that was the point).

Yes, I think it is.

 

[Streakerfreak]

? And see I've driven in the snow for 10 years and never worried about turning mine around, never an issue. Could be that famous Utah powder versus the soggy snow in the east

This is probably the truth. I didn't need to turn the snorkel around when living out West, here in New England it is a must. Our snow is slick, soggy, and heavy. When a storm is coming I have to cover the opening with a plastic bag when it is parked. Learned the hard way a few storms ago.

 

[Azlugz]

For that snow build up, just drill a hole in the bottom of the snorkle up tube for the water to drain out, duh.







































LOL.....J/K :wings:

 

[Palehorse1]

When in Bosnia during late 90's it was common to see vehicles that had snorkels affixed to have the intake routed to the inside of the passenger cabin with many of the snorkels never actually being exposed to the outside of the vehicle at all. Wish I had pictures handy to show it, and to be honest I have no idea how that install method affected performance but thought it was interesting enough then to still remember it now.