Thread: Forced Air due to Snorkels???

I keep reading on this forum and others about the fact / claim / urban myth that an air snorkel helps to force air into the engine. Can anyone prove this, or is this just a justification for the snorkel?

Has someone seen or done tests with a Magnehelic guage or some other mechanism to see if there is a ram effect (ie what is the pressure differential between a snorkel and having it come off the guard), or wants to do some testing and has the equipment?

My reasoning:
Cold air increases performance, hence an intercooler on my TD5 (its main function is to cool the air temp down after the air becoming compressed and heated up going through the turbo) and a snorkel definitely gets cold air in (and cleaner air when on a dusty track), which will help keep the filter clean and allow more air in etc... but it forces the air in??

Whilst I can't get a hold of the reference book now, my recollection on this was that forced air is real when a) the air intake bells is designed to be of the right tuned length (similar to how extractors work), or b) the vehicle is going over a certain speed (can't recall if it was 60 kph or 60 mph - old book (or c - both of a & b).

In case a) the length needed to be tuned for an rpm range etc. as the air is stopped and started (quite a few times a second) there are air wave harmonics due to this chopping effect. An intake bell needed to cater for this, with performance drop off outside of this rpm range.

In a modern car, there are still some with bells in their intake chamber, but the length of the air intake from outside to in is more important (eg a falcon 6 cylinder engine in a ford has the ability to change the length of the intake, to create low end torque with a longer path below a certain rpm and then rev more freely with a shorter path above this rpm - it has its path tuned, to speed up or reduce air flow).

In case b) it is ramming the air into the intake, so that it overcomes the pumping loss of the naturally aspirated engine. Now this was for a race car (ie designed for speed), not a 4wd. Anyone into fluid dynamics would look at the number of twists and turns on a snorkel system and say "yeah, right". You are introducing 4 more angles into the air intake (2 at top, 1 at back of guard, 1 at front of guard) , so it makes sense that the air is being forced in. (not)

If you have a turbo, the argument for the pumping loss is a bit off the radar isn't it, although it allows the turbo to get the supplied air in a bit quicker (perhaps at highway speeds).

In a performance or race car the best place for an air intake is some place where it can flow directly from the outside into the plenum chamber (via filters etc of course), so that the ram effect is there (no lines and as little as possible restrictions). Compare this to a snorkel and the twists and turns in place - there is no comparision.

Even so, in a race car the main effect is cold air and lots of it, which is why the opening is so wide. As the air can't go anywhere else (yes, it is being forced in), and the plenum chamber is smaller than the air intake cross section, there is some pretty rudimentary but effective ramming going on. There is no long lengths of pipe and changes in direction etc for the air to eddy and 'tangle" up on, until it gets into the plenum.

So, am I off the planet with this (ie someone can provide some evidence), or is my reasoning correct? (btw, if it helps convince the minister for finance, keep up the lie, but around others please).

Originally Posted by bob10

Now you have me really confused-- are you saying a snorkel is not necessary off road, the reason I ask is I am travelling up north soon, mostly sealed roads, with a possibility of water to cross, and am considering buying one. As I have a limited budget, and other items to purchase, any advice on this would be welcome.
bOB10

Save your money Bob,
A snorkel is certainly not "necessary off road".
Based on your question and the "with a possibility of a water crossing" you're probably not likely to venture into anything that really needs a snorkel.

I have a snorkel fitted to my D1 and am glad it's there in many instances. The airbox etc is completely sealed to allow some of the crossings I do. The dust claim doesn't apply to me because I generally stay far enough back from the vehicle in front to avoid the dust.
The cleaner airbox/filter also seems to be rubbish to me because the snorkel head seems to pick up every small leaf, insect, caterpillar, flowerpetal etc from every bush/shrub/tree I push past on the narrow tracks in the vic high country.
I also noticed a marginal decrease in fuel economy when I fitted it.

So, for me, I'm glad it's there for the deep water I cross and most of the other claims are ****, If it helps to convince the wife then go ahead and use them

Stevo