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Landyphil

Member Since: 23 Jul 2012
Location: Lake District
Posts: 87

2003 Defender 110 Td5 USW Stornoway Grey

Snorkel Theory.

Evening All,

A multi forum post so my apologies if you see this elsewhere. Please don’t take offence!

Be warned this is a dry subject but one which I’ve pondered on now and again.

I was putting the hi lift jack back on in it’s place on the back of the racer sometime ago and noted that really the jack does sit a bit too close to the air intake unless you offset it to the side on the behind-the-cab snorkel.

I thought I should move the jack and maybe fit something (that can be quickly disconnected) to make sure the air inlet isn’t being affected by the vortex’s that occur round the back of a truck cab and cage. This particular snorkel exists purely because the under bonnet filter was clogging on longer stages where it’s particularly dusty.

Just for reference you can see the snorkel here (on a rally this spring where snow was more common than dust!):

Click image to enlarge

Anyway this got me thinking.

Since 1999 and the release of the td5 I’ve been inwardly somewhat derisory of folk who’s post 1999 Land Rover clearly will never see the dusty plains of the southern latitudes but also haven’t relocated the ECU’s despite the watery nature of round here.
Which to me is the vehicular equivalent of buying a nice waterproof jacket wearing all the time but also wearing shoes made of Sodium.

As a result racer aside I’ve never given snorkels much thought.

BUT.

What if there is another benefit to a snorkel if it’s forward facing scoop type? The question is I just don’t know.
Obviously I know there’s no such thing as “Ram charging” an engine inlet meaningfully above atmospheric pressure at road car speeds no matter how big the “scoop” is. That’s a given and well known however that doesn’t preclude reducing inlet vacuum which is clearly no bad thing and certainly as modern telemetry is more prevalent in motorsport it would seem many an engine makes more torque and power in the real world than at similar temperatures on a rolling road.

I was originally thinking about this for the racer but we’ll use the Puma engined 90 as an example.
So firstly I thought I’d guestimate how much air that engine needs for given revs. Which raises the first fudge in that off boost, on boost figures will be different so air (derr dum tish!) on the side of caution and assume it’s on full boost and then some.

So.

The formula for calculating how much air a 4 stroke engine needs is:
CFM = Cubic Inches x RPM / 3456 x VE%

So a 2400cc engine is 2400 x 0.0610237441 = 146.45 Cubic Inches.

Volumetric efficiency is affected by the level of boost so as said we’ll air on the side of caution and say it’s 150%

So the formula for CFM is : CFM = (RPM x 146.45) / 3456 x 1.5.

So very quickly you can work out how much air you need for given revs:

RPM CFM Required

500 31.8
750 47.7
1000 63.6
1250 79.5
1500 95.3
1750 111.2
2000 127.1
2250 143.0
2500 158.9
2750 174.8
3000 190.7
3250 206.6
3500 222.5
3750 238.4
4000 254.3

Then looking at 3rd gear onwards knowing gear ratios and tyre sizes you can calculate what speed you are doing for given revs in a certain gear. In this case MPH.

3rd Speed 4th Speed 5th Speed 6th Speed RPM CFM Required

Columns below:

6.5 9.2 11.3 15.2 500 31.8
9.8 13.7 16.9 22.8 750 47.7
13.1 18.3 22.5 30.4 1000 63.6
16.4 22.9 28.2 38.0 1250 79.5
19.6 27.5 33.8 45.5 1500 95.3
22.9 32.1 39.4 53.1 1750 111.2
26.2 36.7 45.1 60.7 2000 127.1
29.5 41.2 50.7 68.3 2250 143.0
32.7 45.8 56.3 75.9 2500 158.9
36.0 50.4 62.0 83.5 2750 174.8
39.3 55.0 67.6 91.1 3000 190.7
42.5 59.6 73.2 98.7 3250 206.6
45.8 64.2 78.8 106.3 3500 222.5
49.1 68.7 84.5 113.9 3750 238.4
52.4 73.3 90.1 121.4 4000 254.3

So now we can easily see that at say 22.9mph in 3rd the 90’s doing 1750rpm which is 111Cubic feet of Air per minute.

More importantly at 53mph in 6th it should still need just 111 CFM. This is there the fudge mentioned earlier comes in I imagine in 3rd at 22.9mph the engine will be on very light loading and thus off boost so won’t need as much air as that but in 6th that figure is still probably closer to the truth and probably still too high. But better that than too small!

So onto the snorkel. Obviously there are losses within the shape of the snorkel and inlet tract but what we’re talking about here is the available air in the “mouth” of a forward facing snorkel.

I’m also assuming that where the snorkel mouth is located means it is not unduly starved of “stationary” air ie the air that’s floating about in the road just before you drive through it! Ie like my Series currently.

The equation for this is quite simple. EG. 50 miles per hour is the equivalent of 4400 feet per minute (5280 feet in a mile/ 60 mins in an hour). So at 50mph air is hitting the mouth of the snorkel at 4400 feet per minute. Multiply that by the cross sectional area of the mouth of the snorkel and you have a theoretical volume available in the mouth of the snorkel.

So if the mouth is 3” by 3” that’s 9” square inches or 0.06square feet.

4400 x 0.06 = 275CFM. The engine only needs 111CFM so while you don’t get pressurization I’m pretty sure even with the losses relating to the shape and diameter of the inlet tract you’re not going to get the same level of vacuum.

It’s also easy to work back the other way and say minimum mouth size = (CFM x 1.64) / Speed in MPH Where the minimum mouth size is the “critical size “ whereby the volume of air in the snorkel mouth is the same as the volume of air needed by the engine .In the case of a the 90 that equates to a 8 square inch mouth in 3rd gear and a mere 3.5” for 6th gear… in theory.

So should anyone with a OBDII tool with recording facility be able to record inlet manifold pressure to test the difference? I have the 90 and the laptop with OBD software but no snorkel!

Even if it pushes up the Volumetric Efficiency by a small amount if it overcomes the added drag of having the snorkel in the first place it could make it worthwhile?

Anyone done any experiments on this?

Admin note: this post has had its images recovered from a money grabbing photo hosting site and reinstated

90XS Tdci John Eales
110 CSW G4 Edition
88" Series 3 Racer

25th Jul 2013 6:52pm

DRW58

Member Since: 23 Feb 2013
Location: Perthshire
Posts: 167

And I just thought it was to stp crap coming in with the air

No disrespect intended Phil but are you still taking your medication!!

I built a garage for my Mini
With a place for everything and everthing in its place.
Ten years down the line there's a Mini in there somewhere, and

all's where it should be!!!! Ho hum

25th Jul 2013 7:52pm

JWL

Member Since: 26 Oct 2011
Location: Hereford
Posts: 3443

This is the result of too many sleepless nights due to the minilandyphill

25th Jul 2013 7:55pm

VeeTee

Member Since: 06 Mar 2011
Location: Somewhere
Posts: 1512

Ha, nice - I did exact the same calculations some years ago to calculate air speed and resistance in the snorkel.

Cheers, Vincent
1959 Polynorm 1/4 Ton Trailer, Olive Drab Green (sold)
1970 M416 Military Trailer (Camping Trailer Conversion), Epsom Green (sold)
1975 Series III 88 V6, Light Green (sadly sold)
1996 Defender 110 CSW 300 Tdi, Epsom Green (sold)
2000 Freelander 1 TD4 3-drs, Silver (sold)
2006 Freelander 1 TD4 5-drs Facelift Automatic, Tonga Green (sold)

MySite

25th Jul 2013 8:01pm

theorangebandit

Member Since: 03 Jun 2013
Location: Stowmarket
Posts: 862

So you need a snorkel and a diagnostic to proc this theory come on D2. I have pondered tge snorkel in much the same way and have Hunted in depth testing. Your intelligent rant ha. Proven a theory shame I have neither diagnostic kit or a snorkel

25th Jul 2013 8:08pm

RobKeay

Member Since: 19 Jul 2009
Location: Stafford
Posts: 1585

2014 Defender 110 Puma 2.2 USW Corris Grey

BAS has done some snorkel testing. There's a thread on it somewhere. Think that would answer your question.

He was testing with and without snorkel on his rolling road.

25th Jul 2013 11:10pm

jst

Member Since: 14 Jan 2008
Location: Taunton
Posts: 8099

2011 Defender 110 Puma 2.4 USW Stornoway Grey

interesting points and intrigued to see what falls out of this.

on another note though, Ram air, from my biking days and SRAM i was led to believe there was a benefit of it when you were about 90mph? Cheers

James
110 2012 XS Utility
130 2011 M57 bespoke Camper
90 2010 Hardtop
90 M57 1988 Hardtop

26th Jul 2013 6:43am

Landyphil

Member Since: 23 Jul 2012
Location: Lake District
Posts: 87

No sleep issues so far John........he's rarely grumpy but always hungry!

It's interesting to hear that BAS looked at this but it wouldn't be so much a rolling road more a windtunnel or at least a rolling road with an accurate blown air supply attached to the snorkel to simulate the airspeed.

As for Ram Air this is really the crux of it. Obviously you can't pressurise (above an arbitary amount) intake air through an air scoop or ram at any speed below I think 1/3 of the speed of sound but that doesn't mean you can't reduce the inlet vaccum by providing more air at atmospheric pressure than the engine needs.

Which will give a little benefit. Question is how much?

To do a basic experiment I suppose you could just mod the side grill and make a scoop to fit there although at such close quarters to the wing and arch you'd get some odd aero effects no doubt.

I have no genuine use for a Snorkel on the Puma and idea of modifying a Defender (especially spending money) purely for looks is something that's never going to happen so am wary of spunking about £200, in the case of a gen Safari snorkel on this theory.

But if it did prove slightly beneficial then in the very long term it would be worth it as I'm not planning to get rid of any of the landy's any decade soon. After all even 0.25mpg would make back £200 over 100,000 miles. 90XS Tdci John Eales
110 CSW G4 Edition
88" Series 3 Racer

26th Jul 2013 8:55am

SteveS

Member Since: 05 Oct 2010
Location: Devon & Berkshire
Posts: 388

2009 Defender 110 Puma 2.4 USW Santorini Black

Interesting analysis. I'm not a mech eng but your analysis really works on averages - average speed, average air flow, total displacement etc. The demand for air from each cylinder is peaky as the valve opens and air is sucked in (or pushed in). So I'm thinking there are peaks of pressure (no cyclinders demanding air) and then peaks of vacuum or near atmospheric when the pistons are sucking. My guess would be that these pulses of air demand are sinusoidal as each cylinder moves from TDC to BDC.

So my thinking is that the DYNAMIC demand is far higher than the displacement figures suggest. However, when you consider the turbo is spinning and serves all the cylinders in an average way then this would suggest an averaging effect driven by turbo pressure feeding the demand, the pressured air downstream of the turbo releasing its pressure from manifold when the inlet valve opens into the expanding cylinder

Anyone out there who knows what they're talking about rather than my BS

Post note: anecdotally at motorway speeds it seems to make sod all difference whether the snorkel faces forwards or backwards.

Where's Pete when you need him

26th Jul 2013 9:22pm

dgardel

Member Since: 30 Nov 2008
Location: Veneto (Heart & Head)
Posts: 3586

Re: Snorkel Theory.

Simply

- more pipe line length = more losses due to air friction

- air friction is (fluid speed)^2 dependent (double your speed = 4 time more frictions losses)

=

snorkel is losses from a fluid dynamics point of view.

But should be necessary (dust and/or wading)

Discovery 5 td6 HSE Stornoway Gray Outback Engineering Limited Edition

IID Pro MV License

27th Jul 2013 8:24am

theorangebandit

Member Since: 03 Jun 2013
Location: Stowmarket
Posts: 862

could there be that pressure builds up around the entrance to the snorkel too, what size does the snorkel need to be to actually take in the right amount of air at speed. if wind hits the entrance at 60 mph is the pressure on the rim the partially blocks the entrance there fore decreases its size ? all performance cars with cold air pipe work have massive intakes im sure the snorkel would need to be larger, given also that its not get directly forced air its getting disrupted air from the bungalow-like front of the defender. immediately the air is subject to friction in the pipe work with twists and bends too. performance cars again to increase efficiency in induction they have minimal bends as the also do in exhaust,. (which is the beauty of a defender exhaust pretty much a straight pipe )

27th Jul 2013 8:52am

GREENI

Member Since: 22 Aug 2010
Location: staffs
Posts: 10383

Here's a fact for you (probably)... 97.5% of snorkels are fitted for looks.

27th Jul 2013 4:57pm

abomb1969

Member Since: 23 Jul 2011
Location: Welwyn, Hertfordshire
Posts: 79

1998 Defender 110 Td5 CSW Santorini Black

My TD5 came with a snorkel, and the anti stall didn't work. I un-plumbed it and the anti stall works and there is more low down power.

27th Jul 2013 10:05pm

landybehr

Member Since: 17 Apr 2013
Location: -D-
Posts: 173

abomb1969 wrote:
My TD5 came with a snorkel, and the anti stall didn't work. I un-plumbed it and the anti stall works and there is more low down power.

which is pretty strange. For this moment I doubt there´s been a causality.

Take a look at the "cfm" figures he wrote down. Revs near idle do not need that much air. A resistance (as what we can see the snorkel naughtily) has to do something with flow. The more flow needed the more the resistance shows an effect. It´s like you could easily breath through a drinking straw while reading this thread without stalling. But if you hurry up the stairs you will stall

28th Jul 2013 3:58pm

LandRoverAnorak

Member Since: 17 Jul 2011
Location: Surrey
Posts: 11324

I've fitted a snorkel to my TD5 and the anti-stall works exactly the same as it did before

Darren

110 USW BUILD THREAD - EXPEDITION TRAILER - 200tdi 90 BUILD THREAD - SANKEY TRAILER - IG@landroveranorak

"You came in that thing? You're braver than I thought!" - Princess Leia

28th Jul 2013 4:54pm

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