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Snorkel help and tech wanted


Hybrid_From_Hell
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Yep,

Next after I have modded the roof sides in the new year is a snorkel, have a load of ideas as to how it will look, but I'm wondering as to the ID / OD size I really need... ???

So, anyone technical who can work out air flows ?

4500cc V8, RPM limiter set at 6000 RPM,

what size tube must I have as a minimum so as not to restrict air flow ?....

does the length of the tube have much of an effect ?

Also for those who have snorkels,

what is the ID OD of it, and engine type this will also give me a clue. :P

For some reason I have in my memory the fact Diesels have huge air intake requirements ????

Any help will be gratefully used !

Nige

Edited by Hybrid_From_Hell
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Just a thought (not sure whether it stands up or not but the engineering types will no doubt pitch in!)

Presumably a 2.5 litre turbocharged engine running 1 bar of boost, uses as much air as a 5 litre engine running at the same speed which is naturally aspirated? Twice as much air in each cylinder but half the displacement equals the same amount of air going in per revolution, surely?

If so then anything that will happily feed a 300Tdi (e.g. a Safari) will presumably be OK for a V8 up to 5 litres....?

IMHO anything will give "some resistance" it is just "how much resistance" that is the thing. I'm going to sling my Rebel snorkel in favour of a Safari which is on order and arriving in January, but that is mainly for waterproofing reasons. I have noticed, though, that if you take the front off the air cleaner can (i.e. bypass the snorkel and intake ducting completely so it is sucking air straight into the filter) it does seem to have more power.

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Just a thought (not sure whether it stands up or not but the engineering types will no doubt pitch in!)

As its four in the morning I have no intention of going to measure, but a standard piece of drain pipe is the diameter I've got, about 70mm I suppose, must admit I use a ram type top and didn't restict it at all, thats on a 3.9 v8, left the filter in, only problem I had was when first fitted and running LPG had to adjust the idle setting for the LPG, shes slightly down on power for road use, but I'm not a speed freak anyway, been running it two years now with no problems, shouldn't say that.

I won't run a safari, one I have problems with trees, two won't have a steel pipe I have problems with trees.

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Ive also got a Southdown after trying the paddocks version (mushroom top and a nightmare to seal confidently) and the safari (sticks out the side to far, not really compatable with a cage and always worried about snapping it on trees.) I love the southdown one. Easy to seal, easily adaptable to attach to a roll cage and looks really bling too. (Not cheap though)

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My snorkle is 3" OD.

Stephen was right except, your engine will rev a lot higher than a 300TDi.

At say 2000 rpm, the 300TDi will probably flow more air than your engine, because your throttle will be only part open, whereas a diesel does not have a throttle and is always wide open.

When your throttle is wide open at higher revs than a 300TDi can reach, your engine will be flowing more and a single 3" snorkle will probably limit top end performance.

If you want a lot of top end performance you should consider dual 3" snorkles.

Great snorkles can be made from 3" stainless exhaust tubing and mandrel bends. The scoops such as from Safari are a little larger than 3" inside, but they can be sleeved to suit.

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Guest diesel_jim

I used to have an email from an American chap on the D-90 site, with all the formulae for working out the resistance in the tubing and bends of a snorkel... it was a bit anal to say the least!

Best bet, is "big is best".... use 3" pipe and be done with it!

as a side note, on my 300 when i was running about 24psi of boost, the single snorkel would strangle the air flow quite a bit, so i stuck on a second. i think they look good with 2 snorkels....

HPIM0421.jpg

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Nige / Tonk

I will be making it out odf steel, so ta but no ta. (thought 5mm wall so its strong)

THAT WAS A JOKE FFS :P

Can't use the bought ones as the fittings are all wrong, it will have to be a homemade jobbie.

Trying to use as smaller ID as poss, but have horrible feeling that 3 inch will be restrictive, trying to actaully find something like the anal info above where I know what the ID has to be. wikll go most probably from roof down windscreen along top of wing through the black grill thingy and then join to a Homemade air box and filter (being made)...one poss is to just have connected for off road, ie remove hose, but rather it was up to the job and on all the time ?....

Trying to aviod twin snorkels, 2x the work, and complex, and bit Yoooow Bling innit ? :)

I have "aquired" some serious big bore pipe, but getting it to fit neatly will be a nightmare hence the post.....

Some clever little S must be able to work out the bore size versus air flow :blink:

Maybe ?

Nige

Edited by Hybrid_From_Hell
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Nige - so it it the 0-60 time or MPG you're worried about on a 2-ton brick-shaped vehicle with mud tyres? :rolleyes:

You might try asking Mr Lund, he sems to know his airflow - ISTR he machined a "regulation" restrictor for the racer that flowed more air than the original open system did :blink:

Then again, B&Q do some very smart black drainpipe, you know... :ph34r:

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Fridge - Steve's (@ Lund) restrictor was a very nice job (34mm diameter in case anyone cares), but it did knock 50 bhps off the engine (relative to running without) and about 7 lbft off the max torque (which also shifted 400 rpm down).

That's a very good result for restricting the airflow but it certainly didn't IMPROVE performance... :(

Nige, I think the flow of your pipe has more influence on air restriction than the length of it - the fewer curves you have, the better. This is why sticking a straight bit of pipe on the air intake to test the difference won't give you a good idea of the final outcome of your snorkel. Try to avoid any bends you can.

Also defo a larger diameter pipe will give far less restriction than a smaller one (I don't think it's a linear relationship) - use the largest you can.

Regarding air demand, I suppose a first step could be to say that with WOT at 6000rpm your engine will require the volume of the engine multiplied by the number of times it needs to be filled per minute. At 6000 rpm, the cylinders are filled at a rate of 3000 times per minute (4-stroke, so every other revolution):

4.5 x 3000 = 13500 litres / minute (this of course is filling each cyl completely).

Gives you an idea of possible theoretical max intake, but I guess it'd never get near this figure in reality.

I'm going for 2 x 3" pipes on a 3.9 ltr (I'm using the cage as a windscreen surround, and taking air through that to the engine, from above the windscreen - so no extra pipes, but a few extra bends en route...).

>"Some clever little S must be able to work out the bore size versus air flow"

I'm not claiming to be that person, but there's more to it than that... Like the pressure differential, the geometry etc... Air has inertia... :(

Hope there's something useful in those random thoughts somewhere...

Diesel_Jim - have you still got that email? :)

Al.

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I will be making it out odf steel, so ta but no ta. (thought 5mm wall so its strong)

PMSL! :lol:

I had thought of the revs thing but in practice how often do you rev a V8 over 4000rpm in normal use? I find if I'm in a big F hurry keeping the Disco between 3000 and 4000 it goes like &&&& off a shovel, over about 4500 all you really get is more noise so I don't bother. Also I think V8s sound best as they pass through about 3500 with foot nailed to the floor :)

Another thought: because the cross sectional area of a pipe increases as the square of its radius, a 3.5" pipe is actually 36% bigger in x-s than a 3" pipe - so you can have a useful increase without having to look like an oil rig!

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surely it can only flow as fast as the smallest restiction (ish). could have a foot diamter tube as the snorkel but if its gotta go through a 1" hole at the intake then thats gotta be the most restrictive point? i'm only using wild dimensions to show a point, and i do realise that the ram effect from a large bore tube will force through a smaller tube, guess i've just blown my theory out of the water then :blink:

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If it is any use

My Dakar freelander uses 4.4V8 RR3 air boxes which are around 85mm hose size but there is no reduction into the engine main air intake which is the same for the 2.0lt.

I would be temped to go for 3 1/2" if you can as you engine will need more air than my 4.2 and when I am pushing he I can hear her sucking very loudly which in my mind meens the snorkell is restricting her.

All the newer Land Rovers have much grater air flow

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surely it can only flow as fast as the smallest restiction (ish). could have a foot diamter tube as the snorkel but if its gotta go through a 1" hole at the intake then thats gotta be the most restrictive point? i'm only using wild dimensions to show a point, and i do realise that the ram effect from a large bore tube will force through a smaller tube, guess i've just blown my theory out of the water then :blink:

Yeah, kinda. That would be the MOST restricive point, but not the only factor in total restriction...

If that one inch bit came at the end of a convoluted path of tube with bends, diameter changes etc along it, restrictive filter..., the total resistance would depend not only on the one inch bit, but also the contributions from the other bits - even if you took out the one inch bit it'd still flow badly...

Also the shape of the change from one diameter to the other has a massive effect on how much of a 'restriction' that small diameter actually is.

Like Fridges example of Steve's restrictor for FIA regs - it's a long tube in fact, not a 'restrictor plate' as such, to enable good flow through the 34mm section. If he just used flat plate with a 34 mm hole in, it would have been er... ****e.

Edited to say (having just read Jules' post), that I agree with the above, and if you are only using one pipe, make it a properly fat one.

Al.

Edited by Astro_Al
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Some misc ramblings

A 2" pipe has a cross sectional area of ~20sq cm

A 3" pipe has a cross sectional area of ~45sq cm - more than double ;)

Using Al's 13,500 litres per minute at full chat

The air-speed through the snorkel of 17km/h which whilst fast doesn't sound un-reasonable.

A bog stock 3.5 running maybe 5,000rpm has a trumpet on the air-intake thats what ? Maybe 1.5" across

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I can't do any sums to back it up (forgot the content of my fiziks A level years ago) but I think pressure drop in a pipe due to internal friction etc probably follows much the same theory as voltage drop in a wire. So a short length of 3" tube will have a certain pressure drop, make it 10x the length and it probably increases quite a bit, though whether 10x or not I don't know.

So in the same way as you can shove 240V down a wire through up to about a mile or so, if you try and do it for 10 miles there's a lot missing at the other end. In the electrical model you can increase the wire thickness (reduce resistance) and/or bump up the voltage (a bit like increasing turbo boost) but in a naturally aspirated engine all you can do is minimise the losses, i.e. make it a bigger pipe (less resistance per unit length) to try and get as much as possible of what goes in, out the other end without a pressure drop.

An extreme example would be to make an engine like a 400KV power line - in theory you could feed Nigel's Eales through a drinking straw if you put about 100 bar boost on the end, though the turbo lag might be a bit epic :D

Oooer that nearly sounded as if I knew what i was talking about :blink: now I need to go and sit down :unsure:

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I agree with Bogbuster's analogy.

Increasing the wire thickness is the same as increasing tube diameter - i.e. minimising losses, and I suppose wire junctions equate nicely to tube bends in terms of resistance to flow.

So apart from minimising these by getting fatter tube and fewer bends, the only option you have as far as I see it, is to chuck a sodding great supercharger on the top. Which is analogous to increasing the potential difference.

I'm liking this idea. B)

Al.

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length of tube has to have summat to do with it. take length of carb bell mouths/trumpets for example, i always thought short ones were for acceleration and long ones gave better top end, maybe i'm wrong though :unsure:

Yeah, but are we talking about tuning compression / rarefaction wave pulses to improve air intake into each cylinder during valve-open times, or are we talking about how adding a snorkel to the intake is going to make it harder for the engine to breathe in general?

As far as I know, no-one has ever tuned the length of their snorkel? I don't see why you need to, since you already have the trumpets in the intake (and presumably if you care enough about engine power, you've done the same with the exhaust header lengths for scavenging).

Al.

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