intake snorkel

[F104]

i can't get my head around this. On a 4 cylinder 4cycle you have basically one intake valve open all the time, so a fairly constant flow of air thru the intake system. On our boxers we have a massive intake box behind the airfilter, and one valve opening about every 180 degree crank degrees. So the intake box works as a buffer to supply each cylinder with air when the intake valve opens.

The intake snorkle is 45mm dia at the intake. To keep up with the engine at 8000 rpm, assuming no volumetric losses, and no intake friction losses either, you look at 180kph/115mph (average?) intake air speed. Now is that a restriction, or not? I think it is.

PS it took mine off, found a leaf in there large enough to block 30% of the airfilter. That's another issue with this design, whatever it sucks up stays in there untill you take it apart or it decomposes.. Hence the very protected inlet i guess, but that also implies you need negative intake pressure to accelerate about stationary air to 110mph when you twist the throtte

any views?

 

[Dawg]

No, not really.....

 

[OldCroc]

I have never understood why the air intake is funneled or restricted - especially as the mouth is not directly in the air-flow. Is this all to do with emissions control?
My TDM 900 had a system whereby the air intake had two funnels - one bigger than the other. The smaller one was controlled electronically and shut off at lower revs resulting in very snatchy throttle response. A simple mod disabled the butterfly valve ensuring maximum air and this transformed the rideability of the bike.
Therefore - in my simple mind - more air = happier rider.
I have read elsewhere that there is a bigger snorkel available for the GS but cant find where this was.
OldCroc

 

[davidblythe]

a snorkel can lose a decibel or two on noise levels

did the 3*3 mod on a DRZ400 and de baffled the airbox on a new Triumph Bonneville, both ran significantly quicker esp in the bottom and midrange once rejetted,

having messed around with removing the snorkel imho the GS airbox is restrictive, the midrange leaned out so much,the engine wouldnt accept full throttle on acceleration,

having now got to grips with the PC5 and auto tune, once I can make a substitute plate for the snorkel, will restart testing

 

[davidblythe]

the thread has inspired me to cut the snorkel down

1st stage to just infront of the sidepanel fixing point

off to play to see how the autotune compensates for it

 

[London Mole]

Defender style snorkel

What about a snorkel like those on Landies?

Could help ride in very deep waters...

 

[ducatiparts.110mb]

the thread has inspired me to cut the snorkel down

1st stage to just infront of the sidepanel fixing point

Be careful. If you end up with a sharp edge to the tube you'll reduce the flow capability compared to the smoothly radiussed entry that you get with the oe snorkel.

If you alter the length you'll also affect the ram tuning of the aribox and the resonance of the duct. I'm not saying that you can't improve things because bikes are built around a whole heap of compromises, but I wouldn't assume that you can easily improve things.

Also don't overestimate the tuning effect of making a lot of noise. Loud bikes (chopped about by the owner) feel like they're faster because all that racket kids you into thinking you're really flying but often once the novelty wears off there's not much difference.

To really benefit you'll need a change in the fuelling or as pointed out above all you'll get is a weak mixture.

If you google for "Induct" and "Boxer Performance" you'll find the induction pipe mentioned.

Mark

 

[davidblythe]

I dont believe there is a ram air effect with this airbox certainly not in the 70 to 100mph speeds I tend to ride at

take your point about the radius on entries but am still messing around,but it does remind me of shortening and reshaping the intake on 2 stroke Delly VHSA carbs

The Autotune should remap for any leaness and have my own mad mile for test runs

if it doesnt work, then £50 will get an airbox off ebay

 

[red line]

the length and diameter of the snorkel affects fuelling, and so does the exhaust. the snorkel as been optimised for a wide rev range. if you change these dimensions you will affect performance, good or bad as the air flow resonates down the tube to the intake valves and back again, and this pulse helps to fuel the bike, the same at the exhaust works to expel gasses.

 

[red line]

anyone tried http://www.rainbowbmw.com/wshop/ind...eyword=intake&category_id=121&product_id=2524

 

[ducatiparts.110mb]

I dont believe there is a ram air effect

I wasn't referring to the ram air effect of riding at high speed into still air, instead I was referring to how the air flow within the tube resonates, exactly as described below.

the length and diameter of the snorkel affects fuelling, and so does the exhaust. the snorkel as been optimised for a wide rev range. if you change these dimensions you will affect performance, good or bad as the air flow resonates down the tube to the intake valves and back again, and this pulse helps to fuel the bike, the same at the exhaust works to expel gasses.

As you shorten the tube, as well as altering the frequency at which it resonates, you make it more sensitive to those frequencies, ie with the tube long it will resonate and have a good and bad impact on engine performance but with low peaks of positive and negative effect.

With the tube shortened you'll not only make the peaks and troughs occur at higher frequency, but you'll make them bigger.

 

[F104]

the length and diameter of the snorkel affects fuelling, and so does the exhaust. the snorkel as been optimised for a wide rev range. if you change these dimensions you will affect performance, good or bad as the air flow resonates down the tube to the intake valves and back again, and this pulse helps to fuel the bike, the same at the exhaust works to expel gasses.

I think that is a correct statment for the intake tracts from the filter housing to the inlet valves. But I can't see the snorkel having any effect, in my view it's a simple inlet to the filter housing, and sees a fairly constant airflow. The filter housing is the "buffer", hence the size of it (it must be 3000-4000cc or so).
The snorkel might be there to get and coldest air during all conditions, and dampen intake noise. I'll have a go in the weekend, removing it completely and find a way to keep the filter element in place

 

[OldCroc]

I'll have a go in the weekend, removing it completely and find a way to keep the filter element in place

That was going to be my next question - why have a snorkel anyway and what would be the effect of removing it completely?

OldCroc

 

[red line]

i did my thesis on this and spent many hours in the lab with a test engine and dyno. the filter housing also has a huge effect on fueling and performance.

remove the housing and see for yourself....

 

[davidblythe]

would be nice to read a pdf of the thesis, like to see comtempary updates on work done by Jennings and Bells in the 70's,

my thesis was 25 years ago on the SCOOT (Split Cycle Offset Optimisation Technique) Traffic systems now widely in use, may add with no contribution from my work

 

[ducatiparts.110mb]

But I can't see the snorkel having any effect,

Whether you consider the intake valve 'gulping' air in from the airbox via the intake port, or the airbox 'gulping' air in from the outside world via the snorkel, the effect is the same. In either case you've got a cyclically varying flow through a tube that has a certain length and diameter.

In either case you'll set up resonances along the tube dependant upon the dimensions of the tube. The greater flow fluctuations in the intake tract set up greater resonances, and the airbox does act somewhat as a damper to smooth the flow making the effect of the snorkel less noticeable, but nevertheless if you alter the snorkel you'll alter the way the engine feels across the rev band.

RedLine - if a copy of your thesis is available I'd also be very keen to read it.

 

[Brian ROSEN]

What are we trying to achieve?

Are we looking for increased fuel consumption or greater tyre wear? Both can be achieved more easily by simply opening the throttle wide at every opportunity. Even here in france where the roads are relatively empty and on the autoroutes an indicated 90 mph is not likely to offend anyone, the standard GS will easily outperform virtually every car and any bikes except the racing replicas. If you are looking for more power buy the 1000SS - although nthat sort of hp is not legal here;

 

[davidblythe]

Are we looking for increased fuel consumption or greater tyre wear? Both can be achieved more easily by simply opening the throttle wide at every opportunity. Even here in france where the roads are relatively empty and on the autoroutes an indicated 90 mph is not likely to offend anyone, the standard GS will easily outperform virtually every car and any bikes except the racing replicas. If you are looking for more power buy the 1000SS - although nthat sort of hp is not legal here;

your right, I am never going to have fun or think for myself again, going to join the IAM and smoke a pipe from now on whilst maintaining the status quo

am currently building an engine from a case that has been tigged to open the crankcase to allow much bigger transfer ports, have sourced a conrod from a Jap outboard, mated it to a rg500 main bearing, running a kx250 piston increased the capacity to 248cc from 200cc, barrell has been welded to suit the case and accept a much larger reed valve, skimmed the head and reprofiled it to suit the revised crown height, using packer plates to achieve the port timings i want with a 2mm increased stroke on the crank. ported the exhaust port to 65% increased the timed area of the transfer by widening the secondary tfr aiming more at the centre of the piston, raised the boost port and uisng a reedvalve from a banshee, exhaust will be built to suit the port timings

to what effect, to get a geninue 85mph out of a Lambretta from 62mph as standard, 25bhp instead of 8bhp

why, because I can and standard bores me rigid

Culturally we stand a world apart, no offence meant

 

[Packer]

....to what effect, to get a geninue 85mph out of a Lambretta from 62mph as standard, 25bhp instead of 8bhp...

Do you have the optional rack fitted on the front of the leg shield? If so I recommend attaching a half bag of cement to it.

25bhp? how wide will the power band be? Is there a mod to improve the cable gear change these days?

My LI 150 with standard engine performed somersaults and pirouettes shortly after being introduced to ice at about 50mph on a corner some 38 years ago

 

[red line]

RedLine - if a copy of your thesis is available I'd also be very keen to read it.

it was 23 years ago, and the sad thing is, besides being 12k miles away, I dont know where it is exactly. all i know is, its in a box on about 20 stiffy disks in a family members house in Cape Town

or you could contact the University of Stellenbosch Mechanical Engineering Department