www.boxertrix.com

Yes - I know that every dyno gives different readings, but this was an exercise to ensure that the bike was no longer running too weak! The lower curve is exhaust mixture. This was on a dyno that subjects the bike (or car) to load - not like a lot of basic dyno's that do not.




The spec. is:

Laser 'road' Boxer Cup exhaust system with Y-pipe and baffles removed.
K & N filter
K1200RS fuel pressure regulator
Oxygen sensor disconnected
Cat Code plug removed
Exhaust headers cleaned of excess weld (maybe this is actually worth doing!!)

However - it is not all good news. The 'red' curve is with the mods to the inlet (see below) that I have been suggesting to all and sundry. It shows that if you are after power - then I WAS WRONG - DON'T DO IT!!!! However, the graphs do show that (apart from one small section) between 3500 and 6500 the inlet is flowing more air and for 3800 to 5500 is developing the same or more power than with the standard inlet pipe. This is backed up by seat-of-the-pants feeling. Much more in the mid-range and the loss in the upper ranges is not really noticeable on the road.




Sooner or later I will further open out the holes to try and increase the effect.

Incidentally, later runs (we did 14) with and without the cat code plug, showed that the cat code plug weakened the mixture pretty much evenly throughout the rev range, but made little or no difference to the power.

The most impressive thing was the noise of the bike at high revs in the dyno room!!!

Sandbar

noise was prob something to do with your spec.
quote 'with Y-pipe and baffles removed'

OOPS!!!

Yes - my mistake. I should have written

".................exhaust system (baffles removed)with Y-pipe."

Nevertheless it was a mighty impressive sound!!

Sandbar

I used to run mine minus the front 2 thirds of the snorkel/air duct thingy......it seemed to have much better get up and go...never got it on the dyno tho...may be worth a try on yours??
Bailey.

bigblackfalco wrote:I used to run mine minus the front 2 thirds of the snorkel/air duct thingy......
Bailey.

Interesting idea! Somebody suggested running without the snorkel at all!!
(Apparently instant arrest in Germany - cos of all the intake noise).

My unscientific theory was to open it out immediately after the most restrictive part in an area where there might be a bit of a vacuum, and hope that the speed of the air through the restriction might assist in bringing more air in via my mods!! Some garbled theory I vaguely remember from my schooldays.

It would appear that there is some sort of trade off between top-end power and mid-range when playing about with the air intakes. The tales of results from the Induct would seem to bear this out. Maybe that restriction is a very clever and carefully researched shape!!

Onwards and upwards.

Sandbar

I think you may be right.

The Lennies allows the engine to spin up faster but the initial bite of chunky torque seems to be diminished. Can't say for sure cos I need to adjust the vlave clearance and balance throttle bods.

After the KTM the BMW is a smooth as a straight 6!

sandbar wrote:

bigblackfalco wrote:I used to run mine minus the front 2 thirds of the snorkel/air duct thingy......
Bailey.

Maybe that restriction is a very clever and carefully researched shape!!

Sandbar

You havin a giraffe ?
The intake goes round the side cos they didn't want to lose any more of the (already) pitiful range by routing it thru the tank like what the racers do and the bodywork had already been decided. Always a compromise in packaging a bike and that's one of ours.

boxerpan wrote:
You havin a giraffe ?

Always - always!!

Couldn't agree more about the basic shape of the snorkel pipe - BUT!!
Where it turns to go round the edge of the battery it has a seemingly unnecessary narrowing of the already narrow air path. As it is a moulded part, it does not need to be quite that narrow at that particular place. I was merely trying to suggest that perhaps it is a succesful attempt to speed up the airflow and one that has more effect at higher revs!!

Has anybody had any experience of running without the inlet pipe or do they know of anybody that has?

Sandbar
www.sandbarcomposites.co.uk

Former Trixter Darth 1100s used to run his S without the inlet, I'm sure there was a mention in one of his posts.

Steve

Ran the s on a dyno at a nearby H*rley shop.
Bog std everything minus cat. Yellow cat code plug.
82bhp, 62 odd ft lbs torque. Reasonable fuelling?

Nigel B

sandbar wrote:I was merely trying to suggest that perhaps it is a succesful attempt to speed up the airflow and one that has more effect at higher revs!!

That doesn't really figure. The need to speed up the airflow by adding a restriction would be at lower revs - at higher revs the air's being pulled in fast enough by the natural pumping action of the engine. This is why, when manufacturers use a superbike engine in a naked bike (e.g. Hornet 600/900, CBF1000), they fit smaller diameter throttle bodies or carbs. This tends to help the engine efficiency lower down the rev range by increasing intake velocity but it strangles the engine higher up because there's a limit to how much air you can pull through a small opening.

So IF the restriction in the intake were there on purpose it would be to benefit torque lower down at the expense of power higher up. I can't imagine that the designers would have made this compromise willingly since they were trying to tout the S as having the 'most powerful boxer twin ever'. And in something that's being sold as a sports bike (even if it isn't really) you don't normally restrict peak power to give drive at lower revs. It's just bad/lazy design.

I think you slightly misunderstood my point. I was trying to say that faced with the bad/lazy design of the battery placement, and the necessity of having to route the air intake around it within the bodywork, it seems that BMW may have done a fair amount of work on the exact shape of the snorkel - in the same way that F3 car racers do a lot of work on the shape of their intake system because they need to get their air through a tiny aperture.

There is no doubt that the restriction on that corner ( bearing in mind that it is a moulded part) is a much smaller size than it needs to be. The cross sectional area of the narrowest part could easily (at no cost) be twice as big

Maybe, faced with the design restriction, the shape is cleverer than we give them credit for.

Just a thought

sandbar

Having studied fluid dynamics in a past life, I would have thought that a narrowing of a pipe of fixed length would have made no difference to the airflow. Only sharp areas withiin the pipe that could cause turbulence would affect it.
The narrow area would cause the air to move faster and create a lower pressure in that area, but this would have the affect of trying to suck air from the wider, slower moving air. By having a fixed length tube with no holes along the length, there should be a constant flow of air which would feed the filter at a more constant rate. If that tube were removed, it might give a greater flow at maximum revs but would be detremental to power at lower revs.
The best experiment would be to try and vary the length of the tube, on a dyno, and see what that does. The flow through the tube of a given length could be calculated by the smoothness of the internal surface and the average diameter of that tube. To put a hole in the outside of the narrowest area (and I don't suggest anyone has done this) would cause the low pressure area to suck air into that hole and therefore slow down the air upstream of the hole.
The only thing that might help is to check where the tube bends, as that could be an area where turbulence is produced.

sandbar wrote:There is no doubt that the restriction on that corner ( bearing in mind that it is a moulded part) is a much smaller size than it needs to be. The cross sectional area of the narrowest part could easily (at no cost) be twice as big

But isn't that the theory behind a lennies induct? Aside from removing the turbulence-inducing 'ribbed' wall of the front (flexible) part of the standard intake it ensures that the cross-sectional area is as large as possible all along its length.

It should be relatively easy and cheap (aside from the dyno time!) to test your theory:

Figure the bike using the standard intake, then cut out the restriction on that corner, plate it over with aluminium (sealed with silicone or similar) or even plastic model-making sheet to give a less restrictive cross-section, replace the intake and then figure the bike again. The only change you've made then is removing the restriction at that point which is probably about as controlled an experiment as is feasible.

Of course there may be little or no different in power - the restriction might just affect throttle response which wouldn't show up on the dyno, but would when riding.

I may be missing your point slightly, but as you say the restriction is greater than it appears it needs to be. This is a different situation from the F3 example you gave where the regulations specify a maximum inlet size and engineers work to maximise performance within the constraints of that regulation. In the case of the intake on the S there was no such regulation restricting the size - they had more of a free hand.

Of course the restriction may be nothing to do with engine peformance at all - there's always a chance that it's there for noise reasons.........not to restrict the air getting in but to restrict the induction noise. After all, any aftermarket induction mods (K&N/SJ, lennies, drilling holes, removing the duct or part of it) serve to increase induction noise to varying degrees, almost certainly making the bike louder than BM would have wanted. Maybe they really are cleverer than we give them credit for

madman wrote:Having studied fluid dynamics in a past life, I would have thought that a narrowing of a pipe of fixed length would have made no difference to the airflow. Only sharp areas withiin the pipe that could cause turbulence would affect it.
The narrow area would cause the air to move faster and create a lower pressure in that area, but this would have the affect of trying to suck air from the wider, slower moving air. By having a fixed length tube with no holes along the length, there should be a constant flow of air which would feed the filter at a more constant rate. If that tube were removed, it might give a greater flow at maximum revs but would be detremental to power at lower revs.
The best experiment would be to try and vary the length of the tube, on a dyno, and see what that does. The flow through the tube of a given length could be calculated by the smoothness of the internal surface and the average diameter of that tube. To put a hole in the outside of the narrowest area (and I don't suggest anyone has done this) would cause the low pressure area to suck air into that hole and therefore slow down the air upstream of the hole.
The only thing that might help is to check where the tube bends, as that could be an area where turbulence is produced.