www.boxertrix.com

OK, I've taken the GS tubes off my bike today because I'm concerned about weak mixture at high speeds.
I've got the grey CCP which loads a very lean map into the Mototronic ( hence our 55 mpg / 95 bhp figures ) whilst the GS tubes shouldn't really affect the mixture either way at small to medium throttle openings at wider openings ( motorways ? ) for sustained periods it could be questionable.
It's a shame because I liked the better low down running, but for the time being at least, I'm going to er on the side of caution.
I don't really want to bypass the grey CCP or get another richer one because I like the fuel economy...
More research required .....

http://www.emeraldm3d.com/articles/emr- ... th-intake/

http://forums.bmwmoa.org/showthread.php ... ries-Bikes

kfrogzx7 wrote:OK, I've taken the GS tubes off my bike today because I'm concerned about weak mixture at high speeds.
I've got the grey CCP which loads a very lean map into the Mototronic ( hence our 55 mpg / 95 bhp figures ) whilst the GS tubes shouldn't really affect the mixture either way at small to medium throttle openings at wider openings ( motorways ? ) for sustained periods it could be questionable.
It's a shame because I liked the better low down running, but for the time being at least, I'm going to er on the side of caution.
I don't really want to bypass the grey CCP or get another richer one because I like the fuel economy...
More research required .....

http://www.emeraldm3d.com/articles/emr- ... th-intake/

http://forums.bmwmoa.org/showthread.php ... ries-Bikes

Hi Simon.

Understand your concerns, but things are better than you think.

AF ratio: my first dyno run was with the Gray code plug (+GS choobs). The AF ratio was 14.1 at 2000rpm and fell linearly to 11.5 at 8000rpm. Very safe numbers.

Now at motorway speeds - 70 mph if I recall from my last UK visit - and to which all motorists strenuously (ahem koff koff) adhere, you would be showing abt 3800 rpm, with small throttle opening and often looking for 6th, except that you're already in sixth, your AFR would be in the 13 range, and therefore quite safe. Mind you, you would also be down @ peak 30hp.

Until I twigged to the full role of code plugs, (while I was operating with the original 'gray' code plug in my 'S'), as well as the 0-4000rpm kick, I was also getting that 15-20% mileage improvement (well - unless I was giving it the berries above 4k rpm. Mwaahh harrharrr).

My 'rank amateur' thoughts re the GS tube effect, is that rather than increasing the airflow to the engine, the longer narrower tubes increase the velocity of the air already in the tubes/airbox, causing more cylinder pressurisation on each cylinder fill.

As for the AFR: yes - it should rise (lean out) - since more air for the same injector opening must equal a leaner mixture - but by how much? Given we're measuring a 12-13 AFR range at the speeds in question, whatever leaning out that has occurred has not taken us anywhere near the 14+ danger area.

Returning to basics, before the advent of AFR meters, have you heard any 'pinging' under a full throttle load at varying rpm? You'll know if you have, as you'll think your motor is suddenly full of ball bearings banging about. LOL

OK - going back a few steps: because the cylinders are receiving 'pressureised' air (= better engine efficiency), with a slightly reduced AF ratio, the result is more torque (power) for less fuel, which in turn equals less throttle opening for the same road speed.

Summing up: IMHO you won't sacrifice engine safety by using the GS tubes and the Gray code plug. Whats more you'll get even better fuel economy + better performance by using the combination.

If U choose to use a CCP plug without the '86' to '30' link then whooo hoooo - another 30hp, unless U give it the berries over 4k rpm, no loss in fuel economy.


Cheers mate.

Hope this makes sense.



HF

kfrogzx7 wrote:OK, I've taken the GS tubes off my bike today because I'm concerned about weak mixture at high speeds.
) I've got the grey CCP which loads a very lean map into the Mototronic ( hence our 55 mpg / 95 bhp figures whilst the GS tubes shouldn't really affect the mixture either way at small to medium throttle openings at wider openings ( motorways ? ) for sustained periods it could be questionable.
It's a shame because I liked the better low down running, but for the time being at least, I'm going to er on the side of caution.
I don't really want to bypass the grey CCP or get another richer one because I like the fuel economy...
More research required .....

http://www.emeraldm3d.com/articles/emr- ... th-intake/

http://forums.bmwmoa.org/showthread.php ... ries-Bikes

Orrr wait just a mo.

"I've got the grey CCP which loads a very lean map into the Mototronic (hence our 55 mpg / 95 bhp figure"

Not sure that's right at all. And you can definitely forget the 95bhp stuff. It's 60 bhp, for reasons set out below.

The CCCP table shows the Gray Plug is used to set the ECU for running on fuels with a RON less than 91 octane.

The last thing one should do with low octane fuel (but with unaltered compression ration) is to lean out the AFR, as this will improve the conditions needed for pinging (detonation), and is the the last thing one would want in a remote locatation with sh***y fuel. Do-ooh.

For starters, the first thing is to retard ignition timing, and the next IMHO would be to enrich the mixture, again - to lessen the risk of detonation.

Then there's the Swiss: well they all just think power is dangerous. So it's the Gray Plug for them. LOL

The reason for the Gray Plug fuel economy is that you have 30hp less to be naughty with, you wicked leather-jacketed rocker.

But as I've already said, using the GS choobs with the Gray Plug will result in only benefits.

HTH

HF

Surely airflow is ultimately governed by how much the filter can pass through it, and this limits the actual volume of air. The tubes merely take what's available to them and it's down to the specific geometry as to whether the actual air speed is higher or lower.

What actually matters is how much air the engine requires for a given running condition, and whether the intake design is capable of providing it. My feeling is that the intake and air filter set up more than adequately provides enough volume under any condition, so the GS tube mod is creating faster airflow at the inlet, presumably as a result of a reduction in diameter causing the airspeed to increase.

In summary, the air/fuel ratio is unaffected by this mod, it's just making a more efficient use of the incoming airflow.

Motocod wrote:Surely airflow is ultimately governed by how much the filter can pass through it, and this limits the actual volume of air. The tubes merely take what's available to them and it's down to the specific geometry as to whether the actual air speed is higher or lower.

What actually matters is how much air the engine requires for a given running condition, and whether the intake design is capable of providing it. My feeling is that the intake and air filter set up more than adequately provides enough volume under any condition, so the GS tube mod is creating faster airflow at the inlet, presumably as a result of a reduction in diameter causing the airspeed to increase.

In summary, the air/fuel ratio is unaffected by this mod, it's just making a more efficient use of the incoming airflow.

Could not agree more Motocod, although One could split the odd technical hair here or there should One be so inclined.

As for the real world result: whoo hooo.

Thanks HF & MC,
Yes, I see all that makes sense, I'll mull it over and maybe bung the GS tubes back in sometime - I certainly like the end product from their use !!

Do reflected "pressure" pulses play any part?

Corvus wrote:Do reflected "pressure" pulses play any part?

I think so Corvus.

When one inlet valve closes (thump), the air in the column behind compresses and rebounds along the tube as a +ve pressure wave.

When the wave reaches the open end it momentarily pressurises the air around the opening of the other tube, sending a pressure wave down that tube.

If the other valve is just opening, then viola, pressure to fill that cylinder, and vice versa.

Known as manifold pulse charging. (I've lost the link to where I found this:)

For best performance the facing bellmouths must be 0.75 the tube diameter.




The GS tubes have a natural resonant frequency, as well as higher order harmonics that ear a multiple of base frequency. x2 x3 x4 x5 etc

As rpm rises these various frequencies will go in and out of phase with the inlet vale openings, giving stronger and weaker reinforcement.

This is part of the cause of those wobbles in the torque curve.

Cheers.

.

HerrFlick wrote:

Corvus wrote:Do reflected "pressure" pulses play any part?

I think so Corvus.

When one inlet valve closes (thump), the air in the column behind compresses and rebounds along the tube as a +ve pressure wave.

When the wave reaches the open end it momentarily pressurises the air around the opening of the other tube, sending a pressure wave down that tube.

If the other valve is just opening, then viola, pressure to fill that cylinder, and vice versa.

Known as manifold pulse charging. (I've lost the link to where I found this:)

For best performance the facing bellmouths must be 0.75 the tube diameter.




The GS tubes have a natural resonant frequency, as well as higher order harmonics that ear a multiple of base frequency. x2 x3 x4 x5 etc

As rpm rises these various frequencies will go in and out of phase with the inlet vale openings, giving stronger and weaker reinforcement.

This is part of the cause of those wobbles in the torque curve.

Cheers.

.

Fascinating stuff HF.

But.....

I thought that altering the length of a velocity stack, even on a bike with no airbox and therefore with no link to any adjacent cylinders, would also give changes in the pulse charge rom zone? Or even on a single cylinder bike for example.

??

Yes Corvus, that's my understanding too.
I'm not sure of what the actual process is but the wave rebounds when it reaches the end of the tube and travels back down to the inlet valve.
That's what I've always understood anyway.

kfrogzx7 wrote:Yes Corvus, that's my understanding too.
I'm not sure of what the actual process is but the wave rebounds when it reaches the end of the tube and travels back down to the inlet valve.
That's what I've always understood anyway.

Oh absolutely right.

It's when you've got more cylinders to play with you can use these tricks to make things much more betterer.

HerrFlick wrote:

kfrogzx7 wrote:Yes Corvus, that's my understanding too.
I'm not sure of what the actual process is but the wave rebounds when it reaches the end of the tube and travels back down to the inlet valve.
That's what I've always understood anyway.

Oh absolutely right.

It's when you've got more cylinders to play with you can use these tricks to make things much more betterer.

Cool!

The gains on your torque curve graph looked healthy enough, with surprisingly little loss of max power.

Regarding effect on AF ratio, this phenomenon doesn't raelly seem to be interfering with actual air flow or the various devices monitoring mass flow. Just making sure that what air and fuel mixture does find its way in there is not allowed to be pushed back out. Keeps it tightly packed in there. At the rpm zone in question. Is that a fair comment?

Found this.

A decent article.

http://www.autozine.org/technical_schoo ... haust.html

Corvus wrote:

HerrFlick wrote:

kfrogzx7 wrote:Yes Corvus, that's my understanding too.
I'm not sure of what the actual process is but the wave rebounds when it reaches the end of the tube and travels back down to the inlet valve.
That's what I've always understood anyway.

Oh absolutely right.

It's when you've got more cylinders to play with you can use these tricks to make things much more betterer.

Cool!

The gains on your torque curve graph looked healthy enough, with surprisingly little loss of max power.

Regarding effect on AF ratio, this phenomenon doesn't really seem to be interfering with actual air flow or the various devices monitoring mass flow. Just making sure that what air and fuel mixture does find its way in there is not allowed to be pushed back out. Keeps it tightly packed in there. At the rpm zone in question. Is that a fair comment?

That's the only way I can understand it too Corvus. The AF ratios showed the mixture was not leaning out at all.

Funny thing is that the 'S' has smaller valves than the 'GS' yet makes more power. Huh?

When the GS tubes are put on an RT there's an 8 hp loss at the top end and not quite the same torque gains.

I can only explain this by the gas speed in the 'S' being higher than in the other engines.

In light of this it's sort of sad to see so much money being spent on exhaust systems, air filters, porting power commanders etc for not a lot of gain when the root cause of the problem was in the intake runners. Thing is, had a mate not put me on the RT forum I wouldn't have found this and I'd be out there spending big too. LOL.

I would imagine putting The Choobs on a bike with all the other stuff done would really bring it to life.

One Trixter, SL Parry (?), already had Lennie's sprockets when he fitted The Choobs a couple of years ago. Reckoned all hell broke loose at 4k rpm.

Hoping to fit my rocket sprockets v.soon.





I used the same concepts in the intake manifold on my 928 S4 Porsche. Got similar results. It was the same story there: ppl spending $$$$$ to get OK results but running into a ceiling where, for the money spent the gains weren't all that great.

I'm lucky to have stumbled across this stuff because let me make the 1100 and the 928 so much more fun for not many $$$. My CB750 Four cafe engine is the next on the list

Corvus wrote:Found this.

A decent article.

http://www.autozine.org/technical_schoo ... haust.html

You rotter.

That's just filled my head with more 'stuff' that I'll be thinking about in the wee small hours.

Cheers.