Know your bike 103 – TwinMax, any better tools out there?

[boxermania]

This thread is not intended to demean the readers mechanical knowledge or lack thereof. It is intended to dwell into the reasons behind the specific operation of the boxer engine and for that matter any internal combustion engine.

My philosophy has always been that ridding skill and knowledge of the mechanicals are both highly contributory to the sport of ridding.

That being said:

What does the TwinMax measure and are there any better measurements available?

The first, full correct answer will be showered with accolades from yours truly and be the recipient of a libation of his/her choice when we have the opportunity to meet face to face.....you must remember that I owe you one.......at my age my memory is not too good.....

[mcooperstein]

The twinmax measures vacuum presure and by comparing the relative pressure of one side of the throttle body to the other it can show which side is "high" or "low". It is therefore a pressure differential measuring meter.

Mark

[soggybottom]

I bought a twinmax and sold it to Dallara in Buy and Sell. There was something illogical about it that would not allow my brain to comprehend. I use the ole mercury tubes and do just fine with them. I once took my bike back to complain about a 1500rpm idle I could not lower, the tech readjusted it with twinmax and commented how exceptionally well it ran and said they'll idle high sometimes When I rode away it ran the same as the way I had it synced wiyh the cheap tubes.

[Boxer]

Soggy, I have that same issue. I have gotten so used to seeing the liquid levels of both sides as they go up or down, I just am puzzled by the visual readout of the needle bouncing back and forth. I totally understand how to get it where I want it, but it just doesn't make sense to me.

[Arbreacames]

What does the TwinMax measure?

It measures the average pressure differential between the two throttle bodies.

Are there any better measurements available?

A better measurement (more accurate) of pressure differential is done with a liquid manometer. Using low density fluids such as water or oil provides better accuracy than Twinmax or mercury columns. However, I think that you know all that, and I think that you are asking a trick question.
You are probably asking about a "better measurement" of throttle synchronization, not pressure differential. The ideal measurement would then be to measure the cyclic variation in the rotational speed of the engine. The Hall sensors possess that information because they time each 1/2 revolution. Car engines use that timing to detect misfiring in one of the cylinders. I bet you have found a way to read the Hall sensor signal, or am I reading more into your question than you intended?

[boxermania]

Ahhhh.... Carlos long time no hear.

I can't belive that you think my question is trick.....do I project a cloak and dagger image? What I really meant was: Are there any other means to attain the same or better results than with the TwinMax or manometers?

Actually the answer is obvious if one thinks of the cyclinder as a pump.....nough said.

Your mention of the Hall sensors does bring another interesting consideration.....that being said, I'll take a minute or two to briefly outline their operation and function.

The Hall effect describes what happens to current flowing through a conducting material - a metal, a semiconductor - if it is exposed to a magnetic field, resulting in a voltage (call it a signal) being generated in a field perpendicular to that of the applied current

The Hall effect sensors, and there are two in the boxers one for each cylinder, right behind the front plastic cover, generate a voltage that signals the ECU at the precise time that the ignition coil needs to send the high voltage to bridge the air gap at the spark plugs to sustain combustion.

[boxermania]

MC and boxer.....your answers are not complete.....errr, no cigar...

[Arbreacames]

What I really meant was: Are there any other means to attain the same or better results than with the TwinMax or manometers?

Actually the answer is obvious if one thinks of the cyclinder as a pump.....nough said.

¡Caray! It's still not obvious to me...
A pump, you say? How about this: Could you measure the compression in each cylinder with the throttles closed (idle position)?

[CycleRob]

I think mcooperstein got it partially right when he said:
"It is therefore a pressure differential measuring meter."

It's really measuring the difference between each cylinder's intake manifold vacuum, so it's a vacuum differential meter. The homemade oil filled manometer is hooked up the same way . . . . to read the differential vacuum. I would say the $10 homemade differential oil Manometer is the best one to use because of the oil's low specific gravity (less than 1.0) compared to Mercury at over 13 times heavier. One bad thing . . . . If your bike's synch is WAY OFF, it will suck the oil out of the tube into the cylinder that has the smaller throttle opening IF you didn't provide a much wider top section to allow air to pass by.

All the Mercury Carb Styx measure (I think) absolute vacuum, that is, relative to Atmospheric pressure.

[boxermania]

CYCLEROB is correct in that MC and boxer have the first part of the question correct. The TwinMax and the "homemade" carb stick with oil both measure diferential pressure.

Notice that I call it presure since vacuum is also considered pressure albeit negative. Robbie is again correct in that the mercury manometers are referenced to Atmospheric Presure.

When I asked about another measurement I was actually for FLOW as the answer.........I believe that flow would be a better measurement than pressure because it accounts for everything that the cylinder (the pump) drawis in and includes all restrictions such as the TB butterfly.

What you really are trying to balance is flow into the engine.....pressure pulses are the next best thing.....actually they are related via PV=nRT, theoretically speaking that is.

Unfortunately it is somewhat of a pain to perform this measurement unless you have ready access to the back of the TB. In my case I do and the process takes a couple of minutes, I use a very old UniSyn which was used to balance multiple SU/Zenith carburetors on British cars of the period, such as MG's, Triumph's, Austin Healey's and Jags.

Just in case you get the itch to look at one.....

http://r1150r.smugmug.com/photos/51684782-L.jpg

[bakernks]

And for some time I have wondered with all the electronic engineering we have in this world, if with a simple 2 cylinder engine like the 1150, it could not be engineered that the "A" cylinder TB flow be measured as part of normal data collection, and the info incorporated into the information collected by the ECU. The new ECU would use the flow measurements to operate a stepper motor on "B" cylinder side that allows the throttle imput to be constantly micro-adjusted to match the measured TB flow for "B" cylinder to "A" cylinder's measured flow.
Back-engineer something like this to fit all 1100-1150 engines, that's a lot of sales of a device that auto-syncs the TB. Within limits, and then, when it cannot, a valve adjustment is indicated.
Wishful thinking, and maybe not even practical without hydraulic valve adjustment being used, but it sure would be nice if the TB sync on this engine was automatic. The next Boxer should have both hydraulic valve adjustment and auto TB sync anyway. Listening, BMW?

[CycleRob]

boxermania,

I also have one of those old UniSyn flowmeters. Your pic needs to show the other side where the clear plastic window reveals the red barrel shaped "ball". The airflow lifts up the ball in the increasing diameter tapered tube indicatiing the flow rate. I think it's less accurate than the Mercury styx because of the short scale length. The UniSyn scale is too short to be accurate. Also, you have to use the same unit to measure both TB flows - - - hard to do when checking the on-throttle synch. Then there's sidewall friction. The technical term is hysteresis. (def= The lagging of an effect behind its cause) Mercury inside plastic/glass tubes has none, and I noticed stiction in my UniSyn, unless it was perfectly vertical, the last time I used it.

Being that manifold vacuum can be very accurately measured, compared to any user device that can measure airflow, the vacuum readings for all intents do represent the TB balance and therefore equal cylinder filling. Your mirrors then are less blurry.

[new2BMW]

...and this is why I think the boxer engine would be served better with two separate airboxes and two separate snorkles. The sensors are constantly re-adjusting to pressure in a an airflow that is being sucked at by the other cylynder.

I realize this is happening many times per second, and the average flow measurement is the key, but eliminating the backflow caused by the other cylinder should create a constant positve flow that is easier to adjust to.

[sweatmark]

Answers:

(Part 1)

Mark and Carlos and Rob should share the prize for answering "What does the TwinMax measure?" Diferential pressure is, after all, how the sensor's manufacturer describes the MPX2200DP transducer's function:

http://www.freescale.com/files/sensors/ ... PX2200.pdf

[Sensor part ID taken from the TwinMax schematic PDf found in the following message thread.]

Both Carlos and Rob claim that liquid manometer tubes are potentially superior to TwinMax in several ways. This conclusion is supported within the following ADV Rider thread:

http://www.bmwgs.com/forums/showthread.php?t=76230

And yes, it's true that many similar silicon differential pressure sensors have a "bias" P1>P2 versus P1<P2; I did some experimentation in grad school trying to use various pressure transducers in high-sensitivity, millisecond transient response applications, and ditched the differential-type sensors because of such "bias".

(Part 2)

Agreed: airflow is the best absolute measure for tuning each cylinder in the "pump", but I don't buy boxermania's measurement of flow at the throttle body via an old rotometer gizmo like the Edelbrock Uni-Syn. Why? 'Cause differences between each cylinders' intake tract airflow impedance would (a) mess up tuning, (b) not show up when measuring flow at throttle body with regular intake (all ducting, plenum, filtration) detached, (c) be better "measured" with conventional balancing methods.

New2's right that the best setup for the Boxer twin would be separate intake systems, one for each cylinder, and using hot wire/bead anemometers to measure mass-airflow for each side. Cost & complexity are the pitfalls of such a system. If we only had mass-airflow for each side (and the Hexhead's duel lambda sensors), then twin tuning would be pushbutton-simple.

Here's my question: why isn't fuel injected engine tuning more of a Plug-n-Play proposition in our delightfully computer infested age?!


Mark
Oregon

[CycleRob]

Plug-N-Play tuning will come about, out of necessity, when we get Drive-by-Wire computer controled throttle actuation. Fly-by-Wire technology is absolutely necessary in high performance jet fighter planes and the concept has just hit the automotive production car world this year with cableless throttle control. When I read about that changeover, all I could think about was [Ctrl][Alt][Del] - - - - although I would bet that all it will take to cancel an unwanted or errant throttle response would be to step on the brake.

When it appears in motorcycles, BMW, in light of it's CAN-Bus technology, may be the first. It would be easy for the new Motronic to measure each power pulse's effect on crankshaft angular acceleration as every power pulse occurs, and micro-adjust one throttle servo to equalize each individual cylinder's power contribution. That's when the synch will be truely, functionally perfect - - - flow and vacuum be dammed.

Until then, the TwinMax and liquid manometers give us almost perfect results.

There is a proven method to continually equalize the synch on 2 cylinder bikes. A large, 1/4" I.D. (5mm) balance tube between intake manifolds. Triumph uses it on older twins because the cable actauted system was not stable and IMO, the mechanical precision responsible for balance was not there. Yamaha even incorporated balance tube thinking into it's older 4 cyl bikes with a cast in head balance tube they labeled YICS (Yamaha Induction Control System). It complicated owner/operator service time by requiring the insertion of an elusive YICS block off shaft special tool to synch the carbs. The uninformed, not knowing what YICS is, will check the synch of a YICS equipped bike and always find it's perfect.

Will I drill, tap and install such a system on my bike?
No.
For me, the siamese twin Mercury columns are proof enough.

[new2BMW]

When it appears in motorcycles, BMW, in light of it's CAN-Bus technology, may be the first. It would be easy for the new Motronic to measure each power pulse's effect on crankshaft angular acceleration as every power pulse occurs, and micro-adjust one throttle servo to equalize each individual cylinder's power contribution. That's when the synch will be truely, functionally perfect - - - flow and vacuum be dammed

Yeah Baby! That will be exciting.

Rob; I think I read that Yamaha's latest 600 cc sport bike has an electronic operated throttle. Have you heard this?

[sweatmark]

Think there's any chance of BMW implementing Valvetronic for one of its motorcycle platforms? I thought there might be a (slim) chance that we'd see it on the new K bikes. The K bike four cyl. would more closely resemble initial 1.6L engine application, where variable intake valve lift would complement other "bleeding edge" techno-gadgetry like DuoLever and ESA. Not anticipating Valvetronic for the Boxers though!

Mark
Oregon

[boxermania]

sweatmark.......your input along with the asociated links is very timely as it affords the readers another perspective.

In respect to the flow measurement it is apparent that you didn't read my original post and if you did you missed the part where I state that I no longer run the airbox, but UNI pods directly on the TB's. That being said I've had the opportunity to try all the diferent methods discussed here and I can assure you that I can get a flow measure on my bike, before you zero the Twinmax, or find a place to hang the mercury sticks.

Let me show what I mean with a pic of my set-up

http://r1150r.smugmug.com/photos/17416639-O.jpg

Also as a point of clarification Edelbrock never made the UniSyn....they did make a plastic one that resembled a cork with a rotary flow indicator t designed to be used on the single and twin barrel downdrafts used on the VW's of the early 60's.

Certainly there is a fair amount of engineering that goes into the design of the airbox, along with some compromises, but that is better left for another thread. As Cyclerob mentioned the "balance tube" is an easy way to equalize the pressure pulses, specially in pancake type engines (diirectly opposed cylinders) with fairly large displacement.......

[Beemeridian]

4

[Arbreacames]

Anyone know where can I buy an inexpensive, accurate TB Sync? I prefer not to make one.

I'll sell you one!
Just kidding. Where in VA are you, perhaps there is a poster in your area who can lend you one. Are close to Hampton Roads?