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thehollowmen
14th June 2005, 20:47
I know this sounds really silly, but how would I tell if the CDI is able to advance or retard my timing automatically?

I pick up a 11.5:1 650 fuel injected V twin tommorrow and I'll get less power on 91 if it retards the timing. On the other hand I could get a small amount of SDA (alcohol + small amount of methanol) from work to boost the octane (the manual says 10% etOH or 5%mtOH in petrol) and if it advances... :ride: happy days for me!

Motu
14th June 2005, 21:10
Advance is built into a CDI by just the way it works...as it goes faster the magnetic flux gets cut earlier or some such...it's only a few degrees,but enough for most engines.You can check it with a timing light if you have a hole with timing marks...but they spray oil out.I've checked enough to know that it just works and don't bother anymore.

[edit] - oh,I see - you are wondering if it with change it's advance curve by itself if you change the fuel????? It would need to be closed loop computer controled ign to be able to do that...and bike systems aren't very sophisticated.

thehollowmen
14th June 2005, 22:39
Thanks for explaining that :-) Motu, karma heading your way.

I think I'll stick with 91 for the time being and give 96 a shot when I can really rev the hell out of it.

Brian d marge
15th June 2005, 02:40
Advance is built into a CDI by just the way it works...as it goes faster the magnetic flux gets cut earlier or some such...it's only a few degrees,but enough for most engines.You can check it with a timing light if you have a hole with timing marks...but they spray oil out.I've checked enough to know that it just works and don't bother anymore.

[edit] - oh,I see - you are wondering if it with change it's advance curve by itself if you change the fuel????? It would need to be closed loop computer controled ign to be able to do that...and bike systems aren't very sophisticated.

As far as I know the Cdi works by Hall effect which is an electromotive force which is caused by the interaction of a steady state current in a magnetic field . The magnitude of this emf is proportional to the aount of current flowing and the intensity of the magnetic field . they then switch this by using resistors , or other forms of circuit resistors , to a Scr or a from of transistor , this discharges a capacitor which discharges through the coil a a rapid pace causing a bigger voltage build up in the coil

( i am doing that from memory so ,,,any corrections welcome . )
The advance curve is just made by using differing value circuit resistors, , so at a lower Rpm when the pick up is producing X value Emf by using a lower/higher value resistor the capacitor will dump through the coil earlier/later than before ie advance retard the timing ...
Programable ignitions just use a chip to do the same thing , ( they also sometimes have Knok sensors )
Which is what will happen if you have a higher comp engine and use a lower octane fuel, you will need to retard the ignition to guard against detonation,

Sorry I am watching the 250 race just before going to bed , so any discrepancies sorry bout that , but you should get the drift ...

Good combustion chamber design you can run nearly 13 to one with very little knock on 91 unleaded ...
Most modern jap bike are designed to run on 91 unleaded , if you use 96 in an unmodified engine you run the risk of cold fouling the plugs, They just cant quite burn the crap of and the spark has a hard time

If you were to use methanol in a injected v twin, then the oxygen rich mixture will change the exhaust temp ( usually around 1425 ish ) which will fool the ecu in to injecting more or less fuel ( I cant remember if you use larger or smaller jets in a methonol carb bigger I think ....ie the INjection system will compensate ..not the cdi ......( as motu said the closed loop system will delay signal letting it fire the coil at the most suitable advance/retard position)
The system will run the most suitable advance curve , to guard against detonation , the power loss will be ( I think 9/75 th of not a lot )

Stephen
BTW methanol doesnt like aluminuim I think . becareful ......

What?
15th June 2005, 05:32
I pick up a 11.5:1 650 fuel injected V twin tommorrow and I'll get less power on 91 if it retards the timing.
How do you work that out??????
Fuel it with what the manufacturer recommends. These days, most likely to be 91 (which just happens to be more flamable than 96 - higher octane ratings are to reduce detonation, not increase power)

Motu
15th June 2005, 06:18
No Hall Effect in bike systems...no square wave signals,they are more akin to a lawnmower than a car - but then I have never worked on a modern bike ign system.

thehollowmen
15th June 2005, 06:50
How do you work that out??????
Fuel it with what the manufacturer recommends. These days, most likely to be 91 (which just happens to be more flamable than 96 - higher octane ratings are to reduce detonation, not increase power)

Easy. If it normally runs on 96 at high compression, then that's all well and good and I get my horsepower.

However, if I put in 91 and it doesn't like it, the CDI will retard the timing until it doesn't ping and everything is stable. However in retarding my timing it will give me less power.

*ponders*

logical for someone without a mechanical background... problably more manure to the people with one.

thehollowmen
15th June 2005, 06:53
( i am doing that from memory so ,,,any corrections welcome . )
The advance curve is just made by using differing value circuit resistors, , so at a lower Rpm when the pick up is producing X value Emf by using a lower/higher value resistor the capacitor will dump through the coil earlier/later than before ie advance retard the timing ...
Programable ignitions just use a chip to do the same thing , ( they also sometimes have Knok sensors )
Which is what will happen if you have a higher comp engine and use a lower octane fuel, you will need to retard the ignition to guard against detonation,

(SNIP)

If you were to use methanol in a injected v twin, then the oxygen rich mixture will change the exhaust temp ( usually around 1425 ish ) which will fool the ecu in to injecting more or less fuel ( I cant remember if you use larger or smaller jets in a methonol carb bigger I think ....ie the INjection system will compensate ..not the cdi ......( as motu said the closed loop system will delay signal letting it fire the coil at the most suitable advance/retard position)
The system will run the most suitable advance curve , to guard against detonation , the power loss will be ( I think 9/75 th of not a lot )

Stephen
BTW methanol doesnt like aluminuim I think . becareful ......

Thanks :-) The CDI advancing and retarding timing, I've seen that in some high performance cars almost exactly like you say.

It said it should be ok in my manual, for 5% methanol or 10% ethanol. One of them said something about 'stabilisers' so I might have a good read up again before I put anything into the bike.

scumdog
15th June 2005, 06:58
You MAY have the wrong end of the stick, I'm pretty sure the advance curve is set for 91 which the factory designed the bike for, putting in 96 won't make it 'over-advance' the factory setting to take advantage of the higher octane.

That's why boys who put avgas in their favourite factory tuned toy (normally an old Falcon with 220km on the clock down here!) are tossing themselves off if they think they're going to get 'heaps more power', if it ain't pinking with 91 then it's unlikely to have enough compression and/or timing advance to take advantage of the 100 or more octane of the avgas.

Motu
15th June 2005, 07:14
Yes - unless you have a fully computer controlled system which I doubt many bikes have - you can't ''advance'' timing...only retard,you can't make something happen before it happens.You can build in a lot of advance and then retard it electronicly,but why would the factory build a system like that?...only if the over advanced state was ''normal''.This is how we set up CNG igns back in the old days - overadvance for CNG and then use electronics to retard for petrol,some units had programable advance curves...but as I said,you can only delay and event,not advance it.

Ixion
15th June 2005, 10:09
No Hall Effect in bike systems...no square wave signals,they are more akin to a lawnmower than a car - but then I have never worked on a modern bike ign system.

BMW purportedly use Hall effect sensor in the ignition system.

Paul in NZ
15th June 2005, 10:21
Dude... If you want to know anything about electronic ignitions ask this guy!

http://www.jefferies-au.org/MyECU/index.htm

Cliff is a member of AIGOR and I remember when he started doing this. Basically his bikes ignition shat itself and being a clever clogs he thought, well how hard can it be to build one and.... I mean you have to love Guzzi owners eh!

Cliff is a good guy and cleverer than ... well me for one...

Have a look at this site and be amazed what one clever guy can do with a few basic tools, a bit of knowledge and a ton of patience and determination!

Cheers

vifferman
15th June 2005, 10:22
My bike has one of the more advanced EFI systems, with three modes including 'closed loop', but I'm pretty sure it doesn't alter the ignition timing for different fuels. In 'closed loop' (which is only used when running at constant throttle and/or low revs), it uses the O2 sensors in the zorst to alter fueling, but not ignition timing (apart from the normal advancing of the curve as the revs rise). If I use different fuels, I have to reset the ECU to make it store the new O2 sensor readings for 'closed loop'; for other modes, it just makes it up as it goes along. Despite having umpty-zillion sensors, there's no knock sensor, and as far as I know, no bikes have them, so you just have to make sure you're using the right fuel for your bike, which would be 91 in your case, I would imagine.
I've got a similar compression ratio to yours (11.6:1), but I run with either 98 (96 has too much crap in it), or alternate between 91 and 98 so that the octane is somewhere between 91 and 98, as the recommended rating is 92, and it pinks when taking off when it's really hot, if I use 91.

Motu
15th June 2005, 11:06
BMW purportedly use Hall effect sensor in the ignition system.

But they are German though eh...quality before quanity,unlike their competitors,and in bed with Robert Bosch.Hall effect generators are delecte and a motorcycle enviroment is a bit harsh for them....unless of course you are using car technology in your bike like BMW does....I suspect the hall effect will be tucked away under the front cover nice and safe.

vifferman
15th June 2005, 11:10
But they are German though eh...quality before quanity,unlike their competitors,and in bed with Robert Bosch.Hall effect generators are delecte and a motorcycle enviroment is a bit harsh for them....unless of course you are using car technology in your bike like BMW does....I suspect the hall effect will be tucked away under the front cover nice and safe.
Don't electronic speedo drives use the Hall Effect? Or is it something similar?

Motu
15th June 2005, 11:13
All the ones I've seen on cars just use a simple AC generator like an ABS sensor - but like I said...I just work on cars.

k14
15th June 2005, 11:22
Don't electronic speedo drives use the Hall Effect? Or is it something similar?

Yep the induced emf from the magnet passing a coil can be detected and converted directly a frequency and thus converted to speed knowing the circumference of the wheel.

I thought that most ignition systems are triggered from an inductive pickup that senses off the flywheel. Then the signal from the inductive pickup goes straight to the coil which then goes to the sparkplug. Think thats how it works on my rs anyway, could be different when there is a battery etc involved.

Ixion
15th June 2005, 11:38
But they are German though eh...quality before quanity,unlike their competitors,and in bed with Robert Bosch.Hall effect generators are delecte and a motorcycle enviroment is a bit harsh for them....unless of course you are using car technology in your bike like BMW does....I suspect the hall effect will be tucked away under the front cover nice and safe.

Buggered if I know where it is. I don't understand it or how to fix it. And bits on bikes that I don't understand or know how to fix, I close my eyes and pretend they don't exist. And go back to playing with stuff that I understand .

This prevents me form getting into deep shit meddling beyond my capabilities.

Ixion
15th June 2005, 11:44
..Despite having umpty-zillion sensors, there's no knock sensor, and as far as I know, no bikes have them, so you just have to make sure you're using the right fuel for your bike, which would be 91 in your case, I would imagine.
..

BMW K1200 has a knock sensor (of "new advanced type" whatever that means). Not sure about earlier models, I'd have to go read the manual , which is where I'm not. There's certainly a shit load of magical stuff, all of which the manual indicates is out of bounds for mere mortals.

vifferman
15th June 2005, 11:59
I thought that most ignition systems are triggered from an inductive pickup that senses off the flywheel. Then the signal from the inductive pickup goes straight to the coil which then goes to the sparkplug. Think thats how it works on my rs anyway, could be different when there is a battery etc involved.
Most bikes just fire whenever the inductive pickup causes a pulse, even if the cylinder is on an exhaust stroke, as it doesn't matter. I think they use a spring-loaded plate to vary ignition timing if they don't have an ECU.

The VFR has an ignition pulse generator, which generates a small voltage (less than 0.7V) which is passed to the ignition control circuitry in the ECM, which then sends pulses to the coils, based on other information from another sensor on the cam that tells the ECM what position each cylinder is in, and the program for ignition timing vs. engine revs, throttle position, etc. But no allowance is made for knock.

vifferman
15th June 2005, 12:01
This prevents me form getting into deep shit meddling beyond my capabilities.
Until Mrs Ixion says, "You can feex stuff! Just do eet!" (in the pseudo-Cajun accent of that guy on "The Waterboy".

F5 Dave
15th June 2005, 12:09
Unless the system has a piezo detonantion sensor & closed loop ignition then it won't adjust to the petrol. Take it as it won't. 91 will be just dandy & if you are coming from a GN250 then a bicycle will feel overpowered so how 'bout worrying how to ride it.

TwoSeven
15th June 2005, 12:10
[The following is just my opinion Ė Iím still learning about this area, so it most likely is total bollox].

Building an ECU for a bike is a pretty simple affair if you know electronics. You simply need to charge/discharge a capacitor at a specific interval. I'm told the two most important things are keeping the unit at an ideal temp (i.e. cool) and signal propagation delay (which is why the wiring loom is the length it is).

As to knock sensors; knock will cause incorrect ignition (pre-ignition) which means the fuel wonít be burnt properly - the O2 sensor will pick this up if you have one. However, itís not just as simple as that - the air/fuel ratio that bikes require runs over a huge range depending on temperature of the air and the engine, throttle setting and velocity of the machine. For example, try something like 4:1 on starting, 8:1 on idle and 16:1 on 3/4 throttle stationary, 14:1 on full throttle (not adjusted for variation).

To start measuring that you need to start adding more sensors to the bike, certainly a modern machine should have a throttle position and O2 sensor in it. That makes your ECU more complex as you now need to send a signal to the injectors before sending out the ignition signal. This is done by using a map of pre-set settings (a linear map). But if you want to change the settings for each individual cylinder (say because the inner ones run hotter than the outer), then you need to have a map for each cylinder (a 3d map). Using a map means you donít have to measure sensors (which takes time) and it also means you donít have to perform calculations (which also take time). Remember, at 14,000 rpm you have to make about 60 measurements and calculations per second (roughly).

Changing the type (methane/ethanol etc) of fuel has no real bearing on octane rating since thatís just a measure of the iso-octane a fuel has in it. 0% octane rating means you have a ratio of 89% percent iso-octane (2,3,4 trymethelpentane) to 11% n-heptane (dypropyl methane). 100% octane rating means you have no n-heptane in the fuel. The objective of the mix is to create a detonation wave that propagates at a fixed rate (too fast or slow and the power wave will be buggered) and at a desired temperature with a desired heat output/absorption. You can use any mix of alkanes to do this but the petrol mix is generally the most efficient. (You can find all this info in the wikipedia).

You canít get higher than 100% octane rating no matter what you add to it. The effect of moving to ethanol or methanol just means that the fuel has a higher cooling effect on the engine - you will lose power because it has a lower BTU rating and it will also change the speed of the detonation wave. Cooling the engine more means you can move to a higher compression ratio or you can use more fuel (the latter results in higher compression ratio but more stuff to go bang and more cooling which is what dragsters require whereas road bikes require the former)

Changing the octane rating in petrol doesnít cool the engine as much as using ethanol, instead itís the opposite. It allows you to raise the temperature of the engine and therefore the temp at which ignition of the fuel occurs. The only way you can raise the temp of the engine is to raise the compression.

However, raising the octane also raises the base temperature at which ignition wonít occur (i.e. if its not warmed up, you wont get ignition - you'll notice this sometimes on bikes where a cylinder might not fire on cold mornings until the bike gets warm, then it kicks in). This means you need to change your plug to cope with the new heat range - since an NGK9 plug works at around 400-500C (91 octane at about 11.5:1 compression), going to 96 octane at 11.5:1 would mean the engine would never get hot enough (wouldnít burn efficiently) to ensure the plugs self cleaned themselves hence the cold fouling. If you raised the compression (and therefore the heat) of the engine to say 12.5:1 then you'd be back into the operating range of say an NGK 7 (I cant remember the heat numbers for the plugs sorry) at about 600C which is well within the plugs self cleaning range and operating temp (400-750C).

Anyhow - back on topic. A slight trick to changing the compression and therefore the heat range the engine works at is simply to retard or advance the ignition. Since peak compression say 12.5:1 occurs at TDC advancing the ignition 5 degrees means that compression may be as low as 12:1 or even 11.5:1 depending on the machine. As you can see above, that greatly reduces the heat range that the engine operates at and also the power/torque figures. (Also, increasing octane without increasing compression is the same as retarding the ignition a few degrees). Building this functionality into an ECU suddenly makes things well harder because you need even more sensors on the bike. Having such a wide variation in heat ranges would also make your plugs say nuts as well.

Also, I guess, if you want to get nice and precise, you'll need to ensure that the spark wave front arrives at the piston crown just after the piston has passed TDC (so youíll need to tune the detonation wave). Otherwise, if its too early, you have a spark wave front arriving on an upward moving piston (thatís effectively going to slow it down and in extreme cases burn a hole in the crown) or a wave front that is chasing the piston down the barrel (and cooling resulting in sooting up if the mix is too rich). That means there is a minimum and maximum advance/retard setting that you can use in the engine (I think Honda only allow 2-5 degrees on cibby engines but am not sure).

So in answer to the original question an 11:5:1 ratio engine is likely to be tuned to run on 91 octane petrol using an NGK 8 or 9 plug (If I remember the temps correctly), and changing the fuel content will likely lose you power. The auto retard/advance feature is probably only there to cope with the heat range the engine is designed to go thru.

scumdog
15th June 2005, 12:18
BMW K1200 has a knock sensor (of "new advanced type" whatever that means). Not sure about earlier models, I'd have to go read the manual , which is where I'm not. There's certainly a shit load of magical stuff, all of which the manual indicates is out of bounds for mere mortals.

Speaking of which, where in the South Island is a BMW dealer with the BigBoxofMagic that a late model BMW bike can be hooked to for TuningRepairAndAnalysisOf Problems?? Mate of mine reckons there isn't one south of Christchurch.

Brian d marge
15th June 2005, 14:24
Most bikes just fire whenever the inductive pickup causes a pulse, even if the cylinder is on an exhaust stroke, as it doesn't matter. I think they use a spring-loaded plate to vary ignition timing if they don't have an ECU.

The VFR has an ignition pulse generator, which generates a small voltage (less than 0.7V) which is passed to the ignition control circuitry in the ECM, which then sends pulses to the coils, k.

You know , Dont you just hate it when you feel comfortable with a bit of info , and then 20 years on you have to drag that rusty bit of info from the dark recesses and have a fresh look at it ....

Honda uses both types of ignition , Hall effect and inductive ( I remember the course at honda ...when the I think it was the fireblade( cant remember the model for sure and I dont have the course note at hand ) , and the reluctor ring had changed from 8 or so vanes to 30 odd ( thats why they were harping on about it), now that used a hall effect pulse generator which produced a square wave with a large gap between the reluctor vanes to tell the engine I have done one revolution ie reset the Ecu
As motu says hall effect are delicate , so most use a inductive pickup where the magnetic field is pushed out of the way by a lump of metal causing it to trip( move over) over the wire which is wrapped around a soft iron core causing a current to be created in the wire which then heads off to the ecu .
Now I had a quick trawl through the internet , but there is so much rubbish out there I havent the time to do a complicated search.

I will see if I can locate my notes , ( you know I can see the page in my mind even the location of the picture explaining Hall effect , but stuffed If I can remember the model it was for !!!)
Hall effect btw is when a current flows along a conductor ( usually silicon ) and a manetic field is close by ....all the smoke dust ( see images section for picture of Lucas smoke) , well they all try to move away from the magnetic field ie to one side of the conductor , in doing that they create a voltage difference small but noticeable and at right angles to the current ( smoke) originally flowing,,

I know the original post was about advancing /retatding for differing gasoline , But Motu made me think
I am always up for a reality check now and again ...thanks for that ....

It bugs me , you know when you can remember something clearly, but not quite all of it .... Stufff.....must be getting old ...or was it a mis spent youth , cant remember now
Oh well happy days

Stephen

vifferman
15th June 2005, 14:58
As to knock sensors; knock will cause incorrect ignition (pre-ignition) which means the fuel wonít be burnt properly - the O2 sensor will pick this up if you have one. However, itís not just as simple as that - the air/fuel ratio that bikes require runs over a huge range depending on temperature of the air and the engine, throttle setting and velocity of the machine. For example, try something like 4:1 on starting, 8:1 on idle and 16:1 on 3/4 throttle stationary, 14:1 on full throttle (not adjusted for variation).
On closed loop, the VFR uses two sensors - one for the two left cylinders, and one for the right two. However, closed loop is set up to run ultra-lean to meet EC and US emissions testing up to 2008 or summat. And it uses the O2 sensors only if there's no stored data (ie., the ECU's been reset).


To start measuring that you need to start adding more sensors to the bike, certainly a modern machine should have a throttle position and O2 sensor in it. That makes your ECU more complex as you now need to send a signal to the injectors before sending out the ignition signal. This is done by using a map of pre-set settings (a linear map). But if you want to change the settings for each individual cylinder (say because the inner ones run hotter than the outer), then you need to have a map for each cylinder (a 3d map). Using a map means you donít have to measure sensors (which takes time) and it also means you donít have to perform calculations (which also take time). Remember, at 14,000 rpm you have to make about 60 measurements and calculations per second (roughly).
Phew!
Lotsa sensors on the VFR: external air temp, throttle position, O2, airbox pressure and temp, road speed, cam position, revs, engine temp, barometric pressure...
Then it uses three 3D maps for each cylinder for fuelling. It's supposedly good for up to 16,000 RPM.

But there are problems with the programmed logic - one is that the 'closed loop' mode is too lean, and the other is that in the interests of fuel economy and emissions, the ECU likes to shut the throttle completely if you back off the throttle at low revs, necessitating some clutch-slipping or modification of riding technique in some situations. (Best one is to keep the revs above 5K). :yes:


However, raising the octane also raises the base temperature at which ignition wonít occur (i.e. if its not warmed up, you wont get ignition - you'll notice this sometimes on bikes where a cylinder might not fire on cold mornings until the bike gets warm, then it kicks in).
That's interesting.
This would explain why the VFR's a bit reluctant to kick into life running on 98, now that it's getting cold? It was better this morning, as I chucked $10 of 91 in the tank yesterday, as the blinky thing (tech term) was blinking, and I was in a hurry.

Motu
15th June 2005, 20:41
Speaking of which, where in the South Island is a BMW dealer with the BigBoxofMagic that a late model BMW bike can be hooked to for TuningRepairAndAnalysisOf Problems?? Mate of mine reckons there isn't one south of Christchurch.

The Bosch Hammer maybe - it's used on cars,no problem to have bike data on it too.Most expensive usless piece of diagnostic equipment you can get - Bosch lock them into it...you can be a service agent,or a parts agent,not often both,neither can access the others data,they charge a shit load for the CDs and the diagnostic gear and from all I have heard everyone who has a Hammer is spewing.

I was talking to my diesel man yesterday and he's full of woe - common rail,it's here and will have taken over in 5 yrs.Bosch control it - they will have a service agent in Auck,Wellington and ChCh,no one will be able to asscess information and parts unavailable to any but an authorised service agent.Robert Bosch let diesel technology slip out of his hands once....never again.

thehollowmen
15th June 2005, 20:48
Speaking of which, where in the South Island is a BMW dealer with the BigBoxofMagic that a late model BMW bike can be hooked to for TuningRepairAndAnalysisOf Problems?? Mate of mine reckons there isn't one south of Christchurch.

Doesn't Honda otago (formally uptown motorcycles) in Dunedin have one?
they sell lots of BMWs so I'd be surprised if they didn't.

Pixie
15th June 2005, 23:25
I know this sounds really silly, but how would I tell if the CDI is able to advance or retard my timing automatically?

I pick up a 11.5:1 650 fuel injected V twin tommorrow and I'll get less power on 91 if it retards the timing. On the other hand I could get a small amount of SDA (alcohol + small amount of methanol) from work to boost the octane (the manual says 10% etOH or 5%mtOH in petrol) and if it advances... :ride: happy days for me!
If your bike is fuel injected it will have a fairly sophisticated ignition system too.Taking advantage of the ECU for the fuel system.
It will have a thottle position sensor and the advance curve will be mapped.
Even the humble Bandit has a TPS and it has carbs.
Very few electronic ignitions are CDI -on road bikes.Transistorised switching of 12 Volts to the coils is what they do.
CDI's dump higher voltages into the coil's primary windings,Up to 300V.

Pixie
15th June 2005, 23:31
Don't electronic speedo drives use the Hall Effect? Or is it something similar?
It need only be a reed switch

Cliff Jefferies
16th June 2005, 10:51
Building an ECU for a bike is a pretty simple affair if you know electronics. You simply need to charge/discharge a capacitor at a specific interval. I'm told the two most important things are keeping the unit at an ideal temp (i.e. cool) and signal propagation delay (which is why the wiring loom is the length it is).


Thats old school thinking even it is correct. True the electronics is next to trivial. A single FET transistor will single handedly drive an ignition coil nowadays.

Today its about software/firmware and features.

Hi all.

Its strange this thread has just popped up as I'm currently developing an ignition system for the "older" bikes. The first prototype has gone on to Rob Johnson's ( of AIGOR fame ) road guzzi and soon there will be one on his race bike. The aim is to have a simple system where the rider will be able to select from a number of builtin advance curves. Input can be taken from a number of sources, points, halleffect/optical and reluctor. Anyway end of SPAM. Its not ready yet.

Bikes that have points or other digital input probably don't
do any advance. It is too hard to predict when to spark from the last trigger. My first attempt to run on Robs bike did try this. Above 3000RPM it seemed to run quite well as the flywheel keeps things consistant. Towards 2000RPM it started getting rough and would die off suddenly with a few backfires. This was running only one of the two cylinders and running off the standard points.

Those bikes with coil type pickups can do some advance as the pulse is stretched over time and you can choose the point on the pulse to trigger off so as to change the advance.

Most EFI bikes get many pulses during the cycle so can easily keep track of where the motor is at.

The only bikes I know of that have variable timing are the late model HD and they do this with a knock sensor. Perhaps some BMWs do something fancy also.

A new better technique is to measure the current through the sparkplug ( driven at 400V DC ). This allows you to indirectly measure the pressure within the cylinder. You can then position the pressure peak to be around 20 degrees after TDC to maximise the power. Advancing till it knocks could be too advanced.

pete376403
16th June 2005, 14:18
If you were to use methanol in a injected v twin, then the oxygen rich mixture will change the exhaust temp ( usually around 1425 ish ) which will fool the ecu in to injecting more or less fuel ( I cant remember if you use larger or smaller jets in a methonol carb bigger I think ....ie the INjection system will compensate ..not the cdi ......( as motu said the closed loop system will delay signal letting it fire the coil at the most suitable advance/retard position)
Stephen
BTW methanol doesnt like aluminuim I think . becareful ......
Methanol jets need to be MUCH larger than for petrol - ideal ratio for petrol/air is around 12 - 13:1, for meth it's more like 5 - 6:1. Further meth doesn't contain anywhere near the same amount of energy for a given amount as petrol (which is why you need so much more of it) and it runs a lot cooler. If that doesn't confuse the computer, go for it. And meth will live in an ally tank ok (my speedway bike used the same tank for years).
On the plus side it's very difficult to get a motor detonanting with meth, so the compression ratio can be very high, 14:1 or more. The high comp helps the speedway bikes achieve the acceleration which they need out of the gate and out of the corners.

Brian d marge
17th June 2005, 12:49
Methanol jets need to be MUCH larger than for petrol - ideal ratio for petrol/air is around 12 - 13:1, for meth it's more like 5 - 6:1. Further meth doesn't contain anywhere near the same amount of energy for a given amount as petrol (which is why you need so much more of it) and it runs a lot cooler. If that doesn't confuse the computer, go for it. And meth will live in an ally tank ok (my speedway bike used the same tank for years).
On the plus side it's very difficult to get a motor detonanting with meth, so the compression ratio can be very high, 14:1 or more. The high comp helps the speedway bikes achieve the acceleration which they need out of the gate and out of the corners.

Yes I couldnt remember which way round it went, and I had often wondered about why the Speedway bike all ran high comps ,,,,,So my 5.5 to 1 Enfield is eerr out of the running then .....

Thanks

Stephen