CDI timing advance
Mike Bresnahan
I've seen several discussions of how a CDI (capacitor discharge
ignition) produces a spark, but I have not seen a discussion of how it
advances the timing as a function of engine RPM. Can any describe how
this is done? I'm most interested in how this is done on Japanese
off-road motorcyle engines. Perhaps this is not a subject which is
specific to CDI units and that is why I have not seen it in the same
discussions.
MikeB
--
Michael J. Bresnahan, York & Associates, (612)-905-7300,
mailto:mbre...@yorkconsulting.com, http://www.yorkconsulting.com,
Support the anti-spam amendment, HR 1748. See http://www.cauce.org
Opinions expressed herein are my own and may not represent those of my employer.
Dave Emerson
Mike Bresnahan wrote:
>
> I've seen several discussions of how a CDI (capacitor discharge
> ignition) produces a spark, but I have not seen a discussion of how it
> advances the timing as a function of engine RPM. Can any describe how
> this is done? I'm most interested in how this is done on Japanese
> off-road motorcyle engines. Perhaps this is not a subject which is
> specific to CDI units and that is why I have not seen it in the same
> discussions.
>
Depends on the bike.
Many off-road machines are two-stroke which do not require any ignition
advance.
Simple CDI systems, especially those fitted to later models where the
earliest model had points, still use a mechanical bob-weight system to
advance the ignition. This is the most common.
Some modern electronic systems (not strictly CDI) have the ignition
curve mapped in the ECU. This is more common when combined with fuel
injection.
Was this just curiousity on do you have a specific issue?
--
Dave Emerson
Motorcycle Maintenance Workshop
UK (remove X to reply)
jon_k...@atk.com
Dave Emerson <deme...@Xford.com> wrote:
>
> Mike Bresnahan wrote:
> >
> > I've seen several discussions of how a CDI (capacitor discharge
> > ignition) produces a spark, but I have not seen a discussion of how it
> > advances the timing as a function of engine RPM. Can any describe how
> > this is done? <del>
>
> Depends on the bike.
>
> Many off-road machines are two-stroke which do not require any ignition
> advance.
>
> Simple CDI systems, especially those fitted to later models where the
> earliest model had points, still use a mechanical bob-weight system to
> advance the ignition. This is the most common.
>
> Some modern electronic systems (not strictly CDI) have the ignition
> curve mapped in the ECU. This is more common when combined with fuel
> injection.
This info may be correct for automobiles, but not for 2-stroke bike motors.
The ignition advance is very necessary on high RPM two stroke motors and is
built into the CDI electronics. Traditionally the timing curve has been set
using analog components in the CDI (resistor, inductor, capacitor) but
digital control is becoming far more common. Not sure how it's being done in
current japanese MX bikes but at least some factory race bikes have digital
CDI with a computer interface port so they can program in different timing
curves for each race track.
Jon
-----== Posted via Deja News, The Leader in Internet Discussion ==-----
http://www.dejanews.com/ Now offering spam-free web-based newsreading
Mike Bresnahan
Dave Emerson wrote:
> Many off-road machines are two-stroke which do not require any ignition
> advance.
Are you sure? I'm pretty sure my KDX200 has a timing advance circuit.
Also MSD sells high-performance CDI's for dirt bikes which have
optimized advance curves.
> Simple CDI systems, especially those fitted to later models where the
> earliest model had points, still use a mechanical bob-weight system to
> advance the ignition. This is the most common.
My KDX200 does not have a mechanical advance.
> Was this just curiousity on do you have a specific issue?
Curiosity mostly.
MikeB
Note that a copy of this message was posted to sci.electronics.misc,
rec.motorcycles, rec.motorcycles.racing, and rec.motorcycles.dirt.
Brian McLaughlin
Dave Emerson wrote:
>
> Mike Bresnahan wrote:
> >
> > I've seen several discussions of how a CDI (capacitor discharge
> > ignition) produces a spark, but I have not seen a discussion of how it
> > advances the timing as a function of engine RPM. Can any describe how
> > off-road motorcyle engines. Perhaps this is not a subject which is
> > specific to CDI units and that is why I have not seen it in the same
> > discussions.
> >
>
> Depends on the bike.
>
> advance.
Are you saying that off road bikes or 2 strokes in general don't need
ignition advance.
My TZ has quite a bit of ignition advance (something like 4 steps of 3
degrees in about 3000 rpms).
--
Brian McLaughlin AP #1
TZ250E (1993-95) 2 strokes smoke,
R1100RTA (1997) 4 strokes choke!
EX250 Ninja (1998)
Some Guy on a Bike
Dave Emerson <deme...@Xford.com> whiled away the hours on Tue, 09 Jun
1998 12:42:35 +0100 with the following:
> Many off-road machines are two-stroke which do not require any ignition
> advance.
I know very little about two-strokes, but am tremendously curious.
I'm learning a great deal about it from the people at work, who race
(some of them for a living, pretty much).
Curious; why would a two-stroke need no advace as rpms climb?
===========================================================================
Adam Wade espr...@winternet.com
CIMC #1 DoD #2009 LOMP #2 "The only way I'll stop riding
1976 Kawasaki KZ750 twin (Betty) is if I stop breathing."
http://www.winternet.com/~espresso
===========================================================================
Fisher
>
> Curious; why would a two-stroke need no advace as rpms climb?
The combustion chamber turbulance increases the flame speed enought that
you do not need more ignition lead. Also 2-strokes are suseptable to
melting pistons if too much lead is given. RZ 350's actuall decrease
timing as it goes faster, with max advance (35deg) at 6k and the
(10-15deg)least advance at high rpm.
--
John
Racer 577
MRA EX #577
1990 750 sport (racer)
1995 Buell S-2
Dave Emerson
Mike Bresnahan wrote:
>
> Dave Emerson wrote:
> > Many off-road machines are two-stroke which do not require any ignition
> > advance.
>
> Also MSD sells high-performance CDI's for dirt bikes which have
> optimized advance curves.
You notice my use of the word "many" this relates to the highest
proportion of two-stroke bikes "in the wild". There are always
exceptions, that's what makes life interesting. Competition machinery
(and bikes with such pretensions) need every edge they can get and
indeed many use either machanical or electronic ignition advance.
>
> > Simple CDI systems, especially those fitted to later models where the
> > earliest model had points, still use a mechanical bob-weight system to
> > advance the ignition. This is the most common.
>
> My KDX200 does not have a mechanical advance.
So, if it has advance, it must be electronic. Get out the strobe light
and watch it in action.
>
> > Was this just curiousity on do you have a specific issue?
>
> Curiosity mostly.
>
Curiosity's fine.
Tony Williams
In article <357E43...@Xford.com>, Dave Emerson
<URL:mailto:deme...@Xford.com> wrote:
> So, if it has advance, it must be electronic. Get out the strobe light
> and watch it in action.
I wonder if someone could answer some questions on ignition advance?
What is the precise relationship between the advance angle
and rpm? Is it a linear function, based on the assumption
the combustion takes a constant time to reach mep, or is
it more complex? Is it even calculable, or does it vary
from engine-engine?
--
Tony Williams.
Onestone
Tony Williams wrote:
This lies in the sticky area between automotive jargon, electronics, and
actuality. Advance angle is not really an angle, it is a timing
requirement. It takes approximately 2milliseconds (msecs) for the
combustion process (in a 4 stroke on pulp) assuming a stochiometric
ratio. Fuel/air ratio, type of fuel, air temperature, and many other
factors affect this.In a perfect world advance angle would be a simple
linear function, simple the time taken for combustion + the optimum
angle at which combustion must occur. In real life all of the mentioned
factors, and many others affect the advance angle, this is why modern
EFI system have very complex multi layered fuel and ignition maps. I
believe the ideal system is a trade off between CDI and lower voltage
coil ignition, running individual maps for each cylinder, multi-spark
per cylinder, with variable spark energy, again on aper cylinder basis.
I haven't tried it on a bike, but it makes a Renault 12 and a Daihatsu
Charade go like buggery.
--
Remove -xxx- from my address to respond
John Lundgren
Dave Emerson wrote:
> Mike Bresnahan wrote:
> > Dave Emerson wrote:
> > > Many off-road machines are two-stroke which do not require any ignition
> > > advance.
My old Frod van had a vacuum advance, and it worked when I sucked on the
tube. But the engine wasn't accelerating as well as it should. I found
that somewhere inside the advance was rubbing on something and wouldn't
work right. I put a new diaphragm on it and it started pulling like a
team of wild horses.
> > > Simple CDI systems, especially those fitted to later models where the
> > > earliest model had points, still use a mechanical bob-weight system to
> > > advance the ignition. This is the most common.
I had a Delta Kit CDI on that van, and it made such a hot spark that it
helped keep the plugs clean even tho the engine had over a hundred thou
on it. It put out a really nasty spark.
> > My KDX200 does not have a mechanical advance.
> So, if it has advance, it must be electronic. Get out the strobe light
> and watch it in action.
> --
> Dave Emerson
> Motorcycle Maintenance Workshop
> UK (remove X to reply)
--
Please remove NO and SPAM from my email addr to reply.
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MX Tuner
>> Dave Emerson wrote:
>> > Many off-road machines are two-stroke which do not require any ignition
>> > advance.
>> Are you sure? I'm pretty sure my KDX200 has a timing advance circuit.
>> Also MSD sells high-performance CDI's for dirt bikes which have
>> optimized advance curves.
>You notice my use of the word "many" this relates to the highest
>proportion of two-stroke bikes "in the wild". There are always
>exceptions, that's what makes life interesting. Competition machinery
>(and bikes with such pretensions) need every edge they can get and
>indeed many use either machanical or electronic ignition advance.
I don't recall virtually ANY bikes which don't have some form of spark
advance. Since timing advance is there to keep the end of the
combustion flame happening at the same time relative to piston
position, the spark must be made to begin earlier (again relative to
piston position). Even early '70s points ignition bikes had a basic
mechanical weight system. When the weights stick in the retarded
position, the bike just won't rev out properly.
Virtually every non-points ignition system has an advance feature
built in.
MX Tuner
Rob Hunter
Modern bikes have a 2d map programmed into the CDI unit, this adjusts
ignition timing against RPM. Yamaha's YZ400F has a 3d map, which
computes ignition timing against rpm and throttle opening.
Rob H (NZ)
Tony Williams
In article <357E9459...@bigpond.com>, Onestone
> This lies in the sticky area between automotive jargon, electronics, and
> actuality. Advance angle is not really an angle, it is a timing
> requirement. It takes approximately 2milliseconds (msecs) for the
> combustion process (in a 4 stroke on pulp) assuming a stochiometric
> ratio. Fuel/air ratio, type of fuel, air temperature, and many other
> factors affect this.In a perfect world advance angle would be a simple
> linear function, simple the time taken for combustion + the optimum
> angle at which combustion must occur. In real life all of the mentioned
> factors, and many others affect the advance angle, this is why modern
> EFI system have very complex multi layered fuel and ignition maps. I
> believe the ideal system is a trade off between CDI and lower voltage
> coil ignition, running individual maps for each cylinder, multi-spark
> per cylinder, with variable spark energy, again on aper cylinder basis.
> I haven't tried it on a bike, but it makes a Renault 12 and a Daihatsu
> Charade go like buggery.
Thanks. I had already decided that a lookup table was the easiest
thing for the uP to do, precise values determined on the dyno.
I was just trying to get a preliminary rough cut on seed-values
so that then engine could be run up without damage.
--
Tony Williams.
Onestone
Tony Williams wrote:
> Thanks. I had already decided that a lookup table was the easiest
> thing for the uP to do, precise values determined on the dyno.
> I was just trying to get a preliminary rough cut on seed-values
> so that then engine could be run up without damage.
>
> --
> Tony Williams.
I started with the values from the dizzy for the Renault, and set a
logger onto the Charade, as it's already EFI. Be a little careful with
the dyno only data. One problem with a dyno is that it isn't moving in
free air like your vehicle will be, so some things will change, most
noticably air intake and engine temperatures. If you can, make your maps
programmable and use a pair of knock sensors to determine optimal
advance while moving.
Mike Bresnahan
Onestone wrote:
> I started with the values from the dizzy for the Renault, and set a
> logger onto the Charade, as it's already EFI. Be a little careful with
> the dyno only data. One problem with a dyno is that it isn't moving in
> free air like your vehicle will be, so some things will change, most
> noticably air intake and engine temperatures. If you can, make your maps
> programmable and use a pair of knock sensors to determine optimal
> advance while moving.
What is the "dizzy"?
What are "knock sensors"?
How are the maps made programable? How are they programmed? Is it
possible for an amatuer engineer to preform such an experiment? I don't
have a dyno in my garage. I'm not sure how I would measure head
temperature to avoid a meltdown either. Would a thermister attached to
a head bolt work? Nor do I know at what temperature the head should be.
MikeB
Freddie Smith
>>My old Frod van had a vacuum advance, and it worked when I sucked on the
>>tube. But the engine wasn't accelerating as well as it should. I found
>>that somewhere inside the advance was rubbing on something and wouldn't
>>work right. I put a new diaphragm on it and it started pulling like a
>>team of wild horses.
Awwwww man ..quit.. you just trying to turn me on. sucked and rubbing and
pulling... darn.. where's that Sears catalog when you need it.....
--
Freddie A. Smith One good thing about double jumps..is that
NCR Corp. you have time to see and think about the
Sustaining Engineering pain you are going to suffer when you
freddi...@columbiasc.ncr.com realize you have made a mistake.
Onestone
Mike Bresnahan wrote:
> Onestone wrote:
> > I started with the values from the dizzy for the Renault, and set a
> > logger onto the Charade, as it's already EFI. Be a little careful
> with
> > the dyno only data. One problem with a dyno is that it isn't moving
> in
> > free air like your vehicle will be, so some things will change, most
>
> > noticably air intake and engine temperatures. If you can, make your
> maps
> > programmable and use a pair of knock sensors to determine optimal
> > advance while moving.
>
> What is the "dizzy"?
The distributor on a car.
> What are "knock sensors"?
>
Sensors which output a signal which indicates when your engine is
'knocking', usually caused by too much advance.
> How are the maps made programable?
By storing them in EEROM memory.
> How are they programmed?
Using a simple display/keyboard which connects to the computer
(electronic ignition computer or engine management computer) when tuning
it..
> Is it
> possible for an amatuer engineer to preform such an experiment?
Yes, if you understand the engine, and use a commercial controller. I
wouldn't recommend trying to design and build your own unless you really
undestand what you are up to.
> I don't
> have a dyno in my garage.
Nor do I. For commercial projects I do some preliminary tuning on a
dyno, which I hire. For my own stuff I use an oscilloscope, an exhaust
temperature sensor, an ego sensor, and I tune the vehicle until it
'feels' good, then let some automatic software 'learn' how to optimise
for economy and performance.
> I'm not sure how I would measure head
> temperature to avoid a meltdown either.
Use a thermocouple. I'm mostly into cars, so don't know the temps
either.
> Would a thermister attached to
> a head bolt work? Nor do I know at what temperature the head should
> be.
>
> MikeB
> --
> Michael J. Bresnahan, York & Associates, (612)-905-7300,
> mailto:mbre...@yorkconsulting.com, http://www.yorkconsulting.com,
> Support the anti-spam amendment, HR 1748. See http://www.cauce.org
>
> Opinions expressed herein are my own and may not represent those of my
> employer.
Al
ChrisTos Alexiou
Rob Hunter wrote:
In advanced car ignitions they use a 3rd sensor in the intake manifold
that measures the pressure (vacuum actually). This puts another
dimention
to the advance mapping.
ChrisTos
--
ChrisTos Alexiou
Whenever I tune up my bike or I make a modification, I am never sure if
I gained any power or not. I believe that only the dyno can tell almost
the truth.
Does anyone know a way to build a dyno for motorcycles ?
I would appreciate any kind of help.
Thanx,
ChrisTos.
ChrisTos Alexiou
Mike Bresnahan wrote:
> I've seen several discussions of how a CDI (capacitor discharge
> ignition) produces a spark, but I have not seen a discussion of how it
> advances the timing as a function of engine RPM. Can any describe how
> this is done? I'm most interested in how this is done on Japanese
> off-road motorcyle engines. Perhaps this is not a subject which is
> specific to CDI units and that is why I have not seen it in the same
> discussions.
>
> MikeB
> --
> Michael J. Bresnahan, York & Associates, (612)-905-7300,
> mailto:mbre...@yorkconsulting.com, http://www.yorkconsulting.com,
> Support the anti-spam amendment, HR 1748. See http://www.cauce.org
>
> Opinions expressed herein are my own and may not represent those of my employer.
I just want to mention that the advance on 4-strokes is opposite
to that of the 2-strokes. That is while in a 4-stroke the advance is increased with
rpm in a 2-stroke machine the advance is decreased with rpm. This is due to
different physics that happen in the 2 different combustion chambers.
ChrisTos.
--
ChrisTos Alexiou
Thanx,
ChrisTos.
--
Rich Rohrich
ChrisTos Alexiou wrote:
> I just want to mention that the advance on 4-strokes is opposite
> to that of the 2-strokes. That is while in a 4-stroke the advance is increased with
>
> rpm in a 2-stroke machine the advance is decreased with rpm. This is due to
> different physics that happen in the 2 different combustion chambers.
I must have fell asleep during physics class the day they explained that. Would you be
so kind as to enlighten us with some specific details?
--
Rich Rohrich
Don MacPhail
Rich Rohrich replied to:
He may be smokin' rope as to the reasons, but the advance on my RZ500 does reduce as the revs climb. . . Now, the
sharp drop at the end is a rev-limiting thing, but there is a steady decrease from a high of 29 degrees @ 3500RPM, to 18
degrees at 9000RPM - at which point it falls off a cliff, down to 8 degrees @ 10,000RPM.
cheers,
Don
Jef...@my-dejanews.com
In article <3581394F...@intranet.gr>,
I don't know any way to build a home DYNO. Better motorcycle service
departments will have a dyno, but you'll need to install a street style rear
tire before they will run it for you.
I suggest learning to read your plug and piston crown for correct jetting.
Also, get a service manual and read about the carb on your bike. Once you are
familiar with it, you can purchase a selection of main and pilot jets to
experiment with. I've found more power through proper jetting than just about
any other hop-up.
Jeff>
Mike Bresnahan
Onestone wrote:
> > What is the "dizzy"?
>
> The distributor on a car.
So you measured the advance curve of the mechanical advance mechanism on
the distributer with a timing light?
> > What are "knock sensors"?
> >
>
> Sensors which output a signal which indicates when your engine is
> 'knocking', usually caused by too much advance.
So you're speaking of detonation? How do the sensors work? Do they
detect vibration - are they accelerometers?
> > How are the maps made programable?
>
> By storing them in EEROM memory.
>
> > How are they programmed?
>
> Using a simple display/keyboard which connects to the computer
> (electronic ignition computer or engine management computer) when tuning
> it..
So these units have a certain amount of memory into which you enter CPU
instructions in hex?
> Nor do I. For commercial projects I do some preliminary tuning on a
> dyno, which I hire. For my own stuff I use an oscilloscope, an exhaust
> temperature sensor, an ego sensor, and I tune the vehicle until it
> 'feels' good, then let some automatic software 'learn' how to optimise
> for economy and performance.
What is an "ego" sensor?
Does this software do numeric modeling or does it actually tweak the
engine controller based on sensor readings?
Before I drive you crazy with questions, is there a book which gives a
good explanation of this? I had a year of junior/senior level
undergraduate mechanical engineering training along with my physics
major, but they never taught we anything along these lines.
XR<crunch>4
> He may be smokin' rope as to the reasons, but the advance on my RZ500
does reduce as the revs climb. . . Now, the
>sharp drop at the end is a rev-limiting thing, but there is a steady
decrease from a high of 29 degrees @ 3500RPM, to 18
>degrees at 9000RPM - at which point it falls off a cliff, down to 8 degrees
@ 10,000RPM.
This may be due to varying compression at different RPMs (just taking wild
guesses now). i would guess that increasing compression would require
changing timing, but I haven't a clue of exactly what the required effect
is. Are you savvy on this type of crap Rich? Compression ratio, as I
recall, typically varies from around 8:1 to 11:1 on a two stroke - I'm
guessing due to pressure wave resonance of the pipe.
o_
Jay O\-O
'98 xr400 - '84 mx250lc - '86 xv1100 - '93 klr250
andy the pugh
ChrisTos Alexiou <ca...@intranet.gr> wrote:
> Does anyone know a way to build a dyno for motorcycles ?
>
All you need is a big heavy drum to spin up with the back wheel, drum
spoeed and engine rpm sensors and a bit of widgetry to do the
calculations.
You can calculate the moment of inertia of the drum just by wrapping a
rope round it up to a pulley, fastening a weight to the rope and
watching how fast the drum acclerates.
--
ap
Mike Bresnahan
Don MacPhail wrote:
> He may be smokin' rope as to the reasons, but the advance on my RZ500 does reduce as the revs climb. . . Now, the
> sharp drop at the end is a rev-limiting thing, but there is a steady decrease from a high of 29 degrees @ 3500RPM, to 18
> degrees at 9000RPM - at which point it falls off a cliff, down to 8 degrees @ 10,000RPM.
How did you measure it?
What is a RZ500? Is that a fairly new model? I haven't been keeping up
with the industry for the last few years.
Don MacPhail
Mike Bresnahan replied to yours truly:
> I wrote:
> > He may be smokin' rope as to the reasons, but the advance on my RZ500 does reduce as the revs climb. . . Now, the
> > sharp drop at the end is a rev-limiting thing, but there is a steady decrease from a high of 29 degrees @ 3500RPM, to 18
> > degrees at 9000RPM - at which point it falls off a cliff, down to 8 degrees @ 10,000RPM.
>
> How did you measure it?
It's in the back of the shop manual, and on the hop-up docs I pulled from the net.
> What is a RZ500? Is that a fairly new model? I haven't been keeping up
> with the industry for the last few years.
1984-85 Yamaha V-4 two-stroke sportbike, famous/infamous for their finicky engines, sometimes wonky handling, obcenely
expensive repairs, and ability to power-wheely from 4th gear (!) . . .8)
Oh, yeah - crazy Americans will pay over US$5000 for one in good shape, $10k for fancy versions!
cheers,
Don
DirtCrashr
>> > What are "knock sensors"?
"Knock knock"
"Who's there?"
"Wayne."
"Wayne, who?"
"Wayne, wayne go away; come again another day."
Thank you El Niño...
DoortCrashr - '97xr400
Cadshop
I can give you an overview of how to do this. How large of engines do you want
to test? How much money do you want to spend? How mechanical are you? Do you
have access to equipment for fabrication?
Jack Dannenberg
cad...@aol.com
Erich Coiner
Here are simple but not easy instructions for a dyno.
1. Get Mechanical Engineering degree.
2. 2 Years (min) of shop classes, welding, machining etc.
3. build dyno.
Erich
Some Guy on a Bike
ChrisTos Alexiou <ca...@intranet.gr> whiled away the hours on Fri, 12
Jun 1998 17:21:04 +0300 with the following:
> Does anyone know a way to build a dyno for motorcycles ?
I can't imagine you could design, engineer, and build one for less
than you could buy one for, unless you had already designed a few...
===========================================================================
Adam Wade espr...@winternet.com
CIMC #1 DoD #2009 LOMP #2 "The only way I'll stop riding
1976 Kawasaki KZ750 twin (Betty) is if I stop breathing."
http://www.winternet.com/~espresso
===========================================================================
WCA
at Darcy Racing Products in Ft. Worth, Texas. He built the one that
Kenny Tolbert uses to tune Chris Carr's bikes and many other fast
Harley and Rotax race bikes.
I don't have his number close at hand, but you can look it up with
information service.
Jack Rhodes
Motorcycle Race Announcer
S Wilson
How about a long straightaway and a stopwatch?
If you're consistent enough and keep the variables to a minimum, you
should be able to sense if you're gaining or giving up power.
Just an idea...
Dan Nitschke
Bruce Hearn wrote:
>
> Mike Bresnahan <mbres...@mmm.com> wrote in article
> <35817D...@mmm.com>...
> >
> > What is an "ego" sensor?
>
> Reeky that need an ego sensor. Preferably a sealed unit that they can't
> "improve".
Hey! Are you... talkin' to ME?!
(Well, you should be, if you're not.)
> Bruce in Houston wondering ...
Let's not go there. Thanks.
/* dan: The Anti-Ged, Ignorant Yank (tm) #1, BOF #26, HH #1 */
Dan Nitschke ** peDA...@best.com ** nits...@redbrick.com
----------------------------------------------------------
Ain't no tiger; ain't no little lamb. Suppose you tell me:
who do you think I think I am? -- Don Henley
Bruce Hearn
> > > What are "knock sensors"?
> > >
> > 'knocking', usually caused by too much advance.
>
> So you're speaking of detonation? How do the sensors work? Do they
> detect vibration - are they accelerometers?
Knock sensors are piezo-electric crystals that emit electricity when vibrated.
These are the same type of crystals used in watches, except backwards, i.e.
vibrate when hit with electricity. When detonation occurs in a cylinder, rapid
high-pressure waves are generated which "ring" the combustion space like a
bell. Knock sensors vibrate in response, and the signal is used by the ECU to
retard timing.
> > Nor do I. For commercial projects I do some preliminary tuning on a
> > dyno, which I hire. For my own stuff I use an oscilloscope, an exhaust
> > temperature sensor, an ego sensor, and I tune the vehicle until it
> > 'feels' good, then let some automatic software 'learn' how to optimise
> > for economy and performance.
>
> What is an "ego" sensor?
>
When you find out let me know. There are at least a dozen regulars here on
Reeky that need an ego sensor. Preferably a sealed unit that they can't
"improve".
BTW, you might look for "The Internal Combustion Engine in Theory and Practice.
Volume 2: Combustion, Fuels, Materials, Design. Revised Edition" by Charles
Fayette Taylor. It doesn't go into two-stroke combustion, but it sure opened my
eyes to what's happening during Otto cycle combustion and why. There is some
discussion about ignition timing requirements.
--
Bruce in Houston wondering ...
'98 Suzuki GSF1200S (black) AMA#273468
'94 Sentra SE-R w/ Stillen muffler, STB, SS lines, metal pads
If a little knowledge is dangerous, then I'm the deadliest man on Earth.
Some Guy on a Bike
"Bruce Hearn" <bah...@flash.net> whiled away the hours on 14 Jun 1998
05:02:37 GMT with the following:
> BTW, you might look for "The Internal Combustion Engine in Theory and
> Practice. Volume 2: Combustion, Fuels, Materials, Design. Revised Edition" by
> Charles Fayette Taylor. It doesn't go into two-stroke combustion, but it sure
> opened my eyes to what's happening during Otto cycle combustion and why.
> There is some discussion about ignition timing requirements.
Excellent book. Try vol. 1, while you're at it. I:{> I found it to
be the most useful book on the science of the ICE that I've ever seen.
--
Bruce Hearn
Some Guy on a Bike wrote in article ...
> "Bruce Hearn" <bah...@flash.net> whiled away the hours on 14 Jun 1998
> 05:02:37 GMT with the following:
>
> > BTW, you might look for "The Internal Combustion Engine in Theory and
> > Practice. Volume 2: Combustion, Fuels, Materials, Design. Revised Edition"
by
> > Charles Fayette Taylor. It doesn't go into two-stroke combustion, but it
sure
> > opened my eyes to what's happening during Otto cycle combustion and why.
> > There is some discussion about ignition timing requirements.
>
> Excellent book. Try vol. 1, while you're at it. I:{> I found it to
> be the most useful book on the science of the ICE that I've ever seen.
> --
<snip the sig>
When I finish Volume 2, I'll have to look for Volume 1. I'm reading the book
for grins. I need a life.
--
Bruce in Houston wondering who's got a spare life he can borrow.
Cindi K
Mike Bresnahan wrote:
>
> Don MacPhail wrote:
> > He may be smokin' rope as to the reasons, but the advance on my RZ500 does reduce as the revs climb. . . Now, the
> > sharp drop at the end is a rev-limiting thing, but there is a steady decrease from a high of 29 degrees @ 3500RPM, to 18
> > degrees at 9000RPM - at which point it falls off a cliff, down to 8 degrees @ 10,000RPM.
>
> How did you measure it?
After it falls off a cliff, I'd measure it in feet per second.
--
Cindi Knox
AMA #606868 FSSNOC #3089 ABATE IBA
DoD #2046 B.I.T.C.H. #2
NGG Dangerous Descents
1997 Suzuki LS 650 "That Damn Savage"
cin...@imaxx.net http://www.imaxx.net/~cindik/
cin...@suba.com http://www.suba.com/~cindik/
In order to live within your limits,
you must know where those limits are.
Rich Rohrich
XR4 wrote:
> > He may be smokin' rope as to the reasons, but the advance on my RZ500
> does reduce as the revs climb. . . Now, the
> >sharp drop at the end is a rev-limiting thing, but there is a steady
> decrease from a high of 29 degrees @ 3500RPM, to 18
> >degrees at 9000RPM - at which point it falls off a cliff, down to 8 degrees
> @ 10,000RPM.
>
> This may be due to varying compression at different RPMs (just taking wild
> guesses now). i would guess that increasing compression would require
> changing timing, but I haven't a clue of exactly what the required effect
> is. Are you savvy on this type of crap Rich? Compression ratio, as I
> recall, typically varies from around 8:1 to 11:1 on a two stroke - I'm
> guessing due to pressure wave resonance of the pipe.
>
Here's what I can offer to the discussion.
The idea behind ignition advance is to try and time the peak cylinder pressure
to occur somewhere around 15-20 degrees ATDC, to apply thepressure in the most
mechanically efficient way. As rpm increases and less time is available for
charge burning to take place the engine will need to fire earlier (more advance)
to account for the diminished time. The overall idea is to use the minimum
timing necessary to obtain the best possible torque. That's the Engines 101
version.
Here in the real world there are a number of potential advantages to Retarding
the timing at high speeds. Higher engines speeds reduce the overall burn time
by virtue of, additional turbulence in the combustion chamber, less time
available to lose heat to the surrounding chamber surfaces, and increased
mixture density. In some cases these factors will more than offset the reduced
time available for comcustion to take place, and retarding the timing will
produce more torque. This is a VERY general explanation of the four-stroke side
of things. Two-strokes tend to have even greater reasons to retard the timing
at high speeds. Including the above points, we can add, more efficient
scavenging at high speeds which improves mixture density and speeds combustion.
As Jay pointed out, exhaust valve equipped engines will have higher dynamic
compression ratios which will also help reduce the burn time. But probably the
most important reason for retarding the high speed timing on a two-stroke is to
use some of the available combustion heat to manipulate the pipe wave timing
and improve the scavenging/ram tuning. More radical designs like the TZ and RZ
motors cited in earlier posts have fairly narrow power bands, so they use these
effects to maximum advantage.
So I guess what I'm trying to say is, something as simple as changing the timing
on a late model digital ignition can have unforseen effects. The idea of trying
to effectively map an entire ignition curve without the aid of a dyno, and some
fairly sophisticated test equipment, is an invitation to some serious parts
destruction, and a huge dose of frustration, but people have managed it.
--
Rich Rohrich
Applied Fluid Dynamics
rroh...@interaccess.com
DirtCrashr
Jack Rhodes mentioned:
>The best place to purchase a motorcycle dyno that I know is Phil Darcy
>at Darcy Racing Products in Ft. Worth, Texas. He built the one that
>Kenny Tolbert uses to tune Chris Carr's bikes and many other fast
>Harley and Rotax race bikes.
<snip>
If you're not near Texas (or if that makles a difference), there some guys in
California called Factory Pro who build and sell dynos at:
http://www.factorypro.com/inert.html
they make an eddy-current dyno shown at:
http://www.factorypro.com/dynoindex.html
which costs less than 20,00 clams
and have a list of several USED ones for sale at:
http://www.factorypro.com/dynoused.html
including a buncy of Dynojet ones for 6-8,000 clams
and a comprehensive write-up about each dyno's utility and measurment-states -
in reference to a certain machine:
"With significantly lower LMR than even Dynojet, they are unable to load the
engine to adequate levels to allow the engine to produce a real world shape of
a power curve. If you don't require realistic numbers, these dyno's will
produce graphs, but would be wrong for performance work. I.E., what is optimum
under these load conditions will NOT be optimum in the real world."
Which seems to me to indicate that certain Dyno readings can be far from
accurate or reliable - the numbers CAN and DO lie.
and they support roadracer Kervin Rentzel and a bunch of others...
DirtCrashr - '97xr400
Clifton T. Sharp Jr.
Cindi K wrote:
> Mike Bresnahan wrote:
> > > He may be smokin' rope as to the reasons, but the advance on my RZ500 does reduce as the revs climb. . . Now, the
> > > sharp drop at the end is a rev-limiting thing, but there is a steady decrease from a high of 29 degrees @ 3500RPM, to 18
> > > degrees at 9000RPM - at which point it falls off a cliff, down to 8 degrees @ 10,000RPM.
> >
>
> After it falls off a cliff, I'd measure it in feet per second.
Hey! I only have two, no matter how many seconds you wait.
--
+---------------------------------------------------------------------------+
| Cliff Sharp | Hate spam? Join The Great American Pink-Out! |
| WA9PDM | http://www.ybecker.net/pink/ |
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Mike Bresnahan
ChrisTos Alexiou wrote:
> On a 2-stroke now, as rpm rise, the mixture burns much faster so
> less advance is required. This is because of higher temp (in a 2-stroke) better
> atomization of the mixture (higher mixture speed), higher combustion chamber
> pressure due to exhaust expansion chamber, and other reasons which I do not
> recall right now and I do not have time to look into my books. If I get a chance
> I'll check it out and give you more reasons.
What books do you have?
Rich Rohrich
>
ChrisTos I didn't really expect a reply to my last post. I was really just kidding around,
but as long as you did respond it gives us an excuse to talk more about a really interesting
subject.
ChrisTos Alexiou wrote:
> Well the idea is that in a 4-stroke the flame front speed remains pretty much constant
> as rpm's rise so you need more advance at higher rpm to get the flame at the rightspot the
> right moment.
Numerous research papers disagree with you in this regard. As a general rule, the first half
of combustion 0-50% burned, flame speeds rise in direct proportion to rpm, while the
50-100% burned time flame speeds rise exponentially with rpm. As an example Honda has shown
in some of their research a flame speed of 45 m/sec at 8000 rpm, with an increase to nearly
200m/sec at 16,000 rpm on a small bore test engine. Research in this area all tends to
agree with the above.
> In an XR350 the avance starts at almost 0 degrees under
> 1000 rpm so that the engine will not kick back and work/idle smoothly at low rpm.
> It is true that some power might be lost at low rpm but no one will complain. On
> the other hand the manufacturer is sure that the motor will start and work fine
> at low rpm. Now as the rpm rise the advance increases till about 4000 rpm where
> it reaches 33 degrees. Then on it stays constant. Once more this is not ideal
> but is the easiest and safest way to do it, producing almost full power.
>
>
> On a 2-stroke now, as rpm rise, the mixture burns much faster so
> less advance is required.
This is true with both two-stroke and four-stroke engines.
The basic idea behind ignition advance on any conventional piston engine is to try and time
the peak cylinder pressure
to occur so as to apply the pressure on the descending piston in the most mechanically
efficient way. This tends to be in the range of 15-20 degrees ATDC. As rpm increases and
less time is available for charge burning to take place the engine will need to fire earlier
(more advance) to account for the diminished time. The overall idea is to use the minimum
timing necessary to obtain the best possible torque.
> This is because of higher temp (in a 2-stroke) better
> atomization of the mixture (higher mixture speed), higher combustion chamber
> pressure due to exhaust expansion chamber, and other reasons which I do not
> recall right now and I do not have time to look into my books.
> If I get a chance
> I'll check it out and give you more reasons. Here again though, for low rpm's
> the advance will rise a little, for the same reasons as the 4-stroke plus the
> fact that a 2-stroke does not work very well at low rpm. In an RM250, the
> advance starts low at low rpm and rises to aprox. 21 degrees at 2500 rpm.
> Then it remains constant for another 1500 degrees and then drops linearly
> to 7 degrees at top rpm. In general, 2-strokers have big detonation problems
> and at high rpm's and as a result advance must be reduced. Detonation problems
> make 2-stroke combustion chambers more sensitive to squish band and
> shape and also make cylinder diameter smaller (this last one helps is possible).
>
> Combustion in a 4-stroke is much more regular. The motor has time for intake,
> compression, fire, exhaust. In a 2-stroke almost everything happens together
> so things become irregular.
>
Higher engines speeds reduce the overall burn time by virtue of additional turbulence in the
combustion chamber, less time
available to lose heat to the surrounding chamber surfaces, higher flame speeds, and
increased mixture density. In engines with narrow valve included angles, and efficient
combustion chambers these factors can more than offset the reduced time available for
combustion to take place, and retarding the timing will actually produce more torque. We are
starting to see newer four-strokes take advantage of this fact and using more advanced
digital ignitions that have the ability to retard the timing at the appropriate time. This
is a VERY general explanation of the four-stroke side of things. Two-strokes tend to have
fairly specific reasons to retard the timing at high speeds. Including the above points, we
can add, more efficient scavenging at high speeds which improves mixture density and speeds
combustion, plus the mixture density as a whole is much more dense than on a four-stroke
because of crankcase compression. Dense mixtures burn considerably faster, so less timing is
needed. Once the engine is operating in the range of the pipe tuning, the volumetric
efficiency will be at it's highest which will obviously be the point where maximum cylinder
filling occurs. Again this will improve the mixture density and speed things u, so less
timing is needed. In a two-stroke race engine this tends occur at high rpm Two-stroke
exhaust valve equipped engines will have higher dynamic compression ratios at high rpm which
will also help reduce the burn time. But probably the most important reason for retarding
the high speed timing on a two-stroke is to use some of the available combustion heat to
manipulate the pipe wave timing and improve the scavenging/ram tuning. Less efficient
combustion tends to raise exhaust temperatures, so they are effictively trading off some
thermal/combustion efficiency to improve the scavenging and increase the delivery ratio of
fresh charge. Like most things in engine design, it's a tradeoff based primarliy on the
intended use of the engine. More radical designs like the TZ and RZ motors cited in earlier
posts have fairly narrow power bands, so they use these effects to maximum advantage. Add to
all this the basic simplicity of a two-stroke combustion chamber, which by it's very nature
will provide a fairly fast burn rate and it's pretty apparent that there are probably more
similarities than differences between the 2 engine types , and they have nothing to do with
the physics involved. It's more a case of the differences in the basic environments.
Dave Dude
Rich Rohrich wrote:
snip tech stuff
More radical designs like the TZ and RZ motors cited in earlier
> posts have fairly narrow power bands, so they use these effects to maximum advantage.
snip
OOOOHH he said TZ!!! hehehemehemehehe! ooohhh 87bhp(64kW)@12250rpm!!!
249cc V-type twin cylinder liquid cooled 2-stroke!! Bad-ass or what?
Check it out at:http://yamaha-motor-europe.com/
Gawd I LUV my Yamaha!
Dave Dude
96 YZ250
Brian McLaughlin
Dave Dude wrote:
>
> Rich Rohrich wrote:
>
> snip tech stuff
>
> > posts have fairly narrow power bands, so they use these effects to maximum advantage.
>
>
> OOOOHH he said TZ!!! hehehemehemehehe! ooohhh 87bhp(64kW)@12250rpm!!!
> 249cc V-type twin cylinder liquid cooled 2-stroke!! Bad-ass or what?
> Check it out at:http://yamaha-motor-europe.com/
> Gawd I LUV my Yamaha!
They are a great deal of fun.
--
Brian McLaughlin AP #1
TZ250E (1993-95) 2 strokes smoke,
R1100RTA (1997) 4 strokes choke!
EX250 Ninja (1998)