a little background of what ignition advance even means... some history too....

ignition advance refers to the amount of crank degrees the spark is triggered BEFORE the piston reaches the top (TDC) of the compression stroke...pretty simple...

but why would we want to light the mixture BEFORE TDC..?? wouldn't that push the piston back down?

the reason is that the entire charge doesn't completely combust the moment the spark occurs....there is a slight lag time between the initial spark kernel and full on combustion pressures happening in the cylinder....

if you lit the spark at Top Dead Center.... the inertial rotation of the crank will already be pulling the piston downward before significant combustion takes place....the combustion charge would, in effect, be chasing the piston for a bit, rather than pushing it....which would be a waste of good combustion pressure.....

on the other hand...IF the charge was lit too early before TDC.... you will get NEGATIVE work form your combustion charge in that it will waste inertial crank energy while the crank\piston is still trying to compress the combustion charge..... assuming it doesn't overcome it entirely and push the piston back down the bore without it ever reaching TDC .... some of you have had some shin smacking or knee wrnching experiences during kick starting when that very event happens... i personally have a divot in my right shin from my days of starting high compression 250R's sans boots..... if any of you haven't had the pleasure...and would like to experience it without buying a high compression 250R... just grab a ball peen hammer and swing it , ball end, as fast as possible towards your right shin... you know you've done it right when your eyes water...or you fell as though you want to throw up for no good reason...lol...ah memories....

back to spark advance... many things will influence the burn rate of the combustion charge...:

fuel....combustion chamber shape...temperature..humidity...engine speed..squish velocity...cylinder filling \ throttle opening.....and more..

another thing that should be considered is engine load... or how much resistance the piston is seeing against it's desired travel....high resistance like being in high gear with an open throttle can do some nasty things to the burn rate VS space available...spark knock and detonation....

at low rpm and open throttle conditions you will have significant load on your engine..... combine that with the slower movent of the piston...and you don't want or need a whole lot of spark advance @ low RPM...it would be easy for the combustion process to get too big of a head start in pressure rise against the still upward traveling piston.....

as you engine speed increases, so does the need to ignite the mixture sooner to give it adequate combustion lead time to "push" rather than "chase" the piston down the bore after it reaches TDC....

as engine speed goes up... so does the cylinder filling and charge turbulance...both of which increase flame front speed...and at some point in the RPM band you don't need to add in any more spark advance because the flame speed increasing cylinder filling and turbulance automatically keep pace with speeding up flame travel in step with increasing RPM....

so you can see that there is a lot of optimization that can be done to match the timing of lighting the mixture to match it for most benefit in a pericular engine setup and running condition....

in the "Bad Old Days" of point triggered ignitions (mechanical switches opened and closed by a cam lobe to signal spark events).... you had "base timing" the amount of advance you adjusted the assembly to start at by its positioning... and then there was a centrifically operated spring and weight assembly that adjusted the advance per rpm by mecahnically moving the points in relation to the cam lobe that opened them.....

that is a 2D ignition advance system ... as rpm increased, the weights moved the plate and ignition advance increased...nothing else mattered to the ignition except what rpm the engine was running at..not throttle position or gear selection...nothing but rpm

later on came the mechanical 3D equivalent ignition system....where a vacuum line was plumbed from the intake manifold to a diaphragm assembly that moved the whole point assembly based on the amount of vacuum in order to take some sort of engine load\ throttle position into account.....

lets jump out of that era into more current electronic ignitions...as they apply to our off road dirt bikes and atv's..... where an electronic \ magnetic pickup reads the crank position by a tab on the flywheel...and sends that information to the CDI\ ignition box..... coming into production in the 70's..and were the rule of the day by the 80's...

these were still a 2D style of ignition...the CDI could tell what RPM it was running at.... and pre-set ignition map told it at what point to fire based purely on engine speed.....

during that time, many aftermarket ignitions were made with different available "Maps" to choose from...and it made for better performance and sharper throttle response in lots of instances...but the key then..is the same is it has always been...to match the advance curve to the needs of the particular engine build at hand...and still nothing took into account anything more than engine RPM...so ignitions were mapped for basically best full throttle operation.... and that is a compromise because ignition advance requirements change with percentage of cylinder filling...a lesser filled cylinder will have a power advantage with more spark advance due to the slower burning rate of the lesser fill...

most current performance off road machines have a TPS (throttle position sensor) as part of the carburetor or thropttle body... and the TPS sensor feeds throttle percentage opening to the CDI\ ignition system.....

so we are currently using electronic 3D ignition advance mapping..... which is great.... and it came about as a way to adjust our engine's apark advance curve to take into account agreater amount of variables to optimise our ignition timing for best power and throttle response over a wider range of running conditions.....

the ignition now knows what rpm it is running at...and also how much throttle opening\ cylinder filling is happening via the TPS.....

within the programming is a Map for the entire rpm band @ closed throttle
and a map for the entire rpm band at wide open throttle (WOT)

the percentage of throttle opening is fed to the ignition via the TPS..... and the ignition constantly\instantly interpolates and adjusts the timing advance as a percentage between the fully open and closed throttle advance curves in an effort to maximize power over the widest range of operatiing conditions.....

in all engines (exception being the 5-valve Yamaha's).... the Wide Open Throttle setting requires the least spark advance for best power.... and least advance is also the least dangerous to run with as far as engine pressures are concerned....SO.. in absence of of TPS input, the ignitions are programmed to default to the WOT curve only...giving less than optimal power\ throttle response when not at WOT....and the SAME power as always when @ WOT conditions (like dyno runs & drag racing)....

you have to watch out for the cheap aftermarket ignitions.... as in not Dynatek or Vortex....and most being made by procom with each speed shop slapping their own sticker on the box and selling it as their own....because these cheaper ignitions only have a single 2D curve mapped in them, and don't use any input from your TPS...also they tend to have a big amount of advance...which will make a stock engine feel snappier...but can be detrimental... and even dangerous to run in a fully built engine

i decided to bring this topic up because Kam @ KBR sent me a Dynatek ignition to see what the upper reaches of my new YFZ's power curve looks like..... and then i had to look @ the available YFZ curves on my Dyna programming software.....and had to notice that the YFZ curves were the 100% opposite of all 4-strokes other than this 5-valver...!!

the YFZ runs LESS advance at partial throttle openings (yes, even the stock curve from Yamaha).... and MORE advance at full throttle openings...... the inverse of the rest of the universe...lol...

i'm going to be thinking about that for a while....

and maybe that is why plenty of the YFZ owners have reported better throttle response with the TPS deactivated..??...it runs a maximum advance full time when deactivated.... still seems sort of counter intuitive... but that's because my intuition has been based on 2 & 4 valve combustion chamber curves

anyways...here's some TPS 3D ignition map graphs from the TRX and YFZ to check out....

Click to view attachment

Click to view attachment

Alright now,this is what I have been waiting for. The dyna igntion tested on the YFZ. I'm sure there a great ign but before I was going to spend the money on one I wanted to see on the dyno what if any improvment they would offer. Keep up the good work John and thanks for doing all this research and posting it and thanks to KBR for loaning it to you. You two ROCK!

as i thought, the yamaha's are backwards. lol. they run great regardless. i just hope i see more of them with times going backwards this summer. sure wish honda would have done something for the 04 05 ignition / rev limit. cant beat the stock box, just wont rev out enough. i am keeping mine though. just gonna have to make her faster under the stock rev limit. i cant believe someone has'nt figured a way to alter or reprogam the stock box rev limit. i have seen computer reprograms on cars. thought some electronics wizard out there would figure that out.

many thanks to you sredrum... oh master of enhanced intakes!

everything we run has some of your handiwork in it too!

yea exactly, you can use a stock curve with a greater rpm, if you buy the DYNA programmable, and program it with the stock curve only make it go to 11,000 but that would cost about 400 bucks for hardly any performance gain at all

i had a dyna non programmable and i hate it, sold it and switch to the stock box

i wish there was something that could be done to the stock cdi tho



anyway nice write up, and very good info posted here

Interesting to me how the rest of the motors, except 5 valve yfz, runs better as you stated as that Makes Sense, and yet 5 valve yfz runs theirs opposite Maybe it has more to do with low lift equal and more even cylinder filling and vacuum then we think? Your testing and info certainly describe what I have been told by many many yfz owners... deactivating the tps on the yfz defaulting the curve to WOT and then clearing up some of their "bog" or off idle stumbles... basically making it run cleaner and more crisp.

Now lets put own collective heads together and figure out why Yamaha has done this (why) and why it may or may not be the best thing for throttle response on these things.

Was that Dyna preprogrammed off the shelf or did it have custom curves on it? Any benefits either way?

i was'nt aware you could do that with the dyna program. still costs way to much for this wallet.

Here is the info from a good member on yfzcentral named myk

"TPS is the 3-wire plug and the TORS is the 2-wire plug, I did alot of research on this when I did my EFI conversion.

The TPS has a +5v(blue), signal(yellow) and ground(black/blue) wires. I believe the whole idea behind splicing the wires together is to trick the CDI into thinking it is at WOT all the time which changes the ignition map to a more aggressive advance curve. ***IF*** this is actually what the bypass plug does (I don't have one), then you would splice the +5v wire(blue) and the sense wire(yellow) together, however if you wanted to trick the CDI into thinking you were at idle all the time then you would splice the ground wire(black/blue) and the sense wire(yellow), someone should verify what one of these plugs actually does.

Here is an attached pic of the TPS plug (the one I'm holding), you can see the TORS plug behind it, please ignor the red connectors in the picture, they were used for a wide band O2 sensor that I had installed on my quad when the pic was taken, but I did use the unit to log TPS position with one of the plugs, so I had to research how this plug worked.

Note: These wire colors were on an 06'

Mike"

i was reading somewhere sparks makes a bypass for the tps.. and it is basically hooks the yellow wire to the blue wire

i thought you just unplug the tps wire and left it alone
ive had mine unplugged for years and it runs fine

Wouldn't the Crf ignition be a good one. It is honda...

the dyna that Kam sent me did have the "as delivered" curves altered....Kam told me they were messing around a bit with it and to just go ahead and re-install the original 4 dyna curves... i have the dyna programming software and went right ahead and re-installed their 4 curves as a starting point....

Eric.....

i still don't have any idea why the yamaha would have less advance at less throttle opening\ less cylinder fill........ less cylinder fill always makes for a slower mixture burn...which is why the TPS FCR's were developed inthe first place....to give more ignition advance @ part throttle specifically to make higher power and better response at sub full throttle operation.....

i remember reading about the yz450f dirt bike reviews over the years...and one of the biggest complaints riders had was the abruptness of the throttle response...saying it caused lessened traction and rider fatigue.....

maybe the wierd part throttle curves were part of yamaha's cure to lessen the yz450f's hit..?!... and it was carried over into the quad..... would be interesting to know if that was the case...because if it is...and people do get better throttle response with the tps disabled and having the ignition default to the highest advance curve... it also means that the yamaha would react just like all other engines when fed MORE advance at part throttle settings...and that could easily be programmed with the dyna....not too many atv riders complain about their machines ever having too much rsponse or power...lol...

it's worth looking into anyways....

i will post some dyno runs with ignition cureves & a\fr graphs soon....

i tested the dyna curves on the yfz.... on pump gas compression it ran slightly better with a more advanced curve than stock...and slightly worse with a less advanced curve than stock.....

more testing\ tuning would be interesting to dial it in.... went to 56.79 HP as best with the better curve....

BUT....

different compression ratios and displacements will prefer slightly different timing.... and since i'm going to bump the engine to 470cc @14.25:1 soon...and then stroke it to 501cc's soon after that... i probably wont take the time to dial in much with the current setup....

can we discuss larger bore / stroke variations?

wouldn't a larger bore tend to benefit from more advance than a stock / bore stroke due to the added amount of fuel charge?

now what about added stroke? the piston is moving down farther. the added charge would like more advance but the longer stroke makes me think to retard some to equal it back out... not sure.

I imagine a dyno is the best and only real way to test for ideal timing.

Intersting info on the YFZ ignition curve. Im guessing that the 3rd port/valve reduces cylinder fill at the lower RPM's so they can advance the curve to help bottom end.........cant detonate if dynamic compression is lower, right? Then at higher RPM's the extra port fills much better so we need to retard the timing.

Having the Dyna ignition and programming software, it's fun to go through and look at the stock ignitions of different quads..... I noticed a couple years back that the ignition curve on the YFZ is totally different than how the TRX is, same thing with the banshee, although it's a 2 stroke, it has a very strange curve... not very linear.

John and I had a good long talk about timing with the Yamaha and after acouple of hours I could'nt get it out of my mind why the Yamaha likes more timing then the Honda.

Well after thinking about it more I remembered the Yamaha's have shorter rods and that does play a major role why they need extra timing.

Here are some numbers to look at. It's the ratio of rod length to stroke. I'm not saying there is a perfect number BUT each type of engine will (short rod vs long rod) make different power and need more or less timing.

TRX 04/05 64.85mm stroke and 111.4mm rod =1.719 ratio rod lenght to stroke

TRX 06/07/08 62.mm stroke and 105.5mm rod =1.701 ratio rod lenght to stroke

YFZ 04/05 62.mm stroke and 102.450mm rod =1.652 ratio rod lenght to stroke

YFZ 06/07/08 63.4mm stroke and 101.75mm rod = 1.604 ratio rod lenght to stroke

YFZ aftermarket 68mm short rod crank and 99.45mm rod = 1.462 ratio rod lenght to stroke

YFZ aftermarket 68mm long rod crank and 105.8mm rod = 1.555 ratio rod lenght to stroke

As you can see the rods are shorter on the Yamaha's and because of that the piston drops away very fast when the crank goes past TDC and the piston dwell's or stays on the bottom longer.

Because the piston drops away so fast you must use alot of adv timing to make the most hp/tq. And with the short rod engines they have to be designed different than the long rod engines. The short rods need more timing and they make alot more vacuum just after TDC because the piston travels down so fast compared to the long rods.

Because of that extra vacuum the runners/ports are different for short rod engines. They have to move alot of air/fuel mix early so they are bigger in size (volume) and most of the time the carb is bigger as well.

Cam timing/profile is different as well. For example the intake valves can stay open much longer because the piston dwell's longer on the bottom of the stroke. And it will fill the cylinder to a higher % if the intake cam keeps the valves open longer at BDC and just past that.

Long rod engines like HVP and smaller runners because of how the piston motion is with the longer rod. And there have been many YFZ's and ect that have really done well with the HVP style.

As some of you know I am getting a new head for my YFZ this year. I could get any year head I want. The older 04/05 with bigger runners or the newer 06/07/08 with HVP runners. I dicided because I'm going with a big bore stroker I feel the bigger volume runners will serve me better for my type of engine.

My engine will have a 98mm bore and a 66.4mm stroke with a 103.428mm rod for a ratio of 1.557 and my good friend Wayne (bigwaynester) has a killer engine and the bore is 98mm with a 68mm stroke and 99.45 lenght rod. So his engine has a ratio of 1.462.

Bottomline is his engine will need more timing than mine if compression and ect remains the same. We both have Venom pistons and the same compression. But with that said that brings me to one more topic. The short rods can use more timing using higher compression pistons because the piston drops away so fast that spark knock does not happen in most cases. The chamber volume decreases very rapid because of the short rod. So nitrous or boost does'nt affect the timing with short rods as much as long rod engines.

This is just the surface behind these engines. And I'm sure John can explain this much better than I can. Just food for thought.

awesome awesome info, sredrum..... never thought about it down that far, into rod ratios and stuff, but makes total sense. with that in mind, a +3 Hotrod (shorter stroke) would prefer something different than even a +3 stroked OEM rod crank.... That is some good info to think about.

Yep the HR crank engine would like different timing than a different engine using the same stroke and longer rod.

And thats why the dyna ign does well on the 04/05 TRX but sucks on the newer 06/07/08 TRX with the same curves used on the 04/05 TRX. They need different timing!

The bore,stroke,rod lenght,compression and maybe even the crank sensor firing sensor has changed postion making the timing off even more.

I'm sure John will be lookin into his 06TRX and dyna ign and will make the correct curves to use when he gets time.

Makes sense. Good thinking Chris!

nope... just put the ignition on a flowbench....that's the only engine development tool you would ever need.....dyno's just waste floor space.....lol...

that scenario would make sense.... but that is sort of the opposite of what's going on with the yfz ignition curves////

they retard the he!! out of it at part throttle at all rpms..... and give the highest advance curve at all rpm's during full throttle

2-strokes with good pipes are very different animals.....it is like having a blower that works only during a specific rpm band.....no boost...then lots of boost in a very short rpm difference.....

Sredrum....

thanks so much for your excellent insight and addition to this thread...!!

much appreciated.....

and yes...the dyna was excelent on the 04-05TRX's.....

BUT, for 06+ TRX's, both the beta box dyna sent me ..and the production box also....worked like complete crap on the 06 & up TRX's...down from 1.5 to 2hp across the whole band on every curve...

when i called to ask about why the curves were the same on the 04-05 and the 06+ boxes...even the "STOCK" curve #4....dyna said that they never tested an 06+ TRX...merely changed the plug connections to match, and loaded the 04-05 curves....

and when i asked for a copy of a stock 06+ curve so i could compare baseline oem curves for these 2 COMPLETELY different engines.... they said they have no idea what the never curves look like...never having seen or tested one...... worst answers you would ever want to hear.....

Where's Brad when you need em... lol

Cool stuff.

My bad.....you stated the TRX and YFZ charts.....I assumed they were listed in that order. NOW I see what your talking about, lol.

So they retard at part throttle........dynamic compression must higher at part throttle. What are the cam specs for the YFZ engine?

Great info.......1 thing to remember is that a short rod engine achieves 90 degrees sooner.......so cylinder pressures will be higher which can require you to retarded the ignition timing. Long rod has longer dwell at TDC so it may require you to advanced timing.
All depends on the cam, combustion chamber, comp.

Hey is Advantage Performance a 2D system??? I brought my bike with it and I almost think I should buy a used stock CDI off of ebay....

i wish Bradley was still @ dyna....and on the forums too!

he left Dyna about a year ago to work @ Gale Banks Turbocharging.... he told me it was the same distance drive to work...with only one turn different...

i'm pretty certain there isn't higher cylinder pressures at lesser throttle openings..... that would mean that you would have greater cylinder fill and more power at part throttle than at full throttle.....

and it would also mean that the engines would self destruct rather quickly if the TPS was disabled and the engine ran at full advance at lower speeds with the higher load of lower rpm....on top of higher cylinder filling pressures....

i'm fairly sure yamaha did it to lessen throttle response \ abruptness in the dirt bike... and then just carried it over to the quad...

i don't know about that one.... the only ones i know for sure that use 3D are: Stock, Dyna and Vortex

come on GP... you are a walking encyclopedia of engine dynamics.... throw some tech writing in this thread...!!

i'll start you off with a topic suggestion...lol....

maybe discuss MBT timing and what it means..

I was comparing the rod lengths in general.....no there wouldnt be more cylinder pressure at part throttle.

Here's a link about the TPS on a YZ, interesting info.
http://www.thumpertalk.com/forum/archive/i...p/t-200174.html

Steve.... i hit up that thread @ thumpertalk..... it was interesting to read

nobody there really had any clue at all about the way the TPS curves are really functioning on the yamaha's....

pretty funny to see a bunch of disconnected hunches and half baked theories without even knowing what is actually going on....or bothering to look into it......

"according to husaberg TPS map info, which is not even remotely close to the yamaha desgn, it should all go like this"....lol....

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