ddub

This weekend I plan on playing with some advanced timing after reading Judge ITO's suggestions on timing. I am still undecided about how much total advance I want to run right now, though.

My question is, for those of you that run advanced timing what AFR do you tune to? Is there a general rule of thumb for X degrees of advanced timing means you need to run X amount richer? Lets say I tune for 13.0 AFR with stock timing, then say for 20 degrees total advanced what would be a safe/good AFR to tune to?

ddub

Would it be too dangerous to run 13.0 AFR with ~20 degrees full advance? Would something like 12.5 be better? Trying to get some idea of the best way to tune this.

RotaryResurrection

iTrader: (8)

I'm no tuner, but explain to me what difference it makes how much fuel you inject, when you're messing with the IGNITION map, not the FUEL map? ON an NA, you can turn the timing up quite a ways before you worry about pinging. Pinging, by definition, is preignition, or ignition occuring too early and uncontrolled. Advancing timing, by definition, is ignition occuring earlier in relation to the mechanical position of the engine. SO, it is no stretch of the imagination to realize that regardless of fuel injection volume, if you have your timing out of place, you can preignite/ping. At a certain point you get the ignition event so early that you lose momentum of the rotational inertia...you can get timing to occur at or before "TDC"...it's actually possible to try and push the rotor backwards with early ignition. IF the energy from the combustion event can't travel smoothly downward and push the rotor around as it's meant to (proper timing), then it is a less controlled burst of energy with nowhere to go (preignition/detonation/ping) which is harmful.

I guess what I'm getting at is that timing is indepedent of fuel delivery here. Though EGT's can and will change with changes in timing, changing afr's to attempt to cover up wrong timing won't keep you from tearing something up.

pengarufoo

AFR's are related to ignition timing.

The AFR will affect your flame speed, which will affect how much advance you can run safely.

I have generally found if I tune my full load fuel for a particular AFR, say 12.5 or 13.0, when I go to work on the timing if I advance by any significant amount (more than a couple degrees) without detecting any pinging, I will have to add more fuel to get it back to the previous AFR, and I will often find a bit more power afterwards. You must be careful though, because as you get closer and closer to the edge of the tune, you are eliminating that safety padding that was there before. So you are becoming ever more and more dependant on your correction factors. Though your engine may not have been pinging when you did the tuning, what about tomorrow when it's 10 degrees hotter, or after it is heat soaked in traffic, or tonight when it is significantly colder out, will it ping then? You have to remember to take this into consideration, closer to the edge means it's easier to cross, and you need those correction factors to keep you away from it.

And now a quote, A. Graham Bell on ignition timing:

Both very lean and rich fuel/air mixtures burn slowly and require more spark lead. A mixture close to full power lean burns the fastest and requires less advance. At cruise, for example, road engines are usually tuned to be a little lean in the interests of economy, so more advance is necessary. However, mixture density is also a factor, because in this situation, with the throttle just cracked open, the cylinders do not become crammed with fuel/air mixture, so even when compressed as the piston rises to TDC (or rotor ), the oxygen and fuel molecules are seperated slightly, which in turn slows the speed at which the combustion flame travels through the combustion chamber.

Understanding this you will appreciate that an increase in the compression ratio has the reverse effect. This increases mixture density, so we have to reduce the spark lead. A cam change also influences mixture density, as do any changes made to the intake or exhaust, which affect the VE of the engine. When cam lobe duration is increased, mixture density will be reduced at lower rpm (AKA ported wankel), while in the mid-range and at maximum rpm it will be greater. To compensate, ignition advance will have to be increased at lower engine speeds, then reduced higher up the rev range. Changes to the intake system have a similar effect on mixture density, but the influence of the exhaust system is different.

When an efficient exhaust system is fitted the amount of exhaust gas left unscavenged in the cylinder, or reverse flowing into it, is reduced. This leaves more room in the cylinder to pack in fuel/air mixture, so mixture density increases and the spark lead must be reduced. The other effect of upgrading the exhaust system is that there are fewer inert exhaust gas molecules to seperate the oxygen and fuel molecules, so flame speed through the combustion space is faster, which again calls for less advance.

The fuel compounds used also affect combustion speed. Petrol burns failry rapidly, so requires less advance than other fuel types. Alcohol fuels burn more slowly, and nitro is slower still, which means that these fuels need more spark advance. However, when a flame accelerator compound is added to either alcohol or nitro, spark lead must be reduced.

Obviously in a modified engine some, or perhaps all, of the above factors will have been changed from the stock engine. Therefore the amount of spark advance needed under various engine operating conditions will probably be quite different from that determined by the factory to achieve best power and economy.

end quote - this is from four stroke performance tuning second ed. Good thing I type ridiculously fast

Tofuball

Please post a link to Ito's suggestions on timing

ddub

Timing By Judge Ito

Once a rotary engine is built correctly, ignition timing is first and foremost. Members need to really pay attention to ignition timing.

I have had people that play around and work on rotaries claim all kinds of bull crap to me. **** like: "a rotary engine has 2 top dead center, one for the leading spark plug and one for the trailing spark plug". They go ahead and claim that the factory yellow mark on the timing pulley is 0 degree or TDC for leading plug and that the red timing mark, is 0 deg. or TDC for the trailing plugs. And they go ahead and tune ignition timing according to that. I just scratched my head and said OK what ever works for you.

Factory timing marks on a rotary engine at idle are as follow. Yellow mark 5 deg. After Top Dead Center and red mark is 20 deg. ATDC. Mazda does this to get a smooth idle. Try and advance ignition timing to about 20 deg. before TDC at idle and 80% of the time, you will get a lumpy idle, bring the timing back to -5 and -20 and smooth as a baby's butt.

Once you understand the factory timing marks, then some adjustments could be made, but first understand what you are doing.
For N/A engines running a very little split will land the most amount of power available, Example: 35 degrees BTDC for Leading and 30 deg. (Running a 5-2 deg. split) BTDC for trailing. 31,32 even 33 deg. BTDC for trailing. Mazda Factory Racing recommends no split. 35 for lead and 35 for trail. 30 for lead and 30 for trail. 20 for lead and 20 for trail. you guys get the point.
I always run a split for precaution of getting the trailing plug firing before leading. That is a no, no.

On turbo charged engines ignition timing plays a mayor role, because combustion temperatures are much higher then N/A engines the ignition split needs to be greater, to prevent detonation, basically running a little to no split will increase combustion temperature, for N/A that is fine, but for turbo charge is dangerous, since your dealing with elevate combustion temperatures already from boost.
I have played with all kinds of timing advance. a 12 degree split will land some power and maintain reliability.
Fuel octane is also very important, On 116 octane I have used up to 19 degrees BTDC for leading with 32psi of boost and 7 deg. for trailing with no detonation and making well over 650rwhp on a friends drag racing car. Using 93 octane I keep leading down to 15-16-17 deg. BTDC with a 12 deg. split and depending the amount of boost.

I also have a serious tip on other factors of ignition timing. To be continue..
I would like to try and help fellow online rotorheads that currently play around and work with rotaries. These tips are important and maybe a moderator might want to pin this thread.


Ignition timing and how it works.
Mazda has 2 timing marks on the factory pulley. From 1986 to 95 US models timing marks are -5 and -20 at idle. The 3rd gen. Rx7 only has a -20 timing mark, the -5 has to be added to the pulley. Australian 3rd gen. models have a -5 and -20 timing marks, but the US model doesn't. These timing marks are dead right.

When the engines is revved, timing will advance to the + side or Before top dead center side. At idle the engine is resting in the - side or after top dead center.
I'll like to try and help members understand to which side the timing pulley advances for + timing and how it comes back to - timing @ idle.


If you're standing in front of the car and looking inside the engine bay, the timing pulley has 2 timing marks. The first one, left to right is -20 and usually colored RED, the second timing mark is -5 and usually colored YELLOW. The timing pulley advances timing to your right hand, that would be + timing. Anything to the left side of the timing marks, including the factory timing marks on the pulley are to your left hand. Remember the 2 factory timing marks are -5 and -20 at idle.

Once you learn how to identify the factory timing marks, and to which way the engine advances timing then you move on. The leading spark plug is the engines main spark plug. Timing needs to always be adjusted using the leading 1 spark plug. Trailing 1 gets adjusted later.
Depending if you have an electronic distributor, 86 to 91 crank angle sensor, or adjustable timing EMS like haltech, micro tech, Motec, Autronic, etc,etc, engine needs to be revved to about 4,500 rpms to view total timing advance with a timing light.(total timing advance is when the ignition timing will not advance any more, when the engine is revved) At this point make your adjustments to the leading spark plug.

Depending on application, timing would be set. If your running a naturally aspirated engine, timing could be more on 35,30,25 for the leading spark plugs and a 8-3 degree split between leading and trailing spark plugs.
If your running a nitrous oxide engine, timing could be subtracted from your over all N/A timing according to the amount of nitrous being applied. The general rule of thumb is, every 25 horsepower increase back up 2 degrees from your basic N/A timing map. If you shot a 50 shot back up 4 degrees from your N/A timing map, this way you start to build a nice Nitrous timing map.

If your boosting a rotary it's all together a different timing map. Depending on how much boost and how much octane, timing, could be adjusted. The split between leading 1 spark plug and trailing 1 spark plug, needs to be larger. From 8-3 degrees for N/A and nitrous, to 12-15 degrees for turbo charged engines.

What is also very crucial is the timing light. Rotaries are a 4-cycle engine, but when it comes down to ignition timing, they work like a 2-stroke engine, firing every 360 degrees instead of every 720 degrees like a 4 cycle piston engine.

Make sure you always use a 2-cycle timing light or your ignition timing will always read off. If you use a 4-stroke timing light, just subtract the number in half. Example: If the 4 stroke timing light reads 40 degrees BTDC in all reality your engine is only at 20 degrees BTDC. My timing light is a 2 stroke 4 stroke all in one.

I just realized how long this thread is going to be. I need to address, adjusting timing split between leading and trailing, for early distributors and stand alone ecu's, timing specs that have worked for me across the board and how to use the timing light and avoid a cross magnetic timing signal from one spark plug wire to the other.

I will continue this thread. But if members have questions up to now, just ask me. I'm in the middle of writing a story for Rx Tuner magazine, I'll continue this thread very soon.

TitosToy

that was a great post. i would definately pin this one up. any votes?

ddub

I'm still waiting for some feedback from people who have played with advanced timing. Like, what's a good total degree advance to run for fairly well/highly modded N/A's? Who has done it, what do they run, wait AFR, etc.

GUITARJUNKIE28

only your setup will determine how far you can go, but i've seen a lot of n/a's in the high 20's/low 30's, depending on porting, exhaust, etc...

ddub

Standalone I'm assuming? Or stock ECU? I'm trying to determine how far I can go on the stock ECU, or if it really even matters that much, before I go standalone in the future. Unfortunately I'll have to deal with the trailing being 15 degrees behind the leading, that large of a split kinda sucks but oh well, I'll live with it until I can fund standalone.

pengarufoo

I'm running 30 BTDC on my street port S5 w/e6k and a few degrees of split @ WOT, I have not pushed it to where it starts pinging yet but 30 shows gains over 26 which is where I started. The ideal timing curve for full throttle will vary with your setup obviously, but peak advance won't vary far from 25-30.

You'll want more timing where the VE is down, and back off a little bit around best VE (torque peak). If your motor is ported nicely torque peak will be higher in the rev range than stock setup, but you can't really do much about this with the stock ecu, the curve is fixed. You can just shift the curve higher or lower by turning the CAS. You'll have to balance engine speed timing demands and VE curve when determing the best timing.

If you find your motor wants extraordinarily high advance to make best power you may want to look things over because it suggests poor chamber filling.

I don't think much of this information is going to be a whole lot of help if you are using the stock ecu and just turning the cas though.

GUITARJUNKIE28

ok, no "real" answer for your dilema with the stock ecu, but i'll tell you that on my 87 t2, back when it had the stock computer, i twisted the crank sensor around about 5 degrees and ran 91 and never popped a seal (on that setup anyway).

i'd imagine the octane of fuel you run at this point will start making a difference if you advance timing. about the only real solution is to put the car on a dyno and start twisting the crank sensor--see what happens.

BklynRX7

OK i read the whole thread and it made me worried about my timing. I had the idle at 750, i used the light hooked up to the leading wire and adjusted till the red mark aligned, then repeated for the trailing/yellow. Was this correct?

GUITARJUNKIE28

nope. leading goes on yellow. if that's correct, your trailing is going to be correct. they're not independantly adjustable.

ddub

So what AFR did you tune to for this? Still running 87 octane?

RETed

I'll give you this one warning...

YOU CANNOT TUNE IGNITION ADVANCE BY LOOKING AT AFR OFF A WIDEBAND.

You have been warned.


-Ted

pengarufoo

I street tuned it with the wbo2 for between 12.5 and 13.0, I have not had enough time to refine it though, I started having problems with injector staging @ high rpm... the air filter was becoming a restriction and causing the vacuum to increase at full load around 7000RPM, enough to fall out of staging (go below the staging bar) and run off 2 injectors, which at that rpm were going >100% duty cycle based on the map. I'm currently redoing the map with the staging at a higher vacuum point, and going to get a bigger k&n on there. It's winter though so ... no driving for now.

When I was running 26BTDC it was tuned for around 12.5 throughout the rpm range @ WOT and the staging was not having issues, air filter was brand new then, but it was always close to the staging bar at high rpm with a filter on.

I would aim for 12.5AFR for now, while you get a feel for things.

pengarufoo

Ted, I don't think anyone suggested you can in this thread?

I think everyone here knows thats what EGT gauges are for.

You can hear detonation without EGT gauges however.

ddub

Still 87 octane or higher?

pengarufoo

sorry, 87 on s5 NA rotors - been up since yesterday I'm starting to get loopy.

Kahren was running more timing than me on same octane and cr, also e6k with a different individual throttle configuration, but I believe he did eventually start having some detonation problems... but they were intermittent, so I suspect it was correction factor related, he was just close to the threshold on the base map. I don't think he even had an IAT sensor connected at the time.

Kahren

iTrader: (13)

penga that noise was the tranny and my af meter diying at the same time and the noise 99% similar to detonation, so no timing problems ill talk to you about it later...

RotaryEvolution

iTrader: (30)

i haven't looked but can the crank angle sensor mounts be ovaled out for independent timing? would be interesting the results you could come up with.

pengarufoo

Kahren glad to hear you found out exactly what was going on with that. I'd say hit me up on aim but my account got disabled with a shitload of other naim users during some account cleanup phase. They are supposd to be reenabling the naim accounts because it was an accident, I'm still waiting