There's a mathematical solution for everything; I couldn't find it, but I'm hoping someone knows the formula for calculating ignition timing based on displacement, stroke, and octane.

I'd design an open-source app for it if I just had the damn algorithm... I know it's out there, just waiting, lurking.

Like Tupac.

 

I'd be willing to bet that there probably isn't. There are so many variables including rpm, tps, map, iat, etc. not to mention piston design and turbocharging variables that it'd be impossible to have a single equation to cover everything.

If there was an easy way to calculate ignition values then people wouldn't be paying tuners tons of money to determine the correct ignition timings EXPERIMENTALLY. They'd just plop some numbers into a spreadsheet and then be done.

 

There is a basic calculation for FUEL, but not for ignition timing...sorry.

 

There is some simulation software that might get you close, but why are you trying to calculate it mathematically instead of just dyno tuning it?

 

There is one. It's simple keeping adding timing until your torque curve stops making power. Lol that's the only equation I can think of

 

The idea is to just get it close after making a ton of modifications, so detonation on your way to the dyno is less of a possibility and your tune time will be much less of a headache.

And of course RPM, temp, and pressure are standard variables for the graph. Other multipliers could be easily applied if necessary. But there must be a general calculation that's used by the engineers who design the motors initially...

 

If you dont want to detonate on the way to the dyno, put 5 degrees EVERYWHERE in the timing map and drive to the dyno...car will run, drive etc just fine...with no ill effects.

 

Of course this can be calculated mathematically. Obviously your calculation wont be completely accurate, but it'd be a good to use as a reference.

The biggest factors for timing should be piston speed (you want peak cylinder pressures at the right time), and the time it takes for the flame front to reach the piston (bore, stroke, compression ratio, and pressure should be involved here). The piston speed part is easy. I would look at some stock maps and extrapolate a formula from there.

 

EVERYTHING effects optimal ignition timing. That's why you don't see an equation for it.

 

H22A, there has to be a general equation that can be adjusted per application, how else do engineers design a new motor? Trial and error? I highly, highly doubt that.

Xenocron, I can only assume you meant advance five degrees.

 

There is no equation.

In short, they spend millions of dollars on engine test cells, which utilze 100+ channel data acquisition systems, including in-cylinder pressure monitoring (at a rate of 48,000 samples-per-second). The engine development company I worked for could even control the temperature of the fuel, air, coolant, oil - induce vibrations to attempt to trigger false knock events - run computer simulated ramp-up/ramp-down events... etc etc

The actual design of the engine is done using advanced engine simulation, software packages that you can buy for ~$15,000+ (not including yearly license fees). Or they hire outside contracters (AVL, etc) to perform all this testing.

AVL test cell:

 

I checked three of my ICE engineering books and there is no equation or anything.

You don't understand- igntion timing is affected by about 5000 different variables so it'd be impossible to come up with equation that would cover all of them.

How do engineers design a new motor? Probably a little trial and error coupled with the use of simulation software and thousands of hours of testing. You're forgetting that people have been designing all sorts of engines over the last century so it's not just trial and error.

As for figuring out the ignition timing- they probably do what we do. Put the engine on the dyno. Start with a small ignition advance, increase until knock, back off a few degrees.

 

Nope, I meant fire the plug at 5 degrees before top dead center at every occurrence...AKA, put "5" in every cell in the map if you are trying to be SAFE

 

I would hope that would be safe LMAO.

 

Xeno, that seems like overkill. I understand the recommendation, but retarding five degrees sounds reasonable enough to avoid detonating; starting from a flat table could rack up some excessive dyno time.

 

Yes there is.

This is for you to have a base map considering your compression, stroke, and constant for the chamber. after that you can tweek on a dyno or driving it to obtain better perfomance.

Igition Timing = (0.01737)(Stroke in inches)(given RPM)/compression ratio + 3

Nascar engines have a initial timing set to 10 degrees or whatever the base calculation reult is and then straight up to 38, 40 cause they don't need progression. That gives a fast rev and clean idle.

Turbo engines need progression and retarding according to boost. Ethanol engines handle more abuse on that, therfore more power.

Speaking on Ethanol...a good ignition table is one made after rpm, ex: 2500rpm = 25degrees
2750rpm = 27degrees
3200rpm = 32degrees
that will give you a lot of torque since you don't have the knocking issue happening so soon.


I do hope I have helped anyone.

 

nice! i was playing around a bit with some numbers and it came out pretty close to what the honda factory ecu timing setting are for atmospheric. is this formula primarily for high load? low load? i guess im asking if it can be tweaked depending on the load on the engine.

 

So, this is for the Hi Load. The Low load will be interpolated by your ECU on any stand alone or OEM sistem. Any 2D, 3D map will use the MAP sensor info to decide the interpolation. Ususally low loads will go back to idle timing and as soon manifold pressure is changed it switches back to the map fairly quick.

 

Your questions means many things to many people but There are models (MATHLAB/PHD papers) but you also can estimate your timing curve bearing in some key principles and doing a "analytical review" if that is what you are after (or mean by "calculation")
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For a given engine, and IAT/ECT operating point, Ignition timing is principally a function of the burn rate & VE (torque)

Burn rate a linear function of rpm up of a certain break point and swirl/tumble (for a stock ITR is about 4,000rpm - the ignition curve flattens out (Swirl/tumble is proportional to rpm)
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Just to qualify the above is only talking about cruising to WOT loads (not talking about Timing under Decel, on/off throttle



VE is influenced by intake resonance, exhaust scavenging (you can hear your engines sweet spot)

The Ignition Curve is a "inverse of the torque curve" - assuming your engine burn rate rises with rpm, you should have minimum timing at peak torque ( I guess someone with a maths engineering expertise can write an inverse function)

Bearing the above in mind you can tune your ignition to be pretty close

Pay attention to shape of torque curve and tweak ignition accordingly
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Torque - u get this from the dyno

U then cant get a idea of the shape of burn rate vs rpm

U then tweak the peaks/valley and gradients of ignition curve by eye-balling the torque curve

On your DD you get a feel for your engine
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Look at the stock ITR and D16 maps - u can learn alot (on a D16 OEM timing drops after 4,000rpm)

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Tuning ignition is way more fun than tuning fuel

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Google is your friend.

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There are videos on youtube on MBT/Steady state, but they are always at 3,000rpm/WOT on a chassis dyno - Only on OEM Engine dynos they can hold 8,200rpm/WOT for 10 seconds - This is not not practical for the average Honda-tech forumers or tuner shop (who does no want to break their dyno) - Thus most tuner interpolate with gut feel (which is their un-articulated experience of tuning scores of engines - based on the above (and other) basic principles

Do a search and u will find published combustion models (Phd) that can predict MBT within 5%, that have been verified by dyno runs

If if u (not a OEM) tuned to MBT on a steady state dyno - your ECT/IAT compensation needs to be spot on for you to be getting MBT all the time (Tune in the day run at night) - and if u are a tuner u would know ECT/IAT move around alot in normal driving
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Interesting equation, can I ask it's source?
Is the +3 for octane adjustment?

I.e is (0.01737)(Stroke in inches)(given RPM)/compression ratio for regular(85), +3 for mid range(90), +6 for premium(95+) etc?