Advancing ignition timing - what it means for your cylinder

[i3igpete]

Consider the simulation I ran with a predictive combustion model. Though it's just a simple 4-cylinder model, the same applies for all gas engines. Spark timing has been varied from -18 to -10 degrees. a/f ratio is the same throughout. you may be wondering why the peak power does not go up much. recall from your thermodynamics class that the integral of the PV diagram is the actual work produced by a heat engine. timing increases power by pushing the peak in the corner higher and higher. boost adds power by shifting the entire curve upward.

of course every engine is different, but the principle of how timing adds power is the same. Every car will continue to add power up to a point, at which point the car will begin to lose power as the burn rate happens too quickly before TDC. Of course, the takeaway message here is that even before this point, you're building power at the expense of cylinder pressure (as seen in the P-V diagram). not a good way to build power when you have concerns about lifting the heads.

this is why i cringe when people use the stock ECU without an ITC or emanage to pull back timing. the factory timing is just way too advanced for anything other than a overspun turbo or n/a engine. choosing the right injector size doesn't change this fact, since the entire map, even the "meaty" part is way advanced.

http://i129.photobucket.com/albums/p239/i3igpete/private/timing1.png

[UTRacerX9]

Mmm... how many years has Matt held the fastest 3S record with just a ARC2? ;)

Obviously, having timing control makes it much easier to achieve peak horsepower, but it's been proven to not be necessary to still run great times.

[kywhitelightning]

Mmm... how many years has Matt held the fastest 3S record with just a ARC2? ;)

Obviously, having timing control makes it much easier to achieve peak horsepower, but it's been proven to not be necessary to still run great times.

He uses an ITC, as Pete stated he should.

Jeff

[UTRacerX9]

Really? Since when? I know for years all he had was the ARC2. Hopefully Matt will chime in on this.

[Atrosity]

Is matt even on this board yet?

[Atrosity]

My S-ITC is on ebay just an fyi.

http://cgi.ebay.com/ebaymotors/APEXI-S-ITC-_W0QQcmdZViewItemQQhashZitem45f55d4d1fQQitemZ30046 9275935QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccesso ries#ht_500wt_1022

[B-Man]

My S-ITC is on ebay just an fyi.

http://cgi.ebay.com/ebaymotors/APEXI-S-ITC-_W0QQcmdZViewItemQQhashZitem45f55d4d1fQQitemZ30046 9275935QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccesso ries#ht_500wt_1022

Haha, shameless plugs.

So, Pete, these are all simulations, right? If the graph in the top left is accurate, then why do people run advanced timing (say past -18* point on your graph) at all if it doesn't affect power? Just to keep cyl pressures down?

EDIT: I think I'm getting my negatives mixed up. -18* before TDC is more advanced than -10* before TDC :derr:

[B-Man]

Do you really think stock timing is already past MBT?

[i3igpete]

it might not be, but here's the rub. sure, you'll build more power advancing it to MBT, but is it worth the cost of higher cylinder pressures? law of diminishing returns comes into play, and i'd rather turn up the boost a small bit.

[Jesters Deadd]

What about the 99/98 people able to flash their ECUs... whats your view point on them? Should they retard their timing with anything other than stock turbos?

[B-Man]

There's no real way to see the limit of timing vs cylinder pressure. You just kinda have to know from experience what's too much or do you normally encounter knock before that happens?

[i3igpete]

note that there was no knock in any of the simulation cases. knock pressures are much higher because there are multiple flame fronts.

[KeithMac]

10 degrees of timing makes a hell of a difference on my car, using straight pump fuel I have to pull 17 degrees at some points in my map to avoid knock showing on the logger.

I`ve recently been adding 20% methanol (by volume) to the fuel in the tank and it`s night and day difference, can add 10 or more degrees of timing back in and the car flys!.

[SnakeSkinner]

not when I first got into the 8's, I ran 8.81@166mph with no timing control whats so ever (955 whp). and yrs worth of running 9's, and 10's in meny cars.

I only put on the ITC when I put in the 1000 cc injectors (pressure cranked up and 2 625ML meth nozzles, making 1093 whp at that time, and running 8.74@168 with lots of tire spinn), and it still was fine with it set to 0 it just made a little more power with a few deg of timing PULLED out on the dyno.

[J. Fast]

There's no real way to see the limit of timing vs cylinder pressure. You just kinda have to know from experience what's too much or do you normally encounter knock before that happens?Well it depends, one thing to note is that peak torque may or may not be reached before an engine starts to knock. I have tuned engines where knock has occured before MBT is reached. I have also tuned engines where there's a significant amount of room for more timing advance between where peak volumetric efficiency occurs (which is peak torque) and when knock starts to occur. In these engines, if you add timing after MBT, the engine will lose significant power, but may still not knock. So, it is not safe to say that peak torque will be reached just before the point that an engine begins to knock. This means that even if you have a good method of knock detection, adding timing up until the point just before knock occurs will not always result in an ideal torque output, net the most power, or maintain the highest area under the curve.

The best way to establish an optimum spark timing mark is to inspect your plugs. There's a test called a spark plug hook test. You warm your car up, gap your plugs, do a full pull and then pull the plugs and inspect them. Where the ignition signature lies on the sparkplug hook dictates wether your timing is early, late, or dead on.

Jeremy

[J. Fast]

It entirely depends on the fuel that you're using.

For example if you're running on natural gas with 8 to 1 CR, it will never knock, even with lots of boost. You'll just loose power, get hot and become so jerky it's undrivable.

It is true ignition timing is dependent on fuel type due to different ignition points and kernel speeds. However, when utilizing any fuel you may revert to the spark plug hook test. The ignition signature on the spark plug grounding electrode will allow you to determine the optimum ignition time, regardless of fuel. As illustrated here in my EFI University Notes:

http://i788.photobucket.com/albums/yy163/JFastMotorsports/EFIGroundingelectrodetest.jpg

Jeremy

[akotten]

Consider the simulation I ran with a predictive combustion model. Though it's just a simple 4-cylinder model, the same applies for all gas engines. Spark timing has been varied from -18 to -10 degrees. a/f ratio is the same throughout. you may be wondering why the peak power does not go up much. recall from your thermodynamics class that the integral of the PV diagram is the actual work produced by a heat engine. timing increases power by pushing the peak in the corner higher and higher. boost adds power by shifting the entire curve upward.

That's interesting because we went over that exact concept (PV diagram) this morning in thermodynamics lol. What's your major?

[i3igpete]

Mech E. you'd be surprised how much you use engineering in some fields of work, and absolutely none in others. i guess i'm one of the lucky ones :0:

[akotten]

Mech E. you'd be surprised how much you use engineering in some fields of work, and absolutely none in others. i guess i'm one of the lucky ones :0:

Cool same here. Feeling like there is no end to this major atm though. Thermo, statics, diff eq, and tech comm...all kicking my ass.

[i3igpete]

junior year will be even worse :D

[akotten]

junior year will be even worse :D

Fantastic!

[SpdDmnVR4]

I'm a Mech E too.. I am a junior also. Statics isnt that hard. Thermo is pretty tough for me. Dynamics, solids, and fluids will not be fun either. but thats next semester

[HLxDrummer]

It is true ignition timing is dependent on fuel type due to different ignition points and kernel speeds. However, when utilizing any fuel you may revert to the spark plug hook test. The ignition signature on the spark plug grounding electrode will allow you to determine the optimum ignition time, regardless of fuel. As illustrated here in my EFI University Notes:

http://i788.photobucket.com/albums/yy163/JFastMotorsports/EFIGroundingelectrodetest.jpg


Jeremy

Very interested.. Could you elaborate on how to read the plug?

Would you say this is a better test than comparing "dyno sheets" from that virtual dyno room program?

[11secondFWD]

On my dsm, the only way for me to make more power is to advance the timing (im on e85 at 22* peak) lol. My turbo is so maxed out (small 16g over 25psi) I can't run any more boost and im on 7.8:1 compression still. But good thread pete. I do know downsides of this. When I ran maft v1 on an old dsm, it had to be corrected so much for my 650cc injectors that it added a TON of timing. I was running 30* timing advance and over 20 psi on 93. I had no clue that it was advancing it that much and it blew the rings quick. Looking at the log was too late and not soon enough. That is when I said no more piggybacks, dsmlink all the way so I can control timing advance too. I am scared to trick the ecu airflow because it advances alot of timing. Heck my dsm went to 30* peak, that's 0 psi timing advance numbers.

[i3igpete]

yup, advancing ignition isn't always a bad thing. when you need to get every drop of energy out, it's a great thing for fuel economy. it's a balance like anything else.