spark timing vs lambda

[murfie]

Every one who tunes coyote engines says target a richer lambda and increase spark timing and that is how these engines make the most power. This must be dyno proven even though it goes against normal internal combustion engine tuning.

http://www.innovatemotorsports.com/resources/myths.php

After reading this article is there any real reason behind why the coyote is so different from other engines or is maximum spark/ rich mixture more bad info being spread around the ford tuning community?


found this in an old ford tuning forum:

Spark-Control Basics

Before we get into spark control program-ming, we need to understand the difference between the spark advance the engine needs for MBT, and the spark advance the engine will tolerate before detonation destroys it. Spark advance is definitely not an "if a little is good, more is better" thing.

Without getting into pages of combustion theory, the short story is the engine spark advance needs general change as follows:

large cylinder bore = more spark advance
higher compression ratio = less spark advance
more centrally located spark plug in combustion chamber = less spark advance
A/F ratio leaner than 11.5 = more spark advance
A/F ratio richer than 11.5 = more spark advance
higher inlet air pressure = less spark advance
higher inlet air density = less spark advance
higher engine load = less spark advance
greater charge turbulence = less spark advance
more EGR = more spark advance
advanced cam timing = less spark advance


Now, maximum spark advance will be limited by detonation, of course, so the engine spark advance tolerance changes as follows:

large cylinder bore = less spark advance
higher compression ratio = less spark advance
more central spark location = more spark advance
A/F ratio leaner than 11.5 = less spark advance
A/F ratio richer than 11.5 = more spark advance
higher inlet air pressure = less spark advance
higher inlet air density = less spark advance
higher engine load = less spark advance
greater charge turbulence = more spark advance
more EGR = more spark advance
higher coolant temperature = less spark advance
higher engine rpm = more spark advance
advanced cam timing = less spark advance

If you've been paying attention, you'll notice many of the spark advance tolerance variables conflict with the spark advance needs. In those cases, the spark advance tolerance should take priority.

[Higgs Boson]

i think some tuner blew a few engines (bama??) and was tuning them like other engines (12.75-12.95)....so everyone decided they need to be much richer.

[Plimmer]

Just for the record is .82 to .83 lambda and 26 deg at 7,000 rpm a good starting point for NA?

[Higgs Boson]

Just for the record is .82 to .83 lambda and 26 deg at 7,000 rpm a good starting point for NA?

I would start with 22....depends on your cam timing, too, more cam retard can handle more spark advance with regard to knock but that doesn't mean it's best power.

[murfie]

so starting at 22 degrees. do you want to lean the mixture and lower the advance if knock occurs? Everything I read about coyote motors says to increase advance as much as possible and run .85 or richer. That's exactly what the article says people do to solve knock and it works because it slows the burn rate and corrects the peak pressure point. then it says "The same result (with more power, less emissions and less fuel consumption) could be achieved by leaving the mixture at the leaner optimum and retarding the ignition more instead." So i guess my question is, is there something about the coyote motor that makes it prone to pre iginition and that is why it doesn't like lean mixtures(if you can even call between .85-1 lean) at wot? As far as I can tell the important components are not weak but forged or semi forged quality.

[Higgs Boson]

so starting at 22 degrees. do you want to lean the mixture and lower the advance if knock occurs? Everything I read about coyote motors says to increase advance as much as possible and run .85 or richer. That's exactly what the article says people do to solve knock and it works because it slows the burn rate and corrects the peak pressure point. then it says "The same result (with more power, less emissions and less fuel consumption) could be achieved by leaving the mixture at the leaner optimum and retarding the ignition more instead." So i guess my question is, is there something about the coyote motor that makes it prone to pre iginition and that is why it doesn't like lean mixtures(if you can even call between .85-1 lean) at wot? As far as I can tell the important components are not weak but forged or semi forged quality.

Everyone says the heads flow so well, it must be something about the fuel system/injectors, maybe how the injector is placed/sprays on two valves vs one or where the spark plug is located in the head in a 4 valve motor vs 2......

You are the king of research so I will defer to you to find out. ;-)

[toyoguru]

For one, these cars use a stoich of 14.08, to compute the difference in e10 fuels vs pure gas, so using conventional thoughts of 14.7, the commanded .835-.850 would net a a/f ratio in the low to mid 12's. Add the fact of the higher compression, ability to increase dynamic compression with vct and you can see why these cars like more fuel vs timing to make power. Of course there are other factors involved, but to play it safe, start in the .83-.84 range and stay in the lower 20's for timing and go from there making changes to increase power. Also, if you are working with an 11-14 coyote, Dial in the VCT before making huge timing changes. If you have a 15+ model, VCT tables are either very well dialed in, or there is something else preventing much in the way of gains (save a slightly better torque curve).

[AKDMB]

Preignition is preignition, I'm not sure any motor is meant to deal with it by having a stronger rotating assembly. I always thought preignition happens once and then you pretty much lose a piston no matter what. Could it be the size of the chamber, and having a lot more material/area to absorb heat? I was always under the impression that going aggressive on the ignition timing and conservative on the fueling was just the same same going aggressive on the fueling and conservative on the timing. I think most have found the coyote to like more fuel.

[murfie]

Not much to find. People don't want to post their engine failed. Some look like oil pump gear failures. I can only find ring land failures no melted pistons. Some say they were NA to try to get warranty. One the dealership claimed pressure to high and impossible for na to make. So in all cases FI was involved. Cut aways of coyote motors don't show any sharp edges besides maybe the spark plug. Rich and timing advance is definitely a way to add safe power but if you wanted more power lean and retarding timing would get you more power and still be relatively safe staying away from to much knock. As long as the engine isn't prone to preigntion which everything so far tells me it is not. 14.08 * .9 = 12.7 which isn't super lean just a tad. 14.08* .88= 12.4. On top of that E10 should be less prone to knock compared to non ethonol so you should be able to run it leaner and get great power out of it. Lambda is great in that it doesn't change for the fuel you are running 1 is stoich. I'm thinking maybe low 20*s is just to much ignition advance. It would take a dyno to find the sweet spot which has been done thousands of times. Just interesting .85-.86 is considered to lean when that is 14-15% rich and that is practically what the stock tune is. If some one is looking to push their engine adding timing and fuel is not the way to go. Less timing and leaner is the way to go. Just monitor knock closely and make sure your knock sensors are not being aggressive.


Basically when I see someone running 11 flat on the stock intake and pump gas and they assure me absolutely no nitrous compared to the rich/ high ignition advance tunes. I have to wonder did he really go to .8 to run more advance or go the other way which is what more conventional performance running says to do. More sure= more power. Less fuel in the cylinder means more air. There's got to be a point where it's just to rich and timing advance will not get you more power.

[Jn2]

On my LNF, which was a Direct Injection engine we ran .88 lambda and lower timing. This yielded the most power. Lowering lambda and increasing timing sounds like you something you would do to to make more power conservatively.

When I start tuning mine I'm going to start off at .84 a/f and add timing, then move to .85 and see if registers KR, if it does i'll lower timing. Then move to .86 and do the same. One I get a KR free log for .84, .85, snd .86 ill rent out dyno for a few hours and dyno all 3 calibrations to see which one works better.

Leaner mistures make more power at WOT. The problem is you need fuel that can fight preignition, e85 is great for this, so is 93 octane if you have it. 91, not so much

[AKDMB]

On my LNF, which was a Direct Injection engine we ran .88 lambda and lower timing. This yielded the most power. Lowering lambda and increasing timing sounds like you something you would do to to make more power conservatively.

When I start tuning mine I'm going to start off at .84 a/f and add timing, then move to .85 and see if registers KR, if it does i'll lower timing. Then move to .86 and do the same. One I get a KR free log for .84, .85, snd .86 ill rent out dyno for a few hours and dyno all 3 calibrations to see which one works better.

Leaner mistures make more power at WOT. The problem is you need fuel that can fight preignition, e85 is great for this, so is 93 octane if you have it. 91, not so much

Believe it or not I have heard some say that e85 has less preignition resistance, I highly doubt this, but a different topic for a different day.

[Higgs Boson]

Believe it or not I have heard some say that e85 has less preignition resistance, I highly doubt this, but a different topic for a different day.

hot spots like too hot of a plug cause preignition, lighting the mixture with the piston at BDC rather than a little too soon at TDC (detonation). you can imagine how destructive it is when combustion begins 180 degrees too soon....

http://papers.sae.org/2008-01-0321/

http://www.starquestclub.com/forum/i...owtopic=103128

http://www.learntotune.com/discussio...nition-on-e85/

http://www.3si.org/forum/f1/pet-peev...42/index2.html

[murfie]

hot spots like too hot of a plug cause preignition, lighting the mixture with the piston at BDC rather than a little too soon at TDC (detonation). you can imagine how destructive it is when combustion begins 180 degrees too soon....

http://papers.sae.org/2008-01-0321/

http://www.starquestclub.com/forum/i...owtopic=103128

http://www.learntotune.com/discussio...nition-on-e85/

http://www.3si.org/forum/f1/pet-peev...42/index2.html

The other side of it is a lean mixture burns hotter and creates more residual heat. I think what confused people is E85 is much more sensitive to how lean it can go before creating to much heat. It's more sensitive to mixtures that are to lean. It's more resistant to knock but has a much less forgiving optimal afr range just because it burns slower and more completely.

Lambda is lambda and anything less than 1 is rich. It just gets sketchy with knock the closer you get to 1 because the power level coming out of the fuel is increased exponentially and by the time a knock sensor says there is knock it's too late.

Knock sensors have gotten us into running a rich mixture and making up for it with ignition. I hate knock sensors and can't wait for ionization knock detection technology to surpass it so we can start to run leaner with less ignition safer.

Best we got right now is turn up the gain on the knock sensor and get a little more aggressive on the fuel mixture.

[murfie]

so more research and I have come across a post from shaun @ AED as to why engines were blowing up and it was caused by a torque based commanded lean condition at WOT as values approached lambda. The reason it was not seen on dynos or easy to figure out is that the parameter, which might have something to do with cat over temp protection that kicks in, takes about 15 seconds of WOT and that doesn't normally happen on a dyno. They found this parameter and played with it and found that it 'fixed' the issue. This could be one or any of these things. The fuel imbalance monitor at high load/ high rpm for cylinders 1-8, fuel strategy override commanded lambda value, fuel cyl cutoff commanded value, or fuel cut torque ratio driver demand (or any other source) and torque limit timer. The last one sounds like the biggest culprit to me.


This was also interesting:
http://s36.photobucket.com/user/clif...curve.jpg.html

found the book it came from http://s36.photobucket.com/user/clif...Cover.jpg.html. They start at lambda 1 makes 100% torque and then implement an ignition timing curve and find the maximum lambda efficiency is actually at .86 very interesting stuff.

[dbb2797]

I bet the fuel override is it. And I bet having aggressive spark advancing probably also contributed. I just compared to stock and the fuel override is at 1.00 for stock. And stock is super conservative only starting at 17 degrees at 6,000 RPM and only allows 2 degrees advance limit at WOT. Even if the car went to stoich at WOT on a stock tune, you'd still at worst maybe only have about 20-21 degrees of spark.

So I bet the tunes that were blowing up probably started at a much higher base spark and then increased the advance limit. So in the real world what happens is spark gets added because of no knock and then all of a sudden you've advanced spark at 29 degrees and the car goes to stoich. That I bet is bad!

[murfie]

I bet the fuel override is it. And I bet having aggressive spark advancing probably also contributed. I just compared to stock and the fuel override is at 1.00 for stock. And stock is super conservative only starting at 17 degrees at 6,000 RPM and only allows 2 degrees advance limit at WOT. Even if the car went to stoich at WOT on a stock tune, you'd still at worst maybe only have about 20-21 degrees of spark.

So I bet the tunes that were blowing up probably started at a much higher base spark and then increased the advance limit. So in the real world what happens is spark gets added because of no knock and then all of a sudden you've advanced spark at 29 degrees and the car goes to stoich. That I bet is bad!

Most of the failures if not all are above 650hp and FI. Have not seen any making even maximum N/A power levels that blew up. With FI I could see them targeting some rich lambda and pushing the ignition past a safe spot and then having a fuel modifier kick in and getting in trouble. Higher than stock ignition 20-21 like you said would be too high IMO at those pressures/ power levels almost as obvious as 29+ being to high N/A.

I've been trying to look into our cars knock monitoring system more and it looks quite robust. Ive also been looking into an external professional knock monitoring system that has some noise canceling head phone attachment like a G4+ or a plex system. Any one have any thoughts about the advantage of a external system like that over the stock system if there even is an advantage besides getting to listen to it with head phones your self?

[rhinogt]

There was one guy on SVTP that I can think of that blew NA a couple years ago at the strip, but he had aftermarket cams and valve train. He blamed it on Shaun's tune, then MMR's valve train parts. Shaun claimed he manually over revved it, MMR blamed the cams, and I don't think the guy ever got it settled. However, this was NOT a regular thing that 99.7% of us have to worry about.

[Witt]

I bet the fuel override is it.

Fuel override is also associated with an on/off switch, it works as a test/dyno mode when enabled in the PCM.

It was a few years ago when this was happening but if memory serves correctly it had to do with what HPT calls the fuel cylinder cutoff parameter and a torque limit timer.

[murfie]

Fuel override is also associated with an on/off switch, it works as a test/dyno mode when enabled in the PCM.

It was a few years ago when this was happening but if memory serves correctly it had to do with what HPT calls the fuel cylinder cutoff parameter and a torque limit timer.

yes sounds like you are referring to a fuel source in the fuel cut torque ratio and torque limit timer. That is what made the most sense to me after reading the old post about it. A test/dyno mode would make sense to have in the ECU programming. Probably an emissions no no to leave it enabled on the street, but for safety purposes I don't care.

[AKDMB]

For reference here's the thread about the #8 "fix" that murfie was talking about. Thanks for this info didn't know there was a "fix" tune out there

http://www.svtperformance.com/forums...-little-better